Optimal PWM switching strategy for single-phase AC-DC converters

252 Pages·2016·16.29 MB·English

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Institutional Repository
Optimal PWM switching
strategy for single-phase
AC-DC converters
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• A Doctoral Thesis. Submitted in partial ful(cid:28)llment of the requirements
for the award of Doctor of Philosophy of Loughborough University.
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OPTIMAL PWM SWITCHING STRATEGY FOR SINGLE-PHASE
AC-DC CONVERTERS.
by
Michael Njoroge Gitau
A Doctoral Thesis
in fulfilment for
the the
submitted partial of requirements award of
DOCTOR OF PHILOSOPHY
the
of
Loughborough University Technology.
of
October 1994
Supervisor: Mr. J. G. Kettleborough
Department Electronic Electrical Engineering
of and
Loughborough University Technology
of
© by M. N. Gitau, 1994.
This is dedicated
thesis to
my parents
Willis Gitau Njoroge late Dinah Wambura
and my mother
behalf.
for knowing for
the value of education and the many sacrifices they made on my
ACKNOWLEDGEMENTS.
Mr. J. G.
I like thanks to
would to take this opportunity to express my sincere
Kettleborough for his invaluable
guidance, encouragement and
my research supervisor
I like
patience throughout the course of research and preparation of this thesis. would also
Professor I. R. Smith, director for his
to thank
my of research useful comments and
during
the this thesis.
assistance preparation of
Thanks due to in the Power Electronics Research for their
are also my colleagues group
discussions held
the that together.
support and many useful we
The by is
to the technical
assistance given me staff greatly appreciated.
I The British Council, for financial
to their to
am very grateful my sponsor, support and
The University Nairobi, for leave
to
my employer, of granting me study enable me pursue
this
research.
SYNOPSIS.
The describes harmonic for
thesis elimination strategy suitable single-
an optimal selective
AC-DC drives. The is low-order
to
phase converter-fed traction objective eliminate supply
harmonics, including injected into due load-side
those the to
current supply current ripple.
Other has include
that the to
advantages switching strategy offer over phase-control
improved factor, VA for demand
supply power reduced consumption a given speed and
load, inductance.
torque
reduced and speed ripple and smaller armature circuit smoothing
The field boost dynamic drive is described.
the the
effect of current on response of also
It is field boost helps by increasing
that to the the
shown reduce speed rise-time
during
torque
electromagnetic available acceleration periods.
Closed-loop 4-quadrant DC drive is described between
control of a and a comparison made
PID-control feedback It is
the that
performance of and pseudo-derivative control. shown
feedback has
to
pseudo-derivative control several advantages offer, amongst which are ease
following load
tuning the torque
of of controller gains and a superior performance
disturbances.
A laboratory drive designed built,
to
size system was and and used validate simulation
for both feedback A
the
predictions switching strategy and pseudo-derivative control.
based hardware implementation both digital
the
microcontroller of switching strategy and a
feedback being
the
pseudo-derivative controller was adopted, with switching strategy
implemented
the
using an off-line approach of precalculating switching angles and storing
in look-up
these tables.
The dual-converter IGBTs
armature voltage controller comprises a employing as switching
devices. The IGBTs higher frequencies levels
use of allows switching at significant power
be if GTOs It drive design
than the
would possible were used. also simplifies gate circuit
the to
and minimises need use snubber circuits.
TABLE OF CONTENTS.
Page No.
LIST OF PRINCIPAL SYMBOLS.
vi
1
CHAPTER ONE: INTRODUCTION.
CHAPTER TWO: REVIEW OF CONVENTIONAL 2-QUADRANT
CONVERTER-FED DC DRIVES. 5
2.1 Definition drive 6
of performance parameters.
6
2.1.1 Motor
performance parameters.
2.1.2 Supply-side 7
performance parameters.
2.1.3 Converter load-side 8
performance parameters.
2.1.3.1 Fourier
series representation of converter output
9
voltage.
2.2 Conventional 9
phase-controlled converters.
2.2.1 Output 10
performance parameters.
2.2.2 Supply-side 11
performance parameters.
2.3 Sequence-controlled 11
converters.
2.4 Sinusoidal PWM-controlled 14
converters.
CHAPTER THREE: THEORETICAL ANALYSIS OF CONVENTIONAL
4-QUADRANT CONVERTER-FED DRIVES. 22
3.1 Conventional dual-converter drives. 23
phase-controlled
3.1.1 Operation
24
without circulating current.
3.1.1.1 Discontinuous load 24
current.
3.1.2 Operation 26
with circulating current.
3.2 Natural PWM-controlled dual-converter drives. 27
sinusoidal
3.3 Derivation function.
28
of converter switching
3.3.1 Sinusoidal PWM-control function. 29
strategy switching
1
DC
PWM-CONTROLLED
CHAPTER FOUR: OPTIMAL 4-QUADRANT
33
DRIVES.
