An Improved Variable Switching Frequency Modulation Strategy for Three-Level converters with Reduced Conducted EMI

Three-level inverters with variable switching frequency PWM (VSFPWM) can decrease conducted EMI because of more voltage levels and changed switching frequency. However, there are many distinct EMI spikes remaining in spectrum for most cases of modulation index, which degenerates the effect on suppressing conducted EMI. Therefore, this paper proposes an improved variable switching frequency modulation strategy to eliminate the EMI spikes in spectrum for three-level inverters. The principle of switching frequency change is that the switching frequency obeys normal distribution, which can make the conducted EMI reduce more than 20dB for the full modulation index. Relevant experimental results validate the effectiveness of proposed method on reducing conducted EMI.