Parte 3 Elettronica di potenza: a.Sistemi elettronici

Parte 3 Elettronica di potenza: a. Sistemi elettronici di potenza – cap. 1 M h Mohan. b. Interruttori elettronici di potenza – cap. 2 Mohan. c. Raddrizzatori non controllati – cap. 5 Mohan Mohan. d. Raddrizzatori controllati – cap. 6 Mohan. Copyright © 2003 by John Wiley & Sons, Inc.

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Chapter 1 Power Electronic Systems

Copyright © 2003 by John Wiley & Sons, Inc.

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Power Electronic Systems

• Block diagram • Role of Power Electronics • Reasons for growth

Copyright © 2003 by John Wiley & Sons, Inc.

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Linear Power Supply

• Series transistor as an adjustable resistor • Low Efficiency • Heavy and bulky Copyright © 2003 by John Wiley & Sons, Inc.

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Switch-Mode Power Supply

• Transistor as a switch • High Efficiency • High-Frequency Transformer

Copyright © 2003 by John Wiley & Sons, Inc.

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Basic Principle of Switch-Mode Synthesis

• Constant switching frequency • pulse width controls the average • L-C filters the ripple

Copyright © 2003 by John Wiley & Sons, Inc.

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Application in 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 Copyright © 2003 by John Wiley & Sons, Inc.

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Scope and Applications

Copyright © 2003 by John Wiley & Sons, Inc.

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Power Processor as a Combination of Converters

• Most practical topologies require an energy storage element, which also decouples the input and the output side converters Copyright © 2003 by John Wiley & Sons, Inc.

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Power Flow through Converters

• Converter is a g general term • An ac/dc converter is shown here • Rectifier Mode of operation when power from ac to dc • Inverter Mode of operation when power from ac to dc Copyright © 2003 by John Wiley & Sons, Inc.

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AC Motor Drive

• Converter 1 rectifies line-frequency ac into dc • Capacitor acts as a filter; stores energy; decouples • Converter 2 synthesizes low-frequency ac to motor • Polarity of dc-bus voltage remains unchanged – ideally suited for transistors of converter 2 Copyright © 2003 by John Wiley & Sons, Inc.

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Matrix Converter

• Very general structure • Would benefit from bi-directional and bi-polarity switches • Being considered for use in specific applications Copyright © 2003 by John Wiley & Sons, Inc.

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Interdisciplinary Nature of Power Electronics

Copyright © 2003 by John Wiley & Sons, Inc.

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Chapter 2 Overview of Power Semiconductor Devices

Copyright © 2003 by John Wiley & Sons, Inc.

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Diodes

• On and off states controlled by the power circuit

Copyright © 2003 by John Wiley & Sons, Inc.

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Diode Turn-Off

• Fast-recovery diodes have a small reverse-recovery time

Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristors

• Semi-controlled device • Latches ON by a gate-current pulse if forward biased • Turns-off if current tries to reverse Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor in a Simple Circuit

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For successful turn-off, reverse voltage required for an interval greater than the turn-off interval

Copyright © 2003 by John Wiley & Sons, Inc.

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Generic Switch Symbol

• Idealized switch symbol • When Wh on, currentt can flow fl only l in i the th direction di ti off the th arrow • Instantaneous switching from one state to the other • Zero voltage drop in on-state • Infinite voltage and current handling capabilities Copyright © 2003 by John Wiley & Sons, Inc.

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Switching Characteristics (linearized)

Switching Power Loss is proportional p p to: • switching frequency • turn-on and turn-off times

Copyright © 2003 by John Wiley & Sons, Inc.

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Bipolar Junction Transistors (BJT)

• Used commonly in the past • Now used in specific applications • Replaced by MOSFETs and IGBTs Copyright © 2003 by John Wiley & Sons, Inc.

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Various Configurations of BJTs

Copyright © 2003 by John Wiley & Sons, Inc.

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MOSFETs

• Easy to control by the gate • Optimal for low-voltage operation at high switching frequencies • On-state resistance a concern at higher voltage ratings Copyright © 2003 by John Wiley & Sons, Inc.

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Gate-Turn-Off Thyristors (GTO)

• Slow switching speeds • Used at very high power levels • Require elaborate gate control circuitry Copyright © 2003 by John Wiley & Sons, Inc.

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GTO Turn-Off

• Need a turn-off snubber

Copyright © 2003 by John Wiley & Sons, Inc.

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IGBT

Copyright © 2003 by John Wiley & Sons, Inc.

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Comparison of Controllable Switches

Copyright © 2003 by John Wiley & Sons, Inc.

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Summary of Device Capabilities

Copyright © 2003 by John Wiley & Sons, Inc.

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Chapter 5 Diode Rectifiers

Copyright © 2003 by John Wiley & Sons, Inc.

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Diode Rectifier Block Diagram

• Uncontrolled utility interface (ac to dc)

Copyright © 2003 by John Wiley & Sons, Inc.

