A PWM for Minimum Current Harmonic Distortion in Metro Traction PMSM With Saliency Ratio and Load Angle Constrains

Permanent magnet synchronous motor (PMSM) has the advantages of flexible structure, high power density, and low noise. It is promising to be developed into railway traction system. This application of the PMSM is limited by the low switching frequency of the high power traction inverter. Therefore, it is necessary to restrain the output current harmonics by using the optimized synchronous pulse width modulation (PWM) method. In this paper, the relationship between the load current of PMSM and the output voltage of the inverter using synchronous PWM is analyzed, and the expression of the current harmonics is deduced. Then, a new current harmonic evaluation index considering the saliency ratio and load angle constraints is proposed. Based on this, a novel current harmonic distortion minimization PWM (CHMPWM) algorithm for the PMSM is constructed. Compared with the two existing CHMPWM algorithms, the proposed optimized PWM has better harmonic performance at any modulation index and load angle. Furthermore, according to the results of the proposed CHMPWM, the influence of the load angle variation on optimal switching angle distribution is analyzed when pulse ratio is less than or equal to 11. Experimental results verify the feasibility and effectiveness of the proposed algorithm.