A mixed signal controller for a power quality compensator includes an analog circuit, an analog-to-digital converter (ADC), and a digital circuit. The analog circuit amplifies an input signal from the power quality compensator by a gain factor and outputs an analog signal, which is converted to a digital signal by the ADC. The digital circuit receives the digital signal, calculates the reference compensating current of each phase and then generates a trigger signal via hysteresis PWM to the power quality compensator. The digital circuit includes an evaluation circuit that calculates a value of the system total harmonic distortion after the power quality compensator compensates power and adjusts the gain factor when the value of the system total harmonic distortion reaches a predetermined threshold.