Abstract: For problems of high switching loss and power quality distortion when carrier modulation PWM control method were used in mine—used high—voltage frequency converter. Sinusoidal modulation wave was optimized based on carrier—in—phase disposition PWM control method. The sinusoidal modulation wave is superimposing with the third harmonic and direct current component, so as to obtain an optimized modulation wave with saddle—shaped modulation wave in positive half—cycle and trapezoidal modulation wave in negative half—cycle. The simulation results show that DC voltage utilization of frequency converter is improved, switching loss and total harmonic distortion of output line voltage is reduced by use of the optimized modulation wave.