摘要: One of the greatest challenges faced by Zhoushan Project is that AC-isolated island can easily be formed due to the weakness of the AC grid connected to the VSC system and vulnerability to typhoon attack. A strategy based on frequ... 展开 One of the greatest challenges faced by Zhoushan Project is that AC-isolated island can easily be formed due to the weakness of the AC grid connected to the VSC system and vulnerability to typhoon attack. A strategy based on frequency variation is introduced, which does not rely on breakers' status of AC grid. As a multi-terminal project, the AC-DC topology is complex, which brings new challenge to island mode switching over management. Hence a strategy of assuring only one station switch over to island mode in multiterminal VSC project is developed. A strategy based on alternative current rising and transient blocking of the converter is also designed for switching over back to HVDC mode when a tripped AC line reconnects to HVDC system. The whole strategy is tested in simulation system and applied in Zhoushan Project. In an AC line trip accident in November 2015, the right VSC station shifted to island mode successfully and a blackout was prevented, which proves the whole set of strategy to be useful and reliable. 收起