Naxalism In India Perception And Responses Politics Essay

Naxalism In India Perception And Responses Politics Essay Widespread discontent apathy among the common populace has plagued the Indian polity since independence. This discontent has often led to unrest and resentment sometimes resulting in violence also. Since independence various statutory enactments and institutional mechanisms for addressing the aspects of deprivation and neglect have been brought into being but the irony is that discontent and unrest continue to surface inspite of the measures undertaken. Today, even after six decades of independence, for a large section of the populace, basic survival and making the two ends meet is still the biggest challenge. As 58 per cent of the Indian labour force is still engaged in agriculture and allied occupations, landlessness is an important root of poverty. The Indian State recognized the vital link between land and livelihood soon after independence and launched land reform measures which included three components: abolition of intermediaries such as zamindars, security of tenancy and a c eiling on agricultural holdings for distribution of the surplus to the landless. However, as time passed the commitment to land reform has weakened and it remains an unfinished agenda of governance.  [1]  The poor population in order to meet their livelihood had to depend upon common property resources such as forests, pastures and water sources. The government having realised such resources as sources of profit started exploiting them, thus resulting in the poor being deprived of the access they had to these resources . 2. Today the nation is boasting of an above 9 per cent growth rate and is aspiring to become an economic powerhorse. But the fact of the matter is that the inequalities between the rich and the poor is increasing. With globalisation, awareness of opportunities and possible lifestyles are spreading but the entitlements are receding. The directional shift in Government policies since the early nineties towards modernisation and mechanisation, export orientation, withdrawal of subsidies and exposure to global trade has been an important factor in hurting the poor and increasing their miseries. Equal status and equal dignity is not only a Constitutional right but also a basic human right. The inherited institutions of caste, gender, religion and unequal property have been depriving the majority of the society of this right. The continued practice of social discrimination, untouchability and atrocities against the weaker sections truly reflects the failure of the promises made to the oppr essed people of this nation by the government. 3. This has led to a situation where in a large section of the people have lost faith in the polity and institutions of this country. However the irony is that there has been no sustained effort to eliminate the causes and reduce the discontent of the masses. It is these causes of discontent among the people that has led to the meteoric rise and spread of the Naxalite movement in the country. The Naxalite armed movement which has been challenging the Indian state since more than four decades is based on Maoist ideology and gains its strength through mobilising the poor, underprivileged, discouraged and marginalised especially in the rural and underdeveloped parts of the country. The Naxalite movement are a serious threat to the Indian state and is fast threatening to engulf almost the whole nation under its influence. The dreams of the nation of becoming a regional superpower and economic giant in the near future seems to be a distant reality with Naxalism challenging the inherent id eals of the state. 4. The menace of Left Wing Extremism after making a modest start in 1967 from remote village named Naxalbari in West Bengal plagues almost 235 districts  [i]  across the country in 2011. In some of these districts, the situation has deteriorated to such an extent that the writ of the government cease to exist and can be termed as liberated zones. The Maoists run a parallel government in these areas and are located in most underdevloped parts of the country. Despite being referred to as the most serious internal security threat faced by the nation by the Prime Minister Manmohan Singh himself in 2006, not much has translated at the grass root level to address the issue. On the contrary, the Maoists have been able to strike at targets with impunity and at will causing panic amongst the state and central security forces. 5. The Naxalites with their control over certain areas and their armed fight against the security forces, are challenging the inherent ideals of the state, namely soverignity and monopoly on use of force. In order to fight this menace, the state is focusing on re-establishing of law and order by encountering the Naxalites violently by use of force. However, this approach of the government seems to lack foresight, since the roots of Naxalism are located within the Indias numerous social and economic inequalities. Without addressing the root causes merely use of force will not help the state in solving the problem. If the country does not belong to everyone, it will belong to no one. Tupamaro Manifesto 17. The nation as a concept is universally recognized and .internationally valid for soverign aggregate of human beings in a modern state. If modern states are nation states, then the territorial integrity, political stability and the legitimacy of the state is a basic prerequisite for political and emotional integration of the citizens.  [2]  The collapse of the communist states in the early nineties point to the truth about this statement. It is the collective will of the population of the state that is the sole and most important determinant of contours of a state. India is a nation with vast cultural diversities and geographical.landscapes. The quote from Gitanjali written by noble laureate RabindraNath Tagore aptly sums up the importance of a nation wherein the true values of nationalism can take root: Where the mind is without fear and the head is held high; Where knowledge is free; Where the world has not been broken up into fragments by narrow domestic walls; Where words come out from depth of truth; Where tireless striving stretches its arms towards perfection; 9. Where the clear stream of reason has not lost its way into the dreary desert sand of dead habit; Where the mind is led forward by thee into ever widening thought and action; Into that heaven of freedom my father, let my country awake. 18. The Constitution of India guarantees the protection of all states against external aggression and internal disturbance by the Union of India, however the security being a state subject is rarely given the importance it requires till the situation blows out of proportion and many a times this turns out to be too little too late for the masses which suffer due to these security problems. The nation has faced numerous internal security problems since getting independence in 1947. These have been mainly due to secessionist movements initiated by a certain section of the population, wherein the government failed to provide solutions to their long pending issues. Since independence the country has faced problems in states of Manipur, Meghalaya, Nagaland, Mizoram, Assam, Tripura, Punjab and JK. Though, as on date these states have not been posing serious existential threat to the worlds largest democracy but before coming to some serious resolution of these conflicts a new danger of Nax alism has plagued vast areas of the country. 19. The Naxal movement presently having its influence over some 231 districts in 21 states of our country has been identified as the single largest internal security threat to the nation by the prime minister.  [3]  The Naxal movement as it is known is essentially an ideological movement and not an ethnic or a religious one. It gets its sustenance from social evils such as poverty, unemployment, exploitation of the poor classes and social discrimination. It has drawn vast support of population from the tribal belt into the movement. Before we can find the ways of tackling this issue, there is a need to understand the reasons why this 10. problem has come into existence. This will not only help in finding the real cause of this problem but also the ways and means to eradicate it. 20. To understand the spread of Naxalism in the country, we will have to analyse communism and its evolution in India. The communist Party of India came into existence on 26th Dec 1925 based on the thought that communism was ideally suited for the country with such vast demographic diversity and difference between the haves have not. However, the ban on communist ideology during the British rule prohibited the rise of the party and its ideology. Two notable movements led by communists during the pre independence era needs a mention are, firstly, the Tebhaga Movement led by peasants front of CPI Kisan Sabha in 1946, with the aim to increase the share of peasants in crops from half to two-third and second being the Telangana Uprising against the brutal repression of peasants by feudal landlords during the regime of Nizam in the Telangana region.  [4]   21. The birth and rapid rise of Naxalite movement can also be traced to the development which took place around the globe during the decade of 1960. This was a period in Europe, Asia and America when new radical struggles were breaking out, marked by the reading of Marx. These trends were reflected in the national liberation struggle of the Vietnamese people; the civil rights and anti-war movements in USA; in the students agitations in Western Europe; Che Guevaras self sacrifice in the jungles of Bolivia; and in Chinas cultural revolution. The Naxalite movement was part of this contemporary, worldwide impulse among the radicals to return to the roots of revolutionary idealism.  [5]   22. The year 1967 marks a turning point in terms of the revolutionary armed struggle in India. On 24 May the persistent social and political tensions in the 11. small village Naxalbari in the Darjeeling District of the West Bengal unloaded after a landlord was attacked which led to a full-scale peasant riot. This event has its deep roots in the socio-economic conditions, namely unequal land distribution and forced labour that had persisted since the British rule. At that moment, the general perception of people in these regions remained that the level of economic development, social justice and quality of governance in the states was plagued with a variety of maladies and there was complete lack of concern of the government towards these downtrodden people of the society . 23. The Naxalites, as they are called today emerged on scene as CPI(ML) after splitting from CPI(M). Their pronounced agenda has been to capture political power through an armed and violent revolution. Within a few years of its formation, the organisational network of CPI(ML) and its propagated violence spread in the whole of West Bengal. The campaign spread to parts of Bihar, Andhra Pradesh, Kerala, Tamil Nadu, Punjab, Jammu Kashmir, Uttar Pradesh and Delhi. In 1971 there was maximum violence with killing of 850 so called class enemies landlords, moneylenders, police informers, political activists  [6]  . However, joint operations launched by the state police of West Bengal, Bihar and Orissa quickly curtailed the movement, leading to serious decline in capabilities and influence of the Naxalites. By mid 1970s, the belief was that the movement was dead in totality. During this phase, however, the ideological motivation was existing in top leadership and middle level activists. The supporters consisted of the political class as well as the student base of Delhi University, who were motivated by their ideology. There were large number of journals in English and vernacular languages which were published periodically during that period to increase the ideological fervour in the common populace. The leaders of the movement were provided training, financial support and guidance by active support from China. However post 1972, the arrest and subsequent death of Charu Majumdar led to the total collapse of the movement. 12. 24. After the period of emergency, the remnants of the Naxalite groups made discreet attempts to revive itself primarily, through an agrarian agitation movement, supporting their woes and highlighting the issues plaguing the poor and the downtrodden. In 1980, Peoples War Group(PWG) was formed in Andhra Pradesh under the leadership of Kondapalli Seetharamaiah with a violent agenda. The group clandestinely established underground dalams, operating apparatus in North Telangana and Dandakaranya region. Even Bihar was under revival phase with three naxal groups on the forefront.  [7]  These groups had a sizeable ground level base of revolutionary peasants taking part in violent actions. The groups operating in Bihar were Maoist Communist Centre, Unity Party and anti-Lin Piao group. This concerted effort led to revival of the movement in Andhra Pradesh, Dandakaranya and Bihar. However, these groups were affected by dissentions and splits on one side and unification processes occurring simultaneously. This process of splitting though a setback in the intial stages but however it ensured increase of mass support at ground level as each entity tried its best to gain more and more support of the population in the area, thus ensuring organizational progress. The Naxal violence continued to increase from this period and finally reached its pinnacle in 1991 for a second time when they were able to eliminate sucessfully large number of class enemies. Since then, the organized killing of selected targets has continued.  [8]  The targets of Naxal violence also included those people whose agenda differed that of the Naxalites. Since, this has been a ground level movement, the solution too lies in dealing at that level and conceptualizing strategies at higher levels are of little or of no significance. At the moment every year there are more than 1500 Naxal violence incidents from the affected states involving killing of more than 500 class enemies. There has been a soph istication in the means employed by them in detonating the landmines negating their vulnerabilities to electronic countermeasures. The daring means employed by them to attack police posts and patrols has brought out the vulnerabilities of security forces in the area and the growing might of Naxals. The Naxalites have been running a parallel government in these areas by holding jan 13. adalats wherein they resort to on the spot dispensing of justice. These are notundertaken in any covert manner but in full public view and with advance warnings of a few days. This state clearly highlights the failure of govt at the grass root level. The present strength of armed cadre stands at 8000 excluding 15000 cadres of peoples militia who carry on their routine work, but are ready to serve when the situation demands.  [9]   25. The Naxalites have a design of establish a Compact Revolutionary Zone, from Nepal running across Bihar, Jharkhand, Chhattisgarh and Andhra Pradesh. These areas will be under their total control with administration and governance of their own. Unlike the first phase of the movement, the present phase entails unification and consolidation. In 1998, Unity Party and PWG merged to form CPI(ML)(PW), thereafter, RCCI-Maoist merged with MCC MCCI came into existence. Later, PW and MCCI came together to form CPI(Maoist). This gave the org a backing on ideological front from the Communist Party of Nepal(Maoist), thus complicating the problem and making it trans-border and trans-national. The party has got international linkages through Coordination Committee of Maoist Parties and Organisation of South Asia which includes the Communist parties of Sri Lanka, Nepal Bangladesh and India. The spread of Naxalism has been phenomenal in the recent years. Starting from the peasant movement, the Nax al issue today has a large spatial spread and much better resistance capability. The initiatives undertaken by the Centre and the to contain the movement prevent violence has been a failure. It has not been able to rein in the movement and lower the violence levels. 14. CHAPTER-III SOCIO-ECONOMIC MILIEU OF NAXALISM 26. Poverty and lack of development extract terrible prices and the glaring example of this has been the rapid rise of Naxalism. Naxalite violence in India has claimed thousands of lives till date and the graph is on the upward swing with each passing year. In his address to the nation on 15August 2006, Prime Minister Manmohan Singh termed Naxalism as a threat to Indias national security. Less than a month after this pronouncement, one of his predecessor former Prime Minister V P Singh came up with a completely different viewpoint. He saw no option but to embrace Naxalism in the present model of development, where forceful acquisition of land and displacement of thousands by the State are the order of the day. Both these statements, however, made in their respective contexts, but , both of them are revealing. They clearly indicate towards the rise of Naxalism as a movement that is giving sleepless nights to the highest echelons of governance of this nation. They clearly indicate towa rds the acceptance of the fact among our leaders of the strength and undisputed popularity of this movement. 27. Naxalism started as a peasant movement in 1967, in the tiny and remote hamlet of Naxalbari in West Bengal. The main demand was that of radical land reform and land to the tiller. The only means of realizing this was seen as the violent takeover of power. However, the govt was completely unwilling to yield to the demands, and the movement was brutally crushed. The character of Naxalism has changed with the times. Forced out of West Bengal, it has now regrouped itself outside the state. The movement is threatening to engulf whole of the nation and has got strong presence, largely in heavily forested areas dominated by tribals in the states of Orissa, Bihar, Jharkhand, Chhattisgarh, 15. Maharashtra and Andhra Pradesh. 28. Today,around 42% of Indias total population, lives under the poverty line. One third of the global poor lives in India, 75% in rural areas . The increasing high numbers of farmer suicides because of indebtedness, harassment and discrimination, particularly in the Naxalite affected areas, potrays the miserable condition of large parts of Indias rural population.The lack of human development causes anger and resentments amongst the people. They feel alienated and excluded. In addition often local elites are engaged in exploiting, harassing and even torturing the tribal population  [10]  . 29. Dalits and Tribals form the major support base of Naxalism. The Dalits and tribals together amount for nearly one fourth of Indias population and most of them live in rural India . Their reasons for supporting the Naxal movement are manifold: there is low degree of employment and qualification, new forest policies posing restriction for their livelihoods, cultural humiliation, lack of access to health care, education and power, restriction on access to natural resources, numerous forms of exploitation, social discrimination, frequent displacements, political isolation and suppression. The states which are the most affected have a huge number of people facing deprivation and a high record of crimes that are committed against them as well as displacement owing to economic and development projects 30. In fact 80% of the total displaced persons within the period of 1947- 2000 were tribals. A large number of tribals remained neglected from the various governmental development projects. Attempts by the government to increase its influence in these backward areas resulted in repression of the inhabitants by the various state authorities, such as by the forest department resulting in the destruction of their traditional social bonds. The era of globalization with the liberalisation of Indian economy gave new life to the conflict. There are numerous 16. Indian and foreign companies that are operating in the mineral rich areas of Chattisgarh, Andhra Pradesh, Jharkhand and Orissa which are among the poorest states in India and show a high degree of Naxal affection. Several of these companies have signed memoranda of understanding with the government worth billions for exploiting the mineral resources. However, the irony is that the inhabitants of these areas generally do not benefit from the mineral wealth of their areas. Besides mining, the establishment of Special Economic Zones (SEZ) and construction of huge dam projects results in the displacement of thousands of people. 31. Today, the focus of Naxalism has changed from being an agrarian movement to that of fighting for the attainment of tribal self- determination, control over local resource issues and continued neglect of governmentt towards these areas. This cause of theirs has found ready sympathisers among local communities. In tribal-dominated areas development is largely synonymous with the exploitation of forest resources for commercial gains, primarily controlled by the forest department and other govt agencies. This has almost obliterated traditional community control over forests and forest resources. The successive Government policies have made the very existence of tribals in their own areas difficult, and displaced them from their lands. The Forest Conservation Act, 1980 has barred tribals from using the forest resources, thus forcing them to be termed as encroachers on the land they have inhabited for centuries. However, this tribal alienation from land is not only the outcome of the c ountrys conservation policy only but also the development projects including mining projects. The Naxal movement cleverly tapped and exploited the often justified tribal anger and frustration against this oppression of the government. 32. With Indias major mineral resources concentrated under tribal dominated forestlands, mining and related projects have naturally come into the crosshairs of the Naxals. Today, five of Indias top mineral-producing state Orissa, Jharkhand, Chhattisgarh, Maharashtra and Andhra Pradesh are fighting the rise 17. of the red brigades in most of their mineral-rich districts.Its not development. It is an express highway to speed up exploitationà ¢Ã¢â€š ¬Ã‚ ¦ What they have left for the local people is just air and water pollution, says Communist Party of India (Maoist) central committee member Kosa, while referring to the mega mining projects in Bastar, Chhattisgarh. The Naxal opposition has unnerved the mining industry in this part of the country. According to a report by the risk management consultancy, Hill and Associates based in Hong Kong the viral spread of Naxalism in India has an adverse impact on the development and has termed it as a grave operational risk affecting investment climate in the core extractive sector. The report also points that Naxalism is likely to impact foreign direct investment in the country. It further says The risk exposure would be greater in pockets where Naxalites have joined the tribals in opposing project-induced human displacement. Areas where industrialisa tion is in the initial stages of development are more prone to stiff opposition by Naxalites. Traditionally, the Naxals have been targeting the govt symbols and its institutions but with the present trend Industrial establishments are likely to bear the brunt in the future. In fact, at their ninth congress held in the beginning of 2007, Naxalites clearly expressed their intention of intensifying their operations in areas where mega development projects including special economic zones, irrigation projects and mining enterprises are coming up. 33. The Naxals have used varied tactics for opposing this industrial investment. The rise of Naxalism can be directly linked to the crisis of faith: Indias marginalised population, the poors including its tribals, have lost their trust on governmentt for their livelihoods. The development projects coming in these areas are threatening the very existence of locals and have become synonymous with poverty and insecurity. With no alternative left, these communities have started believing that the only way they can fight for their survival is by adopting the violent ways of the Naxals. The rapid rise and popularity of Naxalism is not only a crisis of political empowerment but also that of sheer economic backwardness of these areas. The irony is that the marginalized have 18. started believing that it is one of the rare opportunities still available to them to express their aspirations. 34. The government and its planners have described Naxalism, as an internal security threat and are of the opinion that Naxalism and its sympathisers must be to be stamped out decisively by use of the States police and army. On one hand the govt claims that the path of violence is not the solution of the problems of the poor. On the other hand, it strongly advocates use of force to suppress the movement and solve the problems of the govt. It is precisely this myopic vision of the govt and its planners which is the real cause of the problem. Poverty, starvation, malnutrition, unemployment, lack of access to basic necessities like health and education, forced eviction of people from their lands in the name of developmental projects do not qualify as threats to internal security for the government. However, reactions and resistance and protests against them raise the hackles and eyebrows. A prime reason for the spread of Naxalism has been the acute failure of the State to provide remote and underdeveloped areas with facilities for health and education, and the prospect for dignified employment. People in these areas have had to cope with an administration that is indifferent, corrupt, an brutal. Meanwhile, the economic development in these areas has been powered by wood, water and minerals found on these lands, and for whose profitable exploitation the locals are forced to make way involuntarily or by force. It is important to understand the fact that the forced eviction of people from their land and livelihood for projects like mining will only bring more poverty and not prosperity as our planners think. 35. Governments need to be sensitive about these issues. They must work to make people in Naxal-infested areas true partners in the development process by assuring them titles on lands cultivated by them, by allowing them the right to manage forests sustainably, and by giving them a solid stake in industrial or mining projects that come up where they live and at the cost of their homes.Thus the locals are not interested into the so-called development projects by the 19. government and even resort to attacking the employees of these companies. These processes create conducive conditions for the support of Naxals and give them ready cadres and recruits. The Naxals only need to exploit the prevailing frustration . 36. Although the nation is enjoying a steadily solid economic growth during the past two decades but the distribution of these benefits is uneven among various social groups and geographic regions. Income disparities have increased and there is huge distinction between living conditions of the people in the rural areas and the metropolis in India. But these contradictions not only exist between rural and urban areas but also within the cities. The Naxals taking advantage of the situation and have started building up popular support in the cities through infiltrating labour unions and targeting the unemployed and students as well as exploiting the socio-economic disparities. Today, big cities like Delhi, Patna and Kolkata have come up as big hubs for Maoist sympathising intellectuals.According to Ernst Bloch the development of Modernity and capitalism can create contradictions within a society. These contradictions are often a consequence of social progress that is not shared by the w hole population. Bloch calls this asymmetric development the simultaneity of the nonsimultaneous. This process can be conflict-promoting especially when the contradictions are exploited by a political force. This concept can be well applied to the Naxalite conflict. 20. CHAPTER-IV IMPACT OF NAXALISM ON THE NATION 37. The spread and influence of Naxalism has almost captured half of Indian territory. The speed with which this menace is spreading its tentacles, the day is not far when the whole of the nation will be under its firm grip. Today, the violence related to Naxalism is a real cause of concern which is degenerating the security fabric of the country. The under mentioned paragraphs highlight the direct and indirect effects of the menace on the nation. Security Implications 38. Shift from ideology. The facts clearly indicate the rising menace of Naxalism and bring to fore that Naxalism in its present form fail to tow their novel ideology conceptualized in the native years, ie, working with a determined and undivided aim of establishing social equality. In fact Left Wing extremists are transforming the movement from menace to serious threat.  [11]   39. Increasing Influence. The viral spread of Naxalism is a growing concern. The Naxal threat seems to have surpassed all other insurgencies in the nation at least from the geographical point of view. Today the Naxalites are dreaming of establishing a red corridor and are putting all their energies towards fulfillment of their goals in this concern. Going with the present pattern they might soon gain a continuous presence along the length and breadth of the nation. 21. 40. Virtual Control. The situation today is such that If partial the Naxalites ever plan to launch coordinated, simultaneous attacks, they would not only be able to drive a wedge through the vital areas of the country but will also give them complete control over huge deposits of minerals, oils and industrialised territory and put them at a position from where they can bargain on their terms.   Gen Shankar Roy Chowdhury former Army Chief had this to say The Naxalite movement is the main threat which is affecting the states today. It is more dangerous than the situation in Jammu and Kashmir or the situation in the North-East.

