Research on the transient stability of HVDC rectifier-side AC system during the whole process of DC restart failure

Abstract HVDC restart failure can cause the DC power interruption, which may further result in the transient power angle of the rectifier-side AC system to go unstable. Concerning this problem, a transient stability analysis method considering dynamic changes of converter topologies during the whole process of the DC restart failure is proposed. First, dynamic energy models of the DC terminal and the AC filter in the whole process of the DC line restart failure are built, including the ‘restart at fault’, phase-shifted triggering and deionization stage. On this basis, according to the Lyapunov’s second theorem, the variation rate of the aperiodic component of generator dynamic energy is defined as the dissipation rate of dynamic energy, which characterizes the accumulation or the consumption trend of total system energy. Thus the stability of the system is assessed according to the dissipation rate of dynamic energy. Then, effects of the dynamic energy of the DC terminal and the AC filter on the dissipation rate of dynamic energy in the whole process of DC restart failure are illustrated, and the cause of the transient instability of the rectifier-side AC system is revealed. Finally, hardware-in-the-loop tests in RT-LAB verify that, when the amplitude of the generator outlet bus voltage rises during the ‘restart at fault’ and phase-shifted triggering stages, the dynamic energy of the DC terminal has a positive effect on the dissipation rate of dynamic energy, induces the total system energy to keep accumulating, which is not conducive for the stability of the system. In the deionization stage, the dynamic energy of the AC filter has a positive effect on the dissipation rate of dynamic energy, which is not conducive for the stability of system.