As the output stage of power system real-time simulation and relay protection testing, the current type power amplifier needs high precision and quick response. There are two kinds of manners to implement the current type power amplifier: linear power amplifier and PWM power amplifier. The PWM power amplifier gains widespread concern due to its high output efficiency. But compared to the linear power amplifier, it needs to resolve the complicated problem of filtering output and closed-loop control. The paper designs three closed-loop control methods applicable to the current type power amplifier, makes detailed numerical analysis and research, contrasts the different emphasis of the three control methods in low frequency accuracy, response speed and amplitude accuracy, and offers suggestion to the choice of three control methods.