MCT 4333Power Electronics

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Reference BooksRequired• Rashid M. H., (2004), Power Electronics:

Circuits, Devices, and Applications, 3rd Edition, Prentice-Hall.

Recommended• Agrawal J. P., (2001), Power Electronics

System: Theory and Design, Prentice-Hall.• Hart D. W., (1997), Introduction to Power

Electronics, Prentice-Hall. • Mohan N., Undeland T. M., and Robbins W. P.,

(2003), Power Electronics: Converters, Applications, and Design, John Wiley and Sons.

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Method of Evaluation

• Quizzes 15 %

• Home Work / Project 20 %

• Midterm Examination 25 %

• Final Exam 40 %

• Total 100 %

Course Outline:

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Contents

Definition of power electronics,Power semiconductor devices, Control characteristics of power semi-conductor devices, Power losses in switches, Types of power electronics circuits.Applications of power electronics.

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Power Electronics

ControlAnalog/ Digital

ElectronicsDevice/Circuit

Power equipmentstatic/rotating

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• Power electronics involves the study of electronic circuits intended to control the flow and conversion of electric power. Thus power electronics combine powerpower, electronicselectronics and controlcontrol.

• The applications of solid-state and linear devices for the control and conversion of electric power.

Power Electronics

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Power Electronics System

• Consists of an input source and a load. • One or more converters for power conversion. • Power semiconductor devices, which are used

as switches to perform the power conversion. • A gating circuit to generate the gate drive signals

for the switching devices. • A feedback control circuit implemented either in

analog and/or digital electronics. • One or more static-switches acting as a circuit

breaker.

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Power Electronics System

Static Applications: No rotating or moving mechanical components. Examples: DC Power supply, Un-interruptible power supply, Power generation and transmission (HVDC), Electroplating, Welding, Heating, Cooling, Electronic ballast.

Drive Applications: for driving moving or rotating equipment such as motors. Examples: Electric trains, Electric vehicles, Air-conditioning system, Pumps, Compressor, Conveyer Belt (Factory automation).

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Control Center

Micro-Turbine Hospital Commercial

Building

Fuel Cell Smart House Performance

Building

Combined Heat and PowerPlant (CHP)FactoryCommercial BuildingHouseApartment Building

Wind Power Plants Village Commercial

Building

Central PowerStation Solar Power Plants

CHP House

Importance of PES• Increasing applications of Power Electronic Equipment in Power Systems

– Availability of high power semiconductor devices

– Decentralized renewable energy generation sources

– Increased power transfer with existing transmissionsystem

– Effective control of power flow needed in a deregulated environment

– Norms for Power quality Future Power System

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Power Semiconductor Devices

Power devices are the key elements of a power converter. The commonly used devices are:

(1) Power Diode

(2) Silicon-Controlled Rectifier (SCR) or Thyristor

(3) Gate Turn-off Thyristor (GTO)

(4) Power Bipolar Junction Transistor (Power BJT)

(5) Power Metal-Oxide Field-Effect Transistor (Power MOSFET)

(6) Insulated-Gate Bipolar Transistor (IGBT)

(7) Mos-Controlled Thyristor (MCT)

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Power semiconductor operating regions

voltage vs

frequency;

current vs

frequency.

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Power Electronic Applications• Distributed generation (DG)

– Renewable resources (wind and photovoltaic)– Fuel cells and micro-turbines– Storage: batteries, super-conducting magnetic energy storage,

• Power electronics loads: Adjustable speed drives• Power quality solutions

– Dual feeders– Uninterruptible power supplies– Dynamic voltage restorers

• Transmission and distribution (T&D)– High voltage dc (HVDC) and medium voltage dc– Flexible AC Transmission Systems (FACTS): Shunt and Series

compensation, and the unified power flow controller

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Function of Power Electronics in Utility Applications

• Enabling technology providing interface between two (ac/dc) electrical systems

Interconnection of two asynchronous ac systems – dc to ac conversion is required to connect fuel cells or

photovoltaic to the utility grid

Converter

Controller

Source Load

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Role of Power Electronics in Important Utility Applications

• Distributed Generation (DG) ApplicationsPower electronic interface depends on the source characteristics

AC

DC

DC

AC

Wound rotorInduction Generator

Generator-sideConverter

Grid-sideConverter

WindTurbine

IsolatedDC-DC

Converter

PWMConverter

Max. Power-point Tracker

Utility1f

Wind Power Generation with Doubly Fed Induction Motors

Photo-voltaics Interface

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Role of Power Electronics in Important Utility Applications

• Power Electronic Loads: Adjustable Speed Drives

Controller

Motor

Utility

Rectifier

Switch-modeConverter

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Ideal PE System

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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Inductors and Capacitors in PE

Inductor: V = L di/dt

• The current in an inductor cannot change instantaneously!

Capacitor: i = C dV/dt

• The voltage across a capacitor cannot change instantaneously!

These passive components are fundamental to the operation of all power electronics.

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Other CharacteristicsBidirectional current capability: TRIAC, RCTUnidirectional current capability: SCR, BJT, MOSFET, etc

See table 1.3 and Figure1.9 of the text book for more information.

Self Study: Characteristics of Ideal switches

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The Practical Switch

1. Limited power handling capabilities, limited conduction current in the on-state, and limited blocking voltage in the off-state.

2. Limited switching speed caused by the finite turn-on and turn-off times. This limits the maximum operating frequency of the device.

3. Finite on-state and off-state resistances, that is, forward voltage drop exists when in the on-state, and reverse current flow (leakage) exists when in the off-state.

4. Because of characteristics 2 and 3, the practical switch experiences power losses in the on- and off-states (known as conduction loss), and during switching transitions (known as switching loss).

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Losses in Power ElectronicsIn semiconductor components:

• Switching losses

• Conduction losses

In passive components (C & L):

• Effective series resistance

Typical efficiencies are in the range of 90-99% for each conversion stage, depending on the exact converter topology.

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Power switch losses

• Why it is important to consider losses of power switches?– to ensure that the system operates reliably under

prescribed ambient conditions, – so that heat removal mechanism (e.g. heat sink,

radiators, coolant) can be specified. Losses in switches affects the system efficiency

– Heat sinks and other heat removal systems are costly and bulky. Can be substantial cost of the total system.

– If a power switch is not cooled to its specified junction temperature, the full power capability of the switch cannot be realized.

Main losses:– forward conduction losses,– blocking state losses– switching losses

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Switching Power Losses

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Conclusions

• Power electronic System and its scope, applications and importance

• Control Characteristics of PE devices.

• Losses in solid state switches

• Types of Power Electronic Circuits.

• Properties of Capacitor and Inductor in PE circuits.