Variable switching frequency PWM for three-phase converter for loss and EMI improvement

Compared with the widely used constant switching frequency PWM method, variable switching frequency PWM can benefit more because of the extra freedom. Based on the analytical expression of current ripple of three-phase converter discussed in “Study of Analytical Current Ripple of Three-Phase PWM Converter” in APEC 2012, variable switching frequency PWM (VSFPWM) methods are proposed to satisfy different ripple requirements. Two methods are discussed in this paper. The first method (VSFPWM1) is designed to arrange the current ripple peak value within a certain value, and can reduce the equivalent switching frequency and EMI noise; the second method (VSFPWM2) is designed to keep ripple current RMS value constant and reduce the EMI noise. Simulation and experimental results show that variable switching frequency control could improve the performance.