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Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure 1 Xiaozhuo Xu School of Electrical Engineering and Automation, Henan Polytechnic University, Jiaozuo, Henan, P.R.China, [email protected] 2 Yinghua Cui, 3Xudong Wang, 4Haichao Feng, 5Jikai Si School of Electrical Engineering and Automation, Henan Polytechnic University, Jiaozuo, Henan, P.R.China Email:*[email protected],[email protected],[email protected],[email protected] 1 Abstract The novel Line-start Permanent Magnet Synchronous Motor (LSPMSM) has widely industrial applications, due to its high efficiency, high power factor and self-starting ability. The starting characteristics of novel LSPMSM with rotor arc straight inserted permanent magnet are studied based on the electromagnetic field theory. A finite element model of a 3-phase 8-pole 22kW LSPMSM is developed under reasonable assumptions as well as the solving region, and the transient electromagnetic field is calculated by the coupled field circuit method. The effects due to the variation of rotor structure parameters and stator winding turns and source voltages on performance of starting torque, current and power factor are analyzed, and the lowest starting voltage is obtained. Under overall consideration, the optimal motor parameters are confirmed and the performance on rated condition is calculated. Finally, the prototype experimental results verify the numerical calculating characteristic of the models. Keywords: Line-Start, Permanent Magnet Synchronous Motor, New Rotor Structure, Starting Performance, Finite Element 1. Introduction In recent years, Line-start Permanent Magnet Synchronous Motor (LSPMSM) has attracted the attention of a large number of scholars and manufacturers, for its advantages of high efficiency, high power factor and wide economic operation range [1-3]. The LSPMSM, which inherits the structure characteristic of induction motor and synchronous motor, consists of permanent magnets and aluminum winding on its rotor. So it can be started up directly by the asynchronous torque generated by squirrel cage winding. Just because of the existence of permanent magnet on the rotor, and asymmetry between rotor d-axis and q-axis magnetic circuit, many magnetic fields with different speeds exist in the motor air gap. With the interaction of these fields, driving torque, braking torque and alternating torque are generated, which make the starting process of LSPMSM very complex [4]. Generally, permanent magnets are arc surface-mounted or rectangular straight inserted [5-7] in traditional LSPMSM rotor, as shown in Figure 1. the former provides nice air gap field but cuts down the motor starting capability, while the latter has good starting capability but provides weaker electromagnetic characteristic. In this paper, a 22Kw LSPMSM with arc straight inserted permanent magnet (ASI-LSPMSM), a new type of magnet which can provide both good starting capability and nice electromagnetic characteristic at meantime are designed, the influence of structure size on starting torque ratio and starting current ratio is compared. Then performance on rated condition is analyzed with the method of finite element numerical analysis, and the starting performance and starting torque are calculated [8, 9]. Finally, influence of supply voltage on starting performance is researched and the lowest supply voltage is obtained. International Journal of Digital Content Technology and its Applications(JDCTA) Volume7,Number6,March 2013 doi:10.4156/jdcta.vol7.issue6.139 1217 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu permanent magnet permanent magnet rotor slot rotor slot (a)Rectangular straight inserted (b)Surface-mounted Figure1. Classical permanent magnet structure 2. LSPMSM Electromagnetic Field Analysis The novel rotor structure, arc straight inserted permanent magnet and combination of flux barrier and air slot are adopted in the motor designed in this paper, and the structure parameters and chart are shown in table 1 and figure 2 respectively. Rated power Table 1. Motor structure parameters 22Kw Number of stator slot 54 Rated voltage Rated speed Insulation class Exciting mode 380V 750r/m B Parallel 48 368mm 259mm 0.5mm Number of rotor slot Stator out diameter Stator inner diameter Air gap length (a) Whole structure (b) Novel rotor structure Figure 2. LSPMSM Structure 2.1. Assumption and solving region Supposing the electromagnetic field is quasi-static, which means displacement current is ignored. Electromagnetic field is disposed as two-dimensional field, which means motor axial length is kept constant and motor end winding is ignored. Materials used in motor is supposed to be isotropy, hysteresis effect of the ferromagnetic material is ignored. Permanent magnet is simulated with equivalent surface current. Conductivity and permeability are just related to the material properties, irrespective of the temperature variation. Eddy currents of the stator core, rotor core and source current region are ignored [10-13]. The field is depicted with magnetic vector potential A, and the transient electromagnetic field definition solution problem can be described as, 1218 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu 1 A 1 A dA S : x ( x ) y ( y ) ( J z dt ) 1 : A 0 1 A 1 A 2 : s 2 n 1 n (1) Where, S is solving region, 1 is the first species boundary condition, 2 is permanent boundary condition, A is magnetic vector potential, s is permanent boundary equivalent surface current density, dA is eddy current density. is permeability, J z is axial current density, dt 2.2. Finite element calculation of LSPMSM During the process of PMSM finite element analysis and solution, formula (1) is taken as Euler equation of a function, the differential equation corresponding functional of the PMSM mathematic model is obtained, with which the conditional variation problem is constituted and solved, and then each motor field quantity can be obtained. With weighted residual method, finite element discretization equation is established. Taking weight function equal to shape function, formula (2) can be got with taking formula (1) weighted integral. 1 A 1 A dA T T T (2) Se ( N [ x ( x ) y ( y )] N J z N dt )dxdy 0 Taking surface integral as the sum of unit integral, formula above is dispersed, if first order linear triangle unit is adopted, the integral of formula (2) first term is, Se (N T [ Where, N e [ N ie N 1 Ae N 1 A 1 A 1 A 1 A ( ) ( )]dxdy ( e ) e ( )dxdy N eT ( )dl Se le x x y y x x y y n N ej (3) N me ]T The line integral of formula (3) can be disposed by boundary condition. If first order linear triangle unit is adopted, the right of formula (3) first term is, bi bi ci ci b j bi c j ci bm bi cm ci Ai 1 (4) b b c c b b c c b i j i j j j j j m b j cm c j A j K e Ae 4 bi bm ci cm b j bm c j cm bm bm cm cm Am The integral of formula (2) second term is, T Se N J z dxdy J z Se Ni Nj T N m dxdy N e I 1 1 1 Ce I e 3aAb T (5) Where, a is number of winding branches in parallel, N e is number of turns in series of one coil side in slot. Ab Is a half slot area(double-layer winding). And, T N e N e N e Ce diag , Ie I I I 3aAb 3aAb 3aAb The integral of formula (2) third term is, dA dA dAe (6) Se N T dt dxdy dt Se N T N e Ae dxdy Te dt 1/ 6 1/ 12 1 /12 Where, Te 1/ 12 1/ 6 1 /12 1/ 12 1/ 12 1/ 6 dt , the discretization equation of formula (1) Combining all the formulas above and making A dA can be got as below, KA T A CI (7) 1219 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu 2.3. Starting process calculation and analysis on rated condition The motor is designed with field-circuit combination method, and transient magnetic field is calculated with finite element method to research starting process of the AIS-LSPMSM. Mechanical motion equation is shown as follow. d J Tem TL (8) dt Where, J is rotary inertia, TL is load torque, which is a approximate constant when motor is on stable operation, Tem is electromagnetic torque, is angular speed. To get the transient performance curve, mechanical motion equation and transient electromagnetic field must be solved simultaneously during the FEM analysis. The solution procedure is that, supposing rotor spins in t , with which motor angular speed at a time can be ascertained. Then finite element equation is solved and magnetic field distribution and electromagnetic torque can be obtained. Taking electromagnetic torque solved above as known conditions, finite element equation is solved to get angular speed . If error between calculation value and assumption value is less than allowable value, the process is continued to calculate at t t . Otherwise, rotary angular must be revised and the former two steps be repeated. With repeated iteration and solution, the performance analysis curve of the LSPMSM can be obtained. Magnetic field distribution plot on initial starting stage and lock-in synchronism stage are shown in Figure 3. Comparison of those two figures shows that no saturation happens in stator core, while saturation happens in the rotor core over against the flux barrier and rotor slot at 0.2s. The reason is that when motor is locked-in synchronism, rotor current is close to zero and stator current is approach to rated current, so the magnetomotive force(MMF) generated by stator and rotor current is small, while rotor core over against flux barrier is very thin, only a little MMF can make the core be saturated. Figure 3.a shows that saturation happens not only in the rotor core over against the flux barrier and rotor slot but also in stator slot teeth at 0.03s. The reason is that at this moment, rotor is at a standstill while currents both in stator and rotor are very large, values of which can be 10 times that of stator rated current. As the MMF is proportional to current, the core in leakage magnetic circuit is highly saturated for the sake of large MMF. Meanwhile, with the adoption of the distributed winding, the direction of the leakage magnetic field in teeth caused by current in adjacent slots is opposite. Saturation in the addendum and tooth tip is more serious comparing with teeth part. (a)0.03s (b)0.2s Figure 3. Magnetic field distributions 1220 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu Figure 4. Electromagnetic torque and speed curve Figure 5. Stator and rotor current curve It can be seen in figure 4 and 5 that motor starting stage is in 0-0.2s. With the effect of asynchronous torque, which is caused by interaction of stator field and field induced by rotor current, rotor speed rises slowly, currents both in the stator winding and rotor are large, and electromagnetic torque is unstable. After 0.2s, motor is in stable operation, armature current presents periodically oscillation, if the harmonic magnetic field is ignored, rotor current is close to zero, and electromagnetic torque is close to rated load torque, these results show that the motor with novel structure owns good starting performance and electromagnetic performance. 