Electrical Power Engineering 3 Power Electronics Dr Ewen Macpherson Dr Sasa Djokic Dr Markus Mueller

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

Electrical Power Engineering 3 Assessment: 60% Exam (Power Systems, Power Electronics) 15% Powerway 25% Castaway

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

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

Power Electronics Dr Ewen Macpherson Lectures –Monday 2-3 (every week) Examples Class –Friday 2-3 (every 3 rd week) Tutorials –Wednesday 12-1 (weeks 4/5 and 9/10)

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

Power Electronics uses Semiconductor Devices to process power (1W to 10,000MW)

Devices Diodep-n8,000A, 6,500V Bipolar transistorn-p-n(rarely used) Thyristorp-n-p-n7,000A, 12,000V Triac150A, 1,500V Power MOSFET100A, 1,200V IGBT (insulated gate bipolar transistor) 2,400A, 6,500V GTO (gate turn off thyristor)4,000A, 6,500V

Circuits Rectifierconverts ac → dc Inverterconverts dc → ac (dc) chopperconverts dc → dc ac controllerconverts ac → ac General term for all: Converter

Applications Motor Speed Control: Speed controlled by varying V dc

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

Applications Uninterruptible Power Supplies:

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

Applications High Voltage DC Power Transmission (HVDC):

Applications Electronic Power Supplies: All electronic equipment needs a power supply Worldwide market: $20 billion?

Thyristor SCR – 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

Thyristor Reverse bias –blocking –reverse breakdown voltage exceeded - dies!

Thyristor Forward bias –blocking –forward breakover voltage exceeded – turns on

Thyristor Forward bias – gate pulse applied –turns on –stays on

Thyristor – Example Circuit Short gate pulse (3V, 20us, 50mA to 1A) –turns on Gate pulse removed –stays on if current > holding current

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

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

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

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