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IDP2 Challenge 2022/23: Future Hybrid Desalination Facility March 2023
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Future Hybrid Desalination Facility
The electrical engineer’s assignment 2 challenge specification
1. INTRODUCTION TO ASSIGNMENT 2
For assignment 1 you completed a group challenge to help solve the problem of water security- a concept design for
a future hybrid desalination facility which filters sea water to produce fresh drinking water. Your facility’s concept
design passed the water through several processing stages: intake, pre-treatment (screening and filtration),
desalination (hybrid technologies), post treatment (disinfection), freshwater storage and brine disposal. You also
considered the whole project’s structure and energy efficiency.
In assignment 2 you will work together in groups to produce a discipline-specific detailed design. There are separate
groups for mechanical, electrical, and civil disciplines. Consequently, you will be working with different people. You
will follow the same process as assignment 1: complete the stage-gate process, be assigned an academic mentor,
and divide the work to work on individual subsystems. You’ll come together to discuss common elements between
systems and to develop an overall model. The detailed design will be assessed by assignment 2.
1 DETAIL DESIGN (ASSIGNMENT 2) - ELECTRICAL: “THE BRAIN”
You’re allocated to a new electrical engineers-only group. You’ll probably come from different assignment 1 groups.
As a result, you’ll have worked on a different assignment 1 concept designs. Your first task will be to pick one of
these concept designs that your new group should adopt for everything you do in assignment 2.
Each group member will produce a discipline-specific detail design and contribute to a group presentation. As an
electrical engineer, you’ll consider simulation of the energy use of the facility– how energy is converted and
controlled in the system. You’ll take the chosen assignment 1 concept design and develop a “digital twin”.
Civil engineers provide expertise in building. Mechanical engineers are experts in designing physical assets. You’ll
provide expertise to power and control loads in throughout the facility by supplying voltages and currents. Your
simulations should focus on matching the power source input(s) to the output(s).
Each person should focus on one part of the facility. A guiding design principle for your individual system and the
overall system is to make it as realistic as possible and maximise energy efficiency. To encourage creativity, many of
the design requirements are open-ended. Table 1 summarises the task
System Requirements Assignment 2
Whole energy system and
structure - All people
Summary of the electrical system covