Frequency Stability Analysis of Time-delay Power Systems Considering Sampling and Holding Characteristics of AGC

Automatic Generation Control (AGC) with long control period and inevitable time delays is a sampled-data control system. This paper proposes an eigenvalue-based frequency stability analysis for time-delay power systems adapting to the sampled-data AGC based on a single-area load frequency control (LFC) system. Firstly, the hybrid continuous and sampled-data LFC model is established by modeling the sampled-data AGC as a proportional-integral (PI) controller with zero-order holder. Then, the Chebyshev discretization is applied to deal with retarded variables in the system model, and the equivalent discrete system is obtained based on a function space approach. In this way, the eigenvalue-based stability criterion is developed. Besides, for illustrating the necessity of the sampled-data characteristic of the AGC, another two kinds of continuous-time LFC models are also established for verifying their conservativeness with the delay margin comparison. Finally, time-domain simulations and frequency-domain analyses on the delay margins are carried out, showing the accuracy of the proposed eigenvalue-based stability analysis. © 2023 Power System Technology Press. All rights reserved.