Transcript Power Electronics

POWER ELECTRONICS
ECE 105 Industrial
Electronics
Engr. Jeffrey T. Dellosa
College of Engineering and Information Technology
Caraga State University
Ampayon, Butuan City
1
Power Electronics

Introduction
Power electronics is the technology of converting electric
power from one form to another using power
semiconductor devices based circuitry.
It incorporates concepts from analog circuits, electronic
devices, control systems, power systems, magnetics, and
electric machines.
2
The converter enables either the following:
DC-DC: conversion
AC-DC: rectification
DC-AC: inversion
AC-AC: cycloconversion
Power Electronics
3
In the power converter, the power semiconductor devices
function as switches, which operate statically, that is,
without moving contacts.
The time durations, as well as the turn ON and turn OFF
operations of these switches are controlled in such a way
that an electrical power source at the input terminals of
the converter appears in a different form at its output
terminals.
Power Electronics
4
Power Electronics
Here power converter high conversion efficiency  is
essential!
High efficiency leads to low power loss within converter.
Efficiency is a good measure of converter performance.
Hence, a goal of current converter technology is to
construct converters of small size and weight, which
process substantial power at high efficiency.
5
Power Electronics
Components used in power electronics circuitry are:
6
Rapid development of power semiconductor devices led to
significant improvement in,
◦ Speed
◦ Power capability
◦ Efficiency
Hence increase the range of applications
◦ DC Servo control
◦ AC motor control
◦ Sophisticated power supplies (switching-mode,
uninterruptible)
◦ High power DC transmission
Power Electronics
7
Power Electronics
Often power loss in power semiconductor device (when
viewed as an ideal switch) is based on the following:
Thus an ideal power semiconductor device is characterized by
zero resistance during ON-state, infinite resistance during OFFstate, zero transient time from ON to OFF and vice-versa.
Practical power semiconductor device has limited voltage and
current handling capability, an ON-resistance greater than zero and
finite switching times.
8
Power Electronics

Power Electronics Devices
◦ Power Bipolar Transistors (BJTs)
◦ Power Metal Oxide Semiconductor Field Effect
Transistors (MOSFETs)
◦ Insulated Gate Bipolar Transistors (IGBTs)
◦ Thyristors
◦ Gate Turn-Off Thyristors (GTOs)
◦ Power Diodes
9
Power Electronics
10
Power Electronics
11
Alternatively power semiconductor devices can be classified into 3
groups according to their degree of controllability.
 Power Diodes - ON and OFF states controlled by the power cct.
Thyristors - Latched ON by a control signal but must be turned
OFF by the power cct.
 Controllable Switches - Turned ON and OFF by control signals.
The controllable switches include
i)
BJTs
ii)
MOSFETs
iii)
Gate Turn-OFF Thyristors (GTOs)
iv)
Insulated Gate Bipolar Transistors (IGBTs)
Power Electronics
12
Power Electronics

Power Diodes
The circuit symbol for the diode and its steady
state v-i characteristics are as shown.
13
Power Electronics

Power Diodes
14
Power Electronics

Thyristors
The circuit symbol for the thyristor and its steady state v-i characteristics
are as shown.
15
Power Electronics

Thyristors
In its OFF state, the thyristor can block a forward polarity voltage
and not conduct, as is shown by the off-state portion of the i-v
characteristic.
The thyristor can be triggered into the ON state by applying a pulse of
positive gate current for a short duration provided that the device is in
its forward-blocking state.
The resulting i-v relationship is shown by the ON state portion of the
characteristics shown. The forward voltage drop in the ON state is only a
few volts (typically 1-3V depending on the device blocking voltage rating).
16
Power Electronics

Power BJTs
The circuit symbol for the BJTs and its steady state v-i
characteristics are as shown.
17
Power Electronics

Power BJTs
As shown in the i-v characteristics, a sufficiently large base current
results in the device being fully ON. This requires that the control
circuit to provide a base current that is sufficiently large so that
I
IB  C
hFE
where hFE is the dc current gain of the device
BJTs are current-controlled devices, and base current must be
supplied continuously to keep them in the ON state: The dc
current gain hFE is usually only 5-10 in high-power transistors.
BJTs are available in voltage ratings up to 1400V and current
ratings of a few hundred amperes.
18
Power Electronics

Power BJTs
BJT has been replaced by MOSFET in low-voltage (<500V)
applications
BJT is being replaced by IGBT in applications at voltages above
500V
19
Power Electronics

Power MOSFETs
The circuit symbol for the MOSFETs and its steady state v-i
characteristics are as shown.
Drain(D)
iD
+
+
Gate(G)
+
VGD
VDS
-
VGS
-
Source(S)
20
Power Electronics

Power MOSFETs
Power MOSFET is a voltage controlled device.
MOSFET requires the continuous application of a gate-source voltage
of appropriate magnitude in order to be in the ON state.
The switching times are very short, being in the range of a few tens of
nanoseconds to a few hundred nanoseconds depending on the device
type.
21
Power Electronics

Power MOSFETs
22
Power Electronics

IGBTs
The circuit symbol for the IGBTs and its steady state v-i characteristics
are as shown.
23
Power Electronics

