Research On The Power Interface Algorithm Of Power Hardware-in-the-loop Simulation For MMC-HVDC

Modular multilevel converter based high voltage direct current(MMC-HVDC)has a significant advantage in the fields of renewable energy power generation connected to the grid,isolated island power supply and regional power grid interconnection,which is the future development trend of VSC-HVDC.Because MMC contains a large number of power electronic devices,the dynamic behavior of the system becomes complicated.The traditional digital simulation is difficult to meet the requirements of characteristic analysis for the MMC and its control system.The dynamic physical simulation is also difficult to realize the simulation of the whole AC/DC hybrid system.Therefore,power hardware-in-the-loop(PHIL)simulation,which combines the advantages of real-time digital simulation and physical simulation,is a feasible method to achieve accurate modeling analysis and engineering design verification of the MMC-HVDC system.Power interface algorithm is a key technology to achieve PHIL simulation,which is an effective means to ensure the stability and accuracy of the simulation.The theoretical and experimental research on the power interface and its algorithm of the PHIL simulation for MMC-HVDC is carried out,which is based on the National Key Research and Development Program of China,and an improved damping impedance method(DIM)interface algorithm of the PHIL simulation for MMC-HVDC is proposed.The overall structure and the modeling equivalence principle of the PHIL simulation for MMC-HVDC system are studied and analyzed,and the stability and accuracy problems of the PHIL simulation caused by power interface is also revealed.The characteristics and application fields of different interface algorithms are analyzed and compared,and the advantages of DIM in terms of stability and accuracy are verified by simulation,then the method is used to design the power interface algorithm of the PHIL simulation for MMC-HVDC system.The accurate Thevenin equivalent models of MMC under the deblocking and blocking operation conditions are built,and the process of impedance calculation is optimized to improve the calculation efficiency of the equivalent impedance.On this basis,the real-time impedance matching method of DIM is proposed.In order to solve the accuracy problem caused by the interface delay,a delay compensation control method is proposed,which is based on the voltage signal reconstructed by dq transformation,to improve the accuracy of the PHIL simulation.A digital simulation system of two-terminal MMC-HVDC is constructed based on the proposed DIM interface algorithm in PSCAD/EMTDC,and the simulation results of the improved DIM and the ideal transformer model interface algorithm are compared under different operation conditions.The results show that the improved DIM interface algorithm can guarantee the stable operation of the PHIL simulation under different disturbances,and the simulation precision is high,which has excellent performance of stability and accuracy.Finally,the effectiveness and practicability of the proposed method are verified by the practical MMC-HVDC PHIL test platform.The research work of this paper has initially realized the PHIL simulation of MMC-HVDC,which will provide an effective simulation tool for the system planning and operation characteristic analysis of AC/DC hybrid system,and have a good application prospect.