In China

with the rapid development of voltage source converter based multi-terminal direct current(VSC-MTDC)transmission technology

the real bipolar wiring mode has become increasingly popular in actual multi-terminal direct current(MTDC)projects. In the pseudo bipolar mode

line overload

generator tripping or load shedding may occur if a direct current line or a converter quits operation

while in the more flexible real bipolar mode

power conversion from fault grid to the non-fault one is permissible under similar conditions. A power conversion strategy for bipolar operation VSC-MTDC system is proposed. Since the positive and negative grid can be independently controlled in the bipolar mode

power surplus of the fault grid can be transferred to the non-fault one by using the proposed strategy under abnormal operating conditions. This strategy has improved the reliability and transmission capability of power grid within the limits of each element capacity. The simulation model based on Zhangbei ±500 kV MTDC demonstration project is established in PSCAD/EMTDC. The validity of the proposed strategy has been proved by the simulation results.