Comparison between space vector modulation and subharmonic methods for current harmonics of DSP-based permanent-magnet AC servo motor drive system

The PWM voltage generated by the space vector modulation method is compared with that generated by the subharmonic method for a permanent-magnet AC servo motor driven by a current-controlled PWM inverter. For the space vector modulation method, the on-times of its two zero voltage vectors are equalised. The experimental waveforms of phase currents, which were produced by the subharmonic and space vector modulation methods, are represented. In addition, the calculated waveforms of the phase currents and torque are shown for both methods. FFT results are indicated for the calculated current waveforms, which show that the current harmonics in the space vector modulation method are reduced by 45% around the carrier frequency relative to its value from the subharmonic method. Furthermore, the relation between the on-time ratio of two zero-voltage vectors and total harmonic distortion is investigated for the calculated current waveforms obtained by the space vector modulation method