Introduction to Power Electronics Students Version 2

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POWER ELECTRONICS

CIRCUITS, DEVICES, AND

APPLICATIONS


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2

Relationship of Power Electronics


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POWER ELECTRONICS TECHNOLOGY

As the technology for the power semiconductor devices and integrated

circuit develops, the potential for applications of power electronics become

wider. There are already many power semiconductor devices that are

commercially available, however, the development in this direction is continuing.

The power semiconductor devices or power electronic converter fall

generally into four categories :

-AC to DC Converter (Controlled Rectifier)

-DC to DC Converter (DC Chopper)

-AC to AC Converter (AC voltage regulator)

-DC to AC Converter (Inverter)

The design of power electronics converter circuits requires design the

power and control circuits. The voltage and current harmonics that are generated

by the power converters can be reduced or minimized with a proper choice of the

control strategy.


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Power Electronics Application

Power Electronics defined as the application of solid-

state (devices) electronics for the control and

conversion of electric power.

Power electronics have already found an important

place in modern technology and are now used in a

great variety of high-power product, including heat

controls, light controls, electric motor control, power

supplies, vehicle propulsion system and high voltagedirect current (HVDC) systems.


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1.Uncontrolled turn on and off (Power Diode)

2.Controlled turn on uncontrolled turn off (Thyristors)

3.Controlled turn on and off characteristic (Power Transistor, BJT,

MOSFET, GTO, IGBT)

4.Continuous gate signal requirement (BJT, MOSFET, IGBT)

5.Pulse gate requirement (SCR(Silicon-Controlled Rectifier), GTO)

6.Bidirectional current capability (TRIAC)

7.Undirectionalcurrent capability (SCR, GTO, BJT, MOSFET,

IGBT)

POWER ELECTRONIC SWITCHING

DEVICES


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Diagram Block of Converters


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Diode Rectifiers. A diode rectifier circuit converts AC voltage into a fixed DC

voltage. The input voltage to rectifier could be either single phase or three phase.

AC to DC Converters. An AC to DC converter circuit can convert AC

voltage into a DC voltage. The DC output voltage can be controlled by varying

the firing angle of the thyristors. The AC input voltage could be a single phase or

three phase.

AC to AC Converters. This converters can convert from a fixed ac input voltageinto variable AC output voltage. The output voltage is controlled by varying

firing angle of TRIAC. These type converters are known as AC voltage

regulators.

DC to DC Converters . These converters can converte a fixed DC input voltage

into variable DC voltage or vice versa. The DC output voltage is controlled by

varying of duty cycle.


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Examples of

SomeApplications


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History of Power Electronics


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Types of Power Devices


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General Purposes Diodes


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Thyristors


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GTOs


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Power Ratings of Devices


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Ratings of Power Devices


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Devices Symbols and Characteristics


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Devices Symbols and Characteristics


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Applications of Power Devices


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Control Characteristics of Devices


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Control Characteristics of Devices


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Switching Characteristics


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Ideal Characteristics

Ideal

Characteristics


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Ac-dc Converter

AC to DC Converters-Single phase, half wave AC to DC converter

Input voltage

Output average voltage :

rms value of Output voltage :

Waveform of single-phase, half wave AC to DC converter


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Ac-dc Converter


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( ) (1 cos )moV

V average

1 sin 2(( ) )

22

m

rms

VV

Ac-ac Converter


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Ac-ac Converter

1/ 2

( )1 sin 2

22

mo rms

VV


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1. AC to DC Converters

-Single phase, Full wave AC to DC converter

The average output voltage can be found from :


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AC to DC Converters

Single phase, Full wave AC to DC converter

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AC to DC Converters

-Three-phase, Half wave AC to DC converter

If the phase voltage is : van= Vm Sin(wt). The

average output voltage for a continuous load current is :


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AC to DC Converters

-Three-phase, Half wave AC to DC converter


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1. AC to DC Converters

-Three-phase, Full Wave AC to DC converter


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2.DC-DC CONVERTER (DC Chopper)

In many industrial application , DC-DC converter is required to

convert a fixed-voltage DC source into a variable-voltage DC source.

Like a transformer, DC-DC converter can be used to step down or

step up a DC voltage source.

Application :

Traction motor control in electric automobiles, trolley cars, marine

hoists, forklift trucks, mine haulers, etc

Advantages :

High Efficiency and fast dynamic response


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2. DC-DC CONVERTER (DC Chopper)Principle Of Step-Down Operation

When the switch SW is closed for a time t1, the input voltage Vs appears across

the load Vo = Vs. If the switch remains off a time t2, the voltage across the load is

zero, Vo= 0.

The converter switch SW can be implemented by using Transistor, MOSFET,

GTO, IGBT, BJT, etc.


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The average output voltage is given by :

The average output current is given by :

The rms output voltage is given by :

=

Where : T is the chopping period

k = t1/T i s the duty cycle

f = 1/T is chopping frequency


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STEP UP DC to DC CONVERTER

When switch SW is closed for t1, the inductor current rises and energy is

stored in the inductor L. If the switch SW is opened for time t2, the energy

stored in the inductor is transferred to load through diode D1and the

inductor current falls.


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When this DC to DC converter is turned on switch SW is closed, the

voltage across the inductor L is :

And this gives the peak-to-peak ripple current in inductor as

The average output voltage is :


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BuckBoost Regulators

A buckboost Regulator provides an output voltage that may be lessthan or greater than the input voltage- hence the name "buck-boost";the output voltage polarity is opposite to that of the input voltage. thisregulator is also known as an inverting regulator.

The circuit operation can be divided into two modes. during mode 1,transistor Q1 is turned on and diode Dm is reversed biased. the inputcurrent, which rises flows through inductor L and transistor Q1. Duringmode 2, transistor Q1 is switched off and the current, which was flowingthrough inductor L, would flow through L, C, Dm, and the load. Theenergy stored in inductor L would be transferred to the load and theinductor current would fall until transistor Q1 is switched on again in

the next cycle. The equivalent circuit for the modes are shown in thenext slide.

The wave-forms for steady state voltages and currents of the buck-boost

regulator are also shown for a continuous load current.


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IGBT i d d C t


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IGBT in dc-dc Converter

( )o average S V V

d C t


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dc-ac Converter

1( )

40.90

2

so rms fundamental S

VV V


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RMS Values of Waveforms


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RMS Values of Waveforms


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Power Converter System


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Power Converter System

Drive System


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Drive System

Smart Power System


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Smart Power System

S


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Summary

The characteristics of the power devices play

a major role in the speed and effectiveness of

the power conversion.

Power electronics uses low power electronics(ICs), control, and switching power devices for

power converter and/or processing from one

form to another.

Documents

Introduction to Power Electronics Students Version 2