Adaptive integrated coordinated control strategy for MMC-MTDC Systems

Traditional double closed-loop PI control and DC voltage-active power droop control are suitable for the modular multilevel converter based Multi terminal flexible DC transmission system (MMC-MTDC). However, due to the strong nonlinearity of the system and the fixed droop coefficient, the system has poor stability under transient conditions, which is prone to full load. In order to improve the anti-interference ability of MMC-MTDC system, this paper proposes an adaptive integrated coordinated control strategy, which consists of adaptive droop control and internal loop current adaptive discrete slip film variable structure control based on discrete reaching law. The control strategy replaces the original fixed coefficient droop control with adaptive droop control. The adaptive synovial variable structure control with the inner loop dq axis current error as the synovial plane is constructed based on the discrete approach law in the synchronous rotating coordinate system. Combined with the Lyapunov function, the global stability analysis of the inner loop control system is carried out. Based on Zhangbei ±500kV four-terminal flexible direct current transmission demonstration project, the simulation model of MMC-MTDC direct current transmission system was built in PSCAD/EMTDC. The simulation results of the proposed control strategy show that the control strategy can improve the adaptability and dynamic performance of the system compared with the traditional control strategy.