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EEE8155 Coursework Handout
Designing sustainable electric propulsion and generation systems: Coursework Specification
1 Introduction
This document contains the details for the Assessment 2(Coursework).
You are set a design problem and have to produce a report detailing your final design and results from Motor-CAD. The final report (.pdf) is due Monday 22nd April 2024 and must be uploaded to canvas. The majority of the work should be done within the EEE81555 teaching block, but we have given you many extra weeks to allow you to manage your workload.
Please follow the name format for your submission.
Format: Last Name_First Name_Student ID_Report.pdf. For example, Deng_Daisy_B123456_Report.pdf.
2 Introduction to FEA
Modern electrical machine design is heavily based on Finite Element Analysis (FEA) software. A number of commercially available packages exist based on the same working principle: the machine is split into a large number of small elements, and the magnetic and electric fields are analysed within each element. The machine geometry is drawn in a CAD like environment, and any machine geometry may be analysed. For more standard machine design, it is possible to use simplified versions of FEA, where the user selects the machine geometry from a library of pre-drawn options. This type of software can be used as a design tool, and in this coursework we are going to use Motor-CAD, as shown inFigure 1. A tutorial of how to build and simulate a brushless PM motor is attached in Modules->Assessment 2 on canvas for your reference. Details of how to access the software are given in Section6below.
Figure 1. Default Brushless PM Motor when you open Motor-CAD for the first time.
3 Coursework: Scenario
We have been approached by a motor manufacturer who wishes to design, build and sell cheap electrical machines for light traction vehicles. The motor manufacturer sells motors to a vehicle manufacturer. The motor manufacturer has provided us with a ‘base design’ which is capable of meeting the required specification, as shown in Table 1. The MotorCAD model of this can be downloaded from Canvas.
Table 1. Existing motor performance and constraints
|
Rated torque |
42 |
Nm |
Peak torque at rated current |
|
Overload Torque |
60 |
Nm |
Peak torque at overload current (short term) |
|
Base speed |
3000 |
Rpm |
Maximum speed where rated torque can be delivered |
|
Maximum speed |
7000 |
Rpm |
Maximum speed where any torque can be delivered |
|
DC voltage limit |
132 |
V |
Will limit V phase |
|
Phase current limit (rated) |
150 |
A |
rms |
|
Phase current (overload) |
200 |
A |
Can only last for 10 seconds before over heating |
The vehicle manufacturer is worried about range of the car, therefore you must consider efficiency over the drive cycle in your design. A simple drive cycle is shown in Table 2.
Table 2. Drive cycle required
|
Time (secs) |
Speed (rpm) |
Torque |
|
30 |
500 |
42 |
|
250 |
2000 |
28 |
|
300 |
5000 |
16 |
|
150 |
4000 |
30 |
4 Coursework: Redesign of a motor
Your project aim is to suggest an improved design to the motor manufacturer in terms of cost, performance, size, mass. Your motor must deliver the performance of Table 1 and you must consider the drive cycle in Table 2. The motor manufacturer is looking for a cheap product, yet the vehicle manufacturer is looking for improved performance and range. You must first model the original motor in Motor-CAD to re-create its operation and prove any improvements in the design.
Any aspect of the motor can be altered, including any topology offered in Motor-CAD (e.g. surface mounted, buried or bread loaf PM machines, or reluctance machine), how you alter the original design is up to you, however you must consider and comment on the impact of your actions on the vehicle design, performance and manufacturing cost.
There is no constraint on the radius, axial length, electrical frequency, winding technique or magnet material used, but all of these parameters will have an impact on the cost, manufacturing technique and performance of the
machine.
4.1.Design criteria
The ideal motor is light, efficient and cheap. Machine design is all about compromise, for example an efficient machine is likely to be more expensive. One way to get the ‘best’ design based on both cost and efficiency is to give these criteria relative importance e.g. if efficiency is more important than cost, the designs can be ranked based on a weighting of 80% efficiency and 20% cost.
e.g. design score = 0.8*efficiency (per unit)+0.2*(1/cost (per unit))
This is only a suggestion you can use your own depending on what you deem to be most important.
The assessment criteria typically used in machine design are given below:
• Mass (kg) – total mass of machine
• magnet mass (kg) – total mass of magnets
• cost (£) – based on mass of material
• efficiency
• volume (m3)
You may also wish to consider disassembly, recycling and other sustainability concerns.
All students should consider as many of these aspects as possible. On canvas, you have been randomly split into 1 of 6 groups (see “ people” tab from course homepage). Each group has a different primary focus.
Group 1
The vehicle manufacture wants a focus on a small compact drive. Your motor must meet the specification with the smallest motor.
Group 2
The motor manufacturer is concerned about cost – evaluate material cost and suggest the cheapest motor which can meet the specification.
Group 3
The motor manufacturer is concerned with carbon footprint of the vehicle, therefore you must design a motor which has norare earth material.
Group 4
The vehicle manufacturer is concerned about performance, you must design a motor which can deliver a higher rated and overload torque.
Group 5
The vehicle manufacturer is concerned about speed, you must design a motor which can operate at 10,000 rpm
Group 6
The vehicle manufacturer is concerned about the cost of the power electronic converter. Converters with a lower switching speed are cheaper, therefore you must design a machine which has a peak frequency of less than 700Hz at 7000rpm.
4.2. Report and Marking Scheme
Two sample design reports have been provided on Canvas to help you consider how your work should be presented. You may also look at the layout of this document for inspiration.
This is an individual piece of coursework. All the work in your report must be done by you alone. You must demonstrate that you have done some design work and you understand the results of the simulations and have made decisions guided by theory (not just playing with software) .
The overall breakdown of marks is 20% Report:
- Style / presentation / quality of language / use of references (it is acceptable to base designs on those found papers etc. (e.g. papers from IEEE Xplore)).
- How well was the space used to put across the information? Adhering to page limit. 80% Investigation:
- Quality of investigation / data gathering / research / theoretical knowledge assessment of effort relating to
Analysis of the existing motor design and design options. Considering the original motor provided, how suitable is it for the drive cycle? What motor types or modifications might be suitable- 20%
Design study in Motor-CAD. Logical and justified investigation of a number of potential designs (e.g. pole number verses performance, motor type verses performance, magnet type verses performance). Marks based on linking results with theory, how adventurous was the study, how many parameters investigated -35%
- Design selection. Discussion and analysis of evaluating performance criteria, and why you may have disregarded others -15%
- Summary and Conclusion. Details of the final design including key changes of your re design compared to the original motor. Summary of key findings of report, summary of why your changes have (or have not) resulted in increased performance and a better product -10%
The report must be a maximum of 3000 words & 10 pages (excluding title / contents page, including references and appendices)
5 Some tips
Useful figures for cost and density are given in Table 3.
Table 3. Cost and density of some materials commonly used in electric motors (2020 values)
|
|
Cost |
Density |
|
|
£/kg |
kg/m^3 |
|
Copper |
3.76957 |
8940 |
|
Steel |
1.16 |
7600 |
|
NdFeB |
125.1282 |
7500 |
|
Ferrite |
5.504834 |
4900 |
In your project you can use these ratings, or other referenced information sources, to guide design choices. You will have to propose and justify a method of incorporating these weightings into your design process.
Note, none of the dimensions or geometries are fixed. For example, the base design has flat teeth,but in many machines there are tooth tips. Teeth can be changed to include a tooth tip, think about implication on winding. Look at the winding layout. The base design has buried magnets, the depth to which they are buried is variable.
Be careful when doing a design study and be careful with your filenames. I advise you to often save your models with a different name and keep them all in case you need to check your results, or the computer crashes.