Adaptive AC Voltage Control Using LCC-HVDC Based on Linearized Reactive Power-AC Voltage Characteristic

Sourcing voltage support from LCC-HVDC is a promising solution for enhancing transmission-level voltage stability. Existing methods contribute to this effort when Thevenin equivalent parameters (TEPs) are available; however, obtaining TEPs requires precise real-time measurements and AC grid modeling. In this paper, an adaptive AC voltage control (A2VC) is proposed to address the challenge of deriving TEPs. Emphasis is put on a linear grid model (LGM) that views the AC grid through a linearized reactive power-AC voltage (Q-V) port characteristic, which results in a locally defined AC grid model that is independent of TEPs. The local LGM is then integrated into the LCC-HVDC control system as an outer loop, enabling the LCC to adjust reactive power in response to AC voltage variations. Compared to existing methods, the proposed method retains simplicity, robustness and adaptability, making it applicable to various grid configurations and conditions. The EMT simulation is used to evaluate the performance of the proposed LGM and A 2VC in both small and large grids. The results reveal a highly linear Q-V characteristic, with the coefficient of determination (R2) exceeding 0.9, as well as a notably reduced AC overvoltage under both reactive disturbances and fault conditions.