分数槽集中绕组内置式与表贴式电机对比

Comparison of Interior and Surface PM Machines Equipped With Fractional-Slot Concentrated Windings for Hybrid Traction Applications

Patel B.Reddy ,Member,IEEE ,Ayman M.El-Refaie ,Senior Member,IEEE ,Kum-Kang Huh ,Member,IEEE ,

Jagadeesh K.Tangudu ,Member,IEEE ,and Thomas M.Jahns ,Fellow,IEEE

Abstract —Electric drive systems,which include electric ma-chines and power electronics,are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector.To have signi?-cant effect,electric drive technologies must be economical in terms of cost,weight,and size while meeting performance and reliability

expectations.This paper will provide details of the design,analy-sis,and testing of two permanent magnet (PM)machines that were developed to meet the FreedomCar 2020speci?cations.The ?rst machine is an interior PM (IPM)machine and the second machine is a surface PM (SPM)machine.Both machines are equipped with fractional-slot concentrated windings (FSCW).The goal of this pa-per is to provide a quantitative assessment of how achievable this set of speci?cations is,as well as a comparison with the state of the art.This paper will also quantitatively highlight the tradeoffs between IPM and SPM FSCW machines especially in the context of traction applications.

Index Terms —Comparison,concentrated,fractional-slot,high speed,interior,machines,permanent magnet (PM),surface,trac-tion,windings.

I.I NTRODUCTION

E

LECTRIC drive systems,which include electric machines and power electronics,are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector.To have signif-icant effect,electric drive technologies must be economical in terms of cost,weight,and size while meeting performance and reliability expectations.

The objective of this paper is to develop high power den-sity,high-ef?ciency permanent magnet (PM)motors at a lower

Manuscript received August 1,2011;revised January 7,2012;accepted March 19,2012.Date of publication May 3,2012;date of current version July 27,2012.This work was supported by the Department of Energy under Award DE-FC26-07NT43122.Paper no.TEC-00338-2011.

P.B.Reddy,A.M.El-Refaie,and K.-K.Huh are with the Electrical Machines Laboratory,General Electric Global Research Center,Niskayuna,NY 12309USA (e-mail:reddy@https://www.wendangku.net/doc/b210357037.html,;elrefaie@https://www.wendangku.net/doc/b210357037.html,;huhk@https://www.wendangku.net/doc/b210357037.html,).J.K.Tangudu was with the Department of Electrical and Computer Engineer-ing,University of Wisconsin-Madison,Madison,WI 53706USA.He is now with the United Technologies research Center,East Hartford,CT 06118USA (e-mail:jagadeesh.tangudu@https://www.wendangku.net/doc/b210357037.html,).

T.M.Jahns is with the Department of Electrical and Computer Engineer-ing,University of Wisconsin-Madison,Madison,WI 53706USA (e-mail:jahns@https://www.wendangku.net/doc/b210357037.html,).

Color versions of one or more of the ?gures in this paper are available online at https://www.wendangku.net/doc/b210357037.html,.

Digital Object Identi?er 10.1109/TEC.2012.2195316

TABLE I

F REEDOM CAR 2020A DV ANCED M OTOR P ERFORMANCE R EQUIREMENTS

cost.The FreedomCar 2020required motor set of speci?cations is summarized in Table I and Fig.1.It can be seen that this is a very challenging set of speci?cations including maximum speed of 14000r/min,continuous power of 30kW over 20–100%speed range,peak power of 55kW for 18s at 20%speed,minimum ef?ciency of 95%over 10–100%speed range,105?C cooling inlet temperature,?xed nominal 325-V dc source,ap-proximately twice the power densities (at maximum speed)of the present state of the art (SoA)[1],and an aggressive cost target of US$275per unit for mass manufacturing in quantities of 100000s.

