Comparative Evaluation of PI, PR, and LQR Controllers for Decentralized Primary Control of Islanded AC Microgrids

Abstract

With the increasing integration of power electronics and renewable energy sources in modern power systems, an efficient control system is critical to ensure stable operation in the islanded mode of a microgrid. This paper presents a comparative evaluation of various control strategies for decentralized primary control of an islanded Alternating Current (AC) microgrid. The study investigates Proportional-Integral (PI), Proportional-Resonant (PR), and Linear Quadratic Regulator (LQR) controllers implemented in single-loop and dual-loop voltage/current control schemes. Two microgrid configurations are considered: a single three-phase inverter and a parallel dual-inverter system, both with an inductor-capacitor (LC) output filter and both subjected to time-varying load disturbances. This paper analyzes 90 control configurations for each inverter case and determines the most effective controller design in terms of various performance criteria. For Case 1 (single-inverter), the best-ranked configuration employs a PI controller in the voltage loop with high gains and a PI controller in the current loop with low gains, achieving a voltage deviation Root-Mean-Square Error (RMSE) of 2.76 V, a frequency deviation RMSE of 2.70 × 10⁻⁴ Hz, and a settling time of 40 ms. For Case 2 (dual-inverter), the optimal configuration employs a PR controller in the voltage loop and a PI controller in the current loop with low gains, achieving a voltage deviation RMSE of 2.90 V, a frequency deviation RMSE of 2.50 × 10⁻⁴ Hz, and a settling time of 24.85 ms. Overall, these findings provide practical recommendations for selecting the appropriate control combination and its gain settings, and they can serve as a foundation for future supervisory control developments.