Multi-end flexible direct-current power transmission system and method for online isolation and grid connection of single station of multi-end flexible direct-current power transmission system

The invention relates to a multi-end flexible direct-current power transmission system and a method for online isolation and grid connection of a single station of the multi-end flexible direct-current power transmission system. The multi-end flexible direct-current power transmission system comprises four converter stations, wherein one of the four converter stations needs to be overhauled. The direct-current side of each converter station comprises two sets of isolation switches, namely, the isolation switches QS1 and the isolation switches QS2, wherein the isolation switches are connected in series, an alternating-current relay Q2 is connected between each isolation switch QS1 and the corresponding isolation switch QS2 in series, and an isolation switch QS3 is connected to the two sides of each isolation switch QS1 and the corresponding isolation switch QS2 in parallel. The alternating-current side of each converter station comprises an alternating-current incoming line switcher Q1 and a converter transformer, wherein each alternating-current incoming line switcher Q1 is connected with the corresponding converter transformer in series, and an isolation switch QS4 is connected between a direct-current circuit and a bus rod in series. By considering the requirement of an electrical power system for overhauling the multi-end flexible direct-current power transmission system, with the help of the control characteristics of the multi-end flexible direct-current power transmission system and the characteristic that an alternating-current circuit breaker can cut off a small current direct-current circuit, the alternating-current circuit breaker is connected to the direct-current side of each converter station in series and plays a role of a direct-current circuit breaker. In order to ensure operation safety of each alternating-current circuit breaker and prolong the service life of each alternating-current circuit breaker, the isolation switch is connected to the two ends of each alternating-current circuit breaker in parallel and plays a role in switching on a normal running current.