This paper presents and compares two PM designs equipped with fractional-slot concentrated windings.The ?rst is a fractional-slot concentrated winding (FSCW)interior PM (IPM)machine,while the second is an FSCW surface PM (SPM)ma-chine.These high-performance FSCW PM machines have been developed,built,and tested to address the challenging perfor-mance metrics imposed by the FreedomCar 2020advanced trac-tion motor speci?cations.Signi?cant efforts have been focused on trying to meet the demanding ef?ciency speci?cations and

0885-8969/$31.00?2012IEEE

Fig.1.FreedomCar2020motor speci?ed torque–speed curve. minimizing the losses.Losses in the copper,iron,and magnets are investigated under a variety of operating conditions,with a focus on high-speed operation.Finite-element analysis(FEA)is utilized to predict the loss components in these machines during the design stage.

Experimental results for both machines will be presented. These results will be compared to their respective predictions from the FEA models.The testing of the two machines has been done at two different locations(using two different lab setups)under different thermal conditions.Due to the difference in mechanical losses between the two lab setups,and in order to have a fair comparison,the focus is mainly on comparing the electrical performance in terms of output power and losses. Key conclusions are drawn based on power density,electrical ef?ciencies,losses,and torque.

II.IPM M ACHINE

Segmented stator structures equipped with FSCW have nu-merous well-established advantages associated with this type of windings including

high slot?ll factor,short-end turns,and high ef?ciency and power density[2]–[9].A ten-pole,12-slot IPM machine using high-strength sintered NdFeB magnets is built with12individually wound tooth structures,making it a double-layer winding pattern.The stator structure along with a couple of teeth of the IPM machine is shown in Fig.2.The rotor is made from laminations with the magnets forming a V-shape within the rotor as shown in Fig.3.The stator and the rotor laminations belong to the HF10material,which is known to have considerably a lower thickness value of0.25mm.This lower thickness value contributes to the reduced iron loss coef-?cients in the laminations,helping to reduce the iron losses at top speeds,where in the frequencies exceed values of1kHz. Every teeth segment of the stator laminations is punched and stacked to provide the building block of the machine.The copper winding is wound around each individual teeth segment to create the double-layer con?guration.The?nal assembled stator is shown in Fig.2.The process of segmentation is able to reach slot?ll factor values of50%(de?ned as ratio of the copper area to the total slot area).

The assembly of the stator structure begins with a single teeth structure,with the winding already wound around it.The adja-cent teeth structures are added in either ends,where in grooves are present in the stator yoke to form a well-de?ned pattern.The Fig.2.Stator of the FSCW-IPM machine.

Fig.3.Rotor of the FSCW-IPM machine.

structure with two assembled teeth segments with windings is shown in Fig.2.Repeating this structure over the entire360?forms the complete stator,which is also shown in Fig.2.

The magnets are made out of Vacodym890material and have a magnetic remanence of1.07T at room temperature,a relative permeability of1.037and a maximum operating temperature of 240?C.

The rotor geometry has gone through a multivariable op-timization in order to achieve the best torque density in the machine along with the best ef?ciency.The parameters chosen were the rotor magnet locations,thickness along with pole arcs of the magnets.The bridge and center-post thicknesses have been optimized for mechanical integrity at150%times of the maximum speed of the rotor.The rotor structure is made with two nonmagnetic end-plates to hold the rotor laminations to-gether.The effect of the end-plates on the motor performance has been described in[10].

The operating points in terms of the d-and q-axis currents of the FSCW-IPM machine along with the predicted loss compo-nents under rated-load conditions(30kW)are shown in Figs.4 https://www.wendangku.net/doc/b210357037.html,bination of2-D FEA and3-D FEA was used to evaluate losses in the magnets and in the stator and rotor lami-nations(including both hysteresis and eddy current losses).The magnet losses are the loss components arising out of the3-D ?nite-element runs with the stator current excitation and magnet segmentation,while it is seen that2-D FEA is quite adequate for

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Fig.4.Predicted I d –I q current over the speed range above 2800r/min under rated-load conditions (30kW)for FSCW-IPM

machine.