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A Simple Circuit

• Resistive load Copyright © 2003 by John Wiley & Sons, Inc.

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A Simple Circuit (R-L Load)

• Current continues to flows for a while even after the input voltage has gone negative Copyright © 2003 by John Wiley & Sons, Inc.

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A Simple Circuit (Load has a dc back-emf)

• Current begins to flow when the input voltage exceeds the dc back-emf • Current continues to flows for a while even after the input voltage has gone below the dc back-emf Copyright © 2003 by John Wiley & Sons, Inc.

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Single-Phase Diode Rectifier Bridge

• Large capacitor at the dc output for filtering and energy storage Copyright © 2003 by John Wiley & Sons, Inc.

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Diode-Rectifier Bridge Analysis

• Two simple (idealized) cases to begin with Copyright © 2003 by John Wiley & Sons, Inc.

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Redrawing Diode-Rectifier Bridge

• Two groups, each with two diodes

Copyright © 2003 by John Wiley & Sons, Inc.

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Waveforms with a purely resistive load and a purely dc current at the output

• In both cases, the dc-side voltage waveform is the same

Copyright © 2003 by John Wiley & Sons, Inc.

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Diode-Rectifier Bridge Input Current

• Idealized case with a purely dc output current Copyright © 2003 by John Wiley & Sons, Inc.

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Diode-Rectifier Bridge Analysis with ACSide Inductance

• Output current is assumed to be purely dc Copyright © 2003 by John Wiley & Sons, Inc.

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Understanding Current Commutation

• Assuming inductance in this circuit to be zero Copyright © 2003 by John Wiley & Sons, Inc.

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Understanding Current Commutation (cont.)

• Inductance in this circuit is included Copyright © 2003 by John Wiley & Sons, Inc.

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Current Commutation Waveforms

• Shows the volt-seconds needed to commutate current Copyright © 2003 by John Wiley & Sons, Inc.

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Current Commutation in Full-Bridge Rectifier

• Shows the necessary volt-seconds Copyright © 2003 by John Wiley & Sons, Inc.

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Understanding Current Commutation

• Note the current loops for analysis

Copyright © 2003 by John Wiley & Sons, Inc.

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Rectifier with a dcside voltage

Copyright © 2003 by John Wiley & Sons, Inc.

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Diode-Rectifier with a Capacitor Filter

• Power electronics load is represented by an equivalent load resistance Copyright © 2003 by John Wiley & Sons, Inc.

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Diode Rectifier Bridge

• Equivalent circuit for analysis on one-half cycle basis Copyright © 2003 by John Wiley & Sons, Inc.

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Diode-Bridge Rectifier: Waveforms

• Analysis using MATLAB Copyright © 2003 by John Wiley & Sons, Inc.

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Diode-Bridge Rectifier: Waveforms

• Analysis using PSpice Copyright © 2003 by John Wiley & Sons, Inc.

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Input Line-Current Distortion

• Analysis using PSpice Copyright © 2003 by John Wiley & Sons, Inc.

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Line-Voltage Distortion

• PCC is the point of common coupling Copyright © 2003 by John Wiley & Sons, Inc.

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Line-Voltage Distortion

• Distortion in voltage supplied to other loads Copyright © 2003 by John Wiley & Sons, Inc.

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Chapter 6 Thyristor Converters

• Controlled conversion of ac into dc Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Converters

• Two-quadrant conversion Copyright © 2003 by John Wiley & Sons, Inc.

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Primitive circuits with thyristors

Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Triggering

• ICs available Copyright © 2003 by John Wiley & Sons, Inc.

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Full-Bridge Thyristor Converters

• Single-phase and three-phase Copyright © 2003 by John Wiley & Sons, Inc.

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Single-Phase Thyristor Converters

• Two groups with two thyristor each Copyright © 2003 by John Wiley & Sons, Inc.

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1-Phase Thyristor Converter Waveforms

• Assuming zero ac-side inductance Copyright © 2003 by John Wiley & Sons, Inc.

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Average DC Output Voltage

• Assuming zero ac-side inductance Copyright © 2003 by John Wiley & Sons, Inc.

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Input Line-Current Waveforms

• Harmonics, power and reactive power Copyright © 2003 by John Wiley & Sons, Inc.

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1-Phase Thyristor Converter

• Finite ac-side inductance; constant dc output current Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Converter Waveforms

• Finite ac-side inductance Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Converter: continuous Mode

• This mode can occur in a dc-drive at light loads Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Converter Waveforms

• PSpice-based simulation Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Converter Waveforms: Discontinuous Conduction Mode

• PSpice-based simulation Copyright © 2003 by John Wiley & Sons, Inc.

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Thyristor Converters: Inverter Mode

• Assuming the ac-side inductance to be zero Copyright © 2003 by John Wiley & Sons, Inc.

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