Multi-module capacitor voltage measuring technique of modular multilevel converters based on sampling instant classification

Abstract

The measurement of the sub-module (SM) capacitor voltages serve as the premise and basis for the realization of control goals of the modular multilevel converter (MMC). This paper presents an improved measuring technique based on sampling instant classification (SIC-MT) with a smaller number of sensors, where an improved calculation process with a correction function is applied for estimation of the capacitor voltages to enhance the measurement accuracy. Furthermore, in practical applications, the impact on the voltage estimation resulting from the auxiliary circuit within each SM is also taken into account to further improve the voltage estimation accuracy. In addition, a grouping strategy is introduced to ease the voltage range/bandwidth requirements of the sensors employed for medium voltage applications. The simulation and the experimental results validate the feasibility and effectiveness of the proposed technique. The results show that the proposed method has higher measurement accuracy than the overall measuring technique (O-MT).