3. Starting performance analysis with different structure parameters The definition of starting torque in the LSPMSM is same with that in induction motor, it is the torque generated when rotor keeps stable when slip ratio is 1, it can be shown as follows. mp U 2 R2 (9) Tst 2 f ( R1 c1 R2 ) 2 ( X 1 c1 X 2 ) From formula (9), it can be seen that starting torque depends on external voltage, stator and rotor resistance and lekage reactance which is influenced by the extent of the magnetic circuit saturation. 3.1. Influence of winding turns Figure below shows the influence of winding turns on starting torque ratio and starting current ratio. (a) Starting torque ratio and starting current ratio (b) power factor Figure 6. Stator per-phase winding turns variation From figure 6, it can be seen that with the increase of winding turns, starting torque ratio and starting current ratio both reduce, while starting current ratio reduces more rapidly, the reason is that starting current is proportional to resistance, with the increase of winding turns, winding resistance increases, and current reduces. With consideration of the power factor, 10 are adopted as stator winding turns per phase. 1221 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu 3.2. Rotor slot height variation (a) Starting torque ratio and starting current ratio (b) power factor Figure 7. Rotor slot height variation Figure 7 shows the influence of rotor slots height variation on starting torque ratio, starting current ratio and power factor, it can be seen in the figure that with the increase of the rotor slot height, starting torque ratio and starting current ratio both increase, power factor increases at first,then it decreases. As the increase of slot height, rotor resistance increases, and rotor lekage inductance reduces, so the starting torque increases. Considering the motor specifications, and 6.8mm are adopted as rotor slot height. 3.3. Height of rotor permanent magnets (a) Starting torque ratio and starting current ratio (b) power factor Figure 8. Permanent magnet thickness variation Keeping pole arc coefficient a constant; permanent magnet (PM) thickness is changed. It can be shown in Figure.8 that, in a certain range, with the increase of the permanent magnet thickness, power factor reduces, starting torque ratio increase, the reason is that magnetic saturation increase with the PM thickness, and leakage reactance reduces gradually. While after the PM thickness increase to 9.4mm, starting torque ratio decrease slightly with the thickness increase, the reason is that when magnetic circuit is approach to saturation, leakage reactance decreases no longer, and the penetrate rate of the flux on silicon steel is greatly influenced by saturation, which also makes starting performance reduce. 1222 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu 3.4. Height of air gap variation (a) Starting torque ratio and starting current ratio (b) power factor Figure 9. Air gap length variation Figure.9 shows that with the increase of air gap length, starting torque ratio, starting current ratio and power factor all reduce when the length is large than 0.4mm. In the LSPMSM, anti-demagnetization ability can be enhanced, leakage flux between poles be reduced, air gap effective flux be enhanced, back electromotive force starting torque be enhanced finally with small air gap length, while if the length is too small, air gap harmonic magnetic field will be enlarged, stray loss and noises be increased, the maximum torque and starting torque be reduced, even friction between stator and rotor will appear. So air gap length has great influence on starting performance. 4.Torque Analyses with Different Supply Voltage Average torque Tav of ASI-LSPMSM during the starting process includes asynchronous torque Tc and power generation torque Tg, both of which are explained as follows. (10) mpu 2 R2/ s Tc 2 f [( R1 c1 R2 / s ) 2 ( x1 c1 x2 ) 2 ] (11) R12 xq2 (1 s ) 2 R E 2 (1 s ) 2 mp Tg 2 1 0 2 f (1 s) R1 xd xq (1 s ) 2 R12 xd xq (1 s) 2 Where, R1 , X1 are stator resistance and leakage reactance respectively, R2 , x2 are rotor resistance and leakage reactance converted to stator side respectively, c1 1 x1 / xm is a factor, and Xm is excitation reactance, E0 is the back EMF. Equations above show that asynchronous torque is relative to supply voltage. (a) Effect of voltage on asynchronous torque (b) Effect of voltage on resultant torque Figure 10. Comparison of electromagnetic torque with different work voltage Figure 10 a) and b) show that with the decrease of voltage, both asynchronous torque and resultant torque reduce a lot. With the existence of power braking torque, resultant torque waveform sinks 1223 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu obviously when the ratio slip is close to 1. If the torque in this period is smaller than rated load torque, motor will not be started up with rated load. The lowest starting voltage is 290V, when voltage is inferior to 290V, large pulsating torque and small asynchronous torque emerge with the interactions of stator rotary magnetic field and permanent magnetic field, and the electromagnetic torque all is assumed as pulsating torque, the motor will not start up. Figure 11. New rotor type and motor Prototype of 22Kw LSPMSM Experiment is done with the prototype shown in Fig.11. Results show that when voltage increases from 320V to 440V, starting time decreases 52 percentage, and armature current decreases 11.6 percentage. It verifies that LSPMSM characteristics are greatly influenced by voltages in industrial application. 