Advanced Electric Drives E-Book

Ned Mohan

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch
• Veröffentlichungsjahr: 2014

Seitenzahl: 184

Beschreibung

With nearly two-thirds of global electricity consumed by electric motors, it should come as no surprise that their proper control represents appreciable energy savings. The efficient use of electric drives also has far-reaching applications in such areas as factory automation (robotics), clean transportation (hybrid-electric vehicles), and renewable (wind and solar) energy resource management. Advanced Electric Drives utilizes a physics-based approach to explain the fundamental concepts of modern electric drive control and its operation under dynamic conditions. Author Ned Mohan, a decades-long leader in Electrical Energy Systems (EES) education and research, reveals how the investment of proper controls, advanced MATLAB and Simulink simulations, and careful forethought in the design of energy systems translates to significant savings in energy and dollars. Offering students a fresh alternative to standard mathematical treatments of dq-axis transformation of a-b-c phase quantities, Mohan's unique physics-based approach "visualizes" a set of representative dq windings along an orthogonal set of axes and then relates their currents and voltages to the a-b-c phase quantities. Advanced Electric Drives is an invaluable resource to facilitate an understanding of the analysis, control, and modelling of electric machines. * Gives readers a "physical" picture of electric machines and drives without resorting to mathematical transformations for easy visualization * Confirms the physics-based analysis of electric drives mathematically * Provides readers with an analysis of electric machines in a way that can be easily interfaced to common power electronic converters and controlled using any control scheme * Makes the MATLAB/Simulink files used in examples available to anyone in an accompanying website * Reinforces fundamentals with a variety of discussion questions, concept quizzes, and homework problems

Leseprobe

Copyright © 2014 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

Mohan, Ned.

    Advanced electric drives : analysis, control, and modeling using MATLAB/Simulink® / Ned Mohan.

            pages cm

        Includes index.

    ISBN 978-1-118-48548-4 (hardback)

1.  Electric driving–Computer simulation.    2.  Electric motors–Mathematical models.     3.  MATLAB.    4.  SIMULINK.    I.  Title.

    TK4058.M5783 2014

    621.460285'53–dc23

                                                                2014005496

Preface

When I wrote the first version of this textbook in 2001, my opening paragraph was as follows:

Why write a textbook for a course that has pretty much disappeared from the curriculum at many universities? The only possible answer is in hopes of reviving it (as we have been able to do at the University of Minnesota) because of enormous future opportunities that await us including biomedical applications such as heart pumps, harnessing of renewable energy resources such as wind, factory automation using robotics, and clean transportation in the form of hybrid-electric vehicles.

Here we are, more than a decade later, and unfortunately the situation is no different. It is hoped that the conditions would have changed when the time comes for the next revision of this book in a few years from now.

This textbook follows the treatment of electric machines and drives in my earlier textbook, Electric Machines and Drives: A First Course, published by Wiley (http://www.wiley.com/college/mohan).

My attempt in this book is to present the analysis, control, and modeling of electric machines as simply and concisely as possible, such that it can easily be covered in one semester graduate-level course. To do so, I have chosen a two-step approach: first, provide a “physical” picture without resorting to mathematical transformations for easy visualization, and then confirm this physics-based analysis mathematically.

The “physical” picture mentioned above needs elaboration. Most research literature and textbooks in this field treat dq-axis transformation of a-b-c phase quantities on a purely mathematical basis, without relating this transformation to a set of windings, albeit hypothetical, that can be visualized. That is, we visualize a set of hypothetical dq windings along an orthogonal set of axes and then relate their currents and voltages to the a-b-c phase quantities. This discussion follows seamlessly from the treatment of space vectors and the equivalent winding representations in steady state in the previous course and the textbook mentioned earlier.

For discussion of all topics in this course, computer simulations are a necessity. For this purpose, I have chosen MATLAB/Simulink® for the following reasons: a student-version that is more than sufficient for our purposes is available at a very reasonable price, and it takes extremely short time to become proficient in its use. Moreover, this same software simplifies the development of a real-time controller of drives in the hardware laboratory for student experimentation—such a laboratory using 42-V machines is developed using digital control and promoted by the University of Minnesota. The MATLAB and Simulink files used in examples are included on the accompanying website to this textbook: www.wiley.com/go/advancedelectricdrives.

