Attenuation of conducted EMI for three-level inverters through PWM

摘要

This paper presents two typical modulations to reduce conducted electromagnetic interference (EMI) for three-level voltage-source inverters. The first modulation called variable switching frequency pulse-width modulation (VSFPWM) based on real-time current ripple prediction is used to reduce differential- mode (DM) EMI noise. This technique can make conducted EMI between kHz and MHz achieve great attenuation. The other method named zero common-mode (CM) PWM is used to decrease CM voltage and current. A comprehensive analysis and comparison between normal SVPWM and zero-CM PWM state that zero-CM PWM pays the prices of higher Total Harmowic Distortion (THD), serious neutral voltage unbalance, more switching loss and lower modulation index to achieve theoretical elimination of CM voltage. Then, combination of VSFPWM and zero-CM modulation is designed to avoid the disadvantages such as large switching loss produced by zero-CM PWM, and the new method has obvious predominance of reducing conducted EMI noise. Relevant experimental results validate the advantages of these modulations.