Single-switch three-phase power factor preregulator under variable switching frequency and discontinuous input current

A three-phase power factor preregulator with input inductor, diode bridge, and a single switch is analyzed. Operation with discontinuous input current and variable switching frequency is considered. Equations for average input current are presented, showing that quasi-sinusoidal waveforms are obtained. Also, the switching frequency equation shows an almost constant frequency operation. A design procedure is presented, where simulation and practical results show the good performance of the approach. Comparison with constant frequency operation also shows that a better harmonic distortion is obtained if the voltage in the switch (with switch off) is not far from the input voltage. Also, in this case, the high-order harmonic content is easily filtered