An Asymmetric Control Strategy for Bipolar VSC-HVDC Connected Islanded New Energy

Under the background of vigorously developing new energy power generation technology, photovoltaic, wind power, and other new energy power generation technologies have been developed continuously. The voltage source converter based high voltage direct current (VSC-HVDC) plays an important role as a transmission technology widely used in large-scale new energy delivery. The reliable and flexible bipolar structure can be adopted to improve the transmission capacity and voltage level of VSC-HVDC, however, the adoption of traditional $V/f$ control strategy for bipolar VSC-HVDC system may lead to instability due to the control of same target of positive and negative poles. In order to realizes the stable operation of the bipolar VSC-HVDC system in the new energy island delivery scenario, an asymmetric control strategy with $V/f$ control adopted by positive converters and the constant active and negative power $(P/Q)$ control for negative converters is proposed. In addition, a power-balancing control approach, which is necessary to balance the active power between positive and negative poles is proposed in this paper. The proposed control strategy is simulated in the case of new energy output power fluctuation and AC fault, and it is verified that the control strategy keeps the power balance of the positive and negative pole and shows excellent dynamic characteristics.