Capacitor Voltage Regulation of Modular Multi-level Converter Using Variable DC Off-set for the Arm Voltages

Half-bridge modular multi-level converter (HBMMC) is a well-established converter topology for HVDC applications. This paper focuses on control aspects of HB-MMC in HVDC transmission systems. The regulation of submodule (SM) capacitor voltages of HB-MMC for satisfactory operation of the converter has such method to regulate the SM capacitor voltages during transient and steady state conditions. This is achieved by allowing the number of SMs inserted in a leg to vary at every instant of time. With the proposed method, the average values of the SM capacitor voltages are tightly regulated at their nominal values. The dynamic and steady state performances of the MMC with proposed method are compared with the method in which fixed number of SMs is inserted in a leg throughout the total duration.