Quasi-Square-Wave PWM Modulation for Modular Multilevel Converter in Variable Speed Motor Drives With Self Voltage Recovery

This article presents a detailed analysis of the Quasi-Square-Wave (QSW) PWM-modulated Modular Multilevel Converter (MMC) inverter used in variable-speed motor drive systems. Through an examination of inserted arm behavior, this study investigates the effects of sub-module capacitance, arm inductance, and delay time on capacitor voltage overshoot. It introduces a component design technique that significantly reduces the requirements for capacitance and inductance, surpassing the capabilities of existing QSW-PWM methods. Additionally, the research uncovers a self-voltage recovery mechanism within the capacitor voltage that simplifies hardware implementation by requiring only steady-state voltage balancing. Simulated results validate the proposed component design method, demonstrating reductions in capacitance and enhancements in hardware control simplicity.