| The direct current(DC)transmission system has great potential in the field of new energy grid-connected power generation due to its advantages such as good economy,high reliability,and low power loss.However,compared with traditional alternating current(AC)transmission systems,the DC transmission system faces more challenges in the field of fault protection.This is mainly manifested in two aspects: On the one hand,the DC network line impedance is low,and traditional DC circuit breakers lack fault current limiting function.When a fault occurs,the fault current will reach its peak value in a very short time,seriously threatening the safe operation of the power grid.On the other hand,the rapid rise of short-circuit current poses high requirements on the fault isolation speed of the circuit breaker.If the fault isolation is not timely,the fault current will break through the electrical equipment.Therefore,the research and development of DC circuit breakers with current limiting capabilities and shortened fault isolation time are of great significance for the protection of DC transmission systems.This paper clarifies the key technologies of hybrid DC circuit breakers progressively from four aspects: the topology structure of hybrid DC circuit breakers,series-parallel connection of power electronic devices with both voltage and current balance strategies,DC arc extinction technology,and control and protection technology.This lays a theoretical foundation for the design of hybrid DC circuit breaker topology structures in the future.This paper proposes a topology structure for a hybrid DC circuit breaker(HCB)with current limiting capability,which addresses the issues of high cost,large size,and lack of current limiting ability associated with traditional HCBs that use a large number of insulated gate bipolar transistors(IGBTs).Firstly,the topology structure and working principle of the proposed HCB are introduced,and its feasibility is analyzed through theoretical deduction.Secondly,parameter analysis and quantitative selection are carried out by considering the impact of device parameters on overall performance.Finally,simulation results confirm the effectiveness and advantages of the proposed HCB topology,which is also validated in a DC grid model.Under the same simulation parameters,the proposed HCB has a lower cost and faster fault isolation speed compared to traditional HCBs,while providing fault current limiting capability.To address the issue of the inability of traditional HCBs to limit fault current and isolate faults quickly in a DC grid,this paper proposes a current-limited hybrid DC circuit breaker(CLHCB)topology that combines the structure of traditional HCBs with a fault current limiter(FCL).CLHCB has both fault current limiting and hybrid DC circuit breaker functions.Which can limit the growth rate of fault current through FCL after a fault occurs,followed by fault isolation by the breaker.In addition,an energy dissipation circuit is connected in parallel to FCL,which can dissipate the energy stored in the current limiting inductor and accelerate the fault isolation process.Simulation and experimental results confirm the feasibility and advantages of the proposed CLHCB,which is also validated in a DC grid.Under the same simulation parameters,CLHCB can effectively limit the growth rate of fault current and reduce the fault isolation time compared to traditional HCBs. |
