The VSC-HVDC technology owns the advantages of low line loss and independent control of active and reactive power. It is the preferred way to realize grid connection of large-scale offshore wind farms. When the VSC-HVDC transmission technology is used for grid connection

the fault ride through（FRT） should be solved when onshore AC side fault occurs. At present

the common solution is to use DC energy breaking device（DBD）. Based on the comparison of the existing typical DBD topologies

a concentrated DBD based on discharge controllable sub-module topology is proposed in this paper. The range of DC voltage fluctuation is reduced by using the step switching on and off strategy

and the accurate controllable discharge strategy of the sub module capacitor is proposed based on the step switching off process. The experiment results of system simulation and Real Time Digital Simulation System（RTDS） show that the proposed DBD and control strategy can support the system to realize fault ride-through smoothly.