Fig.5.Predicted losses over the speed range under rated-load condition (30kW)for FSCW-IPM machine.

the iron loss calculations.From Fig.4,it can be seen that as ex-pected,the q -axis current decreases with speed (due to the lower torque required to maintain constant power operation),[4],[5],while the d -axis current increases with speed due to ?ux weak-ening to keep the voltage within the available limits (based on 325-V nominal dc-bus voltage).

The predicted losses in the IPM machine under rated-load operating conditions (30kW)are shown in Fig.5.It can be seen that due to axial segmentation of the magnets as well as the fact the magnets are buried in the rotor laminations relatively far away from the air gap,the magnet losses are fairly low across the whole speed range [8].Since much attention has been paid to reducing the ac losses in the windings (mainly in terms of the strand size and Litz wire construction),the copper losses are mainly dependent on the current and,as can be seen,the copper loss variation is very similar to the total current variation shown in Fig.4.Also the use of FSCW helps in reducing the copper losses due to the reduction in the copper losses in the end windings.

It can also be seen in Fig.5that the stator and rotor core losses are the dominant components and form the major portion of the total losses in the machine.Both increase with speed as expected.The rich space harmonic contents in the FSCW contribute to higher core losses in both the rotor and stator [9]–[12].Also,the presence of the rotor “slots”(where the magnets reside)introduces additional harmonics,which cause higher stator core losses.In addition,the higher pole count in the FSCW machines (ten poles in this case)contributes to the result that the total losses at higher speeds (especially at 14000r/min)

are

Fig. 6.Experimental measured mechanical losses with unmagnetized

magnets.

Fig.7.Experimental results from the FSCW-IPM machine under rated-load condition.

signi?cant.The total predicted ef?ciency shown later in this paper is well above the minimum requirement over most of the speed range,but at the top speeds,the predicted ef?ciency drops below the required minimum of 95%.

III.E XPERIMENTAL R ESULTS OF IPM M ACHINE

In order to separate mechanical and electrical losses,the ma-chine was ?rst built using unmagnetized magnets.Fig.6shows the test results for the machine with unmagnetized magnets.Based on the test results,more modi?cations are planned to reduce mechanical losses at 14000r/min by ～35%.These in-clude using lower loss bearings,lower loss seals,and reducing churning losses due to the rotor inner bore cooling.

Next,the machine with magnetized magnets was tested.Fig.7shows several measured machine performance parameters at rated power as well as a comparison of measured and predicted ef?ciency.It can be seen that the voltage limit is reached at approximately 5000r/min,which represents the machine corner speed.The output mechanical power (Pmech)is kept in the vicinity of 32kW over the entire speed range,while the overall ef?ciency is higher than 95%over a speed range of 2800–8500r/min.The results show that the machine meets both peak and steady-state power requirements.

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Fig.8.Experimental results from the FSCW-IPM machine under partial-load conditions.

Mechanical losses at higher speeds are seen to cause devia-tion from the predictions at higher speeds.At the top speed,the experimental ef?ciency is approximately87%,which is approx-imately3%lower than the predictions,with most of the drop attributed to the mechanical causes cited previously.

The experimental results under the partial-load20%rated torque conditions over a speed range of1400–14000r/min are shown in Fig.8.A higher difference is seen in the predicted and experimental ef?ciencies under the partial-load conditions.The machine is able to exceed the partial-load minimum ef?ciency requirement of95%at the lower speeds,while it is able to de-liver at least93%ef?ciency up to a speed of8000r/min.The ef?ciency drops to～87%at14000r/min.One of the major sus-pects for causing the lower ef?ciency is the presence of the me-chanical losses in the system along with the current regulation. Since the FSCW-IPM machine has more harmonics in the back electromotive force(EMF)waveform,pure sinusoidal current regulation might not be enough to achieve the required partial-load ef?ciencies.In these machines,the presence of harmonics allows for improvements in ef?ciencies with the introduction of current pro?ling.In[13]and[14],the authors have demon-strated the potential of optimal current pro?ling to improve the ef?ciency and the torque production in electric machines.

