Design of an Asymmetrical Rotor for Easy Assembly and Repair of Field Windings in Synchronous Machines

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Design of n Asymmetricl Rotor for Esy Assemly n Repir of Fiel Winings in Synchronous Mchines Nn Yng 1, Wenping Co 1, Zheng Liu 1, John Morrow 2 1 School of Engineering & Applie Science, Aston

ssemly n repir of fiel winings in synchronous mchines. A new rotor geometry is opte in orer to simplify the mnufcture n mintennce process of instlling the rotor winings.

1 Design of n Asymmetricl Rotor for Esy Assemly n Repir of Fiel Winings in Synchronous Mchines Nn Yng 1, Wenping Co 1, Zheng Liu 1, John Morrow 2 1 School of Engineering & Applie Science, Aston University, Unite Kingom 2 School of Electronics, Electricl Engineering n Computer Science, Queen s University Belfst, Unite Kingom Astrct: This pper introuces new symmetricl rotor esign for esy ssemly n repir of fiel winings in synchronous mchines. A new rotor geometry is opte in orer to simplify the mnufcture n mintennce process of instlling the rotor winings. The symmetricl rotor esign is simulte y the 2-D finite element nlysis (FEA), n verifie y experimentl tests on 27.5 kva prototype mchine. The propose topology cn rive own the mintennce n repir costs of the mchine without impcting on the mchine s electro-mgnetic performnce. This esign will hve significnt economic implictions for mchine esign n repir inustry, especilly for mss prouction mrkets such s win turines n engine-genertors. I. INTRODUCTION Woun rotor synchronous genertors re wiely use in inustry, incluing stem turines, iesel-genertor sets (gensets) n win turines [1]-[3]. For stem turines n ieselgenertor sets, their synchronous mchines re operte t fixe spee. In win turines, vrile-spee opertion in synchronous mchines is lso pplicle. In this cse, geroxes re require to convert the slow win spee to the mchine s synchronous spee wheres power converters re use to control the frequency n voltge for gri connection. In woul-rotor synchronous mchines, oth sttor n rotor winings re require. The instlltion of the sttor wining is reltively simple. Pre-mnufcture coils cn e inserte into the sttor slots one y one to form three-phse istriute wining, s shown in Fig. 1. On the contrry, the rotor wining instlltion is lorious. In generl, the rotor coils re wrppe roun the rotor poles to form DC excittion fiel. This cn lso e one y wining mchine, s shown in Fig. 2. The coils re woun roun the pole shoes which re then mounte on top of the pole oies. As the size of the rotor increses, the wining mchine nees to e very lrge. Therefore, this instlltion ecomes more chllenging, costly n lso ffects the physicl integrity of the rotor. In ition, synchronous mchines re prone to wining filures, which ccount for hlf of the totl mchine filures in the fiel [4]. When these mchines rek own, ecision shoul e me either to replce them or to repir them, usully se on n economic nlysis. If rewining ecomes necessry, the rotor wining will e remove n replce y new one. During the process, the rotor core n the mchine efficiency cn e ffecte [5]. If the rotor coils cn e preprouce n inserte into the rotor (similr to the sttor wining), the wining mchine cn e me smller n the mnufcture costs e reuce significntly. Fig. 1. Arrngement of the sttor wining (istriute). Fig. 2. Arrngement of the rotor wining (concentric). 1

II. LITERATURE REVIEW This work resses the mnufcturing issue ssocite with the rotor fiel wining y moifying the rotor structure to llow for esy ssemly of the rotor coils.

The rotor esigns re then moifie n nlyse y the finite element nlysis (FEA). A typicl four pole synchronous mchine is presente in Fig. 3.

However, this topology is quite complex electromgneticlly n the rotor is symmetricl in the xil irection, 3-D FEA tool must e use in orer to etermine its sturtion level n lekge flux.

