Abstract: For problem that asynchronous motor has inadequate starting torque with heavy load during low-frequency starting under control strategy of constant proportion of voltage to frequency, the paper proposed to use voltage compensation measure to improve carrying capacity of motor in cycloconverter-fed frequency-conversion speed-regulation system. It introduced voltage compensation principle and calculation of compensation values, and compared spectrum, speed and torque with and without voltage compensation, and different voltage compensation effects of the motor with different loads. The simulation results show that the voltage compensation has good compensation effect in the frequency-conversion speed-regulation system: ① The stator output voltage has high harmonic content, the waveform has good symmetry, and motor has strong load capacity under voltage compensation. ② The greater the motor load is, the slower its rotational speed becomes, but the starting torque remains unchanged, and the speed decline maintains substantially constant.