2001 Thesis Project A5 Gareth S Roberts
Table of Contents
Abstract………………………………………………………… i
Acknowledgements………………………………………………. ii
List of Figures and Illustrations………………………………… iii
Chapter 1 – Need/Basis for the thesis project………………… 1
1.1. Project Specification…………………………………. 1
1.2. Available resources………………………………… 1
1.3. What are hyper and electric cars?……………………. 1
1.4. Why do we use an Induction motor?…………………. 3
Chapter 2 – Literature Review………………………………… 5
2.1. The Hybrid concept………………………………… 5
2.2. Induction Motor Theory and Practice………………… 5
2.3. Power Electronics…………………………………… 6
2.4. Field-Orientated Control……………………………… 7
2.5. MATLAB analysis……………………………………. 8
Chapter 3 – The Hardware Design………………………………. 9
3.1. The basic control format…………………………… 9
3.2. The existing motor controller……………………… 10
3.3. Current sensing module……………………………… 11
3.4. The speed sensor…………………………………… 12
2001 Thesis Project A6 Gareth S Roberts
Chapter 4 – The Induction Motor………………………………. 14
4.1. The fundamental operating principles for an
Induction Motor…………………………………… 14
4.2. The Electrical principles of an Induction Motor…… 14
4.3. Torque/Speed generation for an Induction Motor…… 16
Chapter 5 – Field-Orientated Control (FOC)…………………… 19
5.1. An introduction…………………………………… 19
5.2. Transformation between reference frames…………. 20
5.3. The PI controller……………………………………. 21
5.4. PWM – Pulse-Width Modulation………………… 22
5.5. The Overall Design…………………………………. 24
5.6. Conclusions drawn from Chapter 5………………… 26
Chapter 6 – The MATLAB design…………………………… 27
6.1. MATLAB – An introduction……………………… 27
6.2. MATLAB simulation design……………………… 27
6.2.1 Field Orientated Control using SIMULINK……… 28
6.2.2 The Current Controller……………………………… 32
6.2.3 The Motor Model…………………………………… 32
6.3. Simulation of the MATLAB design………………. 34
6.3.1. Speed response analysis……………………………. 34
6.3.2. Analysis of the Field-Orientated Section of the
Design……………………………………………… 38
6.3.3. The significance of feedback……………………… 41
6.4. The conclusions drawn from Chapter 6……………. 42
2001 Thesis Project A7 Gareth S Roberts
Chapter 7 – The Software Design……………………………… 43
7.1. A basic overview of how the software is
organized…………………………………………… 43
7.2. The Main Program – The Field-Orientated Control
Portion of the Software Design……………………. 44
7.2.1. The torque controller & Field Weakening………… 45
7.2.2. Calculation of iqs, ids, cos(rho) and sin(rho)………. 48
7.2.3. The Current Controller section of the software design 50
7.3. The PWM Interrupt Service Routine………………. 51
7.4. The Encoder Interrupt Service Rountine………… 55
7.5. A/D conversion……………………………………. 57
7.6. Concluding remarks………………………………. 58
Chapter 8 – Final Project Performance and Evaluation…… 59
8.1. PWM test program……………………………… 59
8.2. Encoder test program #1………………………… 61
8.3. Encoder test program #2………………………… 62
Chapter 9 – Conclusion…………………………………………. 64
9.1 Summary and Conclusion………………………… 64
9.2 Future work…………………………………………. 64
Bibliography……………………………………………………… 66
APPENDIX A – The proposed software design
APPENDIX B – PWM test program
2001 Thesis Project A8 Gareth S Roberts
APPENDIX C – Encoder detection test program #1
APPENDIX D – Encoder detection test program #2
APPENDIX E – The schematics for the Motor Controller board
2001 Thesis Project A9 Gareth S Roberts
List of Figures
Figure 1.1 – The Honda Insight
Figure 1.2 – The parallel hybrid car
Figure 3.1 – The basic physical design
Figure 3.2 – The existing motor controller board
Figure 3.3 – The current sensing module
Figure 4.1 – The per phase representation of an Induction motor in steady state
Figure 4.2 – The torque/speed curve
Figure 4.3 – Field weakening
Figure 5.1 – The transformation of the stationary reference frame to the rotating
reference frame
Figure 5.2 – The PI controller
Figure 5.3 – Leg A of the full-bridge inverter
Figure 5.4 – PWM VSI schematic and waveforms
Figure 5.5 – The complete FO controller design in a block representation
Figure 6.1 – The Look-up Table
Figure 6.2 – The complete SIMULINK design
Figure 6.3 – The FO_controller block
Figure 6.4 – The dqe2abc block
Figure 6.5 – The Inverse_Park_Transform Block
Figure 6.6 – The Inverse_Clarke_Transform Block
Figure 6.7 – The Current_controller block
Figure 6.8 – The Induction machine in stationary qd0
Figure 6.9 – The MATLAB speed simulation results
Figure 6.10 – The speed response of the control system where the proportional
gain is increased
Figure 6.11 – The speed response of the system with a proportional gain of 90
Figure 6.12 – cos(rho) and sin(rho) signals
Figure 6.13 – The ids and iqs signal curves over time
Figure 6.14 – The applied signal to phase A of the Induction motor and the drawn
current on phase A
Figure 6.15 – The speed response of the system without feedback
Figure 7.1 – The flow chart for this thesis project
Figure 7.2 – The torque controller
Figure 7.3 – Graphical representation of the trapezoidal rule
Figure 7.4 – Limiting the integration result
Figure 7.5 – Calculation of the required rotor flux: Lambdare_r
Figure 7.6 – The results of using the field-orientated technique
Figure 7.7 – Overflow prevention of the slip-angle
2001 Thesis Project A10 Gareth S Roberts
Figure 7.8 – Demonstration of the development of the slip angle over time
Figure 7.9 – Flow-chart demonstrating how the current controller section works
Figure 7.10 – PWM waveforms with dead-band
Figure 7.11 – The PWM infrastructure
Figure 7.12 – The Peripheral Interrupt Expansion Block Diagram
Figure 7.13 – The encoder detection infrastructure
Figure 7.14 – The flow-chart for Encoder detection
Figure 8.1 – Experimentally measured PWM waveforms on the CRO
2001 Thesis Project 1 Gareth S Roberts
1. Need/Basis for the thesis project
1.1. Project Specification
To design a control scheme for a three-phase induction motor drive. This induction
motor drive is proposed to be incorporated into a “hybrid car” or an “electric car”.
1.2. Available resources
• Motor controller board. This was constructed by 1999 thesis student, Mr.
David Finn and was designed to control a brush-less DC motor. However, by
constructing a feedback loop that can detect the outputs of an induction motor, we
can use this motor controller to control an induction machine.
• TMS320F243 DSP controller. This is manufactured by the Texas Instruments
Company and is one of the major components on David Finn’s motor controller.
For this thesis project, a software control design has to be devised that will
correctly control the DSP controller to meet specifications.
• DC bus. This DC bus is made available from SUNSHARK battery packs,
12V
DC
to 140V
DC
. ~40 V
DC
is the most compatible voltage supply for the motor
controller that will be used for this thesis.
• Induction motor. Three-phase, 0.5kW, 4-pole machine. This induction motor
is only used for the prototype design presented in this thesis.
1.3. What are hybrid and electric cars?
Under the supervision of Dr. Geoff Walker, a group of Computer Science and Electrical
Engineering Ph.D. students at the University of Queensland are constructing a hybrid or
an electric car. Both of these types have been inaugurated due to the increasing concerns
of “global warming”. An electric car simply uses an electric engine as the means of
motivating the car instead of the conventional combustion engine. These cars have not
yet been released in the commercial world because the electric engine system (including
2001 Thesis Project A2 Gareth S Roberts
batteries) does not provide the same power per weight as the combustion engine from the
research to date [8].
Figure 1.1. The Honda Insight [14]
Figure 1.2. The internal infrastructure of a parallel hybrid car [14]
A hybrid car was released commercially this year. It combines two or more sources of
power; the gasoline-electric hybrid car, for instance, does just this. The electric engine
2001 Thesis Project A3 Gareth S Roberts
boosts acceleration and reduces demand on the petrol engine, saving fuel and improving
performance in the process [14]. While cruising, power comes solely from the petrol
engine. When the vehicle is coasting downhill, or during deceleration and braking, the
electric motor recharges a nickel metal hydride battery pack. During periods when the
vehicle is stationary, the engine automatically shuts down to save fuel, and then starts up
again when the throttle is pressed. The Honda “Insight” for instance consumes less than
half the fuel of a conventional small car and harmful exhaust emissions are lowered by a
significant 90% [14]. This model features a 10kW electric motor that delivers power to
the front wheels via a five speed manual gearbox.
1.4 Why do we use an Induction motor?
For this application, the only external input for the electric motor applied by the user is
the accelerator; which is essentially a variable torque input. There are two existing
options for an electric motor: the “Direct current (DC)” type or the “Induction” type.
Induction motors are universally used in industry because of their high robustness,
reliability, low price and high efficiency (up to 80% [15]). However, the brush-less DC
motor has been, traditionally, the more attractive option for variable torque control. This
is because the torque can be controlled by varying the “armature current (i
a
)”, while the
flux can be controlled by varying the “field/exciting current (i
x
)”. These two quantities
operate in a decoupled manner, which is highly advantageous from a design perspective.
Also, an induction machine has been difficult to control due to its complex mathematical
model, its non-linear behavior during the saturation effects and the electrical parameter
oscillation that depends on the physical influence of temperature [15].
However, the recent fruition of “digital signal processors (DSPs)” has swung the
pendulum toward the induction motor for torque control. These high computational
power silicon devices have made it possible to realize far more precise digital control
algorithms. Field Orientated Control (FOC), for instance, is a vector control method that
demonstrates the capability of performing direct torque control. FOC provides an
induction motor every advantage that DC machine control can have, while freeing itself
from mechanical commutation drawbacks [9]. It is anticipated that the application of the
2001 Thesis Project A4 Gareth S Roberts
correct control algorithm combined with the inherent efficiency and power potential will
make this design very compatible for use in a hybrid car. Additionally, the induction
machine makes execution of “regenerative braking” relatively simple. Regenerative
braking is a means of using the induction machine as a brake. It is anticipated that the
outcomes from this thesis project support the claim that an induction motor is a better
means of motivating a hybrid or an electric car.
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