This document discusses several applications of power electronics, including: 1) Motor drives and variable speed drives which use power electronics to vary motor speed in an efficient manner and save energy compared to throttling flow with a valve. 2) LED and CFL lighting which use power electronics for power factor correction, constant current regulation and dimming controls. 3) Domestic appliances like fans which now use electronic speed controls instead of wasteful resistive controls.

1. Some Applications of Power Electronics
(Lecture-2)
R S Ananda Murthy
Associate Professor and Head
Dept. of Electrical & Electronics Engineering,
Sri Jayachamarajendra College of Engineering,
Mysore 570 006
R S Ananda Murthy Some Applications of Power Electronics

2. Major Areas of Application of Power Electronics
Motor Drives and Actuators
Illumination Engineering
Energy Efficient Power Supplies
Sustainable Energy Systems
Vehicle and Transportation Systems
Power and Control Core Technologies
R S Ananda Murthy Some Applications of Power Electronics

3. Affinity Laws of Hydraulics
Affinity Laws are applicable to pumps and fans. According
to this law, at a given diameter of the impeller,
Q1
Q2
=
N1
N2
;
H1
H2
=
N1
N2
2
P1
P2
=
N1
N2
3
;
where Q is the flow, H is head, P refers to the power and N
is the speed of the pump or fan.
Keeping the speed constant, the flow can be controlled by
using a valve or a damper. Then, as per equation given
above, the power remains constant even at reduced flow.
This is not an efficient method of reducing the flow.
R S Ananda Murthy Some Applications of Power Electronics

4. Variable Speed Drive Saves Power
Suppose, to reduce the flow by 50 %, if we decrease the
speed by 50%, then,
Q1
Q2
=
N1
N2
=
1
2
; and
P1
P2
=
1
2
3
=
1
8
which shows that the power is reduced by a factor of 8 if
the speed is decreased by a factor of 2.
This is more energy efficient than using a valve or a
damper.
But this requires a variable speed drive.
R S Ananda Murthy Some Applications of Power Electronics

5. Why A.C. Drive?
Most of the industrial pumps and fans are driven by
three-phase induction motors.
The rotor speed of three-phase induction motor is given by
N2 =
120f1
P1
(1−s)
where f1 is the stator supply frequency, P1 is the number of
poles in the stator rotating magnetic field, and s is the slip.
This shows that the speed can be controlled smoothly by
changing the frequency of the supply given to the stator.
R S Ananda Murthy Some Applications of Power Electronics

6. Block Diagram of A.C. Drive
Diode Bridge
Rectifier
3-ph
Supply
PWM
Inverter
Control Circuit
Speed
Reference
Output Voltage
and Frequency
Control Signals
IM
Variable speed induction motor drives are now used to
drive compressors and fans in industries to improve energy
efficiency.
R S Ananda Murthy Some Applications of Power Electronics

7. Other Advantages of A.C. Drive
Limits inrush current at the time of starting preventing utility
supply voltage dips and thereby prevents maloperation of
other equipment connected to the same power supply.
Soft start reduces stress on the insulation of the motor
winding and the power cable and prolong their life.
In an induction motor we have Φm ∝ |V1|/f1 where Φm is
the airgap flux, |V1| is the supply voltage per phase, and f1
is the supply frequency.
Using an A.C. drive we can adjust the motor voltage and
frequency to ensure that iron loss is equal to the copper
loss at all loads so that the motor runs at the highest
efficiency at any load.
R S Ananda Murthy Some Applications of Power Electronics

8. Static Kramer Drive for Slip Ring Induction Motor
Bridge
Rectifier
Bridge
Inverter
Wound Rotor
Induction
Motor
Three-phase
Power Supply
Slip
Power
Transformer
Starting
Rheostats
Input
Power Feedback
Power
This method of speed control is also known as slip-power
recovery scheme.
R S Ananda Murthy Some Applications of Power Electronics

9. D.C. Motor Drive
Controlled
Rectifier
3-ph
Supply
Control
Circuit
Speed
Reference
Output Voltage
Control Signals
M
Field Coil
Diode
Rectifier
+
-
+ -
3-ph
Supply
D.C. motors are now being replaced by squirrel-cage
induction motors driven by A.C. drives because they are
more rugged and need lesser maintenance.
R S Ananda Murthy Some Applications of Power Electronics

10. Domestic Fan Speed Regulators
Power electronic fan regulators, shown above right are
very compact and more energy efficient than inefficient
resistive old fan speed regulators shown above left.
R S Ananda Murthy Some Applications of Power Electronics

11. Brushless D.C. Motor Drive
Brushless D.C. motors (BLDC) are special type of D.C.
motors which are now being increasingly used in
applications where speed variation is needed as in the
case of electric vehicles.
R S Ananda Murthy Some Applications of Power Electronics

12. Brushless D.C. Motor Drive
Bridge
Inverter
Microcontroller
or DSP Based
Control CircuitSpeed
Reference
BLDC
Motor
+
-
Control
Signals
D.C.
Source
Feedback
from sensors
A BLDC motor cannot run without power electronic drive circuit.
R S Ananda Murthy Some Applications of Power Electronics

13. Compact Flourescent Lamp Controllers
EMI
Filter
Rectifier
with C
Filter
1-Ph Power
50 or 60 Hz
Half
Bridge
Inverter
Control
Circuit
L-C Tank
Circuit
CFL
Tube
Brightness
Control
Signals
User
Brightness
Set Point
Current
Sensor
Brightness
Feedback
Compared to incandescent lamps, though CFLs are
costlier, they give the same amount of visible light, use 20-
30% lesser electric power, and last 8-15 times longer.
A CFL can save about five times its purchase price in
electricity costs during the lamp’s lifetime.
R S Ananda Murthy Some Applications of Power Electronics

14. LED Lamp Driver
EMI
Filter
1-Ph Power
50 or 60 Hz
Bridge
Rectifier
Current
Regulator
Power Factor
Correction
Circuit
The power factor correction circuit – which is a power
electronic circuit – maintains high power factor on the
supply side.
The current regulator – which is another power electronic
circuit – maintains constant current through the series
connection of several LEDs.
Some of the modern LED driving circuits also provide
dimming facility.
R S Ananda Murthy Some Applications of Power Electronics

15. Power Electronics in D.C. Power Supplies
Power electronics helps in realizing switched mode power
supplies (SMPS), shown on the right side above, which are
compact and more energy efficient than conventional
regulated power supplies shown on the left side.
R S Ananda Murthy Some Applications of Power Electronics

16. Next Lecture...
In the next lecture we will describe some more applications of
power electronics.
Thank You.
R S Ananda Murthy Some Applications of Power Electronics