EE432537 Power Electronics

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EE432/537 Power Electronics

• Satish Ranade

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What is Power Electronics?

• Conversion of Large Amounts of
• Electric Power and Energy
• ac to dc
• dc to ac
• dc to dc
• Amplification/Waveform synthesis
• .
• With fast control capability and
• High Efficiency

Background Celilo HVDC line Terminal
Sourcehttp//www02.abb.com/
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Is it different from electronics that I know?

• Is it different from electronics that I know?
• Yes, No, maybe so
• We want to build a widget that changes 24 V dc to
  12 V dc and supply a 6 ohm load
• a. resistive divider
• 50 efficiency, fire hazard, lousy voltage
  regulation, no control,smells when hot
• b. Zener
• Low efficiency, super voltage regulation over a
  specific range

12V -
24V -
6O
6O
12V -
2 A
2 A
24V -
6O
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Widget that changes 24 V dc to 12 V dc and supply
a 6 ohm load

• c. Linear voltage regulator
• 50 efficiency, super voltage regulation over a
  specific range

12V -
24V -
6O
Feedback
Ib such that VCE12V For Ic2A
Vo
Vset
Must dissipate 24 W!!!!!!!!
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Widget that changes 24 V dc to 12 V dc and supply
a 6 ohm load

• d. Switching regulator
• Transistor is used as a switch

Ib
Vce
24V
24V -
Vo -
6O
Vo
24V
Voavg12V
Ic
2A
Ib is a square wave at frequency f, period T
1/f Ib 0 for time T/2 do Transistor is off Ib
Ic/gain for time T/2 so transistor is saturated
and Vce0 i.e., transistor is on
Ideally Vce Ic 0 ! No loss in device 100
efficiency
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Widget that changes 24 V dc to 12 V dc and supply
a 6 ohm load

• d. Switching regulator
• Transistor is used as a switch

Ib
F i l t e r
Vce
24V
24V -
Vo -
6O
Vo
12V
Ib is a square wave at frequency f, period T
1/f Ib 0 for time T/2 do Transistor is off Ib
Ic/gain for time T/2 so transistor is saturated
and Vce0 i.e., transistor is on
Ideally Vce Ic 0 ! No loss in device 100
efficiency
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Widget that changes 24 V dc to 12 V dc and supply
a 6 ohm load

• d. Switching regulator
• 70 to 95 efficiency, reasonable voltage
  regulation, reasonable control,
• Noisy(switching) audible noise, electrical
  noise,
• electromagnetic interference, bulky

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Is it different from electronics that I know?

• Is it different from electronics that I know?

At high power levels semiconductors are used
almost exclusively as switches The device loss
(dissipation) is near impossible to manage (
temperature, cooling) if device is in the
linear region As a switch, losses in the
device are ideally zero! In practice there are
on-state and switching losses but things can be
managed In power electronics semiconductors are
used almost exclusively as switches
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Is it different from electronics that I know?

• Is it different from electronics that I know?
• In practice there are
• on-state and switching losses
• Devices are different
• and Larger

110 mm SCR
50 mm SCR Die
Transistor
Intel 386 microprocessor
My Monthly Paycheck
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Power Devices as Switches

• Diodes
• Conduct when forward biased
• Off when current is zero and reverse biased
• 10 kV, several kA ( but not both in same device)
• Thyristor family
• Silicon Controlled Rectifier(SCR)
• Conducts when forward biased and gate current
  pulse applied
• Blocks even if forward biased if already off and
  gate pulse is not applied
• Off if current reduced to zero and reverse biased

Anode A VAK - K Cathode
Ig G gate
Ia
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Power Devices as Switches
Anode A VAK - K Cathode

• Thyristor family
• GTO Gate turn off SCR
• Can be turned off once by application of negative
  gate pulse current and reduction of current to
  zero ( but gain is low)
• ETO
• GTO Mosfet cascodes provide higher turn off gain
  and switching frequency
• TRIAC
• Back-back SCR

Ig G gate
Ia
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Power Devices as Switches

• Bipolar Junction Transistor (BJT)
• Not much used any more
• Exception linear regulator
• Base current 0 off
• Base current Ic/ dc gain
• Saturates
• Vce small On

Collector
Base
Emmiter
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Power Devices as Switches

• Mosfet
• Gate Voltage 0 off
• Gate Voltage VgTh
• Saturates
• On resistance small On

Drain
Gate
Source
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Power Devices as Switches

• Insulated gate bipolar transistor(IGBT)
• Gate Voltage 0 off
• Gate Voltage VgTh
• Saturates
• VCE small On

Collector
Gate
Emmiter
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Power Devices as Switches

• Caveat
• Some switches have no control (diode), some
  control(turn on/ SCR) or complete control ( GTO,
  BJT, MOSFET, IGBT)
• This just says that means are available, with
  high gain, to initiate the turn on and turn off
  processes
• All circuits have some inductance current cannot
  be changed instantaneously. Thus there has a to
  be a way to reduce the current to zero and remove
  the enrgy stored in inductance
• This can happen naturally as in an ac circuit or
  through alternate paths for the current to flow
• If this current zero cannot be achieved, the
  switch that you just commanded to turn off will
  BLOW!

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Basic Structure
i
v
Forward Power Circuit
Sources/Loads
Sources/Loads
High Power
Signals (Low Power)
Feedback Control
Commands
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Basic Structure
Source
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Basic Structure
Source
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Example ApplicationA Photovoltaic system
connected to an electric utility grid

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So what are we going to do in this class?

• introduce students to electronic power control
• develop an understanding of the basic structure
  and analysis of power electronic systems
• explore and illustrate design and application.
• Build a useful power electronic system

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So what are we going to do in this class?
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FAQs

• How do I get an A?
• Put in 6 Hours/week, sometimes more
• Read the book (s)
• Turn in Homework
• Make your project work
• Ask questions

• How do I get an F?
• Dont show up for lab
• Dont do homework
• Let your study and project group down
• Root for Lobos and Miners