基于电气转矩法的 VSC-HVDC 系统直流电压振荡稳定性评估

This paper investigates the DC-link voltage oscillation stability of voltage sourced converter (VSC) based high voltage direct current (HVDC) system using electrical torque method. Firstly, the dynamics of power-controlled converter and voltage-controlled converter are fully explored based on the averaged value model to obtain the model suitable for electrical torque method. Then, the Phillips-Heffron model of a two-terminal VSC-HVDC system is constructed. Based on the proposed model, the damping and synchronizing coefficient are obtained. Since it is indicated by electrical torque method that the system stability is mainly related to the damping coefficient. Accordingly, the stabilizing conditions based on electrical torque method can be derived, revealing the DC-link voltage oscillation instability mechanism and quantifying the impacts of DC grid and DC controller dynamics on system stability. The DC-link voltage oscillation stability can no more be guaranteed once the positive damping provided by DC grids and voltage-controlled converter fails to offset the negative damping generated by power-controlled converter. In addition, reasonable setting of proportional gain of DC-link voltage control can ensure sufficient stability margins under various operating conditions. Finally, the feasibility of electrical torque method in analyzing the DC-link voltage oscillation stability of power-electronics-based power systems and the correctness of the proposed stabilizing conditions are verified by numerical simulation in professional software.