An Improved Switching Frequency Reduction Method for CHB Inverter With Supercapacitor and DC–DC Stage Under Hybrid Modulation Strategy

Low switching frequency of power semiconductor devices is expected to decrease losses in the cascaded H-bridge (CHB) inverter with supercapacitor and dc–dc stage. This paper proposes a switching frequency reduction method accompanied by a hybrid modulation strategy (HMS) for the CHB inverter. By optimizing the comparison output between the reference wave and the triangular carrier, unnecessary state jumps in the switching signals for the H-bridge can be avoided when rotating the switching mode of the H-bridge in the HMS. The proposed method can reduce the average switching frequency among the H-bridges without side effects on capacitor voltage balance and ac outputs. Finally, its effectiveness is demonstrated through simulation results of five SMs based on MATLAB/Simulink.