Some new approaches to improve the power factor and reduce harmonics in three phase rectifier type utility interfaces

In the recent years there has been a significant increase in the use of power converter equipment for variable speed ac/dc motor drives, emergency and standby power supplies for critical loads, magnet power supplies etc. A significant portion of the above loads is fed from a three phase three wire power distribution system. Current static converter hardware employs an uncontrolled ac to dc diode rectifier interface which exhibits over 25% to 80% total harmonic distortion (THD) in the input current with significant magnitude of 5th, 7th, 11th and 13th harmonic currents and therefore contributes to poor power quality. The harmonic currents in the utility lines contribute to increased distortion, malfunction of sensitive electronic equipment and increased loss. Recent standards' IEEE 519 and IEC 555 recommend several limits on harmonic currents and power factor of static converter equipment. However, current power electronic converters cannot meet these standards.; In response to these concerns this research proposes some new approaches to improve the power factor and reduce harmonics in a three phase ac-dc converter type utility interface. The first approach in this research reduces harmonic distortion and improves the power factor associated with a diode rectifier type utility interface by a new passive scheme. The second approach proposed in this research is active schemes to achieve improved performance under varying load conditions. The active power factor correction and harmonic elimination can be accomplished with either of the two different proposed topologies; the back to back SCR's controller or a PWM current controlled converter. The third approach examined in this research is a new active current shaping rectifier topology. A suitable control signal is applied to these boost switches to achieve the power factor correction and the elimination of input harmonic currents. Furthermore, a zero voltage switching (ZVS) strategy for the proposed active power factor correction is described in order to drastically reduce switching losses of the three switches.; Analysis, simulation and design equations are presented for each of the proposed scheme. Finally, experimental results on laboratory prototypes verify the concept. Application aspects for these schemes are also examined.