Reduced sampling rate for cell voltage sensing in high-level Modular Multilevel Converter

Abstract

This paper presents an estimation scheme of cell capacitor voltage for the Modular Multilevel Converter (MMC) to reduce the sampling data and its associated communication time coming from enormous number of cells in HVDC application. For the control of cell capacitor voltage of each cell, it is necessary to know the state of the voltage and it is generally measured by voltage sensors. And, to sample the voltage of each cell at every sampling instant, the associated measurement and communication hardware and signal processing time would be prohibitive as the number of cells in each arm of MMC for HVDC application is above several hundreds. This paper presents an estimation of the cell capacitor voltages using submodule grouping and adaptive observer for estimating cell capacitance in order to reduce real time voltage measurement burdens. The simulation and experimental results verify that the proposed method can guarantees the stable operation of MMC with reduced number of the cell voltage sampling.