Researchof Key Technologies On High Voltage DC Circuit Breaker

With the rapid development of distributed generation, energy storage technology, multi-terminal DC transmission and smart grid, it will be one of future development trends to research a DC transmission and distribution grid which have high reliability, strong controllability and low cost. Although DC transmission technology is relatively mature, it still faces many challenges to build DC grids, one of which is interruption of DC. It has great significance to prevent the spread of fault areas by using DC breakerswhich are key equipments to carry and interrupt normal and fault current within the stipulated time.DC has no natural zero-crossing point, leading to the difficulties of arc extinction, as well as turn-off over-voltage and energy absorption problems.In addition, due to the low impedance and high permeability of DC system, DC breakers need to break high fault current as soon as possible. All problems mentioned above are the main technical difficulties of DC breaker.This paper analyzed and compared different kinds of DC breakers at home and abroad, presents an all-solid-state high-voltage DC breaker topology based on high-power power electronic devices and designed the timing sequence control strategies of the transient process of opening, closing and commutation. Focusing on the dynamic voltage balancing problems, this paper presents an optimization method of snubber circuit in load side. The models of high-power power electronic devices are built in Saber and simulation results showed that the topology can effectively limit the rate of rise of fault current, achieve well dynamic voltage balancing effect and protect power electronic devices reliably. Based on the research above, this paper applied DC breakers to Nan’ao three terminals voltage source converter HVDC project, established joint simulation model based on current characteristics of different kinds of fault and designed fault protection strategies in DC side. Simulation results verified that the protection strategies can quickly and effectively isolate the DC side fault and ensure the stability of DC voltage and reliable operation of other converter stations.