Electrical Machines and Drives for Electric, Hybrid

INVITED PAPER Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Induction and switched-reluctance machines can provide the needed characteristics, but permanent magnet brushless machines offer a higher efficiency and torque density. By Z. Q. Zhu, Senior Member IEEE, and David Howe ABSTRACT | This paper reviews the relative merits of induction, switched reluctance, and permanent-magnet (PM) brushless machines and drives for application in electric, hybrid, and fuel cell vehicles, with particular emphasis on PM brushless machines. The basic operational characteristics and design requirements, viz. a high torque/power density, high efficiency over a wide operating range, and a high maximum speed capability, as well as the latest developments, are described. Permanent-magnet brushless dc and ac machines and drives are compared in terms of their constant torque and constant power capabilities, and various PM machine topologies and their performance are reviewed. Finally, methods for enhancing the PM excitation torque and reluctance torque components and, thereby, improving the torque and power capability, are described. KEYWORDS | Brushless drives; electric vehicles; electrical machines; hybrid vehicles; induction machines; permanentmagnet machines; switched reluctance machines I. INTRODUCTION Electrical machines and drives are a key enabling technology for electric, hybrid, and fuel cell vehicles. The basic characteristics which are required of an electrical machine for traction applications include the following [1]–[3]. †¢ High torque density and power density. †¢ High torque for starting, at low speeds and hill climbing, and high power for high-speed cruising. Manuscript received June 10, 2006; revised November 11, 2006. The authors are with the Department of Electronic and Electrical Engineering, University of Sheffield, S1 3JD Sheffield, U. K. (e-mail: Z. Q. [email  protected] ac. uk; D. [email  protected] ac. uk). Digital Object Identifier: 10. 1109/JPROC. 2006. 892482 Wide speed range, with a constant power operating range of around 3–4 times the base speed being a good compromise between the peak torque requirement of the machine and the volt-ampere rating of the inverter. †¢ High efficiency over wide speed and torque ranges, including low torque operation. Intermittent overload capability, typically twice the rated torque for short durations. †¢ High reliability and robustness appropriate to the vehicle environment. †¢ Acceptable cost. In addition, low acoustic noise and low torque ripple are important design considerations. On an urban driving cycle, a traction machine operates most frequently at light load s around the base speed. Therefore, in general, it should be designed to operate at maximum efficiency and minimum acoustic noise in this region. Typical torque/power-speed characteristics required for traction machines are illustrated in Fig. . Induction machines (IM), switched reluctance machines (SRMs), and permanent-magnet (PM) brushless machines (Fig. 2) have all been employed in traction applications, and can be designed to exhibit torque/power-speed characteristics having the form shown in Fig. 3. In the constant torque region I, the maximum torque capability is determined by the current rating of the inverter, while in the constant power region II, flux-weakening or commutation phase advance has to be employed due to the inverter voltage and current limits. In region III, the torque and power reduce due to the increasing influence of the back-electromotive force (back-EMF). However, the power capability and the maximum speed can be enhanced without sacrificing the low-speed torque capability by employing a dc–dc voltage booster [4], a technique which is employed in the Toyota 0018-9219/$25. 00 O 2007 IEEE †¢ 746 Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 3. Idealized torque/power-speed characteristics. Fig. . Torque/power requirements for traction machines. hybrid system, or by employing series/parallel winding connections, i. e. , series connection at low speed and parallel connection at high speed, as demonstrated in [5] and [6]. In general, however, the design considerations and control methods for the three machine technologies are significantly different, as will be discussed in this paper. Electrical machine design cannot be undertaken in isolation, but must account for the control strategy and the application requirements, both static and dynamic. Hence, a system-level design approach is essential. This paper describes the basic operational characteristics and design features associated with the foregoing electrical machine technologies for traction applications, and reports the latest developments, with particular reference to PM brushless machines, for which there are various topologies. tions are highlighted. Optimal flux, maximum efficiency, and low acoustic noise operation are then discussed. A. Basic Characteristics IMs are robust, relatively low cost, and have wellestablished manufacturing techniques. Good dynamic torque control performance can be achieved by either vector control or direct torque control. For conventional IMs, the constant power range typically extends to 2–3 times the base speed. However, for traction machines, this can be extended to 4–5 times the base speed, which is generally desirable [7]. The torque-speed characteristic of an IM is mainly characterized by the starting torque, the pull-out torque and the associated speed, and the maximum speed. The electromagnetic torque is given by mpVs2 0 Rr s II . INDUCTION MACHINES Of the three electrical machine technologies under consideration, induction machines are the most mature. In this section, the basic characteristics of IMs are briefly reviewed and specific design features for traction applica- T? 2fs !  2 R0 2 Rs ? sr ? Xk (1) and the maximum torque, i. e. , pull-out torque, is 2 Vs2 / s fs Xk Lk Tmax / (2) while the starting torque and corresponding phase current are given by 0 mpVs2 Rr A2 2 i 0 Rs ? Rr ? Xk Tst ? 2fs Fig. 2. Main traction machine technologies. (a) IMVinduction machine. (b) SRMVswitched reluctance machine. c) PMMVpermanent-magnet machine. hA (3) (4) Vs Ist ? q A A 2 0 2 Rs ? Rr ? Xk Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 747 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles where Vs and fs are the supply voltage and frequency, s is the stator flux-linkage, m is the number of phases, p is 0 the number of pole-pairs, s is the slip, Rs and Rr are the stator winding resistance a nd effective rotor cage resistance per phase, respectively, Xk ? Xs ? Xr0 ? fs Lk and Lk are the short-circuit reactance and the total stator and effective rotor leakage inductance per phase, respectively. The pull-out torque is independent of the rotor resistance, approximately inversely proportional to the total stator and rotor leakage reactance, proportional to the square of the stator flux (or voltage), and inversely proportional to the square of the supply frequency. The starting torque is proportional to the square of the supply voltage, while the lower the stator and rotor leakage reactance and the lower the supply frequency, the higher will be the starting torque. Fig. 4. IM traction machine [10]. Rating: 120 Nm, 11. 5 kW at maximum speed of 7600 rpm, 26 kW at base-speed of 2020 rpm. B. Design for Traction Applications In addition to the general requirements cited in the introduction for traction machines, essential design parameters for IMs include the number of poles, the number of stator and rotor slots, the shape of the stator and rotor slots, and the winding disposition. The design process usually involves three stages: 1) making appropriate choices for the pole number and stator/rotor slot numbers; 2) dimensioning the machine and designing the stator winding to achieve a specified power at the base-speed within a specified volume envelope; 3) simulating the machine performance over the full operating speed range. With an inverter fed machine, both a high starting torque and a low starting current can be achieved, since the supply voltage and frequency are variable. Thus, compared with machines designed for constant supply frequency operation certain restrictions, such as the need for a specific rotor slot shape to achieve the required starting torque, are removed. By appropriate choice of supply voltage and frequency, the starting torque can be almost as high as the maximum torque, while a high efficiency can be achieved by minimum slip control [8], [9]. The stator slot number and rotor slot number, and their shape and size should be optimized to minimize the total leakage inductance and resistance. Generally, this favors the use of wide and relatively shallow rotor slots and parallel sided teeth, as opposed to deep bars or double cages in conventional IMs. This results in a lower rotor leakage inductance, which, in turn, improves the power factor and increases the peak torque. In addition, the rotor slot area is more effectively utilized. When combined with the reduced rotor resistance, a lower leakage reactance is also beneficial in reducing the slip frequency at rated torque, and the variation of the slip frequency with load. The speed range of an IM is limited by its pull-out torque at high speed. As will be evident from (2), the pull748 out torque is proportional to the square of the flux-linkage and inversely proportional to the stator and rotor leakage inductances. In the flux-weakening region, the flux reduces with increasing frequency, the consequent reduction in the pull-out torque being exacerbated by the fall in the voltage across the magnetizing reactance due to the influence of the leakage reactance. Therefore, to order to obtain a wide speed range, it is again beneficial to minimize the leakage reactance. In [10], for example, this was achieved by: a) b) c) d) e) increasing the width of the stator slot openings to reduce the stator slot leakage flux; increasing the air-gap length to reduce the harmonic leakage flux; employing relatively wide, open rotor slots to reduce the rotor slot leakage flux; not employing skew so as to eliminate skew leakage; employing a copper cage (Fig. 4). A significant improvement in the available torque at maximum speed was then achieved (Fig. 5). Fig. 5. Torque-speed curve of IM for traction drive [10]. Proceedings of the IEEE | Vol. 5, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Over the maximum envelope of the torque/powerspeed characteristic, encompassing both constant torque and constant power operating modes, the copper loss only varies slightly with speed. In contrast, initially the iron loss increases with speed and is a maximum at the base speed, after which it gradually reduces as the degree of flux-weakening is increased. It is well known that when the iron loss and copper loss are similar the efficiency will be maximized. Therefore, an IM for traction applications should be designed such that the iron loss is higher than the copper loss at around the base speed, and vice versa at low and high speeds [9]. In this way, a high efficiency can be maintained over the entire operating speed range by incorporating optimal flux control, i. e. , by reducing the flux level at low torque, as will be discussed later, since the most frequent operating condition generally demands low torque around base speed. Fig. 6. Variation of sound pressure level with flux and load [14]. C. Optimal Flux, Maximum Efficiency, and Minimum Acoustic Noise High-efficiency operation is a very important issue for traction drives. The optimal flux level for maximum efficiency varies directly with the torque and inversely with the speed [11]. Thus, at low torque it is advantageous to reduce the flux in an optimal manner in order to reduce the iron loss and maximize the efficiency. However, as the torque level is increased the flux must be simultaneously increased until the rated flux level is attained; otherwise, the copper loss will increase excessively due to the low torque per ampere. If optimal flux control is employed, a significant efficiency improvement is achieved at all loads in both constant torque and constant power modes [11]–[13]. Above base speed, in the constant power mode, the flux naturally reduces since it is inversely proportional to the speed due to the limited inverter voltage. Optimal flux control for maximum efficiency also results in lower acoustic noise [14], which, in general, increases with both the load and the flux. By way of example, Fig. 6 shows the variation of the sound pressure level with flux and load, for a constant stator fundamental frequency. It will be observed that: 1) 2) under the same flux level, the sound pressure level increases with load; at light loads, a reduction in the flux can significantly reduce the acoustic noise; however, as the load is increased the noise can increase as the flux is reduced; the optimal flux level for the lowest noise emissions increases with the load. usually has to be determined experimentally, since no general and simple analytical method is available [11]. III . SWITCHED RELUCTANCE MACHINES (SRMs) A. Features of SRMs The design and operational features of SRMs are well-documented [15], [16], and may be summarized as follows. †¢ Simple, robust rotor structure, without magnets or windings, which is desirable for high-temperature environment and high-speed operation. However, it can have a significant rotor iron loss. †¢ Potentially low cost, although relatively high manufacturing tolerances are required due to the need for a small air gap. †¢ Modest short-duration, peak torque capability as the magnetic circuit tends to be relatively highly saturated. Smooth operation at low rotational speeds requires relatively complex profiling of phase current waveforms and accurate measurement of rotor position. †¢ Unipolar operation requires nonstandard power electronic modules, but SR drives have an inherent degree of fault tolerance. †¢ Since their operating is based on the sequential excitation of diametrically opposite stator coils in machines having the basic 6/4 and 8/4 stator/ rotor pole number combinations, the acoustic noise, vibration, and torque ripple tend to be relatively high. The high-speed operating capability of SRMs, their relatively wide constant power capability, and the minimal effects of temperature variations offset, to some degree, Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 749 3) Since both vector control and direct torque control, either indirectly or directly, control the flux and torque, optimal flux control can be readily exercised. However, the optimal flux level for each specific torque and speed Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles their relatively lower power factor. Thus, SRMs have significant potential for use in vehicle propulsion systems [7], [17]–[19]. Typical SRMs are shown in Fig. 7, together with one phase leg of the inverter. When a stator pole is aligned with a rotor pole, the phase inductance is a maximum, while in the unaligned position the inductance is a minimum. When operated as a motor, the phase windings are excited during the period when the inductance is increasing as the rotor rotates. When operated as a generator, the phases are commutated on and off during the period when the inductance is reduced as the rotor rotates. The higher the ratio of the aligned inductance to the unaligned inductance, the higher the torque/power capability. In general, it requires the rotor pole arc to be slightly wider than that of the stator poles. Comparatively, SRMs have relatively few feasible stator/rotor pole number combinations (6/4, 8/6, and integer multiples thereof being the most common). Further, the stator poles are generally parallel-sided and carry a concentrated coil, as illustrated in Fig. . However, several alternative SRM topologies have been proposed, of which the longpitched winding SRM [20] which utilizes the variation of the winding mutual inductances, rather than the variation of the phase self-inductances, to produce torque, and the segmented rotor SRM [21] are arguably the most notable, since they may produce a similar torque density to that of conventional SRMs . 3) the degree of saturation in the magnetic circuit; 4) the allowable temperature rise. Thus, a high overload capability requires thicker stator and rotor back-iron and appropriate thermal management. Above base speed in the constant power region, when the inverter supply voltage is limited, commutation advance is required. Thus, both the turn-on and turn-off angles are gradually advanced as the speed is increased, and the machine eventually enters the single pulse mode of operation. When the machine is motoring, the peak current is determined solely by the turn-on angle, while when generating, both the turn-on and turn-off angles influence the peak current [22]. At very high rotational speeds, i. e. , region III of Fig. , further commutation advance is limited due to the influence of the back-EMF and the winding inductance, since the phase current waveforms become continuous. However, as will be described later, by employing two-phase overlapping excitation and continuous conduction the power capability at high rotational speeds can be enhanced. Clearly, the foregoing operational characteristics of an SRM are appropriate for traction applications. B. Operational Characteristics S RMs are usually operated in the discontinuous current mode, although continuous current operation may be advantageous under certain operating conditions. As was shown in Fig. 3, three operational modes generally exist for traction drives. Thus, in the constant torque region I, the phase currents are controlled by PWM to produce the desired output torque, the peak torque capability depending on: 1) the allowable maximum current from the inverter; 2) the rate of rise of the current after a phase winding has been commutated on; Fig. 7. Typical SRMs and one phase leg. (a) Three-phase, 6/4 SRM. (b) Four-phase, 8/6 SRM. (c) One-phase leg of inverter. C. Constant Power Operation An SRM is capable of extended constant power operation, typically up to 3–7 times the base speed [23]. This is usually achieved by phase advancing the excitation until overlap between successive phase currents occurs. The high-speed performance of an SRM depends heavily on the rotor pole design, and in general, requires a compromise between the constant torque and constant power capabilities. For example, in [23] it was shown that when the leading dimensions of 6/4 and 8/6 SRMs were fixed, and the rotor pole arc was varied, the constant power range was extended to 9 6 times base speed when the rotor pole arc was narrower than the stator pole arc and the depth of the rotor pole was relatively large. However, the machines under consideration had relatively low torque densities. The constant power capability also depends on the number of stator and rotor poles. When the number is increased the constant power capability and the overload capability are reduced, albeit the higher the torque/power density and the higher the power factor and efficiency. By way of example, [23] shows that a 6/4 machine exhibits a much wider constant power range (viz. up to $7 times base speed) than an 8/6 machine (viz. up to $4 times base speed), which compares to a constant power operating speed range of $2 times ase speed for a 24/16 SRM [18]. Often, however, the number of stator and rotor poles is dictated by the space envelope constraints. In summary, not only is the ratio of the aligned to unaligned inductance reduced as the number of stator and rotor poles is increased, but the constant power operating speed range is compromised due to the limited scope for phase advancing, and although the consta nt power performance could be enhanced by reducing the number of turns per phase, 750 Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 9. Overlap excitation techniques for extending constant power operating range. (a) Conventional excitation at high speed with phase advance. (b) Overlapping excitation with commutation advanced. (c) Overlapping excitation with commutation retarded. Fig. 8. SRM with integrated flywheel and clutch for mild-hybrid vehicle [25]. Cranking: 45 Nm (0–300 rpm), continuous motoring: 200 Nm (300–1000 rpm), transient motoring: 20 kW (1000–2500 rpm), continuous generating: 15 kW (600–2500 rpm), transient generating: 25 kW (800–2500 rpm). (a) Schematic. b) Rotor/stator without winding. (c) Assembled unit. this compromises the torque capability for a given inverter voltage-ampere rating. Alternatively, the extended high-speed constant power operation can be improved with continuous phase current excitation, by increasing the number of turns per phase. The torque per ampere capability below base-speed is then not significantly compromised, as has been demonst rated for a 24/16 SRM [24] and an 18/12 SRM [25] (Fig. 8), which shows an SRM which was developed for a mild hybrid vehicle application. The use of conduction overlap between two phases to increase the torque and to reduce torque pulsations is common practice [6]. Fig. 9 illustrates overlapping conduction by advancing [6] or retarding [24] long-dwell commutation [15], both also incorporating phase advance. Bipolar excitation (Fig. 10) [6], [22], [26] can also be employed to improve the torque density and reduce torque pulsations, as well as to increase the efficiency. The long flux paths that are associated with SRMs supplied from conventional unipolar drives then become short flux paths, and the torque and efficiency are significantly nhanced at both low and high speeds. However, the improvement in performance gradually reduces as the excitation current is increased and the magnetic circuit becomes more highly saturated. Finally, a control strategy which employs freewheeling diodes in parallel with the power switching devices in a conventional half-H-bridge inverter together with an appropriate zero-voltage period (F ig. 11) can also be used to boost the power capability when an SRM is operated as a generator [22], [27]. Fig. 10. (a) Conventional excitation. (b) Bipolar overlapping excitation. Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 751 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 12. Idealized back-EMF and phase current waveforms from PM brushless machines. (a) BLDC. (b) BLAC. Fig. 11. Freewheel diode configuration and (a) ‘‘? 