An energy management system is necessary to store the electrical energy transformed effectively from renewable energy, such as intermittent and unstable wind energy. The structure design and simulation analysis of the voltage controller, as an energy management system, is described in this paper in which a reserve capacitor is used as a transient energy storage equipment to coordinate energy the wind turbine generates with the load battery's demands. The constant current and constant voltage charging method is proposed for improving energy storage efficiency. The bidirectional flow of energy is realized by a bidirectional power converter and a simple structure of Buck/ Boost topology is adopted in this research. The feasibility and availability of the designed voltage controller is shown from simulation results by the Simulink module in the Matlab software.