Another interesting spect of the rotor esign is the use of mgnets n flux rriers in the rotor. Two exmples re shown in Fig. 4 for illustrtion. Fig. 5. Exploe view of the clw-pole mchine [12].

2 II. LITERATURE REVIEW This work resses the mnufcturing issue ssocite with the rotor fiel wining y moifying the rotor structure to llow for esy ssemly of the rotor coils. Tritionl rotor esign concentrtes on chnging the rotor geometry to estlish the treoff etween competing optimistion ojects (such s volume to efficiency, mss to efficiency) [6]. The rotor esigns re then moifie n nlyse y the finite element nlysis (FEA). A typicl four pole synchronous mchine is presente in Fig. 3. Their flux istriutions n electro-mgnetic performnce cn e otine n compre. coils cn e clicke into its position etween the two rotor poles. However, this topology is quite complex electromgneticlly n the rotor is symmetricl in the xil irection, 3-D FEA tool must e use in orer to etermine its sturtion level n lekge flux. This type of mchine hs quite high esign n mnufcture costs. Fig. 3. Topology of tritionl slient rotor for synchronous mchines [6]. Another interesting spect of the rotor esign is the use of mgnets n flux rriers in the rotor. Two exmples re shown in Fig. 4 for illustrtion. Fig. 5. Exploe view of the clw-pole mchine [12]. As fr s the rotor pole geometry is concerne, symmetricl rotors were reporte in the literture [12]-[14]. These rotor esigns re chrcterise with unequl pole numers of the sttor n rotor [15] or unlnce rotor slot geometry [16]. Two symmetricl rotor geometries re shown in Fig. 6. Both esigns use the symmetricl rotor geometry for reluctnce mchines which re not ccepte y inustry. This pper opts n symmetricl rotor esign for the purpose of simplifying the ssemly process of the rotor wining in the cse of synchronous mchines. Fig. 4. Rotor esigns with mgnet-se flux rriers [7]. () Design 1. () Design 2. These esigns guie the flux to flow in chosen irections, s to enhnce the ir-gp flux ensity This technology cn e pplie to vrile types of mchines such s synchronous reluctnce mchines [7]-[9], woun-rotor synchronous mchines [10], n sttor woun-fiel synchronous mchines [11]. However, ing the flux rriers n mgnets gives rise to the complexity n mnufcture cost of the rotor. Therefore, this technology is not wiely pplie in inustry. Alterntively, clw-pole lterntors cn provie simple wining instlltion solution [12]. As shown in Fig. 5, the fiel Fig. 6. Existing symmetricl rotor esigns. () Design 1 [13]. () Design 2 [17]. III. PROPOSED MACHINE TOPOLOGY Bse on the existing rotor esigns, new rotor is evelope in wy tht the rotor coils cn e instlle to the pole irectly. A 3-D igrm of the propose rotor is illustrte in Fig. 7. In the propose topology, the fiel coils re premnufcture with insultion n covering. These coils re then instlle onto the rotor pole from the tooth sie n re fixe in the position etween the rotor pole n rotor teeth, s 2

illustrte in Fig. 8. Then, the coils cn slie through the ege of the rotor onto the rotor pole. A non-mgnetic shiel is instlle in the position to fix the coils n to offset the centrifugl force.

It mintins the integrity of the rotor n reuces the mgnetic reluctnce long the rotor pth. Becuse of the symmetricl rotor shpe, the mchine s mechnicl lnce is ffecte.

The excittion wining re set to e wier thn the rotor pole rm ut the ifference is smll (less thn 5% of the with of the wining).

Clerly, the mchine is esigne to operte uniirectionl, which is not n issue for pplictions such s stem turines, gen-sets n win turines, which re the trget of this work. IV.

