Adaptive Integrated Coordinated Control Strategy Based on Sliding Mode Control for MMC-MTDC

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 response speed and stability of the system, an adaptive integrated coordinated control strategy based on sliding mode theory is proposed. The strategy adopts a double closed loop cascade control structure, the outer-loop controller performs adaptive droop control based on the comparison of the MMC real-time power margin with the power reference command, and the inner-loop controller is designed based on a sliding film variable structure with current error as the sliding film plane. The simulation model of MMCMTDC direct current transmission system was built in PSCAD/EMTDC. The simulation results of the proposed control strategy show that the control strategy can effectively avoid the full load margin of the system when the MMC is small, and the strategy also can improve the adaptability and dynamic performance of the system compared with the traditional control strategy.