A NOVEL SINGLE STAGE AC–DC SELF-OSCILLATING SERIES-PARALLEL RESONANT CONVERTER

This project presents an improved self-sustained oscillating controller suitable for the single stage single phase power factor correction circuits. It has a modified active controller, which improves the performance from no-load up to full-load. The steady state characteristics are developed and a design example is given in detail. The proposed controller allows zero voltage switching at any loading condition with a reasonable power factor that satisfies the IEC 61000-3-2 standards together with a promising efficiency. Analytical, simulation, and experimental results verify the achievement the design specifications.

INTRODUCTION

CONVENTIONAL off-line power supplies usually include the full-bridge rectifier and large input filter capacitor at their input stages. They generate highly distorted input current waveforms with a large amount of harmonics. Recently, standards such as IEEE 519 and IEC 61000-3-2 impose a limit on the harmonic current drawn by pieces of equipments connected to an ac line in order to prevent the distortion of an ac line voltage. Therefore, the aimed ac–dc converter is the one that draws a pure sinusoidal current at unity power factor from the mains, also enjoys a precisely regulated output voltage without any ripple. The common operation for switching mode power supplies (SMPS) is to use two separate converter stages, an ac–dc conversion stage and another isolated dc–dc conversion stage, to convert the input ac mains voltage into an isolated and regulated dc voltage. A boost converter is typically used as the ac–dc conversion stage because it can perform power factor correction (PFC) by shaping the input current so that it is sinusoidal and in phase with the input voltage. The dc–dc conversion stage is usually a full-bridge converter for high power applications. 

In order to reduce the cost and complexity associated with operating two separate converter stages, converters that integrate the functions of PFC and isolated dc–dc conversion in a single stage PFC converter are preferable. Most conventional power factor correcting systems introduced so far employ pulse width modulation (PWM) techniques to achieve the features of the PFC converter. 

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