5. Conclusions Through the method of finite element analysis, the model of a 22Kw LSPMSM designed with novel rotor structure is built. Influence of structure parameters on starting performance is researched, along with proper increase of stator winding turns per phase, starting torque ratio and starting current ratio reduce. While with increase of rotor slot height, starting torque ratio and starting current ratio also increase. The performance of motor on rated condition is researched, which shows it has good characteristic. Torque on different voltages is also calculated, and the lowest voltage is obtained. Experimental facility is established. The results verify that good matching attributes are got. The foundation for widely industrial application of this LS-PMSM with novel rotor structure is established with performance research done above. 6. Acknowledgment This work was supported by the National Natural Science Foundation of China (NO.61074095, 51277054), Ministry of Education Research Fund for Doctoral Program of Higher Education(NO.20114116110003), and Henan Province Key Project (NO.122102210121), Ministry of Education Scientific Research Foundation for Chinese Overseas Returnees, Science and Technology Research Project of Henan Province Education Department (13A470337, 12B470003), Natural Science Program of Henan province (2011A470003) , Henan Province Key subjects of Control engineering (KG2011-05), especially the Innovation Talents Foundation of Henan Province (104200510021). 7. References [1] Xueqing Feng, Yaxin Bao, Lijun Liu, Lizhong Huang, Yingming Zhang, “Performance investigation and comparison of line start-up permanent magnet synchronous motor with super premium efficiency”, Proceedings of 20th International Conference on Electrical Machines, pp.424-429, 2012. [2] Weifu Lu, Mingji Liu, Yingli Luo, Yang Liu, “Influencing factors on the demagnetization of line-start permanent magnet synchronous motor during its starting process”, Proceedings of International Conference on Electrical Machines and Systems, pp.1-4, 2011. [3] Xiuhe Wang, Yubo Yang, “Theory designing and testing of Line-start Permanent Magnet Synchronous Motor”, Mechanical Industry Press, China, 2009. 1224 Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure Xiaozhuo Xu [4] Dan Stoia, Mihai Cernat, Adisa A. Jimor, Dan V. Nicolae, “Analytical Design and Analysis of Line-Start Permanent Magnet Synchronous Motors”, Proceedings of IEEE Africon 2009, pp.1-7, 2009. [5] Weili Li, Xiaochen Zhang, “Study of solid rotor line-start PMSM Operation performance”, Proceedings of the 11th International Conference on Electrical Machines and Systems, pp.373-378, 2008. [6] S. Demirbas, C. Gencer, “Matlab/Simulink based modeling and simulation of permanent magnet synchronous motor drive”, Proceedings of International Conference on Technical and Physical Problems in Power Engineering, pp.645-649, 2004. [7] Kazuo Tsuboi, Tsuneo Takegami, Isao Hirotsuka, Masanori Nakamura, “A general analytical method for a three-phase line-start permanent-magnet synchronous motor”, “IEEJ Transactions on Industry Applications”, Institute of Electrical Engineers of Japan, vol.131, no.3, pp.692-699, 2011. [8] Xudong Wang, Haichao Feng, Baoyu Xu, Xiaozhuo Xu, “Research on Permanent Magnet Linear Synchronous Motor for Ropeless Hoist System”, “Journal of Computers”, Academy Publisher, vol.7, no.6, pp.1361-1368, 2012. [9] Yongjuan Cao, Weifeng Chen, Yu Li, “Control and Simulation of a Novel Permanent Magnet Brushless DC Wheel Motor based on Finite Element Method”, “International Journal of Advancements in Computing Technology”, Advanced Institute of Convergence Information Technology, vol.4, no.13, pp.279-286, 2012. [10] Yanfang Wang, Yanping Su, “Simulation and Analysis of Electromagnetic Field for Moving-coil Permanent Magnet Motor”, “International Journal of Digital Content Technology and its Applications”, Advanced Institute of Convergence Information Technology, vol.6, no.13, pp.185-191, 2012. [11] Shouchen Ding, Wenhui Li, Shizhou Yang, Jianhai Li, Guici Yuan, “The Motor Virtual Experimental System Based on Matlab Web Technology”, “Journal of Networks”, Academy Publisher, vol.5, no.12, pp.1490-1495, 2010. [12] Kun Liu, Hui He, Boxiong Yang, “Study on Small Textile Constant Tension Winding Control System in The Phase-Locked Loop Way”, “International Journal of Advancements in Computing Technology”, Advanced Institute of Convergence Information Technology, vol.5, no.1, pp.333-342, 2013. [13] Haitao Zhang, Zhen Li, “Simulation of Networked Control System based on Smith Compensator and Single Neuron Incomplete Differential Forward PID”, “Journal of Networks”, Academy Publisher, vol.6, no.12, pp.1675-1681, 2011. 1225