07-05-2013, 04:44 PM
AC-DC Converter with Quasi-Active Power Factor Correction
AC-DC Converter.pdf (Size: 247.81 KB / Downloads: 24)
Abstract
The proposed ac-dc converter with power factor
correction circuit combines power conversion characteristics of
conventional fly back and boost converters. In The proposed circuit
the auxiliary output of the main converter is connected between the
rectified ac mains and the low-frequency filter capacitor. High
frequency pulsating source is produced due to auxiliary winding. This
is used for shaping the input current by lengthening the input current
conduction angle. The power factor correction circuit is controlled by
using PI controller. The single stage circuit has low total harmonic
distortion (THD) of input current. It does not increase the
voltage/current stress on the active switch used in the switching
Converter due to PFC. Operating principle and simulation results of
the proposed method are presented by using PSIM software.
INTRODUCTION
ONVENTIONAL ac/dc converters using diode bridge
rectifier with a large output capacitor draw a heavily
distorted input current. This distorted current degrades the
input power factor and pollutes the utility lines. To comply
with the harmonic standards, active input current shaping (or
the so-called power factor correction (PFC)) techniques of offline
power supplies are proposed. The most popular
implementation of active PFC is the two-stage approach, as
shown in Fig. 1. In this approach, a boost converter shapes the
input current and supplies a loosely voltage control for the
intermediate dc bus capacitor, with substantial second
harmonic order ripple voltage. Therefore, the cascaded dc/dc
stage which can be designed with high bandwidth feedback
loop is needed to tightly regulate the output voltage. Due to
two-stage power processing, conversion efficiency is reduced.
In addition, the converter cost and complexity increases with
the increased component count. The single stage solutions
present very simple power stage arrangement and control
circuitry since only one switch and one controller is needed. In
addition, although the single-stage scheme is especially
attractive in low cost for power applications due to its
simplified power stage and control circuit.
SIMULATION AND RESULTS
In simulation the circuit is formed by connecting the energy
buffer (LB ) and an auxiliary winding (L3 ) coupled to the
transformer of the dc/dc cell. Transformer having two
auxiliary windings. One is used for output and second is used
for feedback. The output is regulated by controlling the switch
Fig.11.Shows experimental waveforms of input line voltage
and fig. 12. Shows the input line current at nominal line
voltage. A near unity power factor (0.993) is measured and a
sinusoidal waveform is drawn from input line. Fig.14 shows
the regulated output voltage.
CONCLUSION
The proposed converter has harmonic current reduction and
output voltage regulation. The proposed converter is
implemented with a single-switch–single-stage topology and
single control loop.Due to the adding of feedback auxiliary
winding to the transformer of a dc/dc fly back converter, the
proposed circuit achieves the lower THD and high input
power factor. Proposed circuit was compared with the two
stage conversion.