In order to enable the AC systems at the two sides of voltage source converter based high voltage direct current (VSC-HVDC) system to provide frequency support to each other under a fault

an additional frequency control strategy is proposed. The droop characteristics of frequency-active power and DC voltage-active power are introduced in the active power controller

meanwhile the droop characteristics of frequency-DC voltage are introduced in the DC voltage controller. Both the AC systems can participate in each other’s frequency adjustment through VSC-HVDC without interstation communications. The frequency adjustment burden of the AC system under fault will be relieved

and the frequency stability of the DC system will be improved as well. Finally

simulations with PSCAD/EMTDC verify that the proposed control strategy is able to enhance the frequency stability with full use of the frequency adjustment ability.