Restoration Optimization In Hybrid Multi-infeed HVDC Receiving System

With the rapid development and large-scale construction of HVDC,the structural form of the power system is gradually developing in the direction of AC-DC hybrid power system.The increase in the proportion of HVDC transmission in the power system has brought new instability factors to the system,increased the risk of blackouts,and brought new challenges to the safe and stable operation of the power system.At the same time,HVDC transmission can play an active role in the power system restoration,reasonable use can effectively speed up the system restoration process and bring new opportunities for power system restoration problems.Based on the structural characteristics and development trends of China's power system,this paper focuses on the restoration problem of the hybrid multi-infeed DC receiving system after a major power outage,and separately studies the VSC-HVDC control method applicable to the black start process and the grid reconstruction phase problems such as optimization of unit and HVDC restoration sequence and system partition optimization for parallel restoration strategy.The main work and innovations of the paper are as follows:1)This paper proposed a VSC-HVDC control method suitable for the black start process,analyzed the startup characteristics and control methods of VSC-HVDC as the black start power source,and found the limitations of the existing vector control through in-depth analysis of the black start process.Furthermore,a VSC-HVDC control method based on a virtual synchronous machine that can be applied to the black start process is proposed;at the same time,it is feasibility and impactful factors to directly support LCC-HVDC startup by VSC-HVDC in a hybrid multi-infeed DC receiving system were analyzed;based on simulation,the control method of VSC-HVDC during black start was further analyzed and verified.2)An optimization model for generation units and HVDC restoration sequence considering the interaction of the HVDC system was established.The interaction between the AC and DC systems and the DC system during the system restoration process was analyzed.A new receiving system strength index,which taken into account the influence of VSC-HVDC on LCC-HVDC,was used.A multi-objective optimization model for generation units and HVDC restoration sequence in the stage of grid reconstruction is established,and a fast non-dominated sorting genetic algorithm with elite strategy is used to solve the multi-objective optimization model.An example of IEEE-39 nodes system verifies the effectiveness of the proposed method3)A partition optimization method based on local fitness measure,which is suitable for hybrid multi-infeed DC receiving system is proposed.The interaction between AC and DC systems is used to weight the lines,and then the complex network model of the system is established.Further considering the impact of VSC-HVDC on the restoration partition,the partition principle applicable to the restoration of the hybrid multi-infeed DC receiving system is formulated.A partition optimization method based on local fitness measure algorithm is established.The optimization results of IEEE-39 nodes system calculation examples verified the effectiveness of the proposed method.