Automotive Control and Simulation
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Module AE03 – Automotive Control and Simulation
Design Exercise – Cruise Control
Cruise control systems are designed to reduce driver workload on long journeys by maintaining a
constant speed. With cruise control, drivers can easily maintain a constant speed without the need
to keep the right feet on pedals. (Modern adaptive cruise control also incorporates systems to
reduce the speed to avoid collisions, though this is beyond the scope of this exercise – very similar
principles would of course be involved!)
In this exercise, you are given a model for the powertrain for a novel electric vehicle and you are
asked to design an adaptive cruise control for it. Your input is a ‘wheel torque demand’ signal –
controlling the total torque applied at the wheels. This can be positive or negative, and the
transition between electronic braking and mechanical braking is seamless. You will be asked to
explore the model in the exercise, and to explain how it works and what it is representing. The
output is a sensor that measures speed in km/h. The sensor – like most real-world sensors – is
‘noisy’.
You will be taken through a design exercise through a series of five questions. You will start by
obtaining models suitable for control design, then you will design and test controllers with different
techniques. At the end of the assignment, you should have a good practical understanding of the
concepts required to design a basic feedback controller. If you look at the intended learning
outcomes for this module, you will see that they are covered in full by this assignment. As well as
being a ‘summative’ assessment, I hope it will be a useful deep learning opportunity.
Handing this work in
I ask students to submit a write-up on this assignment. It’s not a formal ‘report’ – it just needs to
have answers to the questions. You will need to include enough of your working – your thoughts,
calculations, MATLAB code snippets and screenshots of Simulink models – so that I can see that
you’ve thoroughly answered each question. I cannot mark what I do not see, so if in doubt, please
put it in. (It must all be legible: if it is too small for me to read or otherwise hard to view when
printed out, it will be ignored.)
You do not need to hand in a printed copy, and you do not need to hand in electronic copies of your
MATLAB and Simulink files. (You should give enough detail on these in your write-up.)
You must upload your work on this assignment via Canvas as instructed there. If your work is late,
you risk having your mark capped at 50% or – if it’s very late – failing with a zero mark. I don’t make
these rules, and I don’t have any flexibility to change them – sorry.
Please contact your Student and Academic Support Lead with any questions about handing work in.
You have a week to complete the assignment. Please use this time wisely. Candidates who leave
this assignment to the last minute often struggle, sometimes with disastrous consequences. It’s
considered good teaching practice to allow you some time ‘on your own’ to try to tackle the
problem, but we will be willing to provide help to students with any questions. Please do make good
use of this opportunity. We will offer specific sessions and a discussion forum to help you.
Often, when students are struggling, it’s only a small problem that is getting in their way of their
progress, and I can usually very quickly help. Remember that this exercise is supposed to be ‘hard’.
But please also remember that most students do succeed, and their hard work pays off with good
results. This exercise is a key part of your deep learning: hopefully, you will enjoy it, too.
How this work will be marked
Please bear in mind the university mark scheme for subjective assignments. Design is a subjective
task, and there is rarely a single unique answer to a question.
To get ‘excellent’ marks on a question, it is necessary to ‘push the boundaries’ in your answer.
Candidates who get excellent marks typically display an unusual level of thoroughness and insight.
Obviously, I’d encourage you to strive towards this if you can. If you don’t quite manage this, a
reasonably thorough attempt with no serious mistakes can get a ‘very good’. Work with more
serious mistakes or omissions, but that still indicates a reasonable understanding will be graded as
‘good’ or ‘satisfactory’. Incomplete answers and seriously incorrect work are graded at ‘poor’ or
lower. Each question is graded separately: the marks are added to get a total mark, then rounded to
the nearest whole number.
Candidates should attempt any question: bear in mind that an absent answer gets a zero mark, even
a ‘poor’ answer can be worth up to 40% of the question’s marks. It really is worth having a go at
every question.
The course director has set the minimum mark for this assignment at 50%. Please try to pass first-
time: at Cranfield, retakes are an emergency provision, and not ‘normal’.
Questions
1. A sensor system for measuring electric current has the following schematic:
a) Write down the differential equations describing the relationship between the measured
current and the output voltage.
b) Without using Simscape (i.e. using integrators and the equation methods taught in lectures)
integrating this, implement a Simulink model of the sensor system. By considering a step
input of up to 10 A, illustrate the outputs of your model. (Select a suitable timescale for
plotting, so that the dynamics are obvious.)
c) Using Laplace transforms, convert your differential equation into a transfer function.
Comment on the locations of any poles and zeros and explain how these relate to your
observed simulation behaviour.
[20 marks]
2. You have been given a set of Simulink models representing the EV powertrain. The main one is
called ‘m01_plant_model.slx’.
a) Examine the model, and briefly answer the following questions:
(i) Which (if any) blocks in the model represent nonlinearities? Is the overall model linear
or nonlinear?
(ii) How are noise and disturbances modelled?
(iii) What are the model’s states?
b) Write a MATLAB program to trim and linearize the version of the model in the file
‘linearization_model.slx’ for a steady-state speed of 96 km/h. (You can use the supplied
template to help you get started.) Include a listing for your program in your write-up, as well
as the transfer function. Use Simulink to compare the linear model with the original
nonlinear one.
If you can’t solve this question, there is a MATLAB file containing the outputs you would have
got, which you can use for the rest of the assignment.
[20 marks]
3. Use frequency domain loop-shaping to design a feedback controller for cruise control. Aim for:
A stable system, with phase margin of at least 60 degrees.
Steady-state disturbance rejection such that the variation in speed is imperceptible in the
Simulink model.
Peak-peak noise in throttle signal that is imperceptible when viewed in the Simulink model.
No overshoot in response to a change in set point.
The fastest possible response to a change in set point that (a) doesn’t cause an overshoot,
and (b) doesn’t exceed 0.3 g.