Electrical Power Engineering 3 Power Electronics

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Electrical Power Engineering 3Power Electronics

• Dr Ewen Macpherson
• Dr Sasa Djokic
• Dr Markus Mueller

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Electrical Power Engineering 3

• Power Systems
• 14 lectures
• Power Electronics
• 10 lectures
• Powerway
• lab exercise, 2 mornings
• Castaway
• power system design exercise, weeks 6-11

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Electrical Power Engineering 3

• Assessment
• 60 Exam (Power Systems, Power Electronics)
• 15 Powerway
• 25 Castaway

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Electrical Power Engineering 3

• Powerway
• Starts week 2
• 2 mornings total
• Groups of 8-12
• Work in pairs

Check when you are due to attend! Prepare
Beforehand
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Electrical Power Engineering 3

• Castaway
• Design power system expansion in Sri Lanka
• Starts week 6
• Groups of 5 (approx.)
• Power System simulation (Powerworld)
• Costings required
• Presentation week 11

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Power ElectronicsDr Ewen Macpherson

• Lectures
• Monday 2-3 (every week)
• Examples Class
• Friday 2-3 (every 3rd week)
• Tutorials
• Wednesday 12-1 (weeks 4/5 and 9/10)

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Power Electronics

• Recommended Text
• Power Electronics Converters, Applications
  Design
• Mohan, Undeland Robbins (Wiley)
• (also used for Power Electronics 4)

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Power Electronics uses Semiconductor Devices to
process power (1W to 10,000MW)
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Devices
Diode p-n 8,000A, 6,500V
Bipolar transistor n-p-n (rarely used)
Thyristor p-n-p-n 7,000A, 12,000V
Triac 150A, 1,500V
Power MOSFET 100A, 1,200V
IGBT (insulated gate bipolar transistor) 2,400A, 6,500V
GTO (gate turn off thyristor) 4,000A, 6,500V
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Circuits

• Rectifier converts ac ? dc
• Inverter converts dc ? ac
• (dc) chopper converts dc ? dc
• ac controller converts ac ? ac
• General term for all Converter

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Applications

• Motor Speed Control

Speed controlled by varying Vdc
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Applications

• Uninterruptible Power Supplies (UPS)
• For critical loads where a mains failure is
  unacceptable
• Computers
• Safety systems (oil rigs)
• Emergency lighting (hospitals, cinemas)

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Applications

• Uninterruptible Power Supplies

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Applications

• High Voltage DC Power Transmission (HVDC)

• AC normally used, except
• bulk power transmission, long distances
• submarine cables
• 2000 MW cross-channel link, France-UK
• 500 MW Scotland-Ireland link

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Applications

• High Voltage DC Power Transmission (HVDC)

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Applications

• Electronic Power Supplies
• All electronic equipment needs a power supply

Worldwide market 20 billion?
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ThyristorSCR Silicon Controlled Rectifier

• 4 layer (p-n-p-n) device
• Switched on by applying gate pulse
• Stays on when gate signal removed, if current
  flowing through it
• Like a diode, current only flows in one direction

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Thyristor

• Reverse bias
• blocking
• reverse breakdown voltage exceeded - dies!

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Thyristor

• Forward bias
• blocking
• forward breakover voltage exceeded turns on

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Thyristor

• Forward bias gate pulse applied
• turns on
• stays on

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Thyristor Example Circuit

• Short gate pulse (3V, 20us, 50mA to 1A)
• turns on
• Gate pulse removed
• stays on if current gt holding current

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Thyristor

• Serious problem
• Not easily switched off
• Only switches off when current through it goes to
  zero (or drops below holding current)

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Power MOSFET

• Voltage controlled device
• Remove gate drive to turn off
• Very low gate current
• Very high speed (up to 10MHz)
• Up to 100A, 1,200V

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Gate Turn Off Thyristor (GTO)

• Current controlled device
• Turned off by negative gate pulse
• Very high gain at turn-on
• Low gain at turn-off (typically 4)
• Low frequency (up to 3 kHz)
• Up to 6.5kV, 4kA

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Insulated Gate Bipolar Transistor (IGBT)

• Combines high gate impedance of MOSFET with high
  current capability of BJT
• Medium frequency (up to 100 kHz)
• Up to 2.4 kA, 6.5 kV