Low-order harmonics analysis and suppression method for 400Hz single-phase VSI

It is necessary to insert a dead-time in sinusoidal pulse width modulation (SPWM) voltage source inverter (VSI) to prevent a short circuit in the DC link. However, this will cause the dead-time effect, drop the fundamental voltage and introduce the 3^rd, 5^th and 7^th low-order harmonics into the output voltage. Conventional dead-time compensation methods either average voltage based or inductor current feedback compensation cannot be adopted in the case of high inductor ripple current. Moreover, even with high-precision detection of the inductor current polarity, the conventional methods are still not suitable when unipolar frequency doubling SPWM method is adopted. Dead-time effect is different when different SPWM methods are used. In this paper, dead-time effect of unipolar frequency doubling SPWM is analyzed and a new approach for eliminating low-order harmonics is proposed. Simulation and experiment on a 400-Hz prototype both show satisfactory results and verify the validity of the analysis and the effectiveness of the proposed control method.