Optimal power adjustment scheme based on linear quadratic optimal control for MTDC

With the increasing of the penetration rate of new energy power generation and DC transmission, and resulted effective inertia decreasing, the transient stability of multi-terminal DC systems (MTDC) based on voltage source converters (VSC) has become particularly prominent. In order to solve the rotor-angle stability problem caused by the decrease of the effective inertia and the reduction of the effective damping of the MTDC system, an optimal power adjustment scheme for MTDC system, which is based on linear quadratic optimal control, is proposed. Firstly, the linearization model of the AC- DC hybrid system is obtained by linearizing the MTDC model near the stable equilibrium point. The design scheme of optimal power controller for MTDC system is obtained by using linearization model and adopting the linear quadratic optimal control theory, which uses the minimum rotor speed difference among generators as the control target. The simulations of a 3-generator 9-bus AC-DC hybrid system have demonstrated that the proposed method can suppress the first swing effectively and restore the rotor-angle difference among the generators quickly during disturbances, which can improve the transient stability of AC-DC hybrid system. This work is supported by Science and Technology Program of State Grid Hunan Electric Power Company (No. 5216A018000H).