1’’; (b) ‘‘0’’; and (c) ‘‘A1’’ commutation. D. Acoustic Noise, Torque Ripple, and Their Reduction The acoustic noise which is radiated from an SRM is often cited as a major disadvantage. At low rotational speeds the acoustic noise is due predominantly to resonances that are induced by the torque ripples, and may be reduced by appropriate profiling of the phase current waveform. The key to obtaining the optimal current profile is an effective method for estimating the instantaneous torque. At high rotational speeds the acoustic noise is dominated by radial vibration resonances [28]. The acoustic noise becomes significantly higher at high rotational speeds and loads. However, various techniques have been proposed for reducing the vibration and acoustic noise. The most effective method is to employ a relatively thick stator yoke [29], [30] since this increases the mechanical stiffness and, thereby, reduces the vibrational response. However, the outer diameter is then increased, but this, in general, is advantageous in improving the overload capability since the stator yoke becomes less saturated. Reducing the supply voltage is also usually helpful in reducing the acoustic noise at light load. SRMs also generate significantly lower noise when operated under voltage control rather than current control, due to the fact that random switching of the current controller results in a wide-band harmonic spectra, thereby increasing the likelihood of inducing mechanical resonances [31], [32]. In [33], the relationship between the vibration of the stator and the rate of change of the phase currents at turnoff was highlighted, while a current shaping algorithm to limit the rate of change of current at turn-off and, thereby, achieve a smoother radial force waveform was described in [34] and [35]. However, the method proposed in [36] is arguably the most effective, in that it introduced a zerovoltage loop between two step changes in the applied voltage, such that, together with a knowledge of the stator natural frequencies, anti-phase stator vibrations were induced. However, it has limitations [37], since, while it is 752 very effective when SRMs are operated in both single pulse mode and PWM voltage control, it is much less effective with PWM current control, since this results in a varying PWM switching frequency. A fixed frequency current controller can, however, alleviate the problem. Further, the technique is less appropriate for application to SRMs which exhibit multiple resonances. The vibration and acoustic noise can also be reduced [38] by employing two-phase overlapping excitation, which, as stated earlier, is beneficial for extending the constant power operating range. In general, however, the acoustic noise emissions from SRMs remain a significant issue. I V. PERMANENT- MAGNET BRUSHLESS MACHINES A. Brushless DC and AC Machines and Drives Due to the permanent-magnet excitation, PM brushless machines are inherently efficient [39]–[48]. They are generally classified as being either sinusoidal or trapezoidal back-EMF machines [48] (Fig. 12). The corresponding control strategies are usually classified as being either brushless DC (BLDC), or brushless AC (BLAC). In a BLDC drive, the phase current waveforms are essentially rectangular, while in a BLAC drive the phase current waveforms are essentially sinusoidal. Ideally, in order to maximize the torque density and minimize torque pulsations, it is desirable to operate a machine which has a trapezoidal back-EMF waveform in BLDC mode, and a machine which has a sinusoidal back-EMF waveform in BLAC mode. In practice, however, the back-EMF waveforms may depart significantly from the ideal, and, indeed, irrespective of their back-EMF waveform PM brushless machines may be operated in either BLDC or BLAC mode, although the performance, in terms of efficiency and torque ripple, for example, may be compromised. Similar to induction machine drives, when operating at low torque an optimal flux level exists for minimum iron and copper loss, and hence, maximum efficiency. Fig. 13 shows a schematic of a typical PM brushless drive. In both BLDC and BLAC drives, rotor position information is necessary, although the required position Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 13. Schematic of PM brushless drive. esolution is different. For BLDC drives, in which the phase currents only have to be commutated on and off, low-cost Hall sensors are often employed, while for BLAC drives, in which the phase current waveforms have to be precisely controlled, a relatively high-cost resolver or encoder would be generally used. In addition, however, numerous sensorless techniques have recently been developed or are under development for both BLDC and BLAC drives. Although various rotor topologies and stato r winding dispositions ay be employed, BLDC machines predominantly have surface-mounted magnets on the rotor, and a concentrated nonoverlapping, fractional-slot, stator winding [Fig. 14(a)]. This results in short end-windings and, therefore, a low copper loss, and the potential for a high torque density, while a six-step inverter can be employed with PWM current chopping. Two-phase, 120 elec. conduction is the most common operational mode for a three-phase BLDC machine, while maximum torque per ampere in the constant torque region and extended speed operation can realized by advancing the commutation (Fig. 5). Similar operational characteristics can be obtained in a BLAC drive by controlling the phase currents in such a way that they produce a demagnetizing com- ponent of armature reaction, which reduces the effective back-EMF by flux-weakening. Various design features may be employed to obtain a sinusoidal back-EMF waveform. For example, the stator slots and/or rotor magnets may b e skewed, a distributed stator winding might be employed, or the permanent magnets could be appropriately shaped or magnetized, etc. However, a distributed overlapping winding [Fig. 4(b)], results in longer end-windings, which results in a higher copper loss and a lower torque density, while skewing of either the stator or rotor makes manufacture more complicated. Hence, it is often preferable to either shape the magnets or impart a sinusoidal magnetization distribution [49], which results in an essentially sinusoidal airgap field distribution, which is conducive to a low cogging torque and also a low iron loss. The rotor back-iron in a self-shielding, sinusoidal magnetized PM machine [49] is not essential since negligible flux flows within the inner bore of the magnet. This is, therefore, also conducive to a low rotor inertia, which can be an important consideration. Recently, however, there has been a trend to employ a fractional ratio of slot number to pole number and a concentrated stator winding for BLAC motors so as to achieve a sinusoidal back-EMF waveform and a low cogging torque. However, when the slot number per pole is fractional, the reluctance torque is usually relatively small with a concentrated stator winding. In order to utilize the saliency, an overlapping stator winding is usually required [Fig. 4(b)], as will be discussed in Section IV-D. Dq-axis theory can be used to analyze the electromagnetic performance of a BLAC machine, and the optimal relationship between the d-axis and q-axis currents in vector control and flux-weakening control strategies being determined analytically [50], BLAC motors are relatively Fig. 14. Stator winding dispositions. (a) Nonoverlapping winding. (b) Overlapping winding. Fig. 15. Torque-speed character istics of PM brushless machines. Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 753 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 17. Comparison of torque-speed characteristics which result Fig. 16. Comparison of torque-speed characteristics of BLAC and three-phase, 120 elec. BLDC drives. with two-phase, 120 elec. and three-phase, 180 elec. conduction modes of operation. easy to control and exhibit excellent performance, in terms of maximum torque per ampere control and optimal extended speed operation [51]–[53]. In contrast, the control strategy to realize constant power operation for a BLDC drive is generally more complex. As was shown in [54] and [55], above the base-speed the maximum achievable output power and torque when a machine is operated in the BLAC mode are higher than that which can be achieved when the same machine is operated in two-phase, 120 elec. conduction BLDC mode, irrespective of whether it has a trapezoidal or sinusoidal back-EMF waveform (Fig. 16). At high speed, the phase current waveform will approximate to a sinusoid even in a BLDC drive, due to the influence of the winding reactance, while any harmonics in the back-EMF waveform will cause the flux-weakening performance to deteriorate. However, by employing a three-phase, 180 elec. conduction strategy, the high-speed power capability of a BLDC machine can be improved, although below base-speed its torque capability will be reduced [48], [55]–[58], as illustrated in Figs. 17 and 18. relatively small and the stator windings have a low inductance, since the magnet has a relative permeability which approximates to that of air, i. e. , r $ 1, and the effective air gap is the sum of the actual air gap length and the radial thickness of the magnets. However, the magnets are exposed directly to the armature reaction field, and, hence, are susceptible to partial irreversible demagnetization. SPM machines are also generally to have a relatively limited flux-weakening capability. However, the flux-weakening capability, as well as the merits of PM machines having a fractional number of slots per pole and a concentrated stator winding, will be discussed later. Fig. 19(a-2) shows a schematic of a motor in which the magnets are inset into the rotor surface. The magnet polearc is, therefore, less than a full pole-pitch. However, since the q-axis inductance is now greater than the d-axis inductance, a reluctance torque can be developed. b) Interior Permanent-Magnet (IPM) Machines: Fig. 19(b) shows examples of brushless machines in B. Permanent-Magnet Brushless Machine Topologies In this section, the basic topologies of PM brushless machine, classified according to the location of the permanent magnets, are described. 1) Radial-Field MachinesVPermanent Magnets on Rotor: A radial-field PM brushless machine may have either an internal rotor or an external rotor, while the PMs may be located either on the surface or the interior of the rotor. ) Surface-Mounted Permanent-Magnet (SPM) Machines: This is the most widely used topology for PM brushless machines [Fig. 19(a-1)]. However, since the d-axis and q-axis stator winding inductances of such machines are the same, they exhibit zero reluctance torque. Further, in general, the armature reaction field is 754 Fig. 18. Torque-speed characteristics for brushle ss BLAC and three-phase, 180 elec. BLDC operation. Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles onded ferrite or rare-earth, such a machine can exhibit an extremely wide flux-weakening capability and a high torque density, without the risk of generating an excessive back-EMF should an inverter fault occur at high rotational speeds. However, such a rotor structure is rel atively complex and expensive to manufacture [61], [62]. A virtue of the rotor topology shown in Fig. 19(b-2) is that, when the pole number is relatively high, flux focusing can be exploited and the air-gap flux density can be significantly higher than the magnet remanence. Hence, low-cost, low-energy product magnets, such as sintered ferrite, may be employed. By way of example, Fig. 21 shows a generator, which was developed for an electric vehicle auxiliary power unit [63]. Flux-focusing enables an air-gap flux density of 0. 6 T to be achieved when sintered ferrite magnets, having a remanence of 0. 