Capacitor Voltage Observation for Series-Connected-Double Submodule based Modular Multilevel Converter

Due to the high modularity and easy scalability for voltage and power, modular multilevel converter (MMC) has been the most appropriate converter in the high voltage direct current (HVDC) transmission system. The series-connected-double submodule (SCDSM) based MMC not only own the ability of the dc fault blocking but also features simple topology and control strategy. Then, the SCDSM based MMC has a promising application in the HVDC system. In the MMC system, the number of the submodules and capacitors is very large, which means the number of the voltage sensors is also huge. Reduced voltage sensors could decrease the cost of the MMC and improve the reliability of the MMC system. Based on the topology of the SCDSM, this paper proposes a novel arrangement of the voltage sensors and Kalman filter based capacitor voltage observer. Compared with the traditional arrangement of the voltage sensors, the number of the voltage sensors in this paper is halved. The simulation and experimental results verify the effectiveness of the proposed strategy in this paper.