Abstract: To take single-phase PWM rectifier as AFE of cascaded H-bridge multi-level frequency converter can satisfy requirement that electric drive system of coal mine hoist must have capacity of bidirectional energy flowing, but there are third harmonic in its AC-side current because of the second ripple of output voltage. To slove the problem, a method of steady-state error feed-forward compensation was put forward, namely frequency-doubled sinusoidal error signal of output DC voltage is compensated to set signal of DC voltage in order to reduce influence of voltage ripple on distorted current of power grid. The results of simulation and hardware experiment showed that the method is effective.