A novel method for harmonics and low switching-frequency eliminations for a three-phase PWM inverter

Harmonics and switching frequency cause a major problem in power system. A novel harmonic elimination technique and low switching frequency in a three-phase pulse width modulation (PWM) inverter are proposed in this paper. This inverter is associated with a LC filter. The technique determines the commutation angles based by solving a set of nonlinear system equations. This commutation angles are determined off-line (Pre-Calculed) and stored in the microcontroller memory in order to speed up the online control of the processes. The pre-calculated switching is modelled to cancel the greater part of low-order harmonics and to keep a single-pole dc voltage across the polarized capacitors. LC filter is designed to cancel the high-order harmonics. This approach allows substantial reduction of the harmonic ratio in the AC main output voltage without increasing the switching-frequency per period. Consequently, the duties of the semiconductor power switches are alleviated. To show the validity of the new harmonic elimination and low switching-frequency, DSP based experimental results are presented. These results are very satisfactory and prove the effectiveness of the new approach.