The torque ripple is expected to be very low in the FSCW-IPM machines[2]due to the fact that the lowest common multiple of the stator slots and the rotor poles being very high.This rule[2] is justi?ed by the torque waveform in the machine at a speed of 2800r/min,while providing a power of33kW.The peak–peak torque ripple is seen to be5.5%,while the average is103.2N·m. As shown in Fig.9.

As part of the machine test sequence,steady-state heat runs were performed(times of runs were between45min and1h, time taken to reach steady-state temperatures in windings)on the FSCW-IPM machine from2800to14000r/min under rated-load conditions.The steady-state temperature rise in the ma-chine measured in different locations in the machine(yoke, teeth,teeth-tip,end winding,center of the windings,copper end region in the slot,the casing,the cooling jacket,and the ro-tor)is shown in Fig.10.The machine was able to

successfully Fig.9.Finite element predictions of the torque versus time at2800r/min, 33kW in the FSCW-IPM

machine.

Fig.10.Measured temperature rises in various locations in the FSCW-IPM machine.

withstand the temperature rise in the machine under all the op-erating conditions,with the top temperatures being within the insulation limits.The maximum temperature rises was seen in the copper regions,mainly the end-winding portion along with the slot regions inside the slots.

With a coolant temperature of105?C,the end-winding tem-perature would reach approximately175–185?C,well within the220–240?C temperature limits for the Class C insulation selected for the machine’s magnet wire.Although the teeth tips also reach similar temperatures under some of the operating con-ditions,heat extraction through the laminations is easier since there is no insulation in the thermal path.

IV.SPM M ACHINE

Based on the FSCW-SPM machine models developed in[4] and[15],closed-form analysis has been used in the machine design process.The?nal design of the FSCW-SPM machine is based on the FreedomCar advanced traction motor speci?cations that are summarized in Table I.The design and fabrication of the FSCW-SPM machine has been discussed in[16]and will not be repeated here.Instead,the high-level details are presented. The constraint on the maximum back-EMF voltage of 600V(pk)line-to-line at the top speed of14000r/min is dif?cult to meet in the absence of magnetic saliency.In[17],the special challenges associated with designing an SPM machine to meet

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Fig.11.Stator of FSCW-SPM

machine.

Fig.12.Rotor of FSCW-SPM machine.

the FreedomCar power density requirements while simultane-ously satisfying the maximum current and maximum back-EMF constraints have been investigated.As a result,the maximum back-EMF constraint was relaxed to 800V (pk)line-to-line for this machine design exercise.

Similar to the FSCW-IPM machine,the FSCW-SPM machine has 10poles and 12slots.The stator structure is segmented as shown in Fig.11.The stator laminations are made from HF10material,which has also been used in the IPM motor.The stator of the SPM shares the manufacturing and assembly process as the stator of the IPM motor.On the other hand,the rotor assembly uses a laminated rotor core with ten ?at surfaces to mount the segmented bread-loaf magnets.The magnets are high-strength sintered NdFeB magnets,belonging to the same Vacodym890material used in the IPM motor.The magnets are segmented both circumferentially and axially in order to minimize the eddy current losses.Carbon ?ber banding is tightly wound around the rotor outer periphery to provide the required structural containment at high rotor speeds.A view of the ?nal rotor assembly is provided in Fig.12.A view of the complete cross section is shown in Fig.13.

The variation of the operating currents in the d -and q -axis in the FSCW-SPM machine under rated power conditions,similar to the IPM case,is shown in Fig.14.It can be seen that,compared to the FSCW-IPM machine,?ux weakening begins at lower speeds due to the higher magnet ?ux linkage.

The predicted losses of the FSCW-SPM machine under rated-load conditions (30kW)are shown in Fig.15.The SPM machine has a different loss picture compared to the IPM con?guration.The majority of the losses occur in the magnets and the

stator

Fig.13.

