Chapter 1 Power Electronic Systems
• Introduction
• Power Electronics versus Linear Electronics
• Applications
Electrónica de Potência
© 2008 Jose Bastos
Chapter 1 Introduction
1-1
Power Electronic Systems
• Block diagram
• Role of Power Electronics
• Reasons for growth
Electrónica de Potência
© 2008 Jose Bastos
Chapter 1 Introduction
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Linear Power Supply
• Series transistor as an adjustable resistor
• Low Efficiency
• Heavy and bulky
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© 2008 Jose Bastos
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Introduction: Switching Power Electronics
Linear regulator
Goal: control VX such that Vo=Vo,REF
Plus: simple accurate, high-bandwidth
Minus: low efficiency 

Pout Vo I o Vo


Pin Vin I o Vin
(example: Vin  15V, Vo  5V,   33%)
and power is dissipatedin transistor
Pdiss  VX I o   0
Electrónica de Potência
© 2008 Jose Bastos
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Switching power converters
Vo(t)
VIN
Add filtering
<Vo>
Vo(t)
VIN
<Vo>
Add real devices
Note:
-only lossless elements
-L, C energy storage
Electrónica de Potência
© 2008 Jose Bastos
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Switch-Mode Power Supply
• Transistor as a switch
• High Efficiency
• High-Frequency Transformer
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© 2008 Jose Bastos
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Basic Principle of Switch-Mode Synthesis
1
Voi 
TS
TS
ton
0 voi dt  TS vd
• Constant switching frequency
• pulse width controls the average
• L-C filters the ripple
Electrónica de Potência
© 2008 Jose Bastos
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Application in Adjustable Speed Drives
•
•
Conventional drive wastes energy across the throttling
valve to adjust flow rate
Using power electronics, motor-pump speed is adjusted
efficiently to deliver the required flow rate
Electrónica de Potência
© 2008 Jose Bastos
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Power Processor as a Combination of
Converters
• Most practical topologies require an energy
storage element, which also decouples the input
and the output side converters
Electrónica de Potência
© 2008 Jose Bastos
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Uninterruptable power supply - UPS
220 V
220 V
Batt
24V
~
load
• Converter 1 rectifies line-frequency ac into dc
• Capacitor acts as a filter; stores energy; decouples
• Converter 2 synthesizes line-frequency ac to load
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Power Flow through Converters
• Converter is a general term
• An ac/dc converter is shown here
• Rectifier Mode of operation when power from ac to dc
• Inverter Mode of operation when power from ac to dc
Electrónica de Potência
© 2008 Jose Bastos
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Scope and Applications
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Interdisciplinary Nature of Power Electronics
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