11-04-2012, 11:28 AM
A ZERO VOLTAGE SWITCHING BOOST CONVERTER USING A SOFT SWITCHING AUXILIARY CIRCUIT WITH REDUCED CONDUCTION LOSSES
INTRODUCTION
In modem power applications a reliable ac-dc power converter is required. For
power applications above 250 W, a two stage process is usually used to provide an isolated
and regulated dc output voltage. The first stage of such a converter is a rectifying stage that
converts the ac voltage to dc and the second stage is an isolated dc-dc converter that
converts the dc input voltage into a regulated dc voltage at the output as shown in Fig. 1.1.
One of the most important functions of the rectimg stage is to provide Power Factor
Correction (PFC) of the input current in order to minimise the harmonics in it.
PMM Boos C ONVERTEFROR PFC AP PLICATIONS
The switch mode boost converter can perfonn power factor correction by shaping
the input current to be sinusoidal and forcing it to follow the input voltage wavefonn- This
achieves a power factor close to unity and the hannonics are also reduced. However boost
LOSSES IN HARD SWITCHING
The reason why there are switching losses in any switch mode power converter is
that when the switching element turns on or off, high voltage and current are present
simultaneously in the switch. This leads to very high instantaneous power loss
converters suffer fiom their own set of disadvantages:
RESONENT SOFT SWITCHING SCHEMES
There are two types of resonant soft switching depending on whether the voltage
across switch or the current through switch is made zero:
(i) Zero-Current Switching (ZCS): A switch that operates with ZCS has an inductor in
series with it and a series blocking diode if the switch is bi-directional. The switch is
turned on with ZCS as the series inductor slows down the rate of rise of current afler
voltage across switch goes to zero.
THESIS OUTLINE
The contents of the thesis are as follows:
In Chapter 2 the proposed ZVT converter is described and its operation explained. The
steady state analysis is performed during a single switching cycle of the main switch.
halytical results are given at the end of the chapter.
In Chapter 3 characteristic curves of the converter are obtained based on the steady state
analysis of Chapter 2. These cwves help provide insights into the working of îhe converter.
In Chapter 4 control of the proposed converter for PFC applications is described.
In Chapter 5 a design example is given which makes use of the design curves of Chapter 3.
Experimental results fiom a laboratory prototype are given which ve- the design
procedure and the usefulness of the topology.
INTRODUCTION
In modem power applications a reliable ac-dc power converter is required. For
power applications above 250 W, a two stage process is usually used to provide an isolated
and regulated dc output voltage. The first stage of such a converter is a rectifying stage that
converts the ac voltage to dc and the second stage is an isolated dc-dc converter that
converts the dc input voltage into a regulated dc voltage at the output as shown in Fig. 1.1.
One of the most important functions of the rectimg stage is to provide Power Factor
Correction (PFC) of the input current in order to minimise the harmonics in it.
PMM Boos C ONVERTEFROR PFC AP PLICATIONS
The switch mode boost converter can perfonn power factor correction by shaping
the input current to be sinusoidal and forcing it to follow the input voltage wavefonn- This
achieves a power factor close to unity and the hannonics are also reduced. However boost
LOSSES IN HARD SWITCHING
The reason why there are switching losses in any switch mode power converter is
that when the switching element turns on or off, high voltage and current are present
simultaneously in the switch. This leads to very high instantaneous power loss
converters suffer fiom their own set of disadvantages:
RESONENT SOFT SWITCHING SCHEMES
There are two types of resonant soft switching depending on whether the voltage
across switch or the current through switch is made zero:
(i) Zero-Current Switching (ZCS): A switch that operates with ZCS has an inductor in
series with it and a series blocking diode if the switch is bi-directional. The switch is
turned on with ZCS as the series inductor slows down the rate of rise of current afler
voltage across switch goes to zero.
THESIS OUTLINE
The contents of the thesis are as follows:
In Chapter 2 the proposed ZVT converter is described and its operation explained. The
steady state analysis is performed during a single switching cycle of the main switch.
halytical results are given at the end of the chapter.
In Chapter 3 characteristic curves of the converter are obtained based on the steady state
analysis of Chapter 2. These cwves help provide insights into the working of îhe converter.
In Chapter 4 control of the proposed converter for PFC applications is described.
In Chapter 5 a design example is given which makes use of the design curves of Chapter 3.
Experimental results fiom a laboratory prototype are given which ve- the design
procedure and the usefulness of the topology.