Cross section of FWCW-SPM

machine.

Fig.14.Predicted I d –I q current over the speed range above 2800r/min under rated-load conditions (30kW)for FSCW-SPM

machine.

Fig.15.Predicted losses over the speed range under rated-load condition (30kW)for FSCW-SPM machine.

core,while the rotor core and copper losses are signi?cantly lower.Despite the axial and circumferential segmentation,the magnets mounted in the air gap are exposed to all the harmonics arising from the concentrated windings.These magnet losses are unavoidable and are challenging to dissipate because of the lack of good convection paths aggravated by the presence of the carbon ?ber retaining ring around the magnets.

The measured ef?ciency under partial-load conditions is shown later in Fig.27.The experimental ef?ciency is in the range 93–95%for tested speeds up to 5000r/min and closely matches the analytical and ?nite-element results.

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Fig.16.Experimental back EMF for FSCW-SPM machine at 2800r/min for 50?C

operation.

Fig.17.Harmonic spectrum of back EMF for FSCW-SPM machine at 2800r/min for 50?C operation.

V .E XPERIMENTAL R ESULTS OF SPM M ACHINE

As previously mentioned,the SPM machine was tested using a different lab setup than the IPM machine.One of the issues with the testing was the constraints on the dynamometer ma-chine.With the maximum speed of the dyno machine limited to 6000r/min,all testing on the device-under-test machine has been limited to 5800r/min.Additionally,the absence of liquid cooling for the stator placed additional thermal stress on the ma-chine in terms of the operating temperatures.The only cooling available for the test machine was forced air cooling.However,the machine was tested at room temperature,which allowed for quite a bit of temperature margin in the machine.

The comparison of the open-circuit back-EMF waveform to-gether with the harmonic spectrum is shown in Figs.16and 17,respectively.The experimental back EMF is approximately 6%lower than the predictions at 60?C (magnet operating temper-ature).The harmonic spectrum also shows the clean nature of the phase back EMF of the SPM machine,allowing for better current regulation compared to the IPM machine.The distortion observed in the back-EMF waveform is known to arise from the space harmonic present in the rotor.

Fig.18shows the measured performance of the SPM machine under full load up to a speed of 5800r/min.The machine is able to produce a power of 30kW over this speed range while op-erating from a dc-bus voltage of 300V dc .Moreover,the ?nite element predicted power is seen to be higher than the exper-imentally measured power.One of the major reasons for

this

Fig.18.Measured torque and power performance of the FSCW-SPM machine under rated-load

conditions.

Fig.19.Measured voltage and current of the FSCW-SPM machine under rated-load

conditions.

Fig.20.Measured ef?ciency of the FSCW-SPM machine under rated-load condition.

discrepancy is the lower back EMF that was previously men-tioned.The equivalent phase RMS voltage and the phase current are shown in Fig.19.The current is limited to a maximum of 170A rms ,while the voltage is limited to an equivalent dc-bus voltage of 300V .

Fig.20shows a comparison of the analytical and ?nite-element predictions and the experimental ef?ciency values un-der rated power conditions,as described previously.The FSCW-SPM machine delivers measured ef?ciency values of 95%or higher up to a speed of 5000r/min.

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Fig.21.Measured ef?ciency for FSCW-SPM machine under partial-load

conditions.

Fig.22.Measured temperatures for the FSCW-SPM machine under rated-load conditions at 4000r/min.

The ef?ciency of the FSCW-SPM under the partial-load con-dition (20%of rated torque)is similar to that of the FSCW-IPM machine (see Fig.21).The ef?ciency is in the vicinity of 94%over the speed range up to 4800r/min.

As with the FSCW-IPM machine,heat runs were carried out on the FSCW-SPM machine at 4000r/min,as shown in Fig.22.The machine temperature rise is in the vicinity of 60?C without the presence of liquid cooling on the stator side.The end winding in the FSCW-SPM machine experiences the highest temperature due to the absence of direct cooling.This test shows that the motor could operate under steady-state conditions of 30kW at 4000r/min with only forced air cooling without exceeding temperature limits.