38 T are employed. Such a machine topology also exhibits a higher d-axis inductance since the armature reaction flux only passes through a single magnet, rather than two magnets as in the other machine topologies, making it very suitable for extended constant power operation. ) Radial-Field MachinesVPermanent Magnets on Stator: When the permanent magnets are located on the stator, the rotor must have a salient pole geometry, similar to that of an SR machine, which is simple and robust, and suitable for high-speed operation. The stator carries a nonoverlapping winding, with each tooth having a concentrated coil. The permanent magnets can be placed on the inne r surface of the stator teeth, sandwiched in the stator teeth, or mounted in the stator back-iron. Irrespective of their location, however, the torque results predominantly from the permanent-magnet excitation torque, i. . , the reluctance torque is negligible, although the torque production mechanism relies on the rotor saliency. Compared with conventional permanent-magnet brushless machine topologies, generally, it is easier to limit the temperature rise of the magnets as heat is dissipated more effectively from the stator. a) Permanent Magnets in Stator Back-IronVDoubly Salient PM Machine: The machine topology which is shown in Fig. 22(a) is referred to as a doubly salient Fig. 19. Alternative radial-field PM machine topologies with magnets on rotor. a) Magnets on rotor surface. (b) Magnets inside the rotor. which the magnets are accommodated within the rotor. In Fig. 19(b-1) the magnets are radially magnetized, while in Fig. 19(b-2) they are circumferentially magnetized. General ly speaking, however, leakage flux from the magnets is significantly greater than that in SPM machines. However, since the magnets are buried inside the rotor iron, the magnets are effectively shielded from the demagnetizing armature reaction field during fluxweakening operation. Further, since the d-axis inductance is smaller than the q-axis inductance, a reluctance torque exists, while the d-axis inductance is high compared with that of an equivalent surface-mounted magnet motor topology. Therefore, generally, such machine topologies are eminently appropriate for extended speed, constant power operation in the flux-weakening mode [48], [51]. Indeed, a variant of the topology illustrated in Fig. 19(b-1) is employed in the Toyota hybrid vehicle [4], Fig. 20. The V-shaped disposition of the permanent magnets serves to increase the air gap flux and the distributed stator winding enables the reluctance torque to be utilized. Multiple layers of magnets may also be employed to further increase the saliency ratio, although, in practice, the number of layers is usually limited to 3. An extreme case, however, is to employ an axially laminated PM rotor in which permanent-magnet sheets are sandwiched between the laminations [60]. In this way, a small volume of permanent-magnet material, which is generally a Fig. 20. Open-circuit field distribution in PM BLAC machine in Toyota hybrid vehicle. Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 755 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles permanent magnets is essentially invariant with the rotor position. Therefore, the cogging torque is not significant. However, a major disadvantage is that, due to the unipolar flux-linkage, the torque density is relatively poor compared to that of other PM brushless machines [65], although, as was reported in [66], it can still be higher than that of an induction machine. ) Permanent Magnets on Surface of Stator TeethVFlux-Reversal Permanent Magnet Machine: This machine topology is also commonly referred to as a flux-reversal PM machine [Fig. 22(a)] [67], [68]. Each stator tooth has a pair of magnets of different polarity mounted at its surface. When a coil is excited, the field under one magnet is reduced while that under the other is increased, and the salient rotor pole rotates towards the stronger magnetic field. The flux-linkage with each coil reverses polarity as the rotor rotates. Thus, the phase flux-linkage variation is Fig. 21. Generator for EV auxiliary power unit [63]. 9 kW at 4200 rpm, sintered ferrite magnets (remanence = 0. 38 T), max. air-gap flux density: 0. 6 T. (a) Stator. (b) Rotor. (c) Flux distribution. permanent-magnet machine. For a three-phase machine a magnet is required in the stator back-iron for every three teeth, while for a four-phase machine a magnet is required for every four teeth. The variation of the fluxlinkage with each coil as the rotor rotates is unipolar, while the back-EMF waveform tends to be trapezoidal [64]. Thus, this topology is more suitable for BLDC operation. However, the rotor may be skewed in order to obtain a more sinusoidal back-EMF waveform to make it more appropriate for BLAC operation. Further, it will be noted that the air-gap reluctance as seen by the 756 Fig. 22. Alternative radial-field PM machine topologies with magnets on stator. (a) Magnets in stator back-ironVdoubly salient PM machine. (b) Magnets on surface of stator teethVflux-reversal PM machine. (c) Magnets in stator teethVflux-switching PM machine. Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles ipolar, while the phase back-EMF waveform is, again, essentially trapezoidal. Such a machine topology exhibits a low winding inductance, while the magnets are more vulnerable to partial irreversible demagnetization. In addition, significant induced eddy-current loss may be induced in the magnets, which also experience a significant radial magnetic force. Further, since the airgap flux density is limited by the magnet remanence, the torque density may be compromised. c) Permanent Magnets in Stator TeethVFlux-Switching PM Machine: This machine topology is also referred to as a flux-switching permanent-magnet machine [Fig. 2(c)] [69]–[71]. The stator consists of BU[-shaped laminated segments between which circumferentially magnetized permanent magnets are sandwiched, the direction of magnetization being reversed from one magnet to the next. Each stator tooth comprises two adjacent laminated segments and a permanent magnet. Thus, flux-focusing may be readily incorporated, so that low-cost ferrite magnets can be employed [70]. In addition, in contrast to conventional PM brushless machines, the influence of the armature reaction field on the working point of the magnets is minimal. As a consequence, the electric loading of fluxswitching PM machines can be very high. Therefore, since the phase flux-linkage waveform is bipolar, the torque capability is significantly higher than that of a doubly salient PM machine [65]. The back-EMF waveform of fluxswitching PM machines is essentially sinusoidal, which makes them more appropriate for BLAC operation. In addition, since a high per-unit winding inductance can readily be achieved, such machines are eminently suitable for constant power operation over a wide speed range. ) Other PM Brushless Machine Topologies a) Axial-Field Machines: Axial-field PM machines have an axially directed air-gap flux [72], [73] and can comprise a single-sided stator and a single rotor, a double-sided stator and a single rotor, or a single stator and a double-sided rotor. In each case, a large axial force exists between the stator and the rotor. As with conventional radial-field PM brushless machines, the stator can be slotted or slotless, a lthough it is more difficult to manufacture a slotted stator for axial-field machines. Thus, slotless designs are more common. However, hile this eliminates cogging, it exposes the winding air-gap flux. Hence, a multistranded conductor or Litz wire may be required to minimize the eddy-current loss. Further, since the effective air gap is large, the winding inductance is generally relatively small, which may limit the constant power speed range. b) Transverse-Flux Machine: Generally, transverse flux machines have a relatively large number of poles, all of which interact with the total ampere-conductors of each phase. This enables very high electric loadings and, hence, high torque densities to be achieved [74]–[78]. However, they have a significant leakage flux and a relatively high winding inductance, as well as a poor power factor [79], [80]. This impacts significantly on the associated VA rating of the power electronics converter, which has inhibited its application. C. Design and Control Issues for PM Brushless Traction Machines As stated earlier, traction machines are required to have a high torque density, a high overload capability, a wide operating speed range, and a high efficiency, while it is desirable that they have a degree of a high fault tolerance and are low cost. In this section, design considerations related to the above issues are discussed. However, they often contradict each other. For example, reduction of the cross-coupling magnetic saturation may also reduce the saliency ratio and consequently the reluctance torque; the selection of the base-speed is usually a compromise between the constant torque performance at low speed and the constant power performance at high speed. 1) Torque Density and Overload Capability: The general torque equation for a PM brushless machine, which has both excitation torque and reluctance torque components, is given by 3 A T? p 2 A m Iq A ? Lq A Ld ? Id Iq (5) where p is the number of pole-pairs, m is the stator winding flux-linkage due to the permanent magnets, and Ld , Lq and Id , Iq are the d- and q-axis inductances and currents, respectively. In order to maximize the torque density, it is desirable to increase m by reducing the leakage flux. This can be achieved by introducing airspace flux barriers or interpole magnets, as illustrated in Fig. 23. m can also be increased by utilizing flux focusing [4], [63], as illustrated in Fig. 24. The torque density can also be enhanced by increasing the saliency ratio [3], [81], as illustrated in Fig. 25. Further, since the short-duration torque capability is determined primarily by the demagnetization withstand capability of the magnets and the level of magnetic saturation, reducing the d- and q-axis cross-coupling magnetic saturation by incorporating air flux barriers, as illustrated in Fig. 26, can enhance the overload capability. 2) Flux-Weakening Capability: It is well known [62], [82] that the maximum flux-weakening capability, defined as the ratio of the maximum speed to the base-speed, under supply inverter voltage and current limitations, can be achieved when a PM brushless machine is designed to have 1. per-unit d-axis inductance such that Ld Ir m Ld ? m Ir or ?1 (6) 757 Vol. 95, No. 4, April 2007 | Proceedings of the IEEE Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 24. Flux focusing by appropriate disposition of magnets. ratio is 1. 0. However, the higher the flux-linkage m to achieve a high low-speed torque capability, the more difficult it is to realize wide-speed operation (Fig. 27) [83]. In [62], it was shown that it was possible to design any PM brushless machine to achieve Binfinite[ flux-weakening capability. Clearly, however, if the rated current is high (e. g. the machine is liquid cooled), it is Fig. 23. Reduction of leakage flux by introducing airspace flux barriers or interpole magnets. where m is the stator flux-linkage due to the magnets, Ld is the d-axis inductance, and Ir is the rated current. Although it is possible to design a PM brushless machine which satisfies the foregoing requirement, generally, for most PM machines Ld Ir = m G 1, since the d-axis inductance is relatively low as a consequence of the recoil permeability of the magnets being approximately equal to 1. 0. Nevertheless, the higher the ratio of Ld Ir = m the higher will be the flux-weakening capability [Fig. 7(a)], which, theoretically, is Binfinite[ when the 758 Fig. 25. Improvement of saliency ratio. (a) Lower reluc tance q-axis armature reaction flux path. (b) Multilayer and (c) Axially laminated. Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles theless, it has been shown [86] that, by careful design, the magnet working point in an SPM machine can remain reasonably high up the magnet demagnetization characteristic, even when the machine has Binfinite[ flux-weakening capability, due to the fact that 1. perunit d-axis inductance results primarily from stator slot leakage and end leakage fluxes. 4) Rotor Eddy-Current Loss: PM BLAC and BLDC machines are usually considered to have negligible rotor loss. However, the rotor loss may be important in machines equipped with surface-mounted magnets, in terms of the resulting temperature rise. Eddy currents may be induced in the permanent magnets, the rotor back-iron, and any conducting sleeve which may be employed to retain the magnets, by time and space harmoni cs in the airgap field. More specifically, they result from [87]: a) stator slotting; b) stator MMF harmonics which do not rotate in synchronism with the rotor; and c) nonsinusoidal phase Fig. 26. Reduction of d- and q-axis cross-coupling magnetic saturation. (a) SPM. (b) IPM. much easier to satisfy (6), even for surface-mounted magnet machines, which have a high m and a relatively low Ld . For example, in [84] Binfinite[ flux-weakening capability was achieved with an SPM machine equipped with a self-shielding, sinusoidal magnetized rotor having no back-iron, and in [85] with an SPM machine in which only alternate stator teeth carried a coil. However, in general, it is much easier to achieve a wide operating speed range with machines equipped with an interior permanent magnet rotor, since generally m is lower, while Ld is higher. 3) Demagnetization Withstand Capability: Operation in the flux-weakening mode is a necessary requirement for traction applications, while NdFeB is the most commonly employed permanent-magnet material for PM brushless machines. However, the magnets are required to have an adequate demagnetization withstand capability at the maximum operating temperature, when they are most vulnerable to partial irreversible demagnetization. In addition to effective thermal management, one means of enhancing the demagnetization withstand capability is to provide a low reluctance path for the demagnetizing d-axis armature reaction flux such that it does not pass through the magnets. One example of achieving this is to employ narrower stator slot openings and thick tooth-tips, as illustrated in Fig. 28(a), or thick rotor slot bridges in an IPM machine, as illustrated in Fig. 28(b). However, such features will also have an influence on m and Ld . In general, however, it is easier to realize a high demagnetization withstand capability for IPM machines. Never- Fig. 27. Variation of torque and power capability with machine design parameters, when Ld Ir G m . (a) Variation with Ld Ir = when m and Lq =Ld are constant. m, Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 759 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Fig. 28. Improvement of demagnetization withstand capability by introducing d-axis armature reaction demagnetization flux path. (a) SPM stator design. (b) IPM rotor design. Fig. 27. (Continued) Variation of torque and power capability with machine design parameters, when Ld Ir G when Lq and Ld are constant. . (b) Variation with m, current waveforms, which result from six-step commutation and PWM. In general, however, the rotor eddy-current loss is relatively small compared with the stator copper and iron losses. Nevertheless, it may cause significant heating of the magnets, due to the relatively poor heat dissipation from the rotor. In turn, this may result in partial irreve rsible demagnetization, particularly of sintered NdFeB magnets, which have relatively high temperature coefficients of remanence and coercivity and a moderately high electrical conductivity. It is particularly important to consider the rotor eddy-current loss in a) machines with a high fundamental frequency, e. g. high-speed and/or high-pole number; b) machines with large stator slot openings, e. g. , transverse flux machines; c) high power density brushless dc machines, e. g. , force-cooled traction machines with a high electric loading; and d) machines whose windings span a fractional pole-pitch and which have nearly equal pole and slot numbers [88]. If the eddy-current loss is unacceptable, the magnets may be segmented, axially and/ or circumferentially [89]. 60 5) Stator Iron Loss: Due to the fixed PM excitation, the no-load iron loss increases with the rotational speed, while the full-load iron loss in the constant torque operating range is generally around 20%–50% higher. However, the iron loss which results on load in the fluxweakening mode depends on the machine topology, as illustrated in Fig. 29. In general, SPM machines have the lowest full-load iron lo ss, and despite the increase in fundamental frequency it usually becomes much lower than the no-load iron loss as the degree of flux-weakening Fig. 29. Variation of iron loss in SPM and IPM machines when their open-circuit stator iron loss are designed to be the same. Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles is increased [90]. IPM machines generally have a significantly higher full-load iron loss, which may be comparable to or higher than the no-load iron loss, since the armature reaction field has a higher harmonic content due to the small effective air gap [90], [91]. However, when the magnets are simply inset into the rotor surface the harmonic content in the armature reaction field increases further, and generally results in the highest full-load iron loss [86]. 6) Fault-Tolerance: An important consideration when operating in the extended speed, flux-weakening mode is the consequence of an inverter fault which results in the loss of the demagnetizing armature reaction field and an excessively high back-EMF [92], [93]. In this regard, IPM machines may be advantageous, since, for a given output torque, the PM excitation torque, and, hence, the volume of magnet material and the maximum ack-EMF are lesser. However, the consequences of an inverter fault occurring when a PM brushless machine is operating in the fluxweakening region remains a challenging issue. D. Recent Developments 1) Fractional Slot Machines: SPM brushless machines which have a fractional number of slots per pole and a concentrated winding have been the subject of recent research. T hey have an inherently low cogging torque, short end-windings and, hence, a low copper loss, a high efficiency, and a high power density, as well as excellent flux-weakening performance [85], [94]–[100]. The stator coils may be wound either on all the teeth or only on alternate teeth (Fig. 30) [95], [97]. In the latter case, the phase windings are effectively isolated, both magnetically and physically, and a high per-unit self-inductance can readily be achieved to limit the prospective short-circuit current, by utilizing the relatively high air-gap inductance and the leakage flux at the slot openings. Due to the physical separation of the coils and the negligible mutual inductance between phases, the possibility of a phase-tophase fault is minimized. Therefore, the fault tolerance and flux-weakening capability of such machines can be significantly higher than for more conventional machine designs. Fig. 31 shows a three-phase, 24-slot, 22-pole, PM BLAC machine which was developed for a supercapacitorbased electrical torque boost system for vehicles equipped with down-sized IC engines [99]. However, since the torque is developed by the interaction of a stator spaceharmonic MMF with the permanent magnets, a relatively high rotor eddy-current loss can result from the fundamental and low-order space-harmonic MMFs which rotate relative to the rotor [88], [89]. As stated earlier, however, the magnets can be segmented to reduce the eddy-current loss. A further advantage of such machines is that, due to the fractional number of slots per pole, the cogging torque is very small without employing design features such as Fig. 30. Three-phase, 12-slot, 10-pole, fractional slot PM machines [97]. (a) All teeth wound. (b) Alternate teeth wound. skew. However, the reluctance torque component is negligible even when an IPM rotor is employed. 2) Hybrid PM and Current Excitation: Since the PM xcitation is fixed in a PM brushless machine, the current phase angle has to be progressively advanced as the speed is increased above base-speed so that a demagnetizing d-axis current component is produced which reduces the flux-linkage m with the stator winding. Ultimately, however, this may cause partial irreversible demagnetization of the magnets. At the same time, due to the inverter voltage and current limits, the torque-producing q-axis current component has to be reduced correspondingly. Consequently, the torque and power capability are limited. Thus, a compromise has to be made between the low-speed torque capability and high-speed power capability. Hybrid permanent magnet and field current excitation has been shown to be beneficial in improving the power capability in the extended speed range, enhancing the lowspeed torque capability, and improving the overall operational efficiency. There are several ways of realizing such hybrid excitation. For example, dc winding may be located on the rotor [101] or the stator [102]–[107], which is preferable since it does not require slip-rings. The magnetic circuit associated with the dc excitation may be either in series or in parallel with the magnetic circuit associated with the PM excitation. However, although series excitation is simple it requires a higher excitation Vol. 95, No. 4, April 2007 | Proceedings of the IEEE 761 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles machines equipped with hybrid excitation, based on doubly salient pole [102], consequent-pole [103]–[105], and claw-pole [106], [107] machine topologies. The dc excitation winding enables the air-gap flux, and, hence, the torque capability, to be enhanced at low speed, to be reduced at high speed to facilitate extended speed operation, and to be optimized over the entire speed range to improve the efficiency. It also reduces the likelihood of an excessively high back-EMF being induced at high speed in the event of an inverter fault. Fig. 31. Three-phase, 24-slot, 22-pole, PM BLAC machine with modular stator winding and IPM rotor [99]. Rated output power ? 18. 5 kW, rated speed ? 1700 rpm, rated torque ? 105 Nm. (a) Cross section of three-phase, 24-slot, 22-pole IPM BLAC machine. b) Machine test rig. MMF due to the low recoil permeability of the magnets. On the other hand, parallel excitation is more effective electromagnetically but leads to a more complex machine structure. Fig. 32 shows three examples of PM brushless 762 Fig. 32. Hybrid excited PM machines. (a) Hybrid excitation based on doubly salient pole structure [102]. (b) Hybr id excitation based on consequent pole structure [105]. (c) Hybrid excitation based on claw-pole structure [106]. Proceedings of the IEEE | Vol. 95, No. 4, April 2007 Zhu and Howe: Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles V. CONCLUSION The operational characteristics, design features, and control requirements for induction machines, switched reluctance machines, and permanent-magnet brushless machines for vehicle propulsion systems have been reviewed, with emphasis on their low-speed torque and high-speed power capability. Given that they offer a higher efficiency and torque density, particular emphasis has been given to permanent-magnet brushless machines. Various PM brushless machine topologies have been highlighted, and their relative merits have been briefly described. In general, however, all three machine tech- ologies can meet the performance requirements of traction drives, and each machine technology has merits. h Acknowledgment The authors acknowledge the contributions of colleagues in the Electrical Machines and Drives Group, University of Sheffield, Sheffield, U. K. , and also the support of industrial organizations, in particular, IMRA U. K. Research Centre, Centro Ricerche Fiat, Volvo Te chnology Corporation, and FEV Motorentechnik GmbH. REFERENCES [1] C. C. Chan, BThe state of the art of electric and hybrid vehicles,[ Proc. IEEE, vol. 90, no. 2, pp. 247–275, Feb. 2002. [2] I. Husain, Electric and Hybrid VehiclesVDeign Fundamentals. Boca Raton, FL: CRC, 2003. [3] Y. Honda, T. Nakamura, T. Higaki, and Y. Takeda, BMotor design considerations and test results of an interior permanent magnet synchronous motor for electric vehicles,[ in Proc. IEEE Industry Applications Soc. Annu. Meeting, Oct. 5–9, 1997, pp. 