LECTURE 1 (Ch.
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,
Control deals with the steady
state and dynamic
characteristics of closed
Power deals with static and rotating power
Electronics deals with the solid
state devices and
circuits for signal processing to meet the desired
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.
History of Power Electronics
The history of power electronics began with
introduction of the mercury arc rectifiers in
Devices which were based on the mercury arc
valve technology were used until 1950.
electronic revolution began in 1948
with the invention of the silicon transistor at
Most of today's advanced electronic technologies
are based on the transistor concept.
The next breakthrough was invention of
(SCR) in 1956, which is a PNPN
revolution began in 1958 with
development of the commercial
That was the beginning of a new era of power
Power Semiconductor Devices
Since the first
was developed in 1957,
there have been tremendous advances in the
power semiconductor devices.
Until 1970, the conventional
exclusively used for power control applications.
Since 1970 many types of power semiconductor
devices were developed.
The power semiconductor devices can be
operated as switches by applying a control
signals to gate.
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,
Pulse gate requirement (SCR, GTO)
withstanding capability (SCR, GTO)
voltage withstanding capability (BJT,
Bidirectional current capability (TRIAC)
Unidirectional current capability (SCR, GTO, BJT,
Characteristics and Specification
There are many types of power switching
Each has its own advantages and disadvantages
for an application.
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
on and turn
instantaneously turn on and off
Low gate power for turn on and off
Controllable turn on and off
Turn on and off require a small pulse
Low thermal impedance
Sustain any fault current (i
Equal current sharing for parallel operation
Characteristics of Practical Devices
During the turn
on and turn
off process a
practical device requires:
a finite delay time
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.
Power electronics circuits can be classified into
dc converters (controlled rectifier)
ac converters (ac voltage controllers)
dc converters (dc choppers)
ac converters (inverters)
Design of Power Electronics
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
In the chapters that follow, we will describe
various types of power electronic circuits.
In analysis, the power devices are assumed to be
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.
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:
Operations of power converters are mainly
based on the switching of power semiconductor
As a result, converters introduce current and
voltage harmonics into the supply system and on
the output of the converters.
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.
The following figure shows the block diagram of
a generalized power converter.