This paper proposes and provides the design steps of three robust output feedback controllers to control the frequency of Wind-Diesel-Hydro hybrid system. The first presents a centralized robust based H¥ (CRH¥) controller. The role of H¥ is to minimize the disturbance effect on the system output. The effect of the LMI tuning variables of RH¥ controller on the system dynamic performance is presented and discussed. The controllers are solved using the Linear Matrix Inequalities (LMI) technique and characterized by a similar size as the plant that may be of higher order and thus creates difficulty in implementation in large systems. The second presents decentralized robust based H∞ for each unit (DRH¥). The third is robust PID controllers which are ideally practical for industry and more appealing from an implementation point of view since its size is lower. The optimum parameters of the robust PID controllers are found through the optimization by a novel combination of RH¥ control theories through the Genetic Algorithm (GA) technique. More specifically, the third robust PID controllers are proposed to achieve the same robust performance as decentralized
(DRH¥) controllers, respectively. All controllers are used as load frequency controllers to control the Wind-Diesel-Hydro hybrid system . Comparisons of the performance of the three robust output feedback controllers under diverse tests in different disturbances and variation in the plant parameters are carried out.