An analog controller is disclosed. The controller has a maximum power point tracking unit and a power factor adjusting unit. The maximum power point tracking unit generates a maximum power tracking voltage which is used to control the magnitude of the output current of the inverter so as to extract the most available power from the power generating device. The power factor adjusting unit, which generates a ramp control voltage that will further determine the duty ratio and switching frequency of PWM signal, gracefully tunes the magnitude and reduces the total harmonic distortion of the current injected from inverter into utility grid.