Design And Analysis Of Low-Torque-Ripple Consequent-Pole Permanent Magnet Motor

Servo drive technology is the key technology for the control of Computer Numerical Control(CNC),industrial robots and other industrial machinery.As the core component of the servo system,the performance of the motor is directly related to the quality of the servo system.Consequent-pole permanent magnet(CPPM)motors have received great attention in the servo systems due to their high efficiency,high torque density,and low cost.Integer-slot CPPM motors have the advantages of larger PM torque,stronger resistance to demagnetization,and the absence of winding sub-harmonics.However,the harmonic content of the stator and rotor magnetic motive force(MMF)is high,resulting in high torque ripple.Compared with integer-slot motors,the fractional slot concentrated winding motor has the advantages of short winding end,more sinusoidal back electromotive force(back-EMF),and high reliability.However,there are abundant sub-harmonics and slot harmonics in the winding MMF,which will produce local core saturation,high eddy current loss and torque ripple.In addition,some fractional slot motors will cause the unbalanced air-gap flux density due to the CPPM rotor structure,which causes even back-EMF harmonics and further increases the torque ripple.Therefore,based on the principle of torque ripple generation,this paper reveals the low torque ripple design mechanism of CPPM motor based on asymmetric PM poles,reduces the specific rotor MMF harmonics,and thus reduces the torque ripple of integer-slot CPPM motor;the stator MMF sub-harmonics are reduced by optimizing the winding structure,thereby reducing the torque ripple of the fractional slot concentrated winding CPPM motor.Based on the above research,the following research results are obtained in this paper: 1.The research of CPPM motor and methods to suppress the torque ripple of PM motors are briefly analyzed,and the importance of suppressing the torque ripple of CPPM motor is emphasized.2.Based on cogging torque,PM torque,and reluctance torque,the relationship between the difference of adjacent PM pole-arc ratios and the order of torque ripple in the low-torque-ripple integer-slot CPPM motor is explored,and the mechanism of suppressing the torque ripple of asymmetrical CPPM motor is revealed.3.On the basis of obtaining the torque ripple suppression mechanism,a novel integer-slot asymmetrical CPPM motor is proposed,and the correctness of the theoretical analysis is verified by finite element simulation.4.The harmonic of stator MMF and rotor MMF for torque ripple of fractional slot concentrated winding CPPM motor is clarified,and the optimized six-layer winding is proposed to reduce the torque ripple.Next,Halbach PMs arrays are employed to compensate the torque loss caused by the optimized six-layer winding.5.An experimental prototype of five-phase integer-slot asymmetrical CPPM motor is fabricated.The experimental platform is built and tested.The no-load back-EMF and electromagnetic torque waveforms of the prototype are obtained,which verifies the validity of the theoretical analysis.