Due to the influence of current harmonics in the vector control system of permanent magnet synchronous motor(PMSM),the motor will produce torque ripple.In order to solve this problem,a voltage harmonic injector device using harmonic injection algorithm was designed.The current harmonics to be eliminated were extracted by using the coordinate transformation principle.Considering that the fundamental wave could affect the accuracy of harmonic extraction,a current harmonic extraction structure was designed to eliminate the fundamental wave.Using the extracted current harmonics,a voltage harmonic injector was designed for the 5th and 7th harmonics.Finally,through experimental comparison,it is proved that the proposed method can obviously suppress the torque ripple of motor.