Research On Primary And Secondary Coordinated Protection Of Overcurrent And Overvoltage In Multiterminal VSC-DC Distribution System

Multi-terminal DC distribution system has become one of the important critical technologies of the smart energy and the Energy Internet development trend in the future due to its many advantages.For example,it is advantageous to realize the renewable energy grid connection and consumption,sensitive electronic loads and electric vehicles connection etc.At the same time,it has various operation modes and high-power supply reliability.However,at present,there are few operating experiences of multi-terminal DC distribution system at home and abroad.There are still many basic scientific problems and key technologies concerning multi-terminal distribution system remained to be studied in depth.Among them,overcurrent and overvoltage in fault are one of the important factors threatening the safe and reliable operation of the equipment and system.Therefore,it is necessary to carry out a systematic and in-depth study on the coordination and optimization of the overcurrent and overvoltage protection of the multi-terminal DC distribution system,so as to realize the safe,reliable and economic operation of the multi-terminal DC distribution system.In this paper,the generation mechanism,influencing factors and limiting methods of overcurrent under pole-to-pole fault in ±10k V multi-terminal DC distribution system,as well as the interaction and coordination optimization of the overcurrent and overvoltage protection scheme and protection strategy are studied.Firstly,based on the system topology,this paper analyzes the critical fault condition of the overcurrent and the design principle of current limiting scheme parameters,and based on the theoretical analysis of the equivalent circuit of the fault,the overcurrent theoretical calculation methods are proposed.At the same time,the theoretical calculation methods of current limiting scheme parameters which satisfies the breaking capacity of DC circuit breaker are proposed.Secondly,the influence of load fluctuation on overcurrent is analyzed,and the equivalent modeling method of load is proposed.Based on PSCAD/EMTDC,the electromagnetic transient simulation model of ±10k V threeterminal DC distribution system is established,and the design method of current limiting scheme parameters are verified by simulation.On this foundation,the influence of different current limiting schemes on the overvoltage are simulated and analyzed,and based on the above simulation results,the configuration scheme of the arresters is proposed.At the same time,the switching impulse withstand voltage of key equipment under different current limiting schemes are simulated and analyzed,as well as the overcurrent of typical faults are simulated and analyzed when the system is unconfigured and configured the arresters,so that the coordinated protection method of overcurrent and overvoltage is proposed.At last,the influence of different protection strategies on overcurrent and overvoltage under different current limiting schemes are simulated and analyzed,and then the primary and secondary coordinated protection method of overcurrent and overvoltage is proposed.In this paper,the interaction and coordination of overcurrent,overvoltage and protection strategies are considered.The results can provide a reference for the selection of overcurrent and overvoltage protection schemes in multi-terminal DC distribution system.