Dynamic reactive power reserve assessment method for hybrid AC/DC networks based on a reduced equivalent model of an LCC-HVDC converter process

Abstract

LCC-HVDC technology has been widely applied. Commutation failure is a common disturbance in converter stations. In the absence of an adequate and rapid dynamic reactive power supply, the system is prone to trigger DC blocking. Therefore, it is of paramount importance to assess the dynamic reactive power reserve in the nearby area of converter stations with both speed and accuracy. However, traditional methods mainly apply electromechanical transient differential equations or quasi-steady-state equations to describe the dynamic process of the converter, which cannot accurately capture the fast dynamics of reactive power/voltage levels on a timescale of hundreds of milliseconds during commutation failure. To address this issue, this paper proposes a reduced equivalent model of the dynamic process of an inverter converter, which approximates the accurate reactive power voltage dynamic process of the converter's electromagnetic transient time scale into the core reactive power dynamic process of the electromechanical transient time scale. Based on this reduced equivalent model, a dynamic reactive power reserve assessment method suitable for the nearby area of inverter converter stations is proposed, which considers both calculation speed and accuracy. Finally, the proposed method is validated using an improved IEEE 39 test system, demonstrating its effectiveness in practical applications.