Uniform Distribution Pulsewidth Modulation Strategy for Three-Phase Converters to Reduce Conducted EMI and Switching Loss

It is necessary to suppress the emission level of conducted electromagnetic interference (EMI) for the power electronics converters, and the variable switching frequency pulsewidth modulation (VSFPWM) is an alternative approach to reduce conducted EMI without adding bulky passive components. However, the experimental results indicate that many obvious EMI spikes in spectrum remain so that the conducted EMI reduction for VSFPWM is limited. In order to eliminate the EMI spikes in spectrum, this article first investigates the cause of the EMI spikes for VSFPWM, and the analysis results show that the nonuniform distribution of switching frequency is the primary reason. Then, a novel PWM strategy called uniform distribution PWM (UDPWM) is proposed to eliminate the EMI spikes and to further reduce conducted EMI. The design of a UDPWM is based on the uniform distribution of switching frequency and the principle of less switching loss. Moreover, the analytical formula of switching frequency is also deduced in detail, which adopts fixed variation range of switching frequency whatever the modulation index is. Finally, the experiments are carried out to validate the effectiveness of the UDPWM in reducing conducted EMI and switching loss. The UDPWM can approximately reduce conducted EMI by 20 dB compared with the conventional constant switching frequency PWM, and all obvious spikes in the spectrum are eliminated compared with VSFPWM.