An Optimal Robust Frequency Controller Design for a Two-Microgrid Cluster

This paper presents a new robust design approach to control the frequency of a two-microgrid cluster together with the power of the coupling line. To this end, a two-microgrid cluster including both dispatchable and non-dispatchable source is considered as a study case. The non-dispatchable sources cause power imbalance due to stochastic behavior. The stochastic behavior of these sources leads to the frequency deviation. Furthermore, it affects the power of the coupling line connecting two microgrids. Thereby, a two-level design process is addressed. It includes inner and outer optimization. The outer level determines the weighting functions for the inner level. The inner level designs the robust regulator by solving an optimization problem constrained by a linear matrix inequality in three stages. The first stage, the state feedback is determined in order to provide robust behavior. The second stage, an observer is obtained to estimate the states used for the state feedback. The last stage, the controller is formed using state feedback as well as the state observer. Then, a series of simulations are carried out using the designed controller. The results show that the robust controller can improve the operation of microgrids in comparison with the conventional proportional-integral controller.