Analysis Of The Effect Of Harmonic Current In Permanent Magnet Synchronous Motor Powered By Inverter On Motor Performance

With the development of modern science and technology, frequency conversion technology has entered a new time of rapid development. Modern permanent magnet synchronous motor uses frequency converter as the power supply. Frequency converter produces harmonics in inversion process and forms harmonic currents in motor stator winding which can lead to factors against motor smooth operation such as torque fluctuating and winding heating. It is of great importance to analyze the effect of harmonic current on permanent magnet synchronous motor.The producing reason of harmonic voltage and harmonic current in the process of frequency conversion is analyzed in this paper. It focuses on the harmonic current which is produced in the permanent magnet synchronous motor stator windings during the SPWM inverter. The distribution of harmonic current are closely related to the choice of modulation wave and carrier wave, and it is also inflected by the type of windings connection. A research of the cause and distribution of harmonic currents is made by the way of mathematical derivation and simulation. It concluded that the harmonic currents which influences permanent magnet synchronous motor is mainly the 5th and 7th order harmonic currents and some related data is obtained.Based on the harmonic current data, how the 5th and 7th harmonic currents affect the overall performance of permanent magnet synchronous motor is analyzed with finite element method.Torque ripple and average torque are two important parameters that affect the motor performance and determine the motor's load capacity and operational stability. With the fixed fundamental current, the influence of the variation of the harmonic current amplitude on torque ripple and average torque is analyzed by loading 5th and 7th harmonic current with different amplitude. For the fixed magnitude of 5th and 7th harmonic current, the influence on torque ripple and average torque of different phase angle is also discussed. The results show that the change of the amplitude and phase angle of 5th and 7th harmonic current does not have an obvious impact on the average torque, but affects the torque ripple to some extent. The relationship between torque ripple and the amplitude and phase angle of harmonic current is shown in this paper.By applying different magnitude of 5th and 7th harmonic current with fixed fundamental current, the simulation to analysis the impact on air gap flux density of harmonic current is done by finite element method. The relationship between the maximum of air gap flux density and the amplitude of the harmonic current is obtained in this paper, so is the average. And some relevant conclusions are also drawn here.