VI.C OMPARISON OF THE T WO M ACHINES

As previously mentioned,it is quite possible that the mechan-ical losses are different for the two machines due to differences between the motor mechanical designs and also drivetrains of the two dynamometers.To eliminate this source of discrep-ancy,the two machines are compared in terms of their predicted electrical ef?ciencies.The predicted ef?ciencies of the two ma-chines under rated-load conditions are shown in Fig.23.The IPM machine is predicted to be more ef?cient by approximately 0.5%at lower speeds,while the SPM machine is more ef?cient at higher speeds,though only by 1%.Neither machine emerges as clearly superior in terms of ef?ciency since the impact of the mechanical losses would cause these predicted differences to

be

https://www.wendangku.net/doc/b210357037.html,parison of predicted electrical ef?ciencies of the two FSCW machines under rated-load

condition.

https://www.wendangku.net/doc/b210357037.html,parison of experimental electrical ef?ciencies of the two FSCW machines under rated-load

conditions.

https://www.wendangku.net/doc/b210357037.html,parison of predicted core and magnet losses for the two FSCW machines under rated-load conditions.

marginal over the full speed range.However,it is noteworthy that the two motors achieve such similar ef?ciency values since the loss components are clearly different in the two motors.In order to understand the effect of mechanical losses on the ef?ciency,the experimental ef?ciencies are overlaid in Fig.24.The experimental ef?ciency with the SPM machine clearly falls lower than the prediction by at least a couple of percent of power.However,at this point,it is unclear if the additional losses are due to the electrical or mechanical causes.Further means of resolving this issue would be to use similar approach as the IPM machine i.e.,using a dummy rotor for mechanical losses.

A clearer understanding is obtained comparing the predicted electrical losses under rated-load conditions,as shown in Fig.25.As previously mentioned,the loss breakdown is different in the two machines.Due to the rich harmonic content of the

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TABLE II

K EY M ACHINES P ARAMETERS AND D

IMENSIONS

concentrated windings,the type of rotor matters little in terms of the overall losses.While the FSCW-SPM machine has higher losses in the magnets,the FSCW-IPM machine has higher losses in the stator and rotor cores.While the magnets in the IPM rotor are shielded by the iron,the reduced magnet losses are shifted into the iron.The corresponding results for partial-load conditions are similar to those for rated conditions and are not presented here.

Table II summarizes the key parameters,dimensions,and performance metrics of both machines.Since both machines are designed for the same set of speci?cations and for the same constant power speed range,they are very comparable in terms of mass,volume,and,hence,power density.This is consistent with some of the ?ndings in [16]–[19].Due to the reluctance torque component in the FSCW-IPM machine,it requires lower magnet mass.The FSCW-SPM machine exhibits better over-load capability since it can produce the 55-kW peak power at 320A rms versus 400A rms in the FSCW-IPM machine.This is primarily attributed to lower magnetic saturation effects in the FSCW machine due to its larger effective air gap.

The ?ux density waveforms for each machine are shown in Figs.26and 27for IPM machines,while the similar graphs for the SPM machine are shown in Figs.28and 29,respec-tively.The ?ux density waveform for the loaded condition of 100A rms ,50?gamma (for 2800continuous power operating point)and the open-circuit waveform are shown in Fig.26,while the ?ux density harmonic spectrum is shown in Fig.27.The similar waveforms for the SPM machine are shown in Figs.28and 29,respectively.The IPM machines show

harmonic

Fig.26.Airgap ?ux density for FSCW-IPM machine at 2800

r/min.

Fig.27.Harmonic spectrum of Airgap ?ux density for FSCW-IPM machine at 2800

r/min.