75–82. [4] M. Kamiya, BDevelopment of traction drive motors for the Toyota hybrid system,[ presented at the Int. Power Electronics Conf. , Niigata, Japan, Apr. 4–8, 2005. [5] R. Krishnan, BReview of flux-weakening in high performance vector controlled induction motor drives,[ in Proc. IEEE Int. Symp. Industrial Electronics, Jun. 17–20, 1996, pp. 917–922. [6] J. M. Miller, A. R. Gale, P. J. McCleer, F. Leonardi, and J. H. Lang, BStarter/ alternator for hybrid electric vehicle: Comparison of induction and variable reluctance machines and drives,[ in Proc. IEEE 1998 Industry Applications Soc. Annu. Meeting, Oct. 12–15, 1998, pp. 513–523. [7] M. Ehsani, K. M. Rahman, and H. Toliyat, BPropulsion system design of electric and hybrid vehicles,[ IEEE Trans. Ind. Electron. , vol. 44, no. 1, pp. 19–27, Feb. 1997. [8] Z. M. Zhao, S. Meng, C. C. Chan, and E. W. C. Lo, BA novel induction machine design suitable for inverter-driven variable speed systems,[ IEEE Trans. Energy Convers. , vol. 15, no. 4, pp. 413–420, Dec. 2000. [9] T. Wang, P. Zheng, and S. Cheng, BDesign characteristics of the induction motor used for hybrid electric vehicle,[ IEEE Trans. Magn. , vol. 41, no. 1, pp. 505–508, Jan. 2005. [10] A. Harson, P. H. Mellor, and D. Howe, BDesign considerations for induction machines for electric vehicle drives,[ in Proc. IEE Int. Conf. Electrical Machines and Drives, Sep. 11–13, 1995, pp. 16–20. [11] D. W. Novotny and T. A. Lipo, Vector Control and Dynamics of AC Drives. Oxford, U. K. : Clarendon, 1996. [12] F. M. H. Khater and D. W. Novotny, BEfficiency optimization for constant horsepower operation of induction machines,[ in Proc. Int. Conf. Evolution and Modern Aspects of Induction Machines, Torino, Italy, Jul. 1986, pp. 9–16. [13] D. S. Kirscehn, D. W. Novotny, and T. A. Lipo, BOptimal efficiency control of an induction [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] motor drive,[ IEEE Trans. Energy Convers. , vol. 2, no. 1, pp. 70–76, Mar. 1987. L. Xu, Z. Q. Zhu, and D. Howe, BAcoustic noise radiated from direct torque controlled induction machine drives,[ Inst. Elect. Eng. Proc. -Elect. Power Appl. , vol. 147, no. 6, pp. 491–496, 2000. T. J. E. Miller, Switched Reluctance Motors and Their Control. Oxford, U. K. : Magna Physics and Clarendon, 1993. T. J. E. Miller, Electronic Control of Switched Reluctance Machines. New York: Reed, 2001, pp. 227–245. B. Fahimi, A. Emadi, and R. B. Sepe, BA switched reluctance machine-based starter/alternator for more-electric cars,[ IEEE Trans. Energy Convers. , vol. 19, no. 1, pp. 116–124, Mar. 2004. K. M. Rahman and S. E. Schulz, BDesign of high-efficiency and high-torque-density switched reluctance motor for vehicle propulsion,[ IEEE Trans. Ind. Appl. , vol. 38, no. 6, pp. 1500–1507, Nov. /Dec. 2002. S. S. Ramamurthy and J. C. Balda, BSizing a switched reluctance motor for electric vehicles,[ IEEE Trans. Ind. Appl. , vol. 37, no. 5, pp. 1256–1263, Sep. /Oct. 2001. B. C. Mecrow, BNew winding configurations for doubly salient reluctance machines,[ IEEE Trans. Ind. Appl. , vol. 32, no. 6, pp. 1348–1356, Nov. /Dec. 1996. B. C. Mecrow, J. W. Finch, E. A. El-Kharashi, and A. G. Jack, BSwitched reluctance motors with segmental rotors,[ Inst. Elect. Eng. Proc. -Elect. Power Appl. , vol. 149, no. 4, pp. 245–254, Jul. 2002. M. Krishnamurthy, C. S. Edrington, A. Emadi, P. Asadi, M. Ehsani, and B. Fahimi, BMaking the case for applications of switched reluctance motor technology in automotive products,[ IEEE Trans. Power Electron. , vol. 21, no. 3, pp. 659–675, May 2006. K. M. Rahman, B. Fahimi, G. Suresh, A. V. Rajarathnam, and M. Ehsani, BAdvantages of switched reluctance motor applications to EV and HEV: Design and control issues,[ IEEE Trans. Ind. Appl. , vol. 36, no. 1, pp. 111–121, Jan. /Feb. 2000. S. A. Long, N. Schofield, D. Howe, M. Piron, and M. McClelland, BDesign of a switched reluctance machine for extended speed operation,[ in Proc. IEEE Int. Electric Machines and Drives Conf. , Jun. 1–4, 2003, pp. 235–240. N. Schofield and S. A. Long, BGenerator operation of a switched reluctance starter/ generator at extended speeds,[ in Proc. IEEE Conf. Vehicle Power and Propulsion, Sep. 7–9, 2005, pp. 453–460. [26] C. S. Edrington, M. Krishnamurthy, and B. Fahimi, BBipolar switched reluctance machines: A novel solution for automotive applications,[ IEEE Trans. Veh. Technol. , vol. 54, no. 3, pp. 795–808, May 2005. [27] S. Dixon and B. Fahimi, BEnhancement of output electric power in switched reluctance generators,[ in Proc. IEEE Int. Electric Machines and Drives Conf. , Jun. 1–4, 2003, pp. 849

William Faulkner s A Rose For Emily - 857 Words

William Faulkner’s A Rose for Emily is a dark and tragic tale about a lonely upper-class woman struggling with life and customs in the South. The story deals with themes such as the inevitability of change and the futility in trying to stop it. Faulkner succeeds in creating a suspenseful and mysterious story by the effective use of literary techniques, such as foreshadowing, the themes and symbolism and the unique use of other narrative techniques that elevates the overall suspense in the story. In A Rose for Emily, suspense and interest is first created by predicting the death of the main character in the opening of the story. This method of storytelling is commonly used in other fields of media such as film and other forms of literature. Faulkner uses foreshadowing masterfully by showcasing the result of the narrative in the beginning to create expectations for an action that has not happened yet and has given the audience a specific even to look forward to. In this case, that event is the death of Miss Emily. The question that the reader will naturally ask while reading is, â€Å"How exactly did Miss Emily die?†. Foreshadowing is used extensively in this story. For instance, one of the most important examples of foreshadowing in the story is when Faulkner uses the smell in Emily’s house throughout the story to give subtle hints to Homer Barren’s true fate. After all, only a decaying body can smell so horrendous for so long. It’s stated in the s tory that the townspeople hadShow MoreRelatedWilliam Faulkner s A Rose For Emily951 Words   |  4 Pagesliterary Response to â€Å"A Rose for Emily† â€Å"A Rose for Emily† by William Faulkner was published in 1930. This short story is set in an old southern town. I believe that this and several other combinations of events are what made the main character Miss Emily go insane. Miss Emily was an old school southern woman trapped in a modernizing society. She tried desperately to keep to her old ways, but the changes that happened around her were inevitable. This made me feel like something was going to goRead MoreWilliam Faulkner s A Rose For Emily1316 Words   |  6 Pagesminuscule detail in the writing. In order to fully enjoy William Faulkner’s â€Å"A Rose for Emily† readers must do the latter. Faulkner is a witty writer; some symbols are less obvious than others in his writing. To fully appreciate and obtain full meaning of the text readers must pay attention to his symbols and how they contribute to the greater theme. William Faulkner uses symbolization in â€Å"A Rose for Emily† to develop a theme of personal struggle. Emily faces many personal struggles: her relationship withRead MoreWilliam Faulkner s A Rose For Emily1181 Words   |  5 Pages Is William Faulkner s A Rose for Emily iconic American literature? Faulkner uses setting, theme and plot to show the ways â€Å"A Rose for Emily† is an iconic American literature. Faulkner saw the Forum magazine with his short story he wrote, â€Å"A Rose for Emily† and found out that was his first national publication. The Mississippi Writers Page says, â€Å"The man himself never stood taller than five feet, six inches tall, but in the realm of American literature, William Faulkner is a giant† (MWP). Read MoreWilliam Faulkner s A Rose For Emily1528 Words   |  7 Pagespoint of view is A Rose for Emily told? Why? In William Faulkner s short story A Rose for Emily the reader is given the account of an old woman who is rejected by society. The reader is acquainted with Miss Emily Grierson by a spectator, somebody who is not Miss Emily, but rather part of the town that rejects her. The storyteller has a somewhat omniscient perspective, knowing more than the normal town s individual, however not all that matters there is to think about Miss Emily. The storytellerRead MoreWilliam Faulkner s A Rose For Emily1801 Words   |  8 Pages William Faulkner is known for his many short stories, however, many has wondered what has influenced him in writing these stories. Like his well known, most famous short story â€Å"A Rose for Emily†, which has always been compared to â€Å"Barn Burning†, one of Faulkner’s other short story. It only make sense to compare them two together because these two stories has may similarities , whether it may be in setting , characters or style they favor each other . Nevertheless they also have many differencesRead MoreWilliam Faulkner s A Rose For Emily957 Words   |  4 PagesBereavement While a â€Å"Rose for Emily† by William Faulkner and â€Å"A Good Man is Hard to Find† by Flannery O’Connor share the common themes of unexpected death and the old south, the murders found in each story are vastly different. Both stories tell of strong female protagonists who don’t cope well with change and both foreshadow death right from the beginning, but the murderers themselves come from completely different worlds. Emily Grierson of â€Å"A Rose for Emily and the grandmother in â€Å"ARead MoreWilliam Faulkner s A Rose For Emily879 Words   |  4 Pagesare both similar due to how these emotions cause a human to act irrationally. The lone woman in A Rose for Emily and the cashier, Sammy, in A P both portrayed a greater sense of hate which overcame their love. We as humans, capable of powerful emotion typically act too quickly to even understand the consequences of our actions. One prime example is portrayed in William Faulkner’s A Rose for Emily, Emily loved Homer tremendously, however he did not feel the same way †he liked men, and it was knownRead MoreWilliam Faulkner s A Rose For Emily1682 Words   |  7 PagesLyons Professor Amy Green Writing about Literature COM1102 Oct. 06, 2015 William Faulkner s A Rose for Emily is a short story that has also been adapted into a short film; both have been largely debated. Faulkner’s lack of a normal chronology and situation-triggered memories generates a story that has many understandings among its readers, but surprises everyone at the end. When asked about the title of his story, Faulkner said, [The title] was an allegorical title; the meaning was, here was aRead MoreWilliam Faulkner s A Rose For Emily854 Words   |  4 Pages Literary Response to â€Å"A Rose for Emily† â€Å"A Rose for Emily† by William Faulkner was published in 1930. This short story is set in an old southern town. I believe that this and several other combinations of events are what made the main character Miss Emily go insane. Miss Emily was a old school southern woman trapped in a modernizing society. She tried desperately to try and keep to her old ways, but the changes were inevitable. This made me feel like something was going to go wrong very early inRead MoreWilliam Faulkner s A Rose For Emily1810 Words   |  8 Pages William Faulkner is one amazing writing ,who is known for his many short stories .However, many has wondered what has influenced him in writing these stories . Like his well known, most famous short story â€Å"A Rose for Emily†, which has always been compared to â€Å"Barn Burning†, one of Faulkner’s other short story. It only make sense to compare them two together because these two stories has may similarities , whether it may be in setting , characters or style they favor each other . Nevertheless