True bipolar multi?terminal flexible DC transmission voltage source converter based multi?terminal direct current(VSC?MTDC) new energy side converter station positive and negative converters can be controlled independently. In view of the failure of the converter with constant AC voltage amplitude and frequency control (U/f control), the control strategy of the converter with constant active and reactive power control (P/Q control) is converted into the AC and DC bus voltage under constant U/f control in this papers. Causing the problem that the fluctuation is large and the new energy station would be disconnected from the grid in severe cases. A unified switching control model is established, and a soft switching control strategy based on current following is introduced on the basis of the unified switching control model to realize the reference value of the inner loop current at the moment of switching synchronization. Based on PSCAD/EMTDC, a four?terminal true bipolar VSC?MTDC system with large?scale new energy access is built. Through the simulation under steady state, wind farm power fluctuation, and converter unipolar blocking operation, it is verified that the converter station has a voltage support of new energy access and the ability of smooth transition of the power system during the system switching process provide a reference for further improving the control flexibility of the true bipolar VSC?MTDC system.