Modulation Strategy and Extension for Hybrid Cascade H‐Bridge With Partial DC Power Supply Replacement With Capacitors

ABSTRACT In order to improve the DC side voltage utilization rate of the hybrid cascaded H‐bridge multilevel inverter (CHB MLI), capacitors can be used to replace the DC supplies with low utilization rate of the low‐voltage (LV) cells. However, with the increase of the number of capacitors, the difficulty of mode construction in the modulation strategy increases geometrically. In this paper, we propose a multimode SHEPWM modulation strategy (MMSHE) that reduces the complexity of mode construction by optimizing the mode construction mechanism while effectively coordinating the capacitor charging and discharging requirements. Using this improved modulation strategy, taking the intermediate frequency hybrid CHB MLI with a voltage ratio of 2: 1: 1 as the research object, the nine‐level waveform output of the MLI with a single capacitor unit (SCU) and dual capacitor units (DCU) is successfully realized, and the theoretical analysis of capacitor charging and discharging and minimum capacitance is carried out in the case of containing a single capacitor unit. Then, the MLI is expanded and the idea of modulation strategy construction is introduced. Finally, the correctness of the modulation strategy and its theoretical analysis are verified by simulation and experiment.