In AC microgrids, two factors can degrade the system performance: low inertia and damping of the system due to the presence of static resources, weather changes because of renewable based generations. This paper systematically reduces the adverse effects of these factors by designing a robust proportional-integral-derivative (PID) controller using the quantitative feedback theory (QFT). The proposed controller guarantees robust stability of the closed-loop system and its ability to attain the desired level of external disturbance attenuation. Therefore, this controller can reduce frequency oscillations induced by load and renewable source variations. In comparison with other robust controllers, the proposed PID controller has a significantly simpler structure that leads to an easy implementation and maintenance. Frequency response analysis and time domain simulation studies show that the proposed controller can be successfully applied to AC microgrids.
