This paper addresses robust frequency control in an islanded AC microgrid. In an islanded microgrid with renewable sources, load change, wind power fluctuation and sun irradiation power disturbance as well as dynamical perturbation such as damping coefficient and inertia constants, can significantly influence the system frequency, and hence the microgrid frequency control problem faces some new challenges. In response to these challenges, in the present paper, H∞ and µ-synthesis robust control techniques are used to develop the secondary frequency control loop. In the proposed control scheme, some microsources (diesel engine generator, micro turbine and fuel cell) are assumed to be responsible for balancing the load and power in the microgrid system. The synthesized H∞ and µ controllers are examined on a microgrid test platform, and the controllers’ robustness and performance are evaluated in the presence of various disturbances and parametric uncertainties. The results are compared with an optimal control design. It is shown that the µ-synthesis approach due to considering structured/parametric uncertainties provides better performance than the H∞ control method.
