Coordinated Supplementary Active and Reactive Power Control Strategy for Embedded Voltage Source Converter-Based High-Voltage Direct Current Systems

Abstract

: Voltage source converter-based high-voltage direct current (VSC-HVDC) systems utilize self-commutating power switches and pulse width modulation (PWM), which allows for decoupled regulation of active and reactive power. On this basis, it is possible to stabilize the frequency and voltage of the AC system through supplementary control of VSC-HVDC. Therefore, this paper proposes a supplementary active and reactive power control strategy for transmission systems with embedded VSC-HVDC. First, the equivalent circuit of the transmission system is established, and the mathematical model of VSC-HVDC is derived based on Kirchhoff‘s laws and the Park transformation. Second, a supplementary active power controller is designed for both line-commutated converter based HVDC (LCC-HVDC) and VSC-HVDC systems to enhance active power balancing capability and improve frequency stability. Third, an auxiliary reactive power scheme is introduced, featuring dynamic active current limiters at both converter stations. This design expands the reactive current envelope while eliminating the need for communication be-tween stations. In this way, the VSC-HVDC link can provide voltage support while still participating in active-power regulation, thereby potentially reducing the need for frequent switching of conventional reactive compensation devices. Simulation results verify that the proposed approach effectively restrains DC-voltage excursions under fault conditions, maintains AC-side voltage stability during reactive load disturbances, and improves the frequency and voltage responses under the investigated disturbances.