Research On Hybrid High Voltage DC Current Limiter Based On Thysistor

With the gradual increase of DC transmission voltage level and capacity,the DC grid based on Modular Multilevel Converter(MMC)has become the development direction of the future DC transmission field.However,the core equipment,converter station in the DC grid has the characteristics of low damping.If the DC grid side damping is also small,after the DC side fault occurs,the fault current develops rapidly and the fault has a wide range.The DC circuit breaker is considered to be an effective means to achieve fast cutoff of the fault current.However,the high voltage DC circuit breaker has a high cost and there is a contradiction between the disconnecting speed and the disconnecting capacity.In order to reduce the current stress during the breaking of the DC circuit breaker and reduce the cost of the DC circuit breaker,two new high-voltage DC fault current limiter topologies are proposed in this paper,and related research is carried out.The details are as follows:Firstly,a new hybrid single-port DC current fault limiter(FCL)topology is proposed.The current flow branch of the topology uses mechanical switches and power electronics in series,and the on-state loss is low;the main current limiting circuit uses the thyristor device;the current limiting inductor acts as a main current limiting component,and can quickly exit when the DC circuit breaker is operating.The theoretical analysis of the current limiting process of the new topology is carried out in stages.The relationship between voltage stress,current limiting time and current limiter parameters is analyzed.The design method of current limiter parameters is given.A fast bypass method of current limiting inductor is proposed in the case of open circuit,and the theoretical calculation of the energy consumption of the arrester in the DC breaker is reduced.The correctness of the method for analyzing the dynamic characteristics of the current limiter is verified in the single-ended converter station and the DC grid.The simulation results show that the proposed current limiter can effectively limit the rising rate of DC fault current and significantly reduce energy dissipation during circuit breaker disconnection.Secondly,in order to further reduce the number of DC current limiters in the DC grid,a new multi-port DC fault current limiter(multiport DC Fault current limiter)is proposed based on the single-port DC current limiter.Mp-FCL),the Mp-FCL can be configured at the exit of the converter station instead of multiple single-port FCLs on the DC line to which the original bus is connected.The theoretical analysis of the current limiting process of the new topology is carried out in stages,and the cooperation between Mp-FCL and DC circuit breaker is studied.The relationship between voltage and current stress,energy consumption of arrester and key parameters of Mp-FCL is analyzed,and the design method of Mp-FCL parameters is given.The simulation of the Mp-FCL's operation characteristics is verified.It proves that the Mp-FCL can replace the conventional FCL to achieve effective current limiting and greatly reduce the energy consumption requirements of the arrester in the DC circuit breaker.Finally,the recovery of the high voltage DC fault current limiter based on the thyristor device and the reclosing of the DC circuit breaker are analyzed.Among them,the recovery of the proposed current limiter includes two aspects,one is the discharge of the high voltage capacitor,and the other is the reclosing of the conduction branch.After the current limiter is restored and the faulty DC line is restored to insulation,the DC circuit breakers should be closed again.For this,the transient fault and the permanent fault are simulated and analyzed.