Control Coordination Within a VSC HVDC Link for Power Oscillation Damping: A Robust Decentralized Approach Using Homotopy

Power oscillations can be damped effectively through modulation of both active and reactive power of a voltage source converter based high voltage direct current link. The challenge, however, is how to coordinate the control action properly at the two ends of the link without using a centralized control scheme, which requires fast communication of control signals to remote actuator (converters) sites. A full centralized controller may result in a closed-loop performance worse than that of an open loop in case of a communication loss of feedback signal(s). Alternatively, with a block-diagonal control structure, the individual control loops are decoupled from each other, which is not only easier to implement in a decentralized way, but also shown to guarantee a certain level of performance. Here, the concept of homotopy is applied to obtain a single block-diagonal controller from a set of full controllers, individually designed to ensure specified closed-loop performance for a set of operating conditions. Simulation studies in DIgSILENT PowerFactory are carried out on two test systems to demonstrate both the robustness and control coordination in a decentralized framework.