A Modified Variable Switching Frequency Spread-Spectrum PWM Technique With Reduced Torque Ripple for a Vector-Controlled PMSM Drive

Abstract

The discrete tonal bands introduced in an AC machine’s stator current spectrum by constant switching frequency pulse width modulation schemes, have adverse impacts on the vibration, the acoustic noise, and the electromagnetic interference. Spreading the harmonic spectrum and reducing the magnitude of dominant harmonics is one solution to this problem. Ripples in the electromagnetic torque developed is another major concern in AC drives. Inspired by these factors, this study proposes two novel variable switching frequency schemes for a vector-controlled PMSM drive to disperse the frequency spectrum with a significant reduction in torque ripple. The modulation techniques use linear and trapezoidal variation of sub-cycle sampling period; <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_s</i> during their implementation. Further, these methods would be able to eliminate the difficulty in compensator design, which is a major problem with other variable switching frequency schemes. The presented strategies achieve a maximum of 27 % reduction in torque ripple, 51.8 % reduction in dominant harmonics, and a dispersion index of 1.63, demonstrating their competency as promising variable switching frequency schemes. The suggested techniques also show excellent torque ripple reduction capability in comparison with latest spread-spectrum techniques in literature. The proposed techniques are implemented in simulation using MATLAB/Simulink and are experimentally validated using WAVECT-FPGA controller on a 1.07 kW, surface-mounted PMSM drive.