Stochastic Secondary Frequency Control of Islanded Microgrid Under Uncertainties

As the penetration of renewable energy, generally, uncertainties, increase in microgrids, a more dynamic and complex system is emerging that makes the load frequency control (LFC) of islanded microgrids more challenging due to their stochastic dynamic nature. This stochastic nature can create oscillatory frequency response, which eventually leads to deteriorating control function and instability even under primary and traditional secondary controllers. Due to the uncertainties, the measurements and microgrid states are continually perturbed; hence, they cannot be directly utilized for feedback control. Therefore, it is required to utilize an observer-based stochastic feedback control that correctly recognizes these uncertainties and sieves incorrect states, frequency deviation here, and can properly maintain the balance between the energy sources and the demand. This article develops an optimal observer-based secondary control for LFC, framed in two layers that are the stochastic unknown input observer (SUIO) and linear quadratic regulator. The proposed SUIO not only can address the uncertainties, e.g., renewable energy, load, and measurement noise, with efficient control effort but also performs robust against parameter changes of the microgrid. The simulation results confirm the efficacy of this proposed control as compared to the traditional secondary control method.