ee 442 642 introduction
TRANSCRIPT
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Power Electronics:
an OverviewY. Baghzouz
EE 442-642
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Power Electronics: an Overview
Power electronics is an interdisciplinary subject within electrical engineering.
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Power Electronic System
A power electronic system consists of power electronic switching
devices, linear circuit elements, digital circuits, microprocessors,
electromagnetic devices, DSPs, filters, controllers, sensors, etc.
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Power Converter
Converter is a general term - an AC/DC converter is
shown above.
Rectifier Mode of operation when power from AC to DC
Inverter Mode of operation when power from DC to AC
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Power Electronic Applications
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Example: Fluorescent Lighting
The line-frequency AC is converted to DC, then to high-frequency AC.
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Example: Switch-Mode Power Supply (modern)
Transistor is operated in switch mode (either fully ON
or fully OFF) at high switching frequency.
Electrical isolation achieved by high-frequency
transformer (smaller, lighter and more efficient)
Result: compact and efficient power supply
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Basic Principle of Switch-Mode Synthesis
Constant switching frequency fs pulse width controls the average value of voi L-C circuit filters the ripple, and allows the average
(dc value) to appear across the load
Simplified equivalent circuit
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Example: 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.
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AC Motor Drive
Converter 1 rectifies line-frequency AC into DC
Capacitor acts as a filter; stores energy and decouples
the two converters.
Converter 2 inverts dc to variable frequency ACas
needed by the motor.
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Pure Electric or Electric Hybrid Vehicles
Battery Charger: AC-DC converter
Electric Drive System: DC-AC Converter
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Example: Renewable Power Generation (PV)
PV Inverters: DC-AC Converters
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Example: Renewable Power Generation (Wind)
The rectifier-inverter converts variable-frequency AC to fixed line-frequency AC.
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Example: HVDC Transmission
Because of the large fixed costnecessary to convert ac to dc and then
back to ac, dc transmission is only
practical in specialized applications
long distance overhead power
transfer (> 400 miles)
long underwater cable power
transfer (> 25 miles)
providing an asynchronous means of
joining different power systems.
http://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jpg