A Method for Modifying LCC-HVDC Control Considering Dynamic Reactive Power Balance During AC Fault and System Recovery Period

Current approaches for improving LCC-HVDC recovery ability after AC faults operate in isolation, neglecting the combined impacts of reactive power and phase shift on commutation margin. This paper proposes an integrated control combining reactive power control with firing angle correction to enhance LCC-HVDC system self-restoration. Firstly, this paper illustrates the influence of phase offset on commutation margin and analyzes the feasible region of DC transmission power and inverter-absorbed reactive power under the extinction angle control. Then, a method is proposed for modifying LCC-HVDC control considering dynamic reactive power balance and phase offset during AC fault and system recovery period. Specifically, upon AC fault detection, the system dynamically adjusts DC current and extinction angle references through reactive power control, while implementing different phase-offset compensation in different periods for firing angle correction. Additionally, the critical firing angle, satisfying commutation margin requirements at the intersection of reactive power control and extinction angle control, is established as the operational upper limit. Finally, the modified method is tested in the CIGRE HVDC, Guiguang II, Three Gorges-Shanghai and multi-feed DC Project models. Simulation results confirm significant improvements in commutation stability and DC current continuity during AC fault and system recovery.