PWM-RECTIFIER VOLTAGE-SOURCE INVERTER WITHOUT DC LINK COMPONENTS FOR INDUCTION-MOTOR DRIVE

Voltage-source inverters are normally equipped with an electrolyte cap acitor in their DC link. A voltage-source inverter without DC link com ponents is proposed to eliminate the electrolytic capacitor which has a short life compared with an AC capacitor (metalised polyester film, etc.). This inverter system requires an AC filter composed of L and C in the AC source side. In this case, the most important problem is the reduction of AC filter capacity. To achieve this reduction, the recti fier section is operated by PWM control. The waveform of the AC source current is also improved. Steady-state analysis, the calculated chara cteristics of the AC filter capacity and the waveforms of voltage and current are described for a 0.75 kW induction motor driven by the syst em. The AC filter capacity is reduced to about 38% of the rectifier wi thout PWM. Measured waveforms are presented for a motor slip of 4%. Th e stability with, and without, DC link components, is also discussed.