Lecture-2 : Applications of Power Electronics

Some Applications of Power Electronics(Lecture-2)

R S Ananda Murthy

Associate Professor and HeadDept. of Electrical & Electronics Engineering,

Sri Jayachamarajendra College of Engineering,Mysore 570 006

R S Ananda Murthy Some Applications of Power Electronics

Major Areas of Application of Power Electronics

Motor Drives and ActuatorsIllumination EngineeringEnergy Efficient Power SuppliesSustainable Energy SystemsVehicle and Transportation SystemsPower and Control Core Technologies


Affinity Laws of Hydraulics

Affinity Laws are applicable to pumps and fans. Accordingto 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 Nis the speed of the pump or fan.Keeping the speed constant, the flow can be controlled byusing a valve or a damper. Then, as per equation givenabove, the power remains constant even at reduced flow.This is not an efficient method of reducing the flow.


Variable Speed Drive Saves Power

Suppose, to reduce the flow by 50 %, if we decrease thespeed by 50%, then,

Q1

Q2=

N1

N2=

12

; andP1

P2=

(12

)3

=18

which shows that the power is reduced by a factor of 8 ifthe speed is decreased by a factor of 2.This is more energy efficient than using a valve or adamper.But this requires a variable speed drive.


Why A.C. Drive?

Most of the industrial pumps and fans are driven bythree-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 ofpoles in the stator rotating magnetic field, and s is the slip.This shows that the speed can be controlled smoothly bychanging the frequency of the supply given to the stator.


Block Diagram of A.C. Drive

Diode BridgeRectifier

3-phSupply

PWMInverter

Control CircuitSpeed

Reference

Output Voltageand FrequencyControl Signals

IM

Variable speed induction motor drives are now used todrive compressors and fans in industries to improve energyefficiency.


Other Advantages of A.C. Drive

Limits inrush current at the time of starting preventing utilitysupply voltage dips and thereby prevents maloperation ofother equipment connected to the same power supply.Soft start reduces stress on the insulation of the motorwinding and the power cable and prolong their life.In an induction motor we have Φm ∝ |V1|/f1 where Φm isthe airgap flux, |V1| is the supply voltage per phase, and f1is the supply frequency.Using an A.C. drive we can adjust the motor voltage andfrequency to ensure that iron loss is equal to the copperloss at all loads so that the motor runs at the highestefficiency at any load.


Static Kramer Drive for Slip Ring Induction Motor

BridgeRectifier

BridgeInverter

Wound RotorInduction

Motor

Three-phasePower Supply

SlipPower

TransformerStarting

Rheostats

InputPower Feedback

Power

This method of speed control is also known as slip-powerrecovery scheme.


D.C. Motor Drive

ControlledRectifier

3-phSupply

ControlCircuit

SpeedReference

Output VoltageControl Signals

MField Coil

DiodeRectifier

+

-

+ -

3-phSupply

D.C. motors are now being replaced by squirrel-cageinduction motors driven by A.C. drives because they aremore rugged and need lesser maintenance.


Domestic Fan Speed Regulators

Power electronic fan regulators, shown above right arevery compact and more energy efficient than inefficientresistive old fan speed regulators shown above left.


Brushless D.C. Motor Drive

Brushless D.C. motors (BLDC) are special type of D.C.motors which are now being increasingly used inapplications where speed variation is needed as in thecase of electric vehicles.


Brushless D.C. Motor Drive

BridgeInverter

Microcontrolleror DSP BasedControl CircuitSpeed

Reference

BLDCMotor

+-

ControlSignals

D.C.Source

Feedbackfrom sensors

A BLDC motor cannot run without power electronic drive circuit.


Compact Flourescent Lamp Controllers

EMIFilter

Rectifierwith CFilter

1-Ph Power50 or 60 Hz

HalfBridgeInverter

ControlCircuit

L-C TankCircuit

CFLTube

BrightnessControlSignals

UserBrightnessSet Point

CurrentSensor

BrightnessFeedback

Compared to incandescent lamps, though CFLs arecostlier, 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 inelectricity costs during the lamp’s lifetime.


LED Lamp Driver

EMIFilter

1-Ph Power50 or 60 Hz

BridgeRectifier

CurrentRegulator

Power FactorCorrection

Circuit

The power factor correction circuit – which is a powerelectronic circuit – maintains high power factor on thesupply side.The current regulator – which is another power electroniccircuit – maintains constant current through the seriesconnection of several LEDs.Some of the modern LED driving circuits also providedimming facility.


Power Electronics in D.C. Power Supplies

Power electronics helps in realizing switched mode powersupplies (SMPS), shown on the right side above, which arecompact and more energy efficient than conventionalregulated power supplies shown on the left side.


Next Lecture...

In the next lecture we will describe some more applications ofpower electronics.

Thank You.


Lecture-2 : Applications of Power Electronics

Technology

Transcript of Lecture-2 : Applications of Power Electronics