Optimal Design Method for Maximum Modulation Index of VSC HVDC based on MMC Considering Compensation Signals and AC Network Conditions

This paper deals with Modulation Index (MI) of Voltage Source Converter (VSC) HVDC System based on Modular Multilevel Converter (MMC). In the 2-level converter, the purpose of the MI is to maximize the AC voltage reference at the fixed DC voltage. Unlike 2-level converter, MMC topology is to make the converter a voltage source using capacitor. And the AC voltage reference is distorted by the circulating current, so this circulating current affects the MI. Also, the AC Network conditions such as AC voltage variation, reactive power etc., also affect the MI. It is necessary to optimize modulation index according to internal and external conditions. This paper deals with the optimization method for MI of MMC HVDC System.