Research on Reliability of MMC Type Medium-Voltage Power Quality Control Device Based on NL-PWM

In hybrid modular multilevel converters (HMMC) with integrated half-bridge (HBSM) and full-bridge submodules (FBSM), nearest level pulse-width modulation (NL-PWM) exhibits superior harmonic characteristics in output over conventional nearest level modulation (NLM). However, the reliability would be affected by the difference in the operating conditions of HBSM and FBSM in NL-PWM. Based on this, the paper proposes a reliability computational paradigm that considering the uneven distribution of device-level and submodule-level losses in NL-PWM. Furthermore, this study conducts a comparative analysis of power loss distribution patterns and redundancy strategies across dual HMMC configurations. Experimental findings reveal a strong correlation between increased imbalance in power dissipation and degraded system reliability. Regarding fault tolerance optimization, passive redundancy architectures demonstrate higher survivability rates than active approaches in accelerated aging tests.