DC Voltage Inversion Estimation Method of MMC Submodule Based on Current Information

Abstract

DC voltage detection of sub-modules is very important for the stability of cascaded multilevel converters. Operation and maintenance personnel need a detection algorithm to supplement the uncertainty and risk caused by the traditional redundancy scheme. This paper presented a DC voltage indirect estimation method based on current transformer. The method uses the AC side current value, as well as the sub-module equivalent circuit model and switching state to estimate the DC voltage of the sub-module of the cascade system. The estimation models are established and can be used to the sub-modules of three topologies, i.e., half-bridge, H bridge topology and clamp double sub-module. Simulation and experimental systems are built to testify the proposed method. The results showed that, when [Formula: see text] or 12, the indirect detection model based on AC current met the requirements of detection accuracy within 1% under different calculation steps, and the sampling error had little influence on it. The indirect estimation method could reduce the use of DC transformers and improve equipment reliability and maintainability.