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LECTURE 1 (Ch. 1)
INTRODUCTION
ECE 452
Power Electronics
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Application of Power Electronics

In early days, control of the electric power was
achieved with electric machinery.

Power electronics have revolutionized the
concept of power control for power conversion
and for control of electrical motor drives.

Power electronics combine power, electronics,
and control.
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
Control deals with the steady-state and dynamic
characteristics of closed-loop system.

Power deals with static and rotating power
equipment.

Electronics deals with the solid-state devices and
circuits for signal processing to meet the desired
control objectives.
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
Therefore, power electronics is defined as the
applications of solid-state electronics for control
and conversion of electric power.

Power electronics is based on switching of the
power semiconductor devices.

It covers a variety of switching circuits.
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History of Power Electronics

The history of power electronics began with
introduction of the mercury arc rectifiers in
1900.

Devices which were based on the mercury arc
valve technology were used until 1950.

The first electronic revolution began in 1948
with the invention of the silicon transistor at
Bell Labs.
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
Most of today's advanced electronic technologies
are based on the transistor concept.

The next breakthrough was invention of
Thyristor (SCR) in 1956, which is a PNPN
triggering transistor.

The second revolution began in 1958 with
development of the commercial thyristor by GE.
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
That was the beginning of a new era of power
electronics.
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Power Semiconductor Devices

Since the first thyristor was developed in 1957,
there have been tremendous advances in the
power semiconductor devices.

Until 1970, the conventional thyristors had been
exclusively used for power control applications.

Since 1970 many types of power semiconductor
devices were developed.
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Control Characteristics

The power semiconductor devices can be
operated as switches by applying a control
signals to gate.
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
Power semiconductor switching devices can be
classified on the basis of:

Uncontrolled turn on and off (diodes)

Controlled turn on and uncontrolled turn off (SCR)

Controlled turn on and off (BJT, MOSFET, GTO, IGBT)

Continuous gate signal requirement (BJT, MOSFET,
IGBT)
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
Pulse gate requirement (SCR, GTO)

Bipolar voltage-withstanding capability (SCR, GTO)

Unipolar voltage withstanding capability (BJT,
MOSFET, GTO)

Bidirectional current capability (TRIAC)

Unidirectional current capability (SCR, GTO, BJT,
MOSFET, DIODE)
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Characteristics and Specification
of Switches

There are many types of power switching
devices.

Each has its own advantages and disadvantages
for an application.
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Ideal Switches

In the on-state: carry high forward current,
low forward voltage drop, and low resistance

In the off-state: withstand a high voltage, low
leakage current, and high resistance

During turn-on and turn-off process
instantaneously turn on and off
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
Low gate power for turn on and off

Controllable turn on and off

Turn on and off require a small pulse

High dv/dt & di/dt

Low thermal impedance
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
Sustain any fault current (i2t)

Equal current sharing for parallel operation

Low price
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Characteristics of Practical Devices

During the turn-on and turn-off process a
practical device requires:

a finite delay time

rise time

storage time

fall time
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Types of Power Electronic CKTs

For control of electric power or power
conditioning, the conversion of electric power
from one form to another is necessary.

Switching characteristics of the power devices
permit this conversion.
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
Power electronics circuits can be classified into
six types:

Diode rectifiers

Ac-dc converters (controlled rectifier)

Ac-ac converters (ac voltage controllers)

Dc-dc converters (dc choppers)

Dc-ac converters (inverters)

Static switches
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Design of Power Electronics
Equipment

The design is divided into four parts:

Design of power circuits

Protection of power devices

Determination of control strategy

Design of logic and gating circuits
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
In the chapters that follow, we will describe
various types of power electronic circuits.

In analysis, the power devices are assumed to be
ideal switches.

The effect of circuit resistance and source
inductance is ignored.

Ignoring these parameters will simplify the design
steps, but it is very useful to understand operation
of the circuit and establish the control strategy.
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Determining the RMS Value

The RMS value of current should be known for
determination of conduction losses and current
rating of the device.

The RMS value of a current waveform is:
1 T 2
I rms 
i dt

T 0

Also:
I rms  I  I
2
dc
2
rms(1)
I
2
rms( 2 )
 ...I
2
rms( n )
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Peripheral Effects

Operations of power converters are mainly
based on the switching of power semiconductor
devices.

As a result, converters introduce current and
voltage harmonics into the supply system and on
the output of the converters.
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
These can cause problems of distortion of the
output voltage, harmonic generation into the
supply system, and interference with the
communication and signaling circuits.

Therefore, it is normally necessary to introduce
filters on the input and output of a converter
system to reduce the harmonic level.
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
The following figure shows the block diagram of
a generalized power converter.
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