3 illustrte in Fig. 8. Then, the coils cn slie through the ege of the rotor onto the rotor pole. A non-mgnetic shiel is instlle in the position to fix the coils n to offset the centrifugl force. In this mchine, the segmenttion of rotor poles is no longer necessry for rotor wining instlltion, mking it esy to insert n remove the fiel coils. It mintins the integrity of the rotor n reuces the mgnetic reluctnce long the rotor pth. Becuse of the symmetricl rotor shpe, the mchine s mechnicl lnce is ffecte. However, this is not ig prolem in smll n meium synchronous genertors since they operte in reltively low spee n resonly stle environments. The excittion wining re set to e wier thn the rotor pole rm ut the ifference is smll (less thn 5% of the with of the wining). The empty spce llows for more insultion n oning mterils to e pplie so s to improve therml trnsfer within the rotor. Clerly, the mchine is esigne to operte uniirectionl, which is not n issue for pplictions such s stem turines, gen-sets n win turines, which re the trget of this work. IV. FINITE ELEMENT MACHINE MEDELLING In orer to evlute the effectiveness of the propose esign, two 4-pole synchronous genertors re moelle y the 2-D finite element softwre MgNet. The two use the sme sttor ut two ifferent rotors (one symmetricl n the other symmetricl). The mchine s sttor is from stnr 27.5 kva lterntor while its slient rotor is use s ench-mrk ginst the new esign. A. No-lo opertion A 2-D trnsient nlysis (with motion) of the propose synchronous genertor with DC excittion is first stuie. The ir-gp flux ensity, sptil hrmonics, inuce EMF t nolo conitions re otine n shown in Figs. 9-13, respectively. As cn e seen from Fig. 9, the irection of the flux in the symmetricl rotor hs een shifte towrs one sie. The sence of the rotor teeth on one sie reuces the flux pth, creting n unlnce ir-gp flux istriution. This introuces n ngle etween the rotor n sttor fiels. In this cse, the mgnetic flux is concentrte on the teeth sie of the rotor, mking the re esy to sturte. This feture is foun on the inuce EMF wveforms s well s its sturtion level, s shown in Figs Fig D igrm of the propose mchine. Fig. 8. Instlltion of the rotor coils. Fig. 9. Flux istriution of the mchines t no-lo. () Asymmetricl rotor. () Symmetricl rotor. 3

In ition to the ir-gp flux ensity, n FFT nlysis of the inuce EMF is lso conucte, s presente in Tle 1.

This shoul e crefully exmine in the esign process. () () Fig. 10. No-lo ir-gp flux ensity. () Asymmetricl () Symmetricl. Fig. 12. No-lo EMF voltges.

0234 11 0.162 0.772 THD 7.14% 11.13% Fig. 11. FFT nlysis of the no-lo ir-gp flux ensity.

However, ue to the symmetricl pole geometry, the ir-gp flux ensity of the new esign is higher in the slient pole portion thn the concve portion.

4 In ition to the ir-gp flux ensity, n FFT nlysis of the inuce EMF is lso conucte, s presente in Tle 1. The THD of the symmetricl rotor is still higher thn its symmetricl counterprt s it gives rise to the 3 r hrmonics remrkly. This shoul e crefully exmine in the esign process. () () Fig. 10. No-lo ir-gp flux ensity. () Asymmetricl () Symmetricl. Fig. 12. No-lo EMF voltges. Tle 1 FFT Anlysis of the No-lo EMF Hrmonics Symmetricl rotor (Vrms) Asymmetricl rotor (Vrms) THD 7.14% 11.13% Fig. 11. FFT nlysis of the no-lo ir-gp flux ensity. Overll, the inuce EMF, phse current n flux linkge etween the two mchines re similr. However, ue to the symmetricl pole geometry, the ir-gp flux ensity of the new esign is higher in the slient pole portion thn the concve portion. This symmetricl effect istorts the shpe of the ir-gp flux ensity long the rotor pole. The 3 r hrmonic of its ir-gp flux ensity is increse while other high-orer hrmonics re reuce when compre to the symmetricl mchine. Fig. 13. No-lo chrcteristics. From Fig. 13, it is oserve tht the symmetricl mchine reches sturtion elier thn the symmetricl s the excittion MMF increses. This is cuse y the flux shift where the flux tens to concentrte on the slient sie of the rotor. 4

B. Full-lo opertion The mgnetic flux istriution of the two mchines t full lo opertion re investigte when the fiel wining is excite with the rte c current, n the sttor winings re fe y the rte

() Asymmetricl () Symmetricl Test results shown in Figs. 14-16 re the flux istriution, inuce EMF, n the pull-out torque, respectively.

