A Modified Phase-Shifted Pulse Width Modulation to Extend Linear Operation of Hybrid Modular Multi-level Converter

Recently, hybrid modular multi-level converters, which are configured as full and half bridge sub-modules, are developed and utilized in the wide area of applications. Compared to its non-hybrid counterpart, these converters have several advantages such as the ability to nullify the DC side fault current and controlling AC side reactive power during the faults. This paper proposes a modified phase shifted PWM method (PS-PWM) which uses a combination of an improved PS-PWM with cancelled mismatch pulses and a third harmonic injection method. The proposed method not only reduces output voltage harmonic content and uneven loss distribution between sub-modules but also extends the linear operating range of the inverter, which improves the DC bus utilization. The mathematical analysis is derived for the proposed method and in order to study the efficiency of the system using the proposed method, the loss calculation has been done and compared with traditional PS-PWM method. Simulation results in Matlab/Simulink show the suitable performance of the presented scheme.

Keywords:

DC bus utilization , Hybrid-MMC , Over modulation , Phase-shifted PWM , Third harmonic injection