Adaptive Droop Control of Multi-Terminal HVDC Network for Frequency Regulation and Power Sharing

This paper proposes a novel adaptive droop control strategy for multi-terminal HVDC (MTHVDC) network to provide frequency support and power sharing via a distributed consensus algorithm. The droop coefficient is adaptively tuned by an effective integration of optimization algorithms and frequency consensus method. The optimization control aims to minimize generation cost, frequency deviation cost, and converter losses. Furthermore, the coordination between the consensus-based droop controller and the optimization technique is established by a feedback loop of coupling gain solution method, which is based on coupling gain matrix. The proposed control is successfully applied to a four-terminal MTHVDC system and modified New England 39-bus system on PSCAD. Power sharing is further improved by adding an adjustment factor based on frequency deviation with coupling gain matrix, which redirects power flow in ac and dc sub-grids. In addition, the loss reduction of voltage source converters is presented to demonstrate the proposed control performance.