IGBTs
The IGBT has some of the advantages of the MOSFET, & the BJT
combined.
Similar to the MOSFET, the IGBT has a high impedance Gate,
which requires only a small amount of energy to switch the device.
Like the BJT, the IGBT has a small ON-state voltage even in
devices with large blocking voltage ratings (for example, VON is 2-3V
in a 1000-V device)..
24
Power Electronics

IGBTs
25
Power Electronics

Several Applications of Power Electronics
A laptop computer power supply system .
26
Power Electronics

Several Applications of Power Electronics
An electric vehicle power and drive system.
27
Power Electronics

Transient Protection of Power Devices
dv
dt
Snubber circuit limits
di
dt
,
as well as voltage and peak current in a switching device to safe
specified limits!
dv
Switching device’s
dt
rating is significant during the switching device (e.g. thyristor) turnOFF process. Voltage can increase very rapidly to high levels. If the
rate rise is excessive, it may cause damage to the device.
28
Power Electronics

Transient Protection of Power Devices
29
Power Electronics

Transient Protection of Power Devices
30
Power Electronics

Transient Protection of Power Devices
31
Power Electronics

Transient Protection of Power Devices
32
Power Electronics

Transient Protection of Power Devices
33
Power Electronics

Transient Protection of Power Devices
34
Power Electronics

Power and Harmonics in Non-sinusoidal
Systems
Non-sinusoidal waveforms
are waveforms that are not sine waves.
,
Non-sinusoidal waveforms can be described as being made of
harmonics (multiple sine waves of different frequencies).
Thus for a waveform whose fundamental frequency is , than second
harmonic has a frequency 2 and so on.
Waveforms occurring at frequencies of 2, 4, 6, … are called even
harmonics;
Those occurring at frequencies of 3, 5, 7, ... are called odd
harmonics.
35
Power Electronics

Power and Harmonics in Non-sinusoidal
Systems
Thus for the circuit shown (a non-sinusoidal system), expressing the
circuit’s voltage and current as Fourier series:
,
36
Power Electronics

Power and Harmonics in Non-sinusoidal
Systems
,
37
Power Electronics

Power and Harmonics in Non-sinusoidal
Systems
Expression for average power
becomes
,
So power is transmitted to the load only when the Fourier series of v(t)
and i(t) contain terms at the same frequency.
Eg. if the voltage & current both contain 3rd harmonic, then they lead to
the average power
38
Power Electronics

Power and Harmonics in Non-sinusoidal
Systems
With the rms voltage defined as
,
Inserting Fourier series into the above, an expression of rms voltage
for non-sinusoidal voltage waveform
Notice harmonics always increase rms value & increased in rms values  increased
losses!
39
Power Electronics

Power and Harmonics in Non-sinusoidal
Systems
For efficient transmission of energy from a
source to a load, it is desired
to maximize
,
average power, while minimizing rms current
and voltage (and hence minimizing losses).
Power factor is a figure of merit that measures
how efficiently energy is transmitted. It is
defined as
Notice harmonics always increase rms value & increased in rms values  increased losses!
40
Power Electronics

Basic Magnetics
Inductance (measured in Henry) is an effect which results from the
magnetic field that forms around a current carrying conductor.
Inductance can be increased, by looping the conductor into a coil which creates a
larger magnetic field.
An inductor is usually constructed as a coil of copper wire, wrapped
around a core either of air or of ferrous material.
Core materials with a higher permeability than air confine the magnetic field closely to
the inductor, thereby increasing the inductance.
Inductors come in many shapes. Most are constructed as enamel coated wire wrapped
around a ferrite bobbin with wire exposed on the outside, while some enclose the wire
completely in ferrite and are called "shielded".
Some inductors have an adjustable core, which enables changing of the inductance.
Small inductors can be etched directly onto a printed circuit board by laying out the
trace in a spiral pattern.
41
Power Electronics

Basic Magnetics
Current flowing through an inductor creates a magnetic field which
has an associated electromotive force (emf).
This inductor’s emf opposes the change in applied voltage.
The resulting current in ,the inductor resists the change but does rise!
• An inductor resists changes in current.
• An ideal inductor would offer no resistance to direct current; however, all real-world
inductors have non-zero electrical resistance.
In general, the relationship between v(t) across an inductor with
inductance L and i(t) passing through it is described by the
differential equation:
The inductor is used as the energy storage device in power electronics circuitries.
42
Power Electronics

Basic Magnetics
Transformers
-- widely used in low-power electronic ccts for voltage step-up or stepdown, & for isolating DC from two ccts while maintaining ac continuity.
-- consists of 2 windings linked by a mutual magnetic field. When one
winding, the primary has an ac voltage applied to it, a varying flux is
developed; the amplitude of the flux is dependent on the applied voltage
and number of turns in the winding.
Mutual flux linked to the secondary winding induces a voltage whose
amplitude depends on the number of turns in the secondary winding.
43
Power Electronics

Basic Magnetics
Mutual magnetic flux coupling is accomplished simply with an air core
but considerably more effective flux linkage is obtained with the use of
a core of iron or ferromagnetic material with higher permeability than
air.
The relationship between voltage, current, & impedance between the
primary & secondary windings of the transformer may be calculated
using the following relationships.
44
Power Electronics

Basic Magnetics
The basic phase relationship between the signals at the transformer
input & output ports may be in-phase, or out-of-phase. Conventionally,
the ports that are in-phase 1, and 3, are marked by dot notation as
shown.
45
Power Electronics

Basic Magnetics
EXAMPLE
46