01-08-2012, 04:08 PM
A Review of Single-Phase Improved Power Quality AC–DC Converters
500A Review of Single-Phase.pdf (Size: 569.96 KB / Downloads: 67)
Abstract
Solid-state switch-mode rectification converters have
reached a matured level for improving power quality in terms of
power-factor correction (PFC), reduced total harmonic distortion
at input ac mains and precisely regulated dc output in buck, boost,
buck–boost and multilevel modes with unidirectional and bidirectional
power flow. This paper deals with a comprehensive review
of improved power quality converters (IPQCs) configurations, control
approaches, design features, selection of components, other related
considerations, and their suitability and selection for specific
applications. It is targeted to provide a wide spectrum on the status
of IPQC technology to researchers, designers and application engineers
working on switched-mode ac–dc converters.
INTRODUCTION
SOLID-STATE ac–dc conversion of electric power is widely
used in adjustable-speed drives (ASDs), switch-mode
power supplies (SMPSs), uninterrupted power supplies (UPSs),
and utility interface with nonconventional energy sources such
as solar PV, etc., battery energy storage systems (BESSs), in
process technology such as electroplating, welding units, etc.,
battery charging for electric vehicles, and power supplies for
telecommunication systems, measurement and test equipments
[1]–[25]. Conventionally, ac–dc converters, which are also
called rectifiers, are developed using diodes and thyristors to
provide controlled and uncontrolled dc power with unidirectional
and bidirectional power flow. They have the demerits
of poor power quality in terms of injected current harmonics,
caused voltage distortion and poor power factor at input ac
mains and slow varying rippled dc output at load end.
STATE OF THE ART
The IPQC technology has been developed now at a reasonably
matured level for ac–dc conversion with reduced
harmonic currents, high power factor, low electromagnetic
interference (EMI) and radio frequency interference (RFI) at
input ac mains and well-regulated and good quality dc output
to feed loads ranging from fraction of Watt to several hundred
kilowatts power ratings in large number of applications. It has
been revolutionized in the last couple of decade with varying
configurations, control approaches, solid-state devices, circuit
integration, varying magnetics, etc., for features such as boost,
buck, buck–boost, and multilevel with unidirectional and
bidirectional power flow. A large number of IPQC configurations
have been evolved to suit vastly varying requirements of
different applications while maintaining a high level of quality
at the input ac source and output dc loads. This section contains
the chronological development and the status of the IPQC
technology.
CONFIGURATIONS
IPQCs are classified on the basis of topology and type of
converter used. The topology-based classification is categorized
on the basis of boost, buck, buck–boost, multilevel, unidirectional
and bidirectional voltage, current, and power flow. The
converter type can be step-up and step-down choppers, voltagesource
and current-source inverters, bridge structure, etc. Figs. 1
and 2 show these two types of classifications of IPQCs.
CONTROL STRATEGIES
The control strategy is the heart of IPQCs and normally
implemented in three parts. In the first part of control, the
essential variables used in control are sensed and scaled to feed to
the processors for the use in control algorithm as the feedbacks.
These signals are input ac mains voltage, supply current, output
dc voltage, and, in some cases, additional voltages such as
capacitor voltage and inductor current, which are used in the
intermediate stage of the converters. The ac voltage signal is
sensed using potential transformers (PTs). Hall-effect voltage
sensors, isolation amplifiers, and low-cost optocouplers are
used to sense dc voltages, especially in small power supplies.
These voltage signals are scaled and conditioned to the proper
magnitude to feed to the processors via ADC channels or as the
synchronizing signals for zero-crossing detection.
CONCLUSION
An exhaustive review of IPQCs has been presented to explore
a wide perspective of various configurations of IPQCs to
researchers, designers, application engineers, and end users of
ac–dc converters. A broad classification of IPQCs into eight categories
with further subclassification of various circuits is expected
to provide easy selection of an appropriate converter for
a particular application. These IPQCs can be considered to be a
better alternative for power quality improvement because of reduced
size of overall converter, higher efficiency, lower cost, and
enhanced reliability compared to other means of power quality
improvement. These converters provide improved power quality
not only at the input ac mains but also at dc output for the better
overall design of equipment. These converters have given the
feature of universal input to the number of products which can
have input power either from ac mains of a varying voltage of 90
to 300 V with a varying frequency from 40 to 70 Hz or dc input.