Transcript Introduction to Power Electronics students version 2

POWER ELECTRONICS
CIRCUITS, DEVICES, AND
APPLICATIONS
Eng.Mohammed Alsumady
EPE 352
POWER ELECTRONICS
INTRODUCTION TO POWER
ELECTRONICS
ENG.MOHAMMED ALSUMADY
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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.
Power Electronics Application
• Power Electronics defined as the application of solidstate (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 voltage
direct current (HVDC) systems.
POWER ELECTRONIC SWITCHING
DEVICES
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)
Diagram Block of Converters
•
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 voltage
into 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
Some
Applications
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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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Voltage and Current Waveforms
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Diode Rectifiers
Vo ( average ) 
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2Vm

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Ac-dc Converter
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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 α
Ac-dc Converter
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Vo ( average) 
Vrms
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Vm

(1  cos  )
sin 2

((   ) 
)
2
2 
Vm
1
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Ac-ac Converter
1/ 2
Vo ( rms )
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Vm  1 
sin 2  

       2 
2 

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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 :
Where : T is the chopping period
k = t1/T is the duty cycle
The rms output voltage is given by :
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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Buck – Boost Regulators
•
A buck – boost Regulator provides an output voltage that may be less
than or greater than the input voltage- hence the name "buck-boost";
the output voltage polarity is opposite to that of the input voltage. this
regulator 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 input
current, which rises flows through inductor L and transistor Q1. During
mode 2, transistor Q1 is switched off and the current, which was flowing
through inductor L, would flow through L, C, Dm, and the load. The
energy stored in inductor L would be transferred to the load and the
inductor current would fall until transistor Q1 is switched on again in
the next cycle. The equivalent circuit for the modes are shown in the
next 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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Assuming that the inductor current rises linearly from I1 to I2 in time t1
or
and the inductor current falls linearly from
in time
or
where
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is the peak-to-peak ripple current of inductor L,From Eqs,
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Substituting
Substituting
Substituting
and
, the average output voltage is
into eq(5.78) yields
and
and
from eq(5.79) into eq(5.78) yields
Assuming a lossless circuirt,
and the average input current Is is related to the average output current
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by
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IGBT in dc-dc Converter
Vo( average)  VS
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dc-ac Converter
Vo1( rms  fundamental ) 
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4Vs
 2
 0.90VS
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UPS System
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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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Drive System
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Smart Power System
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Summary
• Power electronics uses low power electronics
(ICs), control, and switching power devices for
power converter and/or processing from one
form to another.
• The characteristics of the power devices play
a major role in the speed and effectiveness of
the power conversion.
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