A three level quasi-two-stage single-phase pfc converter with flexible output voltage and improved conversion efficiency

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A Three-Level Quasi-Two-Stage Single-
Phase PFC Converter with Flexible Output
Voltage and Improved Conversion Efficiency
Abstract
Introduction:
In order to provide flexible dc output voltages, PFC
converters with buck–boost capabilities have been studied in the
literatures and they are usually based on buck-boost, flyback,
Cuk, and single-ended primary inductance converter (SEPIC)
topologies, and can be derived in both nonisolated and isolated
versions. A common problem for these topologies is that there is
no direct energy transfer path during power conversion and all
input power must be processed by active switches and stored by
intermediate passive components (either inductors or capacitors)
before being supplied to the end loads. This indicates that the
components will be working under increased voltage/current
stresses, which may consequently lead to decreased power
density and conversion efficiency. In order to improve the
performance of Cuk and SEPIC-based PFC topologies, their
bridgeless variants have recently been proposed with most of
them being operated in discontinuous conduction mode (DCM).

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In this case, the PFC converter can be constructed with less
semiconductor switches and the on-state conduction losses can
be reduced. The switching losses are reduced as well due to their
DCM operation. However, the main power switches in these
bridgeless topologies are still under high-voltage stress and the
DCM operation also implies that they are only suitable for
relatively low-power applications because of the high peak
current in the boost inductor.
Existing system:
In this approach, there are two independent power stages.
The front-end PFC stage is usually a boost or buck/boost (or
flyback) converter. The boost converter front-end consists of a
boost inductor, boost switch, and rectifier. The PFC controller
senses the line voltage waveform and forces the input current to
track the line voltage to achieve the unit input power factor.
Since the voltage of energy-storage bulk capacitor CB, VB, is
loosely regulated, VB is a dc voltage which contains a small
second order harmonic. This bus voltage is typically regulated at
around 380 Vdc in the entire line input voltage range from 90
Vac to 265 Vac. The high bus voltage VB minimizes the bulk
capacitor value for a given hold-up time. In addition, the
narrow-range-varying VB improves the efficiency of an
optimized dc/dc output stage. The dc/dc output stage is the

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isolated output stage that is implemented with at least one
switch, which is controlled by an independent PWM controller
to tightly regulate the output voltage.
Proposed system:
To provide a simple but effective solution, this paper
presents a high-efficiency single-phase PFC converter that
features sinusoidal input current, three-level output
characteristic, and flexible output dc voltage. Its attractiveness is
that, in case of buck operation mode, the embedded bidirectional
dc/dc converter may only need to process partial input power
rather than full scale of the input power. Also, the PFC stage
exhibits three-level output voltage, and the dV/dt across the
switches are reduced, so as the switching losses. An added
benefit of this converter is that the fluctuating 100/120 Hz
harmonic power in the single-phase system can be almost
diverted into the dc-link capacitor through proper control design,
and the load voltage will be fairly constant and of very fast
dynamic response.

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Block diagram:
Single
phase AC
supply
Diode
bridge
rectifier
LoadFilter
3 level PFC
converter
BUFFER circuit
5VDC
PIC controller
circuit
Gate driver
circuit
12 V DC

LeMeniz Infotech
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Advantages:
 High efficiency.
Applications:
 Plug-in charging from power grid
 Vehicle-to-grid discharge.
 Pumping power to drive electric motor.
 Regenerative braking.
Tools and software used:
 MPLAB – microcontroller programming.
 ORCAD – circuit layout.
 MATLAB/Simulink – Simulation.

A three level quasi-two-stage single-phase pfc converter with flexible output voltage and improved conversion efficiency

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