Research On Fault Response Strategy Of The Source-Storage Node In DC Microgrid

Diesel engines or three-phase permanent magnet generators are commonly connected to the DC microgrids with PWM rectifiers in recent years.Under this design,the generators will be off-grid for protection when a short-to-ground fault occur on the DC bus or its load.This paper describes research of the DC microgrid fault response strategy which aiming the goal of keeping the generator on-grid under the fault and making generator to participate in the restoration of the bus voltage after the fault is eliminated.Aiming at the short-to-ground fault of DC microgrid bus,this paper proposes a source-storage node topology to form a multi-port power converter for switched reluctance generator(SRG)and ultracapacitor(UC)working as input.The basic structure of source-storage node topology includes a buck-boost arm which controls the bi-directional power flow of the ultracapacitor,an asymmetric half-bridge for independent excitation and freewheeling of the switched reluctance generator,and a power electronic breaker which is used to isolate the fault.According to the characteristics,this paper analyzed the mathematical model and described how to establish its simulation model in MATLAB/Simulink which is used to verify the effects of controlling bi-directional power flow,controlling of SRG starting and stop and power electronic breaker fault isolationA steady-state operation control strategy for source-storage nodes is proposed.Ultracapacitor charge in constant current by using Current Closed Control and discharge to maintain the excitation voltage for generator,by using current-voltage double-loop.switched reluctance generator can adjust its power by changing the duty of chopper.The simulation of the steady-state operation of the node was established to verify the feasibility of the steady-state control strategy of the ultracapacitor and the generator by simulating the load switching.This paper proposed a response strategy of the source-storage node to deal with short-to-ground fault.First,making sure the generator is on-grid by isolating the fault and re-stabilizing the excitation voltage.Then generator inject power pluses into faulted bus,which will restore voltage rapidly after the fault is eliminated.Simulation shows that the strategy equipment which under preset parameters,can maintain the excitation voltage for generator after the fault is isolated.The generator does not off-grid when the fault occurs,and it can recover the bus voltage rapidly after the fault is eliminatedAfter all,this study proposes a form of non-permanent magnet generator and fast energy storage,which can ensure the generator which will keep on-grid state in the case of a short circuit to the ground fault occur to DC bus or its load.It can save some time when DC microgrid is recover from fault.It improves the performance of the DC microgrid under faults.