Damping Oscillation and Removing Resonance in a RE Based DC Microgrids

Disturbances, including uncertinities are a common phenomenon in power grids, and they can occur in source or load side at different time or simultaneously in both sides. Among the most frequent disturbances, source and load uncertainties are considered as the most catastrophic features. These disturbances can deteriorate the performances of the associate controller and contribute to oscillation and resonance. Conventional Proportional Integral (PI) controllers fail to provide supply quality assurance and system security against moderate to strong disturbances. If a disturbance occurs, it usually deteriorates both controller performance and supply voltage quality at DC bus in microgrids. This issue, however, has not been fully understood and addressed in the existing literature. Hence, this paper presents the effect of the conventional PI controller in a DC microgrid under disturbances. Consequently, a few case studies has been conducted with traditional single-variable controllers in a real time simulation environment and found that disturbances can causes overshoot or undershoot, along with power oscillation at DC bus. Thus, to overcome this oscillation and to enhance the stability and resilience of the DC microgrid, a Linear Quadratic Regulator (LQR) controller is proposed. Results demonstrate that the LQR controller can handle small to moderate disturbances and stabilise the voltages at the DC bus when compared to a conventional PI controllers. It can also minimize overshoot and undershoot along with damping power oscillation at common DC bus and removing the possibilities of resonance.