Multi-rate pulse-width modulation for VSIs to reduce baseband harmonics distortion

A multi-rate filtered PWM (FPWM) is proposed to improve both harmonics performance and the switching loss of the voltage source inverters (VSIs). In the conventional SVPWM, it is a tradeoff to select between a lower harmonics distortion or a lower switching loss. In the proposed scheme, the dependency of harmonics distortion and switching loss is alleviated by separating the modulator into two blocks with different operating frequencies — optimal filter block that operates at calculative frequency and switching generation block that switches at carrier frequency. Therefore, the harmonics components are attenuated by increasing the calculative frequency and the switching loss is reduced with low carrier frequency. Two simulations are done in this work. The first one drives the ideal five-phase VSI by using SVPWM and the proposed multi-rate FPWM. Time/frequency domain analysis of the produced phase voltages under various carrier frequencies are shown. Second, the proposed modulator is applied to the 3-phase PMSM speed control. Both current and voltage waveforms are analyze to confirm the effectiveness of the proposed scheme.