Variable carrier frequency mixed PWM technique based on current ripple prediction for reduced switching loss

Abstract

Since carrier based pulse width modulation (PWM) has several advantages such as applicability for simple V/f control and equal distribution of stress among all switching devices, it is still widely used in the industrial drives. Switching loss can be reduced by varying the carrier frequency based on current prediction, in such a way that the current ripple always meets the exact requirements. There are two commonly used PWM methods, discontinuous PWM (DPWM) which clamps one of the phases and switches the other two and space vector PWM (SVPWM) which switches all the three during the switching period. Since the locus of the current ripple differs by applying different PWM methods, less switching loss can be obtained by selecting optimal PWM in each control period. A method using combination of DPWM and SVPWM with variable carrier frequency in order to achieve lower switching loss is proposed in this paper. It is shown in the presented simulation results that the proposed method has lower switching frequency compared with those of DPWM and SVPWM under certain modulation index.