Post on 31-Mar-2015
Electrical Power Engineering 3
Power Electronics
Dr Ewen MacphersonDr 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 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)
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
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
Circuits
• Rectifier converts ac → dc
• Inverter converts dc → ac
• (dc) chopper converts dc → dc
• ac controller converts ac → ac
General term for all: Converter
Applications
Motor Speed Control:
Rectifier
Control Circuit
E
IaRa If
Vdc
3-phase
ac
Speed controlled by varying Vdc
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:
Rectifier Inverter Loadacdcac
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):
Rectifier
Inverter+
-
3 phaseac
3 phaseac
UK
FRANCE
Applications
Electronic Power Supplies:
All electronic equipment needs a power supply
Power Supply
+24 V dc+12 V dc+5 V dc0- 12 V dc
230 V50 Hz
Worldwide market: $20 billion?
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
Thyristor
ReverseBreakdown
Voltage
ForwardBreakover
Voltage
ReverseLeakageCurrent
LatchingCurrent
HoldingCurrent
ON
OFF
I
• Reverse bias– blocking
– reverse breakdown voltage exceeded - dies!
Thyristor
ReverseBreakdown
Voltage
ForwardBreakover
Voltage
ReverseLeakageCurrent
LatchingCurrent
HoldingCurrent
ON
OFF
I
• Forward bias– blocking
– forward breakover voltage exceeded – turns on
Thyristor
ReverseBreakdown
Voltage
ForwardBreakover
Voltage
ReverseLeakageCurrent
LatchingCurrent
HoldingCurrent
ON
OFF
I
• Forward bias – gate pulse applied– turns on
– stays on
Thyristor – Example Circuit
ControlCircuit
V
I
IG
R
A
CG
• Short gate pulse (3V, 20us, 50mA to 1A)– turns on
• Gate pulse removed– stays on if current > holding current
Thyristor
ControlCircuit
V
I
IG
R
A
CG
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