In order to solve the problems of flexible DC blocking caused by the failure of bypass switch of sub-module in flexible converter stations,the action principle and force analysis of bypass switch action process are carried out.Next,from three aspects,that is,on-site inspection,fault recording and the recurrence test of bypass switch closing fault,the fault causes for bypass failure event of a flexible DC sub-module is analyzed in depth.And then,an improved design strategy for bypass switch rejection based on auxiliary voltage criteria is proposed for the non-turning thyristor module.At the last,the effectiveness and reliability of the improved strategy is verified through experiments under four different operating conditions,which avoids the sub-module cracking and converter valve blocking,and further improves the reliability of sub-module operation in flexible HVDC engineering in operation.
sub-modulebypass switch rejectionclosing testimproved strategyauxiliary voltage criterion
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