A Virtual Phase-Lead Impedance Stability Control Strategy for the Maritime VSC-HVDC System

In the maritime VSC-HVDC system supplying power to passive network on the island, the dc side of the system is prone to oscillation and even instability, which is resulted from the negative incremental input resistance characteristic of the inverter station. First, a virtual phase-lead impedance stability control strategy aiming at rectifier station is proposed. This control strategy can effectively mitigate the dc-side oscillation of the VSC-HVDC system without affecting the load performance of the inverter station. Then, the dc impedance model of the VSC-HVDC system is built, including the output impedance of the rectifier station, dc cable impedance, and the input impedance of the inverter station. In addition, the oscillation mechanism of the VSC-HVDC system is analyzed by impedance-based Nyquist stability criterion. The reason why rectifier station fails to mitigate the dc side oscillation using traditional virtual resistance stability control is that the output impedance of the rectifier station exhibits negative damping characteristic outside the control bandwidth of voltage outer loop. For this issue, the proposed control strategy can correct the output impedance of the rectifier station to exhibit positive damping characteristic outside the control bandwidth of voltage outer loop, thus mitigating the dc-side oscillation of the VSC-HVDC system. Finally, simulation and experiment results validate the proposed control strategy and analysis.