Research On Short-circuit Characteristics Of DC Distribution Network Containing Photovoltaic And Solid State Circuit Breaker

With the continuous development of renewable energy technologies,more and more distributed energy sources are connected to distribution networks through power electronic devices,which brings new challenges to the protection of distribution systems.Compared with AC systems,DC systems can effectively improve power quality,reduce power electronic conversion steps,reduce power consumption and operating costs,and improve system reliability,and fully enhance the distribution of the value and benefits of energy,so the DC micro-grid system has attracted extensive attention from domestic and foreign experts.DC protection technology is one of the key technologies that hinder the development of DC systems at this stage.The research on the characteristics of fault current under different short-circuit fault modes of distributed renewable energy access to DC microgrids is the premise of isolation and short-circuit faults in DC microgrid systems.DC solid state circuit breakers are an essential means of isolation and short circuit faults in DC microgrid systems.Firstly,this paper introduces the development status of DC microgrids at home and abroad from the aspects of topology structure,key technologies,etc.Then the development status of short circuit fault analysis in DC protection technology and the classification of DC solid state circuit breakers are introduced in detail.A circuit topology suitable for photovoltaic power generation access to a DC microgrid is proposed,and an equivalent mathematical model of a DC microgrid containing photovoltaic power is deduced.Based on different short-circuit fault modes of distributed renewable energy access to DC microgrid,the transient characteristics of short-circuit faults in DC system are analyzed in detail.This paper concludes that the short circuit fault of the PV system's access to the DC system leads to the collapse of high transient fault currents and severe transient DC voltages,and further studies the influence of system parameters on the short-circuit faults of the DC distribution network.Aiming at the influence of system parameters on faults,this paper proposes a current limiting protection technology for DC distribution networks based on impedance adjustment.The working principle of the DC distribution network is described in detail,and the design parameters are further discussed.The fault characteristics of the DC distribution network before and after the impedance adjustment are discussed.A comparative analysis shows that this method can effectively suppress the rise of fault current and the collapse of DC bus voltage,In the face of DC system short-circuit faults,the most effective and reliable method is to use DC circuit breakers to isolate faults.For this reason,a self-powered ultra-fast DC solid state circuit breaker design method is proposed in this paper.And elaborates topological structure and working principle on the DC solid state circuit breaker in this paper,focus on the circuit breaker detection circuit energy transfer process,self-power supply performance and drive circuit optimization methods.Aiming at the characteristics of the two-way energy flow of the DC microgrid with distributed renewable energy,the design idea of the bidirectional DC solid state circuit breaker is further proposed.Finally,the design of DC short-circuit experimental platform and the development of self-powered ultra-fast DC solid state circuit breaker prototype are discussed.Based on the DC short-circuit experiment platform,the self-power characteristics of the DC solid state circuit breaker detection circuit,the quick-action of the drive circuit,and the reliability and fast protection characteristics of the isolated fault current of unidirectional and bidirectional circuit breakers were verified through experiments.