True Bridgeless PFC Converter Achieves Over 98% Efficiency, 0.999 Power Factor: Part 2

Aug 1, 2010 12:00 PM
Dr. Slobodan Cuk, President, TESLAco

Note that in the conventional three-phase rectification using six current rectifiers, the resulting rectified dc voltage ripple would require a proportionally large output capacitor C. Although the direct rectification of the three-phase line would result in a relatively good power factor, the harmonic distortion present in each phase will not meet regulation requirements and would therefore require active or passive PFC control for reduction of harmonic currents.

Connection to a Future DC Transmission System

Solar generation is starting to provide increased power to complement the power generated by traditional sources, such as coal, oil, nuclear and hydropower. Solar sources generate a DC power leading to the planning of a future DC transmission lines at high DC voltages. Clearly, such DC transmission lines would be most effective as a three-wire DC transmission system with neutral or ground and positive and negative DC voltages available for long distance transmission.

The Three-phase Bridgeless PFC converter shown in Fig. 8 would be an ideal link between the three-phase AC transmission system and a future DC transmission system. Note that the Three-phase Bridgeless PFC converter can take the same advantage as the single-phase, Bridgeless PFC implementation of Fig. 7 and convert its power to a three-wire DC transmission system.

Second “Impossible” Converter Solution

The bridgeless PFC converter will find its way into other applications as design engineers seek to take advantage of the circuit’s size and performance attributes. The second in the series of “impossible” converter solutions, “Single-Stage Isolated Bridgeless PFC Converter” , will be published in the September issue of Power Electronics Technology. This isolated Bridgeless PFC converter, shown in Fig. 10, provides both PFC and isolation in a single-stage power processing consisting of an active switch S on primary side and two current rectifiers on the secondary side and one magnetic core. The design achieves an ultra-high conversion efficiency of over 97%.

Editorial Note: For questions regarding this article and for contact information to the author,readers are directed to TESLAco’s web site at www.teslaco.com.
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Footnote: Bridgeless PFC Converter™ and Single-Stage PFC Converter™ are trademarks of TESLAco.

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