A large-scale submodule group based algorithm for modeling and high-speed simulation of modular multilevel converter

During the simulation of high-voltage modular multilevel converter (MMC) with high capacity and that of MMC based HVDC power transmission system, due to the large-number of submodules the simulation speed is slow. In allusion to this, the electrical behavior of the converter-arm of MMC is analyzed and mathematical models under blocking state and de-blocking state are established. After simplifying the established models, equivalent circuit and equivalent electrical relation of the converter-arm are created to make the established models enable to simulate the blocking state and de-blocking state of the converter-arm. To validate the accuracy between the equivalent circuit of the converter-arm and the equivalent electrical relation, a flexible HVDC transmission system is designed and HVDC transmission systems based on the detailed MMC model and the simplified MMC model are constructed in the simulation system respectively to simulate such process of HVDC transmission system as startup, de-blocking, steady state and DC fault. Simulation results show that the behaviors of the detailed MMC model and the simplified MMC model are basically the same, thus, the simulation accuracy by the simplified MMC model can be ensured. ©, 2015, Power System Technology Press. All right reserved.