This ngle cn e expline y the ifference of the sttor n rotor fiel orienttion.

5 B. Full-lo opertion The mgnetic flux istriution of the two mchines t full lo opertion re investigte when the fiel wining is excite with the rte c current, n the sttor winings re fe y the rte three-phse c current (38A pek). Fig. 15. Inuce phse voltges of the mchines t full-lo. () Asymmetricl () Symmetricl Fig. 16. The pull-out torques. Fig. 14. Flux istriution of the mchine t full-lo. () Asymmetricl () Symmetricl Test results shown in Figs re the flux istriution, inuce EMF, n the pull-out torque, respectively. Agin, the phse current n flux linkge in the two mchines re very similr. Due to the symmetricl rotor geometry, the position of the mchine for chieving mximum torque is lso shifte. This ngle cn e expline y the ifference of the sttor n rotor fiel orienttion. However, since most of the flux is concentrte on the teeth sie of the rotor, the non-teeth sie is is not effectively utilise. Therefore, there is room for optimising the rotor pole geometry to improve the electromgnetic efficiency. C. Clcultion of L n L q The mesurement of the irect-xis rectnce n qurntxis rectnce is crrie y low-slip test following the stnr metho [10]. The rotor is riven y prime mover to rotte t rpm (0.01 slip) while the fiel wining is open-circuite. The sttor is fe with 50 Hz, 4A c current. The reltive position of the sttor n rotor mgnetic fiels is chnging to reflect the ifferent ir-gp istnce, n the test results re presente in Fig

Fig. 17. Simulte low-slip test results. () Asymmetricl () Symmetricl The mximum n minimum flux-linkges for the symmetricl rotor re 0.094W n 0.068W, respectively.

L 0.092 / 2 0.046H,X L 7.15 (3) L 0.061/ 2 0.031H,X L 4.82 (4) q q q Due to the trnsformtion of the rotor geometry, sliency of the rotor hs een chnge.

6 Fig. 17. Simulte low-slip test results. () Asymmetricl () Symmetricl The mximum n minimum flux-linkges for the symmetricl rotor re 0.094W n 0.068W, respectively. The irect-xis n qurnt-xis rectnce re L / H,X L 7.3 (1) L / H, X L 5.3 (2) q q q The mximum n minimum flux-linkges for the symmetricl rotor re 0.093W n 0.061W, respectively. L / H,X L 7.15 (3) L 0.061/ H,X L 4.82 (4) q q q Due to the trnsformtion of the rotor geometry, sliency of the rotor hs een chnge. This sliency chnge hs its impct on the torque output of the lterntor. Per the equtions in [10], the output torque t ny spee cn e erive s: 1 2 T X I f Is cos (X X q)i s sin 2 (5) 2 X, X = per unit irect xis synchronous n mgnetizing rectnce t one per unit spee X q = per unit qurture xis rectnce t one per unit spee. Fig. 18. Phsor igrm With Vs efine s the sttor voltge n Is s the phse current, first component of the eqution cn e consiere s the sttor-rotor fiel interction. The secon prt is the reluctnce torque cuse y the sliency of the rotor. A phsor igrm of the slient pole woun rotor synchronous mchine is shown in Fig. 18. Oviously, given y the mesurement of -q rectnce, the rotor geometry chnge shoul hve its impct on the torque prouction. Therefore, it is possile to moify the sliency of the rotor y moifying the geometry of the rotor inste of introucing extr component into the rotor. D. Power loss n efficiency The core loss n copper losses re clculte using the Infolytic MgNet. The t re shown in Tle.2. From this tle, the two esigns hve the sme copper loss ue to the sme sttor configurtion n supply. The symmetricl mchine hs slightly lower torque n iron loss. With the sme input power, the symmetricl mchine hs lower efficiency thn the symmetricl mchine. However, this reuction is very insignificnt. Tle 2 Loss n efficiency of tow synchronous genertors Item Asymmetricl rotor Symmetricl rotor Copper loss (W) Iron loss (W) Torque (Nm) Spee (rpm) Efficiency 97.4% 97.5% V. EXPERIMENTAL TESTS AND RESULT ANALYSIS After roun of optimizing the rotor esign n nlysing the mchine performnce, the rotor esign is finlise n the rotors re prototype, s shown in Fig. 19. Sttor of the mchine is uplicte of stnr Cummins BCI-184F mchine. Two rotors re mnufcture for compre. Detils of the mchine re given in Tle. 3. 6

A series of experimentl tests hve een conucte on the propose mchine with the two ifferent rotors. () A.

The DC motor is use s prime-mover for keeping the spee of the rotor t synchronous spee (1500rpm). The sttor is open-circuite n connecte to 3-phse power nlyser to recor the instntneous quntities.

() Sttor, () Asymmetricl n Symmetricl Rotors Tle 3 Specifictions of two genertors Rte Power (kva) 27.

8 Stck Length (mm) 50 200 36 Pole Numers 4 310 Sttor ID (mm) 192 188 Sttor wining rrngement Doulelyer Str For sttor wingings, they re oule-lyer str connecte winings with 144mm 2 for ech lyer.

7 A series of experimentl tests hve een conucte on the propose mchine with the two ifferent rotors. () A. Constnt spee-vrile excittion test A constnt spee-vrile excittion test is conucte y coupling the test mchine with DC rive motor. The DC motor is use s prime-mover for keeping the spee of the rotor t synchronous spee (1500rpm). The sttor is open-circuite n connecte to 3-phse power nlyser to recor the instntneous quntities. The excittion is fe from 3-phse AC supply through rectifier. The excittion current is mesure y n mmeter t the output terminl of the rectifier. Fig. 19. Photos of the prototype synchronous mchine. () Sttor, () Asymmetricl n Symmetricl Rotors Tle 3 Specifictions of two genertors Rte Power (kva) 27.5 Rte Spee (rpm) 1500 Rte Voltge (V) Rte Power Fctor Sttor Slot Numer Sttor OD (mm) Rotor OD (mm) () 380 Rte Frequency (Hz) 0.8 Stck Length (mm) Pole Numers Sttor ID (mm) Sttor wining rrngement Doulelyer Str For sttor wingings, they re oule-lyer str connecte winings with 144mm 2 for ech lyer. For rotor winings, 76 turns of copper coil (2.3mm rius ech) re use on symmetricl rotor coils. However, ue to the mnufcture requirement, symmetricl rotor opts hn-woune 1.5mm copper wires with 200 turns. This will ffect the rte excittion current so the MMFs re use to escrie the excittion in the following experiments. Fig. 20. Comprison of the constnt spee-vrile excittion test etween the two mchines. When crrying the no-lo test, the excittion is chnge in step from high to low voltge using pproximtely even istriute points, strting from the rte vlue own to zero following the IEEE stnr proceure. The rmture voltge (in RMS) t the terminl versus the excittion current (in per unit) t rte spee re plotte in Fig. 20. It is cler tht the performnce of the two mchines is similr with the symmetricl mchine more likely to enter sturtion erlier thn the symmetricl one. The reson is s stte in the previous chpter. The concentrtion of the flux on the teeth-sie of the rotor mke the symmetricl rotor esier to sturte. The comprion etween FEA simultion n Experiment results re lso inclue in this figure to confirm the ccurcy of the FEA simultion. B. Constnt excittion -vrile spee test In this test, the excittion is fixe while the DC motor rives the test mchine to rotte t vrile spees. The rmture phse voltge is plotte ginst spee in Figs Agin, the two mchines perform lmost ienticlly. 7

