The photovoltaic MPPT system structure and working principle are analyzed. Variable step voltage perturbation method is used as the power/voltage optimization controller. In order to achieve fast and stable PV MPPT response, this paper focuses on the optimized design of the voltage-loop of PV output voltage controller. The voltage feed-forward compensation plus PI regulator method is used to design a composite voltage controller of PV MPPT. Voltage closed-loop transfer function is obtained through the establishment of the PV output voltage controller mathematical model. To get fast and stable MPPT control, the best PI controller parameters are calculated. The simulation results and experimental results indicate that this compound controller of voltage can quickly achieve a stable photovoltaic MPPT response.