Load frequency control for wide area monitoring and control system(WAMC) in power system with open communication links

As is known, there exist usually unreliable factors in open communication links, such as time delays and communication failures. When open communication infrastructures are embedded into modern power system to support vast amounts of data exchange, it becomes more challenging to keep the complex power system reliable and stable. In this paper, the modeling and robust controller design problems of load frequency control (LFC) are investigated for power system with communication delays. In specific, we consider a general case that there exist time varying delays in two channels. One is the feed-forward channel in which control centers send control signals to remote terminal units (RTUs). The other one is the feedback channel where measurement signals are transmitted from RTUs to the control centers. The state space models of LFC including two channel time varying delays are presented. Based on Lyapunov-krasovskii stability theory, a delay dependant controller is designed to compensate performance degradation brought by time varying delays. Two-area LFC model is used to conduct case studies. The dynamic performances are compared between conventional PI controller and the proposed delay dependant for LFC with and without time varying delays. It is shown that the proposed controller can keep the power system robustly stable even when there are time varying delays in both channels mentioned in this paper.