| With the development of renewable energy and the continuous growth of power system capacity,the traditional AC power system has been difficult to meet the needs of users.In recent years,high-voltage direct current(HVDC)technology has been widely concerned by the industry at home and abroad with its advantages of flexible power regulation,convenient transmission line erection and small operation loss.As the key technology to realize the engineering application of high-voltage flexible multi terminal DC distribution system,the research and development of high-voltage DC circuit breaker(HVDCCB)faces many technical difficulties: On the one hand,there is no zero-crossing point in the DC system current,so it is difficult for the circuit breaker to extinguish arc after fault.On the other hand,there is a contradiction between the rapid cut-off of the fault current by the circuit breaker and the accurate determination of the system fault by the protection system because the current rises quickly and the peak value is high after the DC system is shorted.Therefore,it is of great significance to study the large-capacity DC circuit breaker to promote the engineering application of the multi-terminal DC transmission system.At present,scholars at home and abroad are at the preliminary stage of research on superconducting current limiting DC circuit breakers,and the topology is not perfect.In this paper,a new topology of superconducting current limiting DC circuit breaker is proposed on the basis of the existing structure research.It has the following outstanding advantages: Combined with superconducting current limiting technology to suppress the initial rise rate of fault currents,alleviate the contradiction between system sensitivity and reliability,reduce the need for rapid switching of mechanical switches,and ensure the service life of superconducting strips by design.Add clamp circuit to realize arc-free breaking of mechanical switch during commutation process.Solid-state switches combine the advantages of full-control and semi-control power devices to increase circuit breaker capacity and reduce the cost of engineering application.Subsequently,in order to improve the optimization of the new superconducting current limiting DC circuit breaker topology,two-way switching topology scheme and second-order commutation topology scheme are proposed.Firstly,this paper describes the research background and development status of HVDC circuit breakers.Analyze the working principles,advantages and disadvantages of the four basic topological structures of DC circuit breakers and the research status at home and abroad,and point out that hybrid DC circuit breaker is used as the basic structure of superconducting current limiting DC circuit breaker because it combines the advantages of simple structure of mechanical DC circuit breaker and flexible and controllable structure of solid-state DC circuit breaker.Secondly,by summarizing and discussing the key technologies involved in the research of DC circuit breakers,it provides theoretical support and technical support for the subsequent analysis of the working principles of the topological structure of each scheme and the establishment of simulation models.Based on the analysis of the working principle of each topology,the mathematical model of the main circuit scheme of the circuit breaker and the second-order commutation topology scheme are established,which provide the basis for the selection of simulation parameters.Then,the ground short circuit model of 10kV/3kA DC system is established in MATLAB/Simulink environment,and the current limiting characteristics and breaking characteristics of circuit breakers under each scheme are simulated and verified.Finally,the traditional forced commutation DC circuit breaker is built to compare and analyze the performance of the new superconducting current limiting DC circuit breaker,and the improved scheme is compared with the main topology scheme to analyze the optimal characteristics of the circuit breaker.The simulation results show that the new superconducting current limiting DC circuit breaker topology proposed in this paper can effectively break the large fault current and complete the arc-free breaking of the mechanical switch,achieving the expected effect. |