As a final note, this textbook is not intended to cover power electronics and control theory. Rather, the purpose of this book is to analyze electric machines in a way that can be interfaced to well-known power electronic converters and controlled using any control scheme, the simplest being proportional-integral control, which is used in this textbook.

Ned Mohan

University of Minnesota

Notation

1.  Variables that are functions of time

v

,

i

,

λ

2.  Peak values (of time-varying variables)

, ,

3.  Phasors

,

4.  Space vectors

, , , , ,

For space vectors, the exponential notion is used where,

Note that both phasors and space vectors, two distinct quantities, have their peak values indicated by “.”

Subscripts

Stator phases

a, b, c

Rotor phases

A, B, C

dq

windings

d, q

Stator

s

Rotor

r

Magnetizing

m

Mechanical

m

(as in

θ

m

or

ω

m

)

Mechanical

mech

(as in

θ

mech

or

ω

mech

)

Leakage

ℓ

Superscripts

Denotes the axis used as reference for defining a space vector (lack of superscript implies that the d-axis is used as the reference).

*

Reference Value

Symbols

p

Number of poles (

p

 ≥ 2, even number)

θ

All angles, such as

θ

m

and the axes orientation (for example,

e

j

2

π

/3

), are in electrical radians (electrical radians equal

p

/2 times the mechanical radians).

ω

All speeds, such as

ω

syn

,

ω

d

,

ω

dA

,

ω

m

, and

ω

slip

(except for

ω

mech

), are in electrical radians per second.

ω

mech

The rotor speed is in actual (mechanical) radians per second:

ω

mech

 = (2/

p

)

ω

m

.

θ

mech

The rotor angle is in actual (mechanical) radians per second:

θ

mech

 = (2/

p

)

θ

m

.

fl

Flux linkages are represented by

fl

in MATLAB and Simulink examples.

Induction Motor Parameters Used Interchangeably

1Applications: Speed and Torque Control

There are many electromechanical systems where it is important to precisely control their torque, speed, and position. Many of these, such as elevators in high-rise buildings, we use on daily basis. Many others operate behind the scene, such as mechanical robots in automated factories, which are crucial for industrial competitiveness. Even in general-purpose applications of adjustable-speed drives, such as pumps and compressors systems, it is possible to control adjustable-speed drives in a way to increase their energy efficiency. Advanced electric drives are also needed in wind-electric systems to generate electricity at variable speed, as described in Appendix 1-A in the accompanying website. Hybrid-electric and electric vehicles represent an important application of advanced electric drives in the immediate future. In most of these applications, increasing efficiency requires producing maximum torque per ampere, as will be explained in this book. It also requires controlling the electromagnetic toque, as quickly and as precisely as possible, illustrated in Fig. 1-1, where the load torque TLoad may take a step-jump in time, in response to which the electromagnetic torque produced by the machine Tem must also take a step-jump if the speed ωm of the load is to remain constant.

Fig. 1-1

    Need for controlling the electromagnetic torque

T

em

.

1-1    History

In the past, many applications requiring precise motion control utilized dc motor drives. With the availability of fast signal processing capability, the role of dc motor drives is being replaced by ac motor drives. The use of dc motor drives in precise motion control has already been discussed in the introductory course using the textbook [1] especially designed for this purpose. Hence, our emphasis in this book for an advanced course (designed at a graduate level but that can be easily followed by undergraduates) will be entirely on ac motor drives.

1-2    Background

In the introductory course [1], we discussed electric drives in an integrative manner where the theory of electric machines was discussed using space vectors to represent sinusoidal field distribution in the air gap. This discussion included a brief introduction to power-processing units (PPUs) and feedback control systems. In this course, we build upon that discussion and discover that it is possible to understand advanced control of electric drives on a “physical” basis, which allows us to visualize the control process rather than leaving it shrouded in mathematical mystery.

1-3    Types of ac Drives Discussed and the Simulation Software

In this textbook, we will discuss all types of ac drives and their control in common use today. These include induction-motor drives, permanent-magnet ac drives and switched-reluctance drives. We will also discuss encoder-less operation of induction-motor drives.

A simulation-based study is essential for discussing advanced elec­tric drive systems. After a careful review of the available software, the author considers MATLAB/Simulink®