To solve the problem that traditional DC system is not capable of transmitting electrical power alone

the instability mechanism of HVDC transmission system for islanded wind farm is analyzed

and the lack of auto-suppressing measures for unbalanced power is regarded as the reason of the incapability of cooperation between wind farm and HVDC. A solution is proposed to introduce an additional VSC with stability control strategy at the sending end of AC bus so the external characteristic of the sending end source performs similarly as a voltage source and the unbalanced power can be suppressed. On one hand

VSC provides three-phase voltage rotating vector to maintain the regular operation of DFIG. On the other hand

the capacity voltage of VSC is fed back to monitor the frequency fluctuation at the sending end of HVDC and adjust the transmitted power to suppress the unbalanced power. Thus

the stable operation of the system is achieved. A closed loop is verified by real time digital simulator（RTDS） carried on

and the results indicate that the proposed suppressing mechanism is a valid method for the cooperation of wind farm and traditional DC system

and the capacity of the introduced VSC is only about 1% of the DC transmission capacity.