Double Bridge Type All-Solid-State High Voltage DC Circuit Breaker

The traditional energy crisis needs to be solved by large-scale development of new energy sources,while new energy sources used must be converted into electricity.Multi terminal flexible DC can realize long distance transmission and multi point for power gradually come into people's field of vision.But when the DC side short circuit occurred the short-circuit current will rise rapidly and reach a high level,and because the DC current does not exist the natural zero crossing point and lower system impedance,it will be very difficult to switch on.The development of an appropriate DC circuit breaker has become a hot spot in the development of multi terminal flexible DC transmission.The technical characteristics and research status of the three traditional high voltage DC circuit breakers are briefly introduced,and analyzes and compares their advantages and disadvantages with typical topologies of their respective main circuits.The comparison results show that the solid state high voltage DC circuit breaker has the absolute predominance in the three important indexes of the breaking speed,the breaking time and the interrupting process whether have arc in the interrupting process of the DC circuit breaker.The key technologies such as voltage sharing,current sharing,overvoltage and overcurrent protection,breaking control strategy and snubber circuit for solid state high voltage DC circuit breaker are analyzed,provide technical and theoretical support for the DC breaker scheme below.A topology of double bridge type all-solid-state high voltage DC circuit breaker is presented,which consists of two whole bridges sharing bridge arm.The topological structure can share the long-term branch current path in normal flow,and can share the main cut off branch way when the fault current is switched off,thus saving the device and saving the cost.Specific advantages are as follows:(1)breaking fault current is fast and time is short;(2)the current flow capacity is stronger,and the through flow loss is small;(3)compared with the similar high-voltage DC circuit breaker proposed by predecessors,the cost is reduced and the breaking loss is reduced.In the simulation software PSCAD/EMTDC,the circuit topology of the proposed circuit breaker is modeled and simulated,and the current and voltage waveforms of the breaking process are obtained to verify the topological characteristics and feasibility.In view of the contradiction between the breaking time and the voltage sharing of the conventional RCD series sharing voltage absorption circuit,an improved RCD series voltage sharing absorption circuit is proposed.The static voltage sharing is realized by combining a set of big and small resistors with equal numerical value at each end of each IGBT,wherein the small resistance is used as a detecting resistor of the overvoltage whenthe static voltage sharing task is completed.The dynamic voltage sharing circuit has a small capacitor connected in series with the capacitor of the original RCD sharing voltage absorption circuit,and a auxiliary IGBT is connected in parallel with the small capacitor as a short circuit switch of the small capacitor.By comparing the results of the two methods on the simulation software PSPICE,it is proved that the improved RCD sharing circuit can balance the breaking time and the voltage sharing effect very well.The principle of the proposed circuit breaker is verified by using a low voltage and low current proto type built in the laboratory.Experimental results show that the main circuit topology design of double bridge type solid state high voltage DC circuit breaker provided in this paper,based on the fast and reliable fault breaking current,can reduce the number of used devices,reduce the cost of circuit breaker making machine.