Fig.28.Airgap ?ux density for FSCW-SPM machine at 2800r/min.

numbers of 7th,15th,17th,and 19th,which are a source for additional iron losses in the IPM machine,while the SPM shown in Figs.28and 29,do not contain the 7th,17th,and the 19th harmonic,respectively.These waveforms show that the iron losses in the rotor are more prominent in the IPM machine.Figs.30and 31show comparisons of the two FSCW machines to the FreedomCAR speci?cations and SoA machines (based on the test results published in [1]).Both FSCW machines have

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Fig.29.Harmonic spectrum of Airgap ?ux density for FSCW-SPM machine at 2800

r/min.

https://www.wendangku.net/doc/b210357037.html,parison of torque densities and active materials cost for the two FSCW machines with the state-of-the-art machines as well as the FreedomCar 2020

speci?cations.

https://www.wendangku.net/doc/b210357037.html,parison of measured rated ef?ciencies for the two FSCW ma-chines with the state-of-the-art machines as well as the FreedomCar 2020speci?cations.

signi?cantly higher continuous torque density (based on active mass)compared to the SoA machine,even though the FSCW machines have lower dc-bus voltage,325V ,and higher coolant inlet temperatures,105?C,compared to the SoA machines that operate at 650-V dc-bus voltage and 65?C coolant inlet temperatures.

Although the cost target is not currently met,the active mate-rial cost for the FSCW machines is signi?cantly lower compared to the SoA machines.This is seen as a result of the thermal bene-?ts arising from the lower copper losses in the FSCW machines,which also leads to size reduction.

Fig.31shows that both FSCW machines have comparable rated-load ef?ciency values.Even though the 95%ef?ciency target can be met only up to ～9000r/min,the ef?ciency at the maximum speed is signi?cantly higher than the SoA machines.

VII.C ONCLUSION

IPM and SPM machines equipped with FSCW can provide high performance and meet several of the very challenging Free-domCar 2020speci?cations.Two machines,one interior PM and the other surface PM,were designed to meet these speci?cations.The analytical and experimental results for both machines have been compared and the design tradeoffs have been highlighted.The performance characteristics of both machines have also been compared to those of SoA traction motors.Based on the test results of the prototype machines built to date,the 30/55-kW 14000-r/min advanced IPM-and SPM-FSCW machine archi-tectures achieve signi?cant improvements in full-load power density and ef?ciency compared to the SoA machines.

A CKNOWLEDGMENT

The authors would like to thank T.Bohn at Argonne Na-tional Laboratory for his support of the FSCW-SPM machine development.

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1–6.

Patel B.Reddy(S’07–M’10)received the Bache-

lor’s degree in electrical engineering from the Indian

Institute of Technology,Kharagpur,India,in2003,

during which he worked in the area of stability of

power electronic converters.He received the Ph.D.

degree in electrical and computer engineering from

the University of Wisconsin-Madison,Madison,in

2010.

From2004to2010,he was a Research Assis-

tant with the Wisconsin Electric Machines and Power

Consortium.Since2010,he has been with the Electri-cal Machines Laboratory,General Electric Global Research Center,Niskayuna,

NY.His interests include electrical machines and

drives.

Ayman M.El-Refaie(S’95–M’05–SM’07)received

the B.S and M.S degrees in electrical power engi-

neering from Cairo University,Giza,Egypt,in1995

and1998,respectively,and the M.S.and Ph.D.de-

grees in electrical engineering from the University

of Wisconsin-Madison,Madison,in2002and2005,

respectively.

Since2005,he has been a Senior Engineer at the

Electrical Machines and Drives Laboratory,General

Electric Global Research Center,Niskayuna,NY.Be-

tween1999and2005,he was a Research Assistant at the University of Wisconsin-Madison in the Wisconsin Electric Machines and Power Electronics Consortium group.Between1995and1998,he was an Assistant Lecturer at Cairo University and the American University in Cairo. His interests include electrical machines and drives.He has25journal and39 conference publications,with several others pending.He has13issued U.S. patents and25U.S.patent applications with several others pending.At Gen-eral Electric,he has worked on several projects that involve the development of advanced electrical machines for various applications including,aerospace, traction,wind,and water desalination.He was the Program Manager and Princi-pal Investigator of a$5.6Million Department of Energy(DOE)-funded project to develop next generation traction motors for hybrid vehicles.He is currently the Program Manager and Principal Investigator of a$12Million DOE-funded project to develop next-generation traction motors for hybrid vehicles that do not include rare-earth materials.

