A New Recovery Strategy of HVDC System During AC Faults

To overcome the disadvantage of voltage dependent current order limiter of HVDC control system, which cannot achieve decoupling control of reactive power and active power, a novel ac fault recovery strategy is proposed in this study. By virtue of such recovery strategy, the exchange of reactive power between the ac system and the converter station can be controlled quantitatively to find the correspondence between dc order and ac bus voltage. In order to determine the expected reactive power consumption of converters, the instantaneous reactive power theory is used to calculate the reactive power compensated by ac filters. According to the quasi steady-state calculation equations of the HVDC system and the operational range of converter firing angle, the constraint relation between the maximum permissible operating value of dc and ac bus voltage under different ac fault types is obtained. Then, by comparing the dc order and the maximum value of dc, the smallest of them is taken as the final dc order so as to improve the recovery performance of the ac-dc system in real time. Finally, the effectiveness and robustness of the proposed control strategy in suppressing subsequent commutation failures and improving the system recovery performance are verified in the CIGRE benchmark model for HVDC controls.