Three Phase VVVF Power Invertor Using Resonant Pulse Density Modulation

Abstract

The resonant DC link invertors have been developed these years for avoiding the switching loss of the conventional multi-pulse PWM invertors. This paper proposes a three phase VVVF power invertor using resonant pulse density modulation for induction motor speed-control. The invertor is composed of a cascade connection of a resonant DC-DC convertor and a multi-pulse PWM invertor. The output waveform depends on the gate pulse patterns of the invertor valves. This paper proposes three kinds of pulse patterns for obtaining the outputs of trapezoidal waveform and of sinusoidal waveform, and describes also the experimental results. The V/f characteristics for induction motor speed-control and the regenerative braking operation will be examined and the circuit behaviors will be discussed.