Fault Ride-through Strategy for Fixed Power MMC Converter Station in Three-terminal Hybrid UHVDC Transmission System
The hybrid UHVDC transmission system with LCC at the sending end and MMC at the receiving end is one of the important development directions of HVDC transmission technology.In this system,each pole of each converter station consists of two valve groups,high and low DC side in series.When an AC fault occurs at MMC,the existing ride-through strategy may cause the failure of the voltage balancing between the valves,which leads to the problem of submodule overvoltage.To address this problem,the AC fault characteristics of the system are analyzed,and then,the internal mechanism causing the failure of the voltage balancing is studied and a coordinated inter-station strategy based on the active power limit value is proposed.Besides,in order to make it applicable to asymmetric fault,a zero-se-quence voltage injection method is used to balance the DC component of the arm current between the phase units.Fi-nally,we build a model based on the PSCAD/EMTDC simulation platform.Through simulation comparison,it is veri-fied that this strategy can take into account the bridge arm overcurrent and sub-module overvoltage risks of different re-ceiving stations,achieve reliable AC fault ride-through,and improve the power transfer capability during the fault as much as possible.
hybrid UHVDC transmission systemsteady state voltage balancing sectorAC fault coordinated ride-throughzero sequence voltage injectionpower limit value
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维普