Dr.El-Refaie received several management awards at General Electric in-cluding the prestigious2011Albert W Hull Award,the highest individual award for early career researchers.He also received“The2009Forward Under40”from the Wisconsin Alumni Association awarded to outstanding University of Wisconsin alumni under the age of40and the IEEE Industry Applications So-ciety(IAS)“2009Andrew Smith Outstanding Young Member Award.”He is currently the Vice Chair for the IEEE IAS Transportation Systems Commit-tee and an Associate Editor for the Electric Machines Committee.He was a Technical Program Chair for the IEEE2011Energy Conversion Conference and Exposition(ECCE).He will be the General Chair for ECCE2014.He is a member of Sigma

Xi.

Kum-Kang Huh(S’03–M’09)was born in Seoul,

Korea.He received the B.S.and M.S.degrees in con-

trol and instrumentation engineering from Korea Uni-

versity,Seoul,in1993and1995,respectively,and the

Ph.D.degree in electrical engineering from the Uni-

versity of Wisconsin-Madison,Madison,in2008.

Since2008,he has been with the General Electric

Global Research Center,Niskayuna,NY,where he is

an Electrical Engineer with the Electric Power and

Propulsion Systems Laboratory.Between1995and

2002,he was with the Mando R&D Center,Korea, where he developed electric vehicle traction systems and electric power steering systems.His research interests include modeling,controls,and diagnostics of electric machines,and power electronics

systems.

Jagadeesh K.Tangudu(S’08–M’11)received the

B.E.degree from Andhra University,Visakhapatnam,

India,the M.E.degree from Indian Institute of Sci-

ence Bangalore,Bangalore,India,and the M.S.and

Ph.D.degrees in electrical and computer engineering

from University of Wisconsin-Madison,Madison.

Since2011,he has been with United Technolo-

gies research Center,East Hartford,CT,developing

advanced electrical machines for various UTC busi-

nesses including wind,elevator,and air conditioners.

Prior to his doctoral thesis work,he worked with GE Global Research Center and GE Energy for four years working on large turbo generator,next-generation locomotive motors.He has nine conference

papers.

Thomas M.Jahns(S’73–M’79–SM’91–F’93)re-

ceived the S.B.and S.M.degrees in1974and the

Ph.D.degree in1978from the Massachusetts In-

stitute of Technology,Cambridge,all in electrical

engineering.

He joined the Faculty of the University of

Wisconsin-Madison,Madison,in1998as a Profes-

sor in the Department of Electrical and Computer

Engineering,where he is also an Associate Director

of the Wisconsin Electric Machines and Power Elec-

tronics Consortium.Prior to coming to University of Wisconsin-Madison,he was with GE Corporate Research and Development (now GE Global Research Center)in Schenectady,NY,for15years,where he pursued new power electronics and motor drive technology in a variety of research and management positions.His research interests include permanent magnet synchronous machines for a variety of applications ranging from high-performance machine tools to low-cost appliance drives.During1996–1998, he conducted a research sabbatical at the Massachusetts Institute of Technol-ogy,where he directed research activities in the area of advanced automotive electrical systems and accessories as a Co-Director of an industry-sponsored automotive consortium.

Dr.Jahns is the recipient of the2005IEEE Nikola Tesla Award.He received the William E.Newell Award by the IEEE Power Electronics Society(PELS)in 1999.He has been recognized as a Distinguished Lecturer by the IEEE Industry Applications Society during1994–1995and by IEEE-PELS during1998–1999. He has served as the President of PELS(during1995–1996)and Division II Director on the IEEE Board of Directors(during2001–2002).