Electromechanical Modelling of Modular Multilevel Converter Based HVDC System and Its Application

This paper introduces the electromechanical modelling method of modular multilevel converter based high voltage direct current (MMC-HVDC) system and studies the Chongqing-Hubei project based on the model. Firstly, the steady load flow model is established in this paper. Then, the transient stability model, which includes the AC side model, DC side model and control system model, is described in detail. For improving the transient stability, an additional control method, which combines a frequency controller and emergency power support strategy, is added on the control system model. Moreover, the modulation model is studied and discussed in case of fault conditions. The model is implemented on PSASP and its validity is verified through comparison with electromagnetic model. At last, the simulation is carried out based on the real grid date. The simulation results demonstrate the benefits of MMC-HVDC and the improvement in transient stability by applying the additional control method.