Study of frequency and voltage characteristics of islanding HVDC system and the corresponding control strategy

The HVDC power transmission system will be fallen into islanding operation mode under the following condition, the AC system at the sending end of the HVDC transmission system is disconnected from the main power grid due to the fault at transmission line. In the circumstance, the disturbances in AC/DC system can easily lead to the instability of frequency or voltage. For improving the frequency stability of the sending end, a kind of frequency limitation control (FLC) is proposed, which changes the HVDC current order according to the change of system frequency. While, measures to maintain the stability of the islanding system voltage are also investigated in this paper. Using PSCAD/EMTDC, a closed-loop simulation system is built to test the above-mentioned strategy. The control measures to improve the stability of the frequency or the voltage are proposed and validated by simulative tests, which may provide valuable reference for islanding operation system.