Equivalent Magnetic Network Model And Performance Study Of Eccentric Pole-cut Multiphase Permanent Magnet Moto

Multi-phase permanent magnet motor is widely applied in military,industrial and commercial fields because of its high efficiency,high power density,low vibration and noise,et al.Eccentric pole-shaping treatment of equal thickness magnetic pole can improve the sinusoidal degree of air gap flux density distribution and reduce the harmonic content,which effectively reduces cogging torque and motor vibration.The research on the performance of the surface-mounted permanent magnet motor needs to be carried out from the magnetic field distribution of the motor.In this paper,the equivalent magnetic network(EMN)method is introduced to analyze the magnetic field of the eccentric pole-shaping multi-phase permanent magnet motor.This method has the advantages of simplifying the calculation amount,parameterization,and considering the magnetic circuit saturation,which is favorable for determining the initial design scheme of the motor.In this paper,an eight-pole nine-phase surface-mounted eccentric pole-shaping permanent magnet motor is taken as an example to establish the EMN model.The electromagnetic performance of the motor is analyzed and calculated based on the EMN model.Based on the magnetic circuit theory and Ampere circuital theorem,the calculation formula of the magnetic permeance unit of the motor is deduced.Combined with the structural characteristics of the surface-mounted eccentric pole-shaping multi-phase permanent magnet motor,the stator,air gap,the permanent magnet pole and the rotor of the motor are divided respectively.The magnetic permeance units are calculated and their magnetic network models are established.The thickness of the eccentric pole-shaping permanent magnet pole and the corresponding air gap length function are derived by geometric analysis.The magnetic network model of the eccentric pole-shaping multi-phase permanent magnet motor under a pair of poles is established.Based on the node magnetic potential method,the EMN equation is solved.The electromagnetic properties of the eccentric poleshaping multi-phase permanent magnet motor under no-load and load conditions,such as air gap flux density,back EMF and torque,are analyzed.The results are compared with the finite element and experimental test results to verify the effectiveness of the EMN model of the eccentric pole-shaping multi-phase permanent magnet motor.Based on the EMN model,the influence of the main permanent magnet parameters of eccentric pole-shaping,including pole-arc coefficient,the maximum thickness of permanent magnet and eccentricity,on the electromagnetic performance such as air-gap magnetic field,cogging torque and electromagnetic torque is studied.By analyzing the influence law of a single pole parameter on various electromagnetic properties,the foundation for the multi-variable and multi-objective optimization of eccentric poleshaping permanent magnet motor is established.The analysis results of EMN model are compared with the finite element analysis results,which proves the effectiveness and accuracy of the established EMN model.Aiming at the multi-pole parameter optimization of the eccentric pole-shaping multiphase permanent magnet motor,the design method based on the EMN model is combined with the particle swarm optimization algorithm.Taking pole arc coefficient and eccentricity as optimization variables,the maximum electromagnetic torque and the minimum harmonic distortion rate of no-load air gap flux density as optimization objectives,the multi-objective optimization problem is transformed into a single objective problem by using signal-to-noise ratio and setting weight factors,so that the motor optimization objective produces a unified quantitative analysis standard.The multi-variable and multiobjective particle swarm optimization model is established.The optimization model is applied to optimize the structural parameters of the magnetic pole,and the optimal structural parameters of the eccentric pole-shaping permanent magnet pole are obtained.The electromagnetic performance of the optimized motor is solved.