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20MTE03 – �Power Electronics and Drives

Unit 1: Power Electronics Devices:

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Concept of power electronics – Power semiconductor devices - Principle of operation – Steady state and switching characteristics of power diodes, power BJT, power MOSFET, IGBT – Firing circuit for thyristor- Steady state and switching characteristics of SCR –Two transistor model of SCR – DIAC – TRIAC – GTO

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Definition of Power Electronics

To convert, i.e to process and control the flow of electric power by

supplying voltages and currents in a form that is optimally suited

for user loads

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Power Processor

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Controller

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Load

measurement

reference

POWER

INPUT

POWER

OUTPUT

vi , ii

vo , io

Source

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Power Electronics (PE) Systems

  • To convert electrical energy from one form to another, i.e. from the source to load with:
    • highest efficiency,
    • highest availability
    • highest reliability
    • lowest cost,
    • smallest size
    • least weight.

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  • Static applications
    • involves non-rotating or moving mechanical components.
    • Examples:
      • DC Power supply, Un-interruptible power supply, Power generation and transmission (HVDC), Electroplating, Welding, Heating, Cooling, Electronic ballast

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  • Drive applications
    • intimately contains moving or rotating components such as motors.
    • Examples:
      • Electric trains, Electric vehicles, Air-conditioning System, Pumps, Compressor, Conveyer Belt (Factory automation).

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Application Examples

Static Application: DC Power Supply

FILTER

LOAD

DC-DC

CONVERTER

DIODE

RECTIFIER

AC voltage

AC LINE Voltage

(1 or 3 )

Φ

V

control

(derived from

feedback circuit)

Drive Application: Air-Conditioning System

Φ

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Power Semiconductor Devices

5

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7

Power Electronics Converters

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p-n Junction

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9

p-n Junction (Depletion Region)

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Power Diode

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Power BJT

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Power MOSFET

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Power IGBT

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c) Basic Structure showing parasitic transistors

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d) Exact equivalent circuit

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e) Circuit symbol

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Thyristor (Silicon Controlled Rectifier – SCR)

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tq (Turn off time) = trr (Reverse Recovery Time) + tgr (Gate Recovery Time)

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tc=Circuit turn off time = Provided by the power circuit

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Reversal of Anode current after t1 due to the presence of carriers stored in four layers

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Reverse recovery current removes the excess carriers at t3

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Thyristor (Silicon Controlled Rectifier – SCR)

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Thyristor (Silicon Controlled Rectifier – SCR)

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DIAC (Bidirectional Thyristor Diode)

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TRIAC

(Bidirectional Thyristor Diode with Three Terminal)

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GTO (GATE Turn Off Thyristor)

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Unit 2: AC-DC and DC-AC Converter

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Principle of phase controlled converter with R and RL load - Freewheeling diode- Single phase full wave converter – Single phase semi converter – Three phase semi converter – Three phase fully controlled converter – Applications of AC-DC converter. Introduction to inverter –Single phase and Three phase voltage source inverters –PWM inverters – Applications of DC-AC converter.

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Principle of phase controlled converter with R load

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Principle of phase controlled converter with RL load

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Principle of phase controlled converter with RL load & Freewheeling Diode

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Single Phase Full converter Mid Point Converter

(M-2 Connection)

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Single Phase Full converter Bridge Converter

(B-2 Connection)

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Single Phase Semi Converter