Energy control of modular multilevel converter with a novel analytic filter

The complex topology of the Modular Multilevel Converter (MMC) requires some additional controllers to keep its functionalities. One of the important requirements on the MMC control is to balance the energy stored in the distributed capacitors in the arms on the three legs. However, due to the superimposed internal DC and AC power flows in the converter, the energy stored in the arms contains intrinsic oscillations. This paper provides a thorough analysis on those intrinsic oscillations on the internal energy of the MMC. Based on the analysis, a novel analytic filter is proposed, which enables to extract average value of the energy while keeping other internal dynamics stable. The proposed filter is implemented on an EMTP-RV platform. The simulation demonstrates its improved dynamic response and reduction of the internal losses compared to the existing solutions.