8 This shoul e crefully exmine in the fult nlysis since the short-circuit current is smller. Fig. 21. FEA n mesure results of the output voltge. D. Inuctive lo test Inuctive los re the most common type of los connecte to the power system. Therefore, the mchine s response to such lo chnges is of criticl importnce in terms of the system stility. This lo test is esigne to compre the performnce of the two esigns uner the sme conitions. In the test, the sttor terminls re connecte to power nlyzer in prllel with n inuctive lo nk. The phse voltge n current re mesure y the power nlyzer n the excittion is mesure y n mmeter t the output terminl of the rectifier. Fig. 22. Comprison of constnt excittion-vrile spee test etween the two mchines. C. Sustine three-phse short-circuit test The sustine three-phse short-circuit test is crrie out y keeping the rotor spee t 1500rpm while three-phse winings re short-circuite t the sttor terminls. The short-circuit current is recore. The excittion is juste in steps from high to low current using pproximtely even istriute points, strting from the rte excittion current. The rmture currents re mesure t the terminls. The rmture current versus the excittion current t rte spee is shown in Fig. 23. Fig. 23. Comprison of the two mchines in sustine threephse short-circuit test. For given excittion current, the short-circuit current in the symmetricl mchine is lower thn the symmetricl one. c Fig. 24. Comprison of the two mchines t vrying inuctive los. The excittion current is initilly juste to chieve given rmture voltge (i.e. rte EMF). Then, the inuctive 8

9 lo is grully increse from 0 to 5 kw in steps. The voltge, current re recore, n presente in Fig. 24. The test results show tht the EMF voltge of the mchine with the symmetricl rotor is less sensitive to the lo vritions. As result, the propose esign cn improve the system stility uner lo vritions. E. Resistive lo test The resistive lo test hs the sme setting s the inuctive lo test. The voltge n current re recore s well s the lo. The test results re presente in Fig. 25. Test results show the sme tren s the inuctive lo test. The symmetricl rotor performe etter in oth cses. This confirms the excellent performnce of the propose mchine uner ifferent lo conitions. Through simultion n experimentl tests, the effectiveness of the symmetricl rotor esign is verifie. In ition to the moifie rotor geometry for esy ssemly, the esigne rotor lso shows potentil in sliency-enhncement. However, it is lso notice tht this esign suffers from high sturtion level s well s lower power fctor. Therefore, further optimistion shoul e consiere in further stuies. VI. CONCLUSION This pper hs presente new rotor esign of synchronous genertors trgete for iesel-generting sets. The rotor pole is symmetricl, effectively shifting the mgnetic fiel to chnge the sliency of the rotor. As result, the power output is influence s well s its power fctor rnge. By opting n symmetricl rotor geometry, fiel winings cn e esily instlle on the rotor, thus simplifying mchine ssemly n repir proceures. Simultion results from 2-D finite element nlysis n experimentl results from testing 27.5 kva prototype mchine hve verifie the new rotor esign. Overll, the power profile cn e improve, in ition to esy ssemly of the fiel winings. The evelope technique cn significntly reuce the mintennce n repir costs of synchronous genertors, especilly for those very lrge lterntors n for mss prouction mrkets such s gen-sets n win power genertion. Mchine esigners, mnufcturers n repirers cn enefit from this esign in terms of reuce cpitl n mintennce costs. REFERENCES [1] Dley JM, Sicilino RL.: 'Appliction of emergency n stny genertion for istriute genertion. I. Concepts n hypotheses', IEEE Trnsctions on Inustry Applictions, 2003, 39, (4), pp [2] Hssn I, Weronick R, Bucci R, Busch W.: 'Evluting the trnsient performnce of stny iesel-genertor units y simultion', IEEE Trnsctions on energy Conversion., 1992, 7, (3), pp [3] Mrtin J, Tinll C, Morrow DJ.: 'Synchronous mchine prmeter etermintion using the suen short-circuit xis currents', IEEE Trnsctions on Energy Conversion., 1999, 14, (3), pp c Fig. 25. Comprison of the two mchines t ifferent resistive los. [4] Stone GC, Culert I, Boulter EA, Dhirni H.: 'Slient Pole Rotor Wining Filure Mechnisms n Repir. Electricl Insultion for Rotting Mchines: Design, Evlution, Aging, Testing, n Repir',

