Basics of Power Electronics 2
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Transcript of Basics of Power Electronics 2
Basics of Power Electronics
Dr.Mohamed Ansari M.Nainar
Sr.Lecturer, ME
BN-1-026, COE
UNITEN, Malaysia
Tel Ext: 2213
Email: [email protected]
ELECTRO-MECHANICAL
SYSTEMS (EEEB413)
Book Reference
Theodore Wildi, Electrical Machines, Drives, and Power Systems, IE,
6th Edition, Prentice Hall
Basics of Power Electronics
• Electronic systems – Power technology
• Solid-state electronic device for control and
conversion of electric power or Semi-
conducting switching devices (eg: Diodes,
Thyristors and Transistors)
• Advances in Power electronics: GTOs, BPT,
MOSFETs, IGBT’s.
• Conversion of AC power to DC power and
vice-versa (eg.rectifiers, inverters, converters)
3
Potential Level – Example1
• Potential level w.r.t
reference potential,
T1(0V)
• Potential level of T2
is 80V w.r.t T1
• Potential level of T3
w.r.t T1 and T2 based
on time factor, t1…tn.
Battery
AC source
Potential level of terminals 1,2 and 3
4
Potential Level – Example 2
• Potential level w.r.t
reference potential,
T3(0V)
• Potential level of T1
is w.r.t T3
• Potential level of T2
w.r.t based on time
factor, t1…tn.
Potential level of terminals 1,2 and 3
Battery
AC source
5
Voltage across some circuit elements
• Potential at Source
• Potential across a
switch (E1 = E2)
• Potential across a
Resistor E3 = E4 = IR
• Potential across a coil
or Inductance
E=L(dI/dt)
• Potential across a
Capacitor,E=const; I=0
Potential level of some circuit elements
Switch
Resistor
Inductor
Capacitor
6
Basic electronic components
• DIODE
• THYRISTOR
– GTO Thyristor
• TRANSISTOR
– BPT
– MOSFET
– IGBT
7
The Diode and Diode Circuits
• A diode is an electronic
device possessing two
terminals, A and K
• Rules:R1 – R4 – R1 : E= 0, then Open switch (OS)
– R2 : Inv.Voltage (E2) - OS
– R3 : For.Voltage (E1>0.7V) – Closed switch
(CS)
– R4 : If I=0 for 10µsec, - OS
• A perfect diode is a normally open
switch when A becomes +ve, then
it behaves as a CS and when I
drops to 0 then it behaves as an
OS again.
Basic rules governing diode behaviour
Diode
8
Main characteristics of a diode
• Peak Inverse Voltage
– Maximum inverse voltage before the diode breaks down.
– The peak inverse voltage (PIV) ranges from 50V to 4000V, depending on the
construction.
– If the rated PIV is exceeded, the diode begins to conduct in reverse and in many
cases, is immediately destroyed.
• Maximum Average Current
– Average current limit for a diode to carry.
– Max. current ranges from few 100 mA to over 4000 A.
– Nominal current rating depends upon the temperature of the diode, which depends
upon the mountings and cooling systems.
• Maximum Temperature
– Voltage across a diode X current it carries = Power loss (Heat)
– The temp. of diode must not exceed the permissible limit.
– Si diodes : -50 0C to +200 0C.
– Heat sink, fans, oil or deionized water (For cooling of diodes) 9
Thyristors • A thyristor is an electronic switch
similar to a diode, but wherein the
instant of conduction can be
controlled.
• Like diode, a thyristor possesses an
anode and a cathode, in addition a
third contact terminal called a gate
is present.
• If the gate is connected to the
cathode, the thyristor will not
conduct, even if the anode is
positive. (Blocked)
• Conditions: a. The anode must be positive
b. A current ‘I’ must flow into the gate for
at least a few microseconds.
Thyristor Conditions
Thyristor
10
GTO Thyristor • A GTO thyristor is similar to a thyristor , both can be controlled
by the gate current and voltage.
• To initiate conduction, anode voltage must be positive
w.r.t.cathode. Under this condition, thyristor may be turn-on by
any of the following techniques:
– Gate Triggering
– High Voltage
– Thermals
– Light
– dV/dt
GTO Thyristor
GTO Thyristor Properties 11
Transistors • A transistor is a semiconductor device
used to amplify and switch electronic
signals.
• It is made of a solid piece of
semiconductor material, with at least
three terminals for connection to an
external circuit. A voltage or current
applied to one pair of the transistor's
terminals changes the current flowing
through another pair of terminals.
• Because the controlled power can be
much more than the controlling (input)
power, the transistor provides
amplification of a signal.
FET – Field Effect Transistor
BPT – Bipolar Junction Transistor
MOSFET – Metal oxide
semiconductor Field Effect Transistor
12
Transistors
• High switching speed as compared with thyristors.
• Extensively employed in dc-dc and dc-ac converters.
• Have certain limitations and are restricted to some applications
(e.g. High voltage, high current).
• Characteristics and ratings of each type should be carefully
examined to suit a particular application.
BPT – Bipolar Junction Transistor
13
Transistors
• A power MOSFET is a voltage-controlled device only a very
small gate current is required
• Very high switching speed (the switching times are of the order
of nanoseconds)
• Applications in low power high-frequency converters.
• Problems of electrostatic discharge and require special care in
handling.
MOSFET – Metal oxide
semiconductor Field Effect Transistor
MOSFET MOSFET Properties 14
Transistors • Combines the advantages of BPTs and MOSFETs
• High input impedance, like MOSFETs
• Low on-state conduction losses, like BPTs
• A voltage-controlled device similar to a power MOSFET
• Lower switching and conduction losses
• Ease of gate drive, peak current capability and ruggedness
• Inherently faster than a BPT
• The current rating can be up to 400A, 1200V
• Medium-power applications such as d.c. and a.c. motor drives and
power supplies.
IGBT-Insulated Gate Bi-polar Jn Transistor
IGBT Properties
IGBT 15
Basic electronic circuits
• RECTIFIER (AC- DC)
– Single-Phase Bridge Rectifier
– Three-Phase 3Pulse Rectifier
– Three-Phase 6Pulse Rectifier
• INVERTER (DC-AC)
– PWM Inverter
• CONVERTER (DC-DC)
– DC Choppers
16
Rectifiers • A rectifier is an electrical device that converts
alternating current (AC) to direct current (DC),
a process known as rectification.
• Rectifiers have many uses including as
components of power supplies and as detectors
of radio signals.
• Rectifiers may be made of solid state diodes,
vacuum tube diodes, mercury arc valves, and
other components.
(b) (c)
(a) Single-phase bridge rectifiers
(b) Three-phase, 3 pulse rectifier
(c) Three-phase, 6 pulse rectifier
17
Rectifiers
(a) Single Phase Bridge Rectifier
Ed = 0.90 E …………..(1)
Where, Ed = DC voltage of the Rectifier
E = Supply AC line voltage (V)
0.9 = constant (2√2 )/π
Id = Ed /R………………..(2)
Where, Id = Rectified current
18
Rectifiers (i) Rectifier with Inductive Filter
(ii) Rectifier with Capacitive Filter
Ed = 0.90 E ……………...(1)
Id = Ed /R………………..(2)
The peak-to-peak ripple,
Ripple = 5.5 P/f.WL…(3)
Where, ‘WL’ is the energy stored in the
Inductor,
‘P’ is the dc power drawn by the load [W],
‘f’ is the frequency of the 3ph, 6-pulse
source [Hz]
5.5 is the coefficient factor of units
19
Rectifiers (b) Three-Phase, 3 Pulse (Bridge)Rectifier
Ed = 0.675 E …………..(1)
Where, Ed = DC voltage of the 3
Pulse Rectifier
E = Supply AC line voltage (V)
0.675= constant [3/(π√2 )]
Id = Ed /R………………..(2)
Where, Id = Rectified current
20
Rectifiers (c) Three Phase, 6 Pulse Rectifier
Ed = 1.35 E …………..(1)
Where, Ed = DC voltage of the 6-
Pulse Rectifier
E = Supply AC line voltage (V)
1.35 = constant (3√2 )/π
Id = Ed /R………………..(2)
Where, Id = Rectified current
The peak-to-peak ripple,
R = [0.17 P]/f.WL.……….(3)
Where, WL is the energy stored in
the Inductor,
P is the dc power drawn by the
load [W],
F is the frequency of the 3ph, 6-
pulse source [Hz]
21
PROBLEMS
1. An AC source has an effective voltage of 240 V, 60Hz. The
load draws a DC current of 30A.
Calculate: (a) The DC voltage across the load.
(b) The average DC current in each diode.
2. We need to build a DC power supply of 110V,10A using a
single-phase bridge rectifier and an inductive filter. The P2P
current ripple should be about 15%. If a 50Hz AC source is
available, calculate the following values:
(a) The effective AC supply (Source)
(b) The energy stored in the inductor
(c) The inductance of the inductor
(d) The P2P current ripple
22
PROBLEMS
3. A 3-phase bridge rectifier has to supply power to a 360kW, 240
V DC load. If a 600V, 3-phase, 60 Hz feeder is available,
calculate the following:
a. Voltage rating of the 3-ph transformer
b. DC current per diode
c. PIV across each diode
d. P2P ripple in the o/p voltage and its frequency.
e. Calculate the inductance of the choke required, if the P2P ripple is 5 %.
f. Does the presence of the choke modify the P2P ripple in the o/p
voltage EKA?
23
Converter (DC-DC)
• DC to DC converters
– Based on I/O voltage levels (Buck convertor or Boost Converter)
– Based on output voltage and current (Class A, Class B, Class C and Class D)
– Based on circuit operation (One quadrant, Two quadrant or Three quadrant)
– Based on commutation (Natural or Forced)
– Duty Cycle (D) = Ta/T
– T is the period of one cycle
– Ta is the on time of the switch
DC Choppers
24
Converter
Switching Losses:
DC Choppers
EA = D EH
EB = (1-D) EH
ELL = EA - EB
= DEH - (1-D) EH
ELL = EH (2D – 1)
25
PROBLEMS
4. The switch opens and closes at a frequency of 20Hz and
remains closed for 3ms per cycle. A DC ammeter is connected
in series with load Eo indicates a current of 70 A.
a. If ammeter is connected in series with the source, what current will it
indicate?
b. What is the average current per pulse?
26
Inverter • An inverter is an electrical device that
converts DC) to AC; the converted AC
can be at any required voltage and
frequency with the use of appropriate
transformers, switching, and control
circuits.
Types of Inverters:
- 2 quadrant
- 4 quadrant
PWM – Pulse Width Modulated
Inverter
27
PROBLEMS
5. We wish to generate a 3-phase, 245V, 60Hz source using the
converter of Fig.21.93. The DC supply voltage EH is 500V and
the carrier frequency fc is 540Hz: Determine the following
a. The peak value of the fundamental voltage between terminal L and
floating neutral N of the load.
b. The period T of the triangle wave and the corresponding angular
interval, in degrees
c. The PWM program
d. The waves shapes of the PWM voltage between terminals A and Y
during one cycle.
e. The waveshapes of the PWM voltage between terminals A-Y, B-Y,
and C-Y.
f. The waveshapes of the PWM voltages between terminals A-B, B-C,
and C-A.
28
SUMMARY
We have studied the following sub-topics:
1. Introduction to Power Electronics and their devices
2. Electronic components such as Diode, Thyristor
and Transistor
3. Power electronic circuits such as Rectifier circuit,
Convertors and Inverters.
29