Principal–Slave Control Strategy for SLCC DC Interconnection System Considering Principal Station Capacity Margin

In flexible DC transmission and AC-DC interconnection systems, the Self-Adaption Station and Line Commutation Converter (SLCC) integrates static var compensation with conventional thyristor conversion functionality. This enables dynamic reactive power support at the valve side while improving commutation conditions, thereby enhancing the voltage support capability and operational robustness of DC systems. Under high renewable energy penetration, power fluctuations and sudden ramping challenges principal–slave controlled SLCC DC interconnection systems with a trade-off between principal-side DC voltage regulation and capacity margin constraints: Disturbance-induced active power demands may exceed available margins, causing DC voltage deviations and increasing protection trip risks. Leveraging the active/reactive decoupling characteristics of the SLCC topology, this paper proposes a principal–slave coordinated control strategy that accounts for principal station capacity margins. Methodologically, capacity margins are explicitly embedded into the principal station control mode. By reconstructing key variables in the DC voltage outer loop and introducing a closed-loop suppression mechanism with “over-capacity power” as feedback, the principal station maintains continuous voltage regulation while avoiding entry into over-capacity operation zones. On the slave side, a power support mechanism is designed to coordinate regulation among generation, storage, and load under power balance and equipment capacity constraints. This coordination process is formulated as a multi-objective optimization problem balancing disturbance economic losses with generation/storage utilization, solved using NSGA-II. Simulation results demonstrate that this strategy suppresses the risk of principle station overcapacity, enhances power sharing coordination during disturbance conditions, and improves DC voltage dynamic performance.