DC Circuit Breaker Configuration And Coordination In DC Grid Protection

With the development and utilization of wind power and photovoltaic in the world,their proportion of power generation has been increasing.As an effective means of using new energy sources,flexible DC grid has become an important direction for power grid development.However,the DC grid is mainly composed of power electronic equipment.Its components are weak in overcurrent capability.The DC grid is small in system inertia and short in time scale.Therefore,the fault current rises rapidly and in large amplitude.In order to ensure the safe and stable operation of the system and equipment,the DC grid has to isolation the DC fault quickly.At present,the research on DC circuit breaker mostly focused on the topology of the high voltage DC circuit breaker.However,as the size of the DC grid become larger,the high voltage DC circuit breaker installed will increase sharply.If the design of the protection timing sequence is not appropriate,it will result in failure to isolated the fault quickly and expand the fault area.In view of the above problems,this paper presented a DC grid protection scheme for the configuration and timing coordination method of high voltage DC circuit breaker.In the high voltage DC circuit breaker timing coordination method,this paper presented a timing coordination method for the DC circuit breakers when some DC circuit breakers refused to isolated the fault.At the same time,this paper proposed a fast DC fault detection method for the timing coordination scheme.In the high voltage DC circuit breaker configuration scheme,this paper presented a cost-effective DCCB topology.In this paper,a four-terminal flexible DC grid model was used for simulation to verify the correctness and effectiveness of the configuration and timing coordination method proposed in this paper.The details were as follows:Firstly,the development of high voltage DC circuit breaker was reviewed.The topology and control strategy of high voltage DC circuit breakers were analyzed.The DC fault characteristics of the four terminal bipolar flexible DC grid were analyzed.Secondly,the requirements of timing coordination when the DC circuit breakers failed to isolated the fault were analyzed.Based on the requirements of rapidity and selectivity,this paper presented a timing coordination method for the DC circuit breakers when some DC breakers were failed to isolated the fault.This method effectively reduced the time for DC circuit breakers to isolate the fault,it also reduced the current stress on DC circuit breakers while breaking the fault current,when some DC circuit breakers were failed to isolated the fault.Furthermore,this paper presented a fault detection method suitable for the timing coordination scheme.Finally,the requirements of high voltage DC circuit breaker configuration scheme were analyzed.Because of the different current stress on high voltage DC circuit breakers while breaking fault current in different directions in the DC grid,this paper presented an economical DCCB topology.This topology structure could reduce the number of components and reduce the construction cost under the ensuring of the fault isolated normally.In addition,this paper designed the configuration scheme of high voltage DC circuit breaker in the four-terminal flexible DC grid simulation system according to the topology.