| Summary: | Academic studies on the Automatic Voltage Regulator (AVR) have focused on a linear mathematical model which lacks protective features. A more accurate model of the AVR system includes protective features as described in IEEE standards. The AVR models without protective features, namely limiters, result in less accurate control performance since the outputs of real controllers are always bounded. In the present study, the controller outputs are limited between −0.9pu and 1.0pu, and the upper bound of exciter output is limited by 3.1pu with the direction of IEEE standards. The effect of limiters on the controller performance is investigated. Two controllers with a novel sliding surface function are proposed based on a mathematical model of the AVR and its approximate reduced-order model. The proposed controllers having only two parameters are optimized with improved particle swarm optimization (PSO) algorithm. After optimization, the robustness of the controllers is compared with the results of various operating conditions identical to the previous studies. Although controller inputs and exciter outputs are limited, the maximum overshoot is measured as less than 0.1% at no-load conditions. Nominal time constants of the AVR constituents are perturbed from −50% to 50%, and ±10% load disturbance is applied to the output. The robustness of the controllers against parameter uncertainties is measured with an average overshoot at the output. Another superiority among the reported results in the literature is obtained from the proposed controllers, where the minimum average overshoot rates are obtained. In addition, when ±10% load is applied to the output of the AVR, the proposed controllers generate accurate control inputs to reject the load disturbance successfully. Furthermore, the proposed controllers keep the output within the ±5% band if there is a monotonic change at the output. All the results show that the proposed controllers with the improved PSO have drawn the best performance from the perspective of time-domain specifications in comparison with the recently reported controllers.
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