10 [5] IEEE St (Revision of IEEE St ): 'IEEE Stnr for the Repir n Rewining of AC Electric Motors in the Petroleum, Chemicl, n Process Inustries', 2006 [6] Smith, T., Jones, M.: 'Moeling of slient-pole wounrotor synchronous mchines for popultion-se esign', IEEE Trnsctions on Energy Conversion., 2011, 26, (2), pp [7] Zho W, Chen D, Lipo TA, Kwon B-I.: 'Performnce Improvement of Ferrite-Assiste Synchronous Reluctnce Mchines Using Asymmetricl Rotor Configurtions', IEEE Trnsctions on Mgnetics., 2015, 51, (11), pp. 1 4 improvement in surfce inset PM motors', IEEE Trnsctions on Mgnetics., 2015, 51, (3), pp. 1 4 [16] Chitroju R, Srngni C.: 'Phse shift metho for ril mgnetic force nlysis in inuction motors with non-skewe symmetricl rotor slots', Electric Mchines n Drives Conference, 2009 IEMDC'09 IEEE Interntionl; 2009: IEEE. [17] H. Aspen, UK Ptnt GB A, mngnetic reluctnce motor, [8] Vrtnin R, Toliyt HA.: 'Design n comprison of n optimize permnent mgnet-ssiste synchronous reluctnce motor (PM-SynRM) with n inuction motor with ienticl NEMA Frme sttors'. in 2009 IEEE Electric Ship Technologies Symposium, 2009, pp [9] Prieto D, Dgusé B, Dessnte P, Vil P, Vnnier J-C.: ' Effect of mgnets on verge torque n power fctor of synchronous reluctnce motors ', Electricl Mchines (ICEM), 2012 XXth Interntionl Conference on; 2012: IEEE. [10] Liu W, Lipo TA.: 'On sliency enhncement of slient pole woun fiel synchronous mchines', Energy Conversion Congress n Exposition (ECCE), 2016 IEEE; 2016: IEEE. [11] Zhu Z, Zhou Y, Chen J, Green JE.: 'Investigtion of Nonoverlpping Sttor Woun-Fiel Synchronous Mchines', IEEE Trnsctions on Energy Conversion., 2015, 30, (4), pp [12] Liu H-C, Jeong G, Hm S-h, Lee J.: 'Optiml rotor structure esign of clw-pole lterntor for performnce improving using sttic 3D FEM couple-circuit moel', Electromgnetic Fiel Computtion (CEFC), 2016 IEEE Conference on; 2016: IEEE. [13] Li G, Oje J, Hlioui S, Hong E, Lecrivin M, Gsi M.: 'Moifiction in rotor pole geometry of mutully couple switche reluctnce mchine for torque ripple mitigting', IEEE Trnsctions on Mgnetics., 2012, 48, (6), pp [14] Hrinto CA, Suhoff SD.: 'A rottionlly symmetric reluctnce mchine with improve torque ensity', IEEE Trnsctions on Energy Conversion., 2013, 28, (1), pp [15] Zho W, Lipo TA, Kwon B-I.: 'Optiml esign of novel symmetricl rotor structure to otin torque n efficiency 10

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