An Improved HVDC Synchronous Firing Control Method Based on Order Switching and Phase Compensation

Synchronous reference frame phase-locked loop (SRF-PLL) is adopted in high-voltage direct current (HVDC) synchronous firing control to output the synchronous phase. The synchronous performance directly affects the accuracy of the firing pulse, and even affects whether the inverter can successfully commutate during AC asymmetric faults. Therefore, an improved HVDC synchronous firing control method based on order switching and phase compensation is proposed in this paper. The improved SRF-PLL has the functions of extracting the fundamental frequency positive sequence (FFPS) phase and switching the order. When the fault detection detects that a fault has occurred, PLL is converted from the second-order system to the first-order system, so as to shorten the out-of-lock time and make it quickly enter the resynchronization. Then, for the phase shift of commutation voltages caused by fault, the zero-crossing sampling method is used to detect the change of the commutation voltage phases, and the synchronous phase of each commutation voltage is compensated selectively. Finally, the improved method is tested in CIGRE HVDC benchmark model and Three Gorges-Shanghai (3GS) DC project model, respectively. The results show that the improved method has better effect on suppressing commutation failure.