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Predicting communication delays in open networks for frequency control of smart grids

The use of open communication networks in wide-area power systems (WAPS) introduces random delays into the transmissions of frequency measurements and control signals, which deteriorate the load frequency control (LFC) performance. Current works focus on providing sufficient delay margin or proposing robust controller to maintain the WAPS stability. In this paper, a Smith predictor is designed to further compensate the LFC performance reduction caused by unreliable communication. Time delays are predicted via the discrete hidden Markov model (DHMM) and via the exponentially weighted moving average (EWMA) model, and are the input to the Smith predictor. The case study is carried out on a single-area WAPS with the Ethernet-based network, implemented via the Truetime simulator. The results show that the use of Smith predictor is more effective in eliminating load disturbances and enhances robustness against delays as compared to delay-margin-based and robust controllers. Furthermore, the Smith predictor using the DHMM can achieve better LFC performance than the one using the EWMA.