In this paper, we discuss the load-frequency control problem of microgrids. Control is applied to maintain a balance between electric-power demand and supply by controlling the outputs of generators in power systems. However, because of the large-scale introduction of energy from renewable-energy sources, it has become more difficult to maintain this balance. To solve this problem, we consider two approaches in this study. First, we use dispersion-type power sources such as batteries, and secondly, we apply new control theories. Therefore, we focus on a microgrid that comprises a wind-turbine generator, a diesel generator, and a battery, and we propose a technique based on static H_∞ control. First, we design a generalized plant considering the differences in the response speeds of diesel generators and batteries. Then, we apply static H_∞ control to the generalized plant. Moreover, we combine a linear matrix inequality (LMI) condition with static H_∞ control to avoid control gains that will result in control inputs that are too large. We perform numerical simulations to verify that the controller can suppress the frequency deviations and deviations in the residual capacity of the battery. Furthermore, we show that the approach can be employed to design controllers with lower dimensions, and to avoid undesirable control gains. Finally, we perform experiments using a generator and a variable resistance to confirm the effectiveness of the controller.