Design and simplified stability analysis of wide-area damping control with variable feedback delay

Poorly damped low-frequency inter-area oscillations are a major concern in large power systems. Wide-area damping controllers which modulate power flow using power electronic systems like HVDC links and FACTS can be used to improve the damping of the critical modes in a targeted manner. These controllers use wide-area measurements, which are communicated from several remote locations. The communication time delay is generally variable in nature, and the data from different locations arrive at the controller with different delays. The overall delay in synthesizing the controller input signal affects the closed-loop damping performance. This paper proposes a delay-handling strategy and derives a discrete-time model which is used to characterize its performance. The relative insensitivity of the mode shape of swing modes to the damping controller is used to facilitate a simplified analysis. A strategy for the adaptation of controller gain when the delays are excessive and persistent is also presented. A case study is presented to illustrate the delay-handling and gain adaptation strategies.