Unipolar Isolated Power Factor Correction (PFC) Converter

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Unipolar Isolated Power Factor Correction (PFC) Converter [Copy link]

Unipolar Isolated Power Factor Correction (PFC) Converter

One of the main development trends of modern switching power supplies is to improve the power factor of the input end of the AC/DC converter and reduce the harmonic pollution to the power grid. The input end of the traditional AC/DC switching converter is a diode rectifier-capacitor filter combination circuit. The input current waveform is pulse-shaped, the power factor on the AC grid side is only 0.6~0.7, and the total harmonic distortion THD (Total Harmonic Distortion) of the current reaches 100%. (When the power factor is 0.999, the THD is about 3%) [1]. Therefore, grid-side power factor correction has become one of the current research hotspots.

The most researched and applied isolated high power factor converter currently uses two-stage DC/DC switching converters in series, which increases the cost by 15% to 20%. The biggest disadvantage of this circuit is that it requires multiple components, high cost, and low efficiency, which is very uneconomical when used in small and medium power applications. For low-power AC/DC converters, single-stage high power factor circuits are being studied and developed at home and abroad, with a power factor of 0.9 and a cost increase of only 5%. Therefore, research on single-stage power factor correction and conversion technology has become a very urgent requirement.

In order to reduce the size and cost of PFC converters, researchers have tried to integrate PFC and isolated DC/DC conversion into a single power stage to achieve the functions of input power factor 1 and constant output voltage. R. Erickson[2] proposed a simple power factor rectifier based on a flyback converter as early as 1990. In the following years, MHKherulawa[3] and others proposed several single-stage PFC technologies, but all of these schemes have the disadvantages of slow output voltage regulation, complex control and low efficiency. In 1994, Richard Redl[4] and others proposed a series of new single-stage isolated power factor correction converters that overcome the above disadvantages and have the advantages of fast output voltage regulation, only one or two switches controlled together, a PWM control circuit and automatic line current adjustment. Richard Redl's technology was patented. Later, many researchers developed various more complete single-stage isolated PFC converters based on this. Compared with the converters previously studied, they have made great improvements in reducing the voltage of the energy storage capacitor, reducing harmonic distortion and fast output response.