Photovoltaic energy storage system meets the ever-growing demand for electricity, while ensuring the stability of power supply. Research of renewable energy-based microgrid system has become a hot topic, especially the study of Maximum Power Point Tracking (MPPT) and energy storage unit control strategies. This paper proposes an MPPT technique that combines gradient step size with conductance increment method, in order to achieve fast maximum power tracking and to avoid shock and error at the Maximum Power Point (MPP). On the basis of small signal model, bidirectional Buck/Boost converter and full bridge converter are designed to form the inner current loop and the outer voltage loop of battery charging/discharging controller under different control strategies, so as to realize the bidirectional flow of energy. A simulation model of energy storage unit is built in MATLAB/Simulink environment, and the simulation results verify the effectiveness of the control strategy.