34
4.1 Performance
parameters.
35
4.2 Effects load-side
the current.
of current ripple on supply-side
35
drives.
4.2.1 PWM-controlled
converter-fed
drives. 38
4.2.2 Phase-controlled
converter-fed
38
4.3 Selective harmonic (SHE)
elimination switching strategies.
39
4.3.1 Ideal load-side
current conditions.
40
4.3.2 Load
current with significant second-harmonic ripple.
44
4.3.3 Modified function.
switching
51
4.4 Converter
voltage gain.
CHAPTER FIVE: MATHEMATICAL MODELLING OF 4-QUADRANT
58
CONVERTER DRIVES.
58
5.1 Separately-excited DC
motor equations.
58
5.1.1 Armature
circuit equations.
59
5.1.2 Electrodynamic
equations.
60
5.1.3 Field
circuit equations.
5.1.4 Field Field boost. 60
current control:
5.2 General drive 63
the
analysis of converter-motor system.
5.2.1 Mathematical 67
model of speed controller.
67
5.3 Combined
converter-motor system.
5.3.1 Power 68
mode.
5.3.2 Free-wheeling 70
mode.
5.3.3 Coasting 71
mode.
5.3.4 Regeneration 72
mode.
5.4 Effects 74
of commutation overlap.
CHAPTER SIX: POWER AND ASSOCIATED AUXILLIARY CIRCUITRY. 82
6.1 Switch 82
selection and sizing.
6.1.1 SCR (Thyristor). 82
6.1.2 GTO.
82
11
83
6.1.3 IGBT
84
6.2 Switch losses heatsink
and sizing.
84
6.2.1 IGBT loss
conduction
84
loss
6.2.1.1 IGBT
switching
85
6.2.2 Series fast diode.
recovery
85
6.2.2.2 Heatsink
sizing.
86
6.3 DC
smoothing choke.
86
6.4 Protection
circuits.
86
6.4.1 Overvoltage
snubbers.
6.4.1.1 RC design. 87
overvoltage snubber
6.4.1.2 Group 88
suppression.
6.4.2 Current interventionist 88
system.
88
6.4.2.1 Current
monitoring circuit.
6.4.2.2 Dead-band 89
current comparator.
6.5 Synchronisation 89
circuit.
90
6.6 Auxilliary
power supplies.
6.7 IGBT drive 90
gate circuitry.
6.7.1 Isolated drive 90
gate power supplies.
6.7.1.1 DC design. 90
transformer
power supplies
6.7.1.2 Voltage filter for DC 92
unregulated supply.
6.7.2 Isolated drive 93
gate circuit.
CHAPTER SEVEN: CLOSED-LOOP SPEED CONTROL. 102
7.1 DC 102
motor model.
7.1.2 Operation field boost during 103
transients.
with speed
7.2 Controller 103
model.
7.2.1 Current 104
regulation.
7.2.2 Analog PID-controller. 106
7.2.2.1 Determining 107
the
proportional gain.
7.2.2.2 Determining derivative 109
the
gain.
7.2.2.3 Determining integral 110
the
gain.
7.3 Digital PID-Controller. 111
7.4 Analog feedback 114
pseudo-derivative controller.
7.4.1 Digital feedback
116
pseudo-derivative controller.
111
130
CHAPTER EIGHT: DRIVE CONTROL USING A MICROCONTROLLER.
8.1 Introduction Intel 80C196KC. 131
to the
8.1.1 CPU. 131
8.1.2 Memory Map. 131
8.1.2.1 Register File. 131
8.1.2.2 Special Function Registers. 132
8.1.3 High Speed Input/Output 132
unit.
8.1.3.1 Timers. 132
8.1.3.2 High Speed Input 133
unit.
8.1.3.3 High Speed Output 133
unit.
8.1.3.4 Software 134
timers.
8.1.4 Interrupt 134
structure.
8.2 Hardware implementation drive. 134
the
of microcontroller
8.2.1 System 135
clock.
8.2.2 Speed 135
monitoring circuit.
8.2.2.1 Speed interfacing 136
encoder circuit.
8.2.2.2 Digital 137
speed measurement scheme.
8.2.2.3 Demand interfacing 138
speed circuit.
8.2.3 PWM interface
switching pattern and control signal processing
logic 139
circuit.
8.2.4 Analog 141
speed signal circuit.
8.2.5 Speed display 141
circuit.
8.3 Software design.
8.3.1 Open-loop
142
control.
8.3.1.1 HSI Data Available interrupt 143
service routine.
8.3.1.2 EXTINT 1 interrupt 144
service routine.
8.3.1.3 HSO interrupt
145
service routine.
8.3.2 Closed-loop
146
control.
8.3.2.1 HSI Data Available 146
service routine.
CHAPTER NINE: ANAYSIS OF DRIVE PERFORMANCE. 165
9.1 Load-side
165
performance parameters.
iv