Research On Key Technologies Of New Type Multiport Mechanical DC Circuit Breaker

With the rapid development of power electronics technology,the size of DC power grids is expanding.It is necessary to configure a large number of DC circuit breakers to ensure its safe and reliable operation.The high cost of each DC circuit breaker has become an important factor limiting its wide range of applications.As one of the mainstream technologies of the existing DC circuit breaker,the mechanical DC circuit breaker has better economy.However,the existing commutation technology applied to the mechanical DC circuit breaker has defects affecting its working performance.Aiming at the problems existing in the current commutation technology for mechanical DC circuit breakers,this paper proposes a dual-capacitor oscillatory commutation technology.The dual-capacitor oscillatory commutation technology can reduce the technical requirements of fast switching and capacitor charging systems in DC circuit breakers.And it has the advantages of low cost and easy expansion to a larger converter capacity,which greatly improves the performance of the DC circuit breaker.In this paper,the numerical model of the process of high-frequency oscillating current generation and the process of arc-extinguishing of fast mechanical switch is established,which provides the basis for the selection principle of the components of the current commutation branch.Finally,the feasibility of dual-capacitor oscillatory commutation technology is verified by simulation.Based on the dual-capacitor oscillatory commutation technology,this paper proposes a new type multiport mechanical DC circuit breaker.The new type DC circuit breaker broadens the protection range of a single DC circuit breaker by sharing the main breaking branch,thereby enabling protection of multiple lines and greatly reducing the number and cost of DC circuit breakers in the DC grid.The article describes its working principle in detail and verifies the feasibility of the application of the new DC circuit breaker in the system through simulation models.Focusing on the main body of the circuit breaker,the electrical stability and transient electrical characteristics of the circuit breaker were studied by constructing the test platform and the prototype.The2 k V new multiport DC circuit breaker test prototype built in the test can break the 2.6k A fault current within 2.05 ms.As an essential component in a DC circuit breaker,the parameters of the metal oxide varistor also has an important influence on the performance of the DC circuit breaker.In this paper,the residual voltage is determined as the key parameter through the detailed analysis of the energy absorption process in the DC circuit breaker when the fault current is broken.Furthermore,the relation between residual voltage and wake time,residual voltage and energy absorption is deduced,and the principle of parameter selection is determined.