Research On Fault Features And Corresponding Protection Strategy Of MMC-HVDC Based On PSCAD/EMTDC

Module Multilevel Converter(MMC), because of its high output voltage quality, low harmonic, low switching frequency, small loss and other characteristics, is widely used in the field of Flexible HVDC project in recent years. In view of Flexible HVDC based on MMC has little research in the fault characteristics and protection strategies at home and abroad. Therefore, this paper studies and analyses the control strategy of the MMC-HVDC system and different fault characteristics in depth, and then put forward the corresponding protection strategy, and verify the simulation, the results prove the reliability of the protection strategies. This paper structure is as follows:Firstly, studying the working principle of MMC HVDC, including the topology structure and working mechanism of MMC, and its modulation and control strategies. To provide the theoretical foundation and basis for MMC-HVDC system modeling in PSCAD/EMTDC, fault feature analysis and the corresponding protection strategy.Secondly, modeling the MMC-HVDC system in PSCAD/EMTDC, and verify the start-up control strategy, circulation inhibitory control strategy, sub-module capacitor voltage balance control strategy and direct current control strategy. The results show the accuracy and reliability of the model.Finally, simulating and analyzing on the fault of sub-model, DC bus bipolar, AC bus three-phase grounding fault, and MMC-MTDC asymmetric AC system fault connected with wind farm. And then provide the corresponding protection for different faults, and simulation results prove the feasibility of the protection strategies.