In this paper, a new bi-objective control technique is proposed for the load frequency control in microgrids. The first objective is to set the system frequency to its desired value despite uncertainties in the system inertia and damping caused mainly by the penetration of renewable energy sources. The employed strategy to address this objective is based on the virtual inertia concept. The second objective is to design an automatic mechanism for charging/discharging of the battery storage units. By achieving this objective, it is possible to attain a compromise between the main mechanical units and the backup units to participate in supplying the load. The strategy to address this objective is to estimate the load change and then design a controller to track this signal by the mechanical units. A multivariable observer-based proportional-integral (PI) controller is designed to simultaneously achieve both objectives. Applying the proposed method not only compensates for the adverse effects of the uncertainties and disturbances, but it also decreases the needed capacity of energy storage resources. Simulation results show that the proposed method can improve the microgrid load frequency characteristic while robust stability and performance are guaranteed with the limited energy storage capacity.
