This paper proposes a dual channel additional frequency pole assignment control strategy to improve thetransmission capacity of HVDC under islanding operation

suppressing the subsynchronous oscillation and lowfrequency oscillation at the same time.Using the improved TLS-ESPRIT recognition algorithm

identifies the lowfrequency and subsynchronous oscillation open-loop transfer function of system under islanding.Then using the rootlocus diagram of system

by adjusting the gain of the system

can preliminarily get some closed-loop poles thatmakes the system stable

and gradually adjusting the real part of the closed-loop poles

achieves the desired pole aswell as the observer poles

and then using the method of pole assignment with observer

gets the controller transferfunction which makes the system stable.To compare the effect of pole assignment controller with other controller

thePID controller is designed to compare with it.By electromagnetic transient simulation software PSCAD simulationshows that the effect of pole assignment controller suppressing low frequency and subsynchronous oscillation at thesame time of systems under islanding operation is good

and changing the operation mode

it has good adaptability

and the robustness is better than the PID controller;The traditional PID controller requires higher operation of thesystem

and changing the operation mode

the effect becomes worse than before

and the robustness is bad.Thus

the pole assignment controller designed by this paper can implement to suppress the low frequency andsubsynchronous oscillation of HVDC at the same time under islanding operation mode

having good robustness

which has some reference value in engineering.