Controller Design for MTDC to Enhance Power Sharing and Stability

Voltage droop control is considered as a reliable control approach for multi-terminal DC (MTDC) grid system. A low value of droop constant may result in a high dynamic variation associated with oscillations for power and DC voltage deviation. Thus, the stability of the MTDC grid is at risk. This study presents a linear quadratic regulator (LQR) control design with an adaptive droop to achieve appropriate power sharing among the converter terminals. A control strategy with the combination of adaptive droop and LQR is designed in this study. The weights of LQR are tuned using the Gramian analysis. The closed-loop stability analysis is carried out using Lyapunov's stability approach. The proposed control scheme improves the closed-loop system dynamics by reducing the overshoots/undershoots and time to reach steady-state condition. In addition, power sharing according to converter rating is appropriately achieved. The performance of the proposed control scheme is validated on five terminal MTDC grid system simulated in MATLAB®.