Distributed Controllers for Multiterminal HVDC Transmission Systems

High-voltage direct current (hVDC) is an increasingly commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper, the voltage-droop method is reviewed, and three novel distributed controllers for multiterminal hVDC (MTDC) transmission systems are proposed. Sufficient conditions for when the proposed controllers render the equilibrium of the closed-loop system asymptotically stable are provided. These conditions give insight into a suitable controller architecture, for example, that the communication graph should be identical to the graph of the MTDC system, including edge weights. Since the equilibria of the closed-loop systems are asymptotically stable, it is shown that the voltages asymptotically converge to within predefined bounds. Furthermore, a quadratic cost of the injected current is asymptotically minimized. The proposed controllers are evaluated on a four-bus MTDC system.