The objective of this research work has been to design a robust digital controller in order to control the voltage of an isolated hybrid energy system. The only load of the microgrid is resistive and variable, and it is fed through an inverter and its associated LCL filter. Once the issues rose, the modeling of the plant is explained. Then, its oscillatory behavior and the dependence of this behavior with respect to the resistive load are analyzed. Afterwards, the structure and the design of the global controller which contains two loops in cascade are described. The first loop concerns the current regulation, while the second is linked to the voltage. The controllers related to these loops are designed emphasizing in their robustness and their ability to damp the closed-loop behavior. To finish, some simulations are carried out to study the dynamical behavior of the loops in regulation and tracking at different operating points. The results demonstrate the quality of the control in terms of robustness, damping and speed of the response. Keywords: Hybrid Energy System, Robust Control, Pole Assignment, Digital Control, Non-Stationary System, Inverters