Research on a Novel Reactive Power Emergency Control Strategy for HVDC Receiving System

In the renewable power system, the renewable energy fed by the high voltage direct current transmission system (HVDC) replaces the conventional unit output near the landing point of the HVDC receiving end power grid, resulting in a relatively tense state of dynamic reactive power near the landing point of the HVDC. When induction motors are the main loads of HVDC receiving power grid, after the fault occurs in AC system, the load bus voltage may continue to decline, and the problem of voltage stability, especially the transient voltage stability, is becoming increasingly prominent. In order to recover the voltage quickly, this paper proposes a method of using HVDC converter station as emergency reactive power supply to realize the emergency control of transient voltage stability in HVDC receiving power grid by temporarily reducing DC current. Aiming at the quantitative calculation of DC current, this paper establishes a nonlinear optimization model with the objective of minimizing the energy transmission reduction of HVDC transmission, and uses the global orthogonal configuration method to convert the differential equations in the objective function and constraints into algebraic equations, so as to convert the optimization model into nonlinear programming problem, and obtain the optimal DC current control scheme, namely, reactive power emergency control strategy, which greatly reduces the difficulty of solving the optimization model. Finally, a modified IEEE-14 node benchmark is used to verify the effectiveness of the method.