It provides brief introduction about the electronics components

1. Power Electronics System
• Convert electric power from one form to
another using power electronics devices.
• Power Electronics system block diagram:
1
EPPB2034 prepared by Toh Chuen Ling
Converter Classification
2
EPPB2034 prepared by Toh Chuen Ling
• AC-DC (Rectifier)
• DC-AC (Inverter)
• DC-DC (Chopper/Booster)
• AC-AC (Cyclo-converter)
Applications
3
Adjustable frequency
EPPB2034 prepared by Toh Chuen Ling
Application:
• Wind turbines generate variable voltage in
magnitude and frequency due to the fact that
wind speed and power is not constant over a day.
In order to transfer power from the generator into
a grid, power converters are required to adjust the
frequency and magnitude.
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2. EPPB2034 prepared by Toh Chuen Ling
Interdisciplinary Nature of Power Electronics
5
Power Electronics Concepts
6
?
EPPB2034 prepared by Toh Chuen Ling
Copyright © 2011 by McGraw Hill.
Solutions:
1. Voltage divider
2. A switch circuit
Low-Pass Filter + Switch
control
7
EPPB2034 prepared by Toh Chuen Ling
Copyright © 2011 by McGraw Hill.
Devices Power Diodes
(Uncontrolled)
Thyristors
(Semi-controlled)
Power Transistors
(Fully controlled)
Types • General purpose
• High speed (Fast
Recovery)
• Schottky
• Silicon Carbine (SiC)
• Silicon-controlled
Rectifier (SCR)
• Power BJT
• Power MOSFET
• IGBT
Power Semiconductor Devices
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3. Power Diode
• The ON and OFF states are determined by
voltages and currents in the circuit.
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Conduction i-v Ideal case diode
Forward-biased
(ON)
Current id positive Short circuit
Reverse-biased
(OFF)
Voltage vd is
negative
Open circuit
EPPB2034 prepared by Toh Chuen Ling
Copyright © 2011 by McGraw Hill.
Reverse Recovery
i
t2
t1
t
ON
OFF
trr = (t2 – t1 )
The current is decreases and momentarily becomes negative before
becoming zero.
The time trr is usually less than 1 µs.
10
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EPPB2034 prepared by Toh Chuen Ling 11
Thyristors (SCR)
Copyright © 2011 by McGraw Hill.
• Gate Turn-Off Thyristor (GTO)
– Behave like normal thyristor, but can be turned off using gate signal
– However turning off is difficult. Need very large reverse gate current
(normally 1/3 of the on-state anode current).
• Triac
– Capable of conducting current in either direction
– Equivalent to two antiparallel SCRs
• MOS-Controlled thyristor (MCT)
– voltage controlled device
– Low voltage drop in the on state at relatively
high currents
– Faster switching speed in s range.
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Thyristors
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* A thyristor is turned on by
applying a gate current thru gate
node while its in the forward
biased state. The device will remain
on so long as the current flows
thru the thytristor is positive
regardless of the gate current.

4. Power Transistors: Metal-Oxide-Semiconductor
Field Effect Transistor
– Voltage controlled device
– Supply a sufficient vGS to trigger ON the device.
(vGS  20V)
– ON state: voltage drop across Drain-Source terminal, vDS.
[RDS(ON)  m]
– Switching frequency in MHz range.
EPPB2034 prepared by Toh Chuen Ling 13
Copyright © 2011 by McGraw Hill.
– Current controlled device
– Supply a sufficient iB to trigger ON the device. (iB must be
supply continuously to keep the BJT ON)
– ON state: voltage drop across Collector-Emitter terminal,
vCE  1-2V
– Rarely used in new applications, being surpassed by
MOSFET and IGBT.
Power Transistor: Bipolar Junction Transistor
EPPB2034 prepared by Toh Chuen Ling 14
Copyright © 2011 by McGraw Hill.
Power Transistor:
Insulated Gate Bipolar Transistor
• Combine the advantages of MOSFET, BJT, and
GTO.
– Small amount of energy to switch on the device,
– Small on-state voltage drop, VCE(ON) is 2-3V.
– Block negative voltages
• Medium switching speed
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Summary of Device Capabilities
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5. • Power usually refers to average power,
which is the time average of periodic
instantaneous power:
• Instantaneous Power, p(t) = v(t)i(t)
– Positive p(t): absorbing power
– Negative p(t): supplying power
Power
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Copyright © 2011 by McGraw Hill
Instantaneous Power,
p(t) = v(t)i(t)
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Copyright © 2011 by McGraw Hill
Effective Value/Root-Mean-Square (rms) value
• The effective or rms voltage:
• The effective or rms current:
EPPB2034 prepared by Toh Chuen Ling 19
Copyright © 2011 by McGraw Hill
Distortion
Component
RMS value of non-sinusoidal waveforms
EPPB2034 prepared by Toh Chuen Ling 20
 








1
2
,
2
,
1
2
,
0
2
0
0
1
n
rms
n
rms
rms
T
t
t
rms
I
I
I
dt
t
i
T
I
       





1
1
0
n
n t
i
t
i
t
i
t
i
Copyright © 2011 by McGraw Hill

6. Apparent Power and Power Factor
Apparent Power S:
• Apparent power is the product of rms
voltage and rms current magnitudes:
Power Factor:
– How effectively the load draws the real power:
EPPB2034 prepared by Toh Chuen Ling 21
Copyright © 2011 by McGraw Hill
Power Computation for Non-Sinusoidal
Periodic Waveforms
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Copyright © 2011 by McGraw Hill
Fourier Analysis of Repetitive Waveforms
• A non-sinusoidal waveform f(t) repeating with
an angular frequency  can be expressed as
23
 
 
1
0
1
( )
1
cos( ) sin( )
2
o h
h
h h
h
f t F f t
a a h t b h t
 




 
  


EPPB2034 prepared by Toh Chuen Ling
Fourier Series Analysis
• The instantaneous output voltage and load current
can be expressed in Fourier series, due to it
harmonics contain.
• Fourier Series
   
 











1
0
1
0
sin
cos
)
(
)
(
n
n
n
n
n
t
n
b
t
n
a
F
t
f
F
t
f


 
     
     
t
d
t
n
t
f
b
t
d
t
n
t
f
a
dt
t
f
T
F
n
n
T














2
0
2
0
0
0
sin
1
cos
1
1
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EPPB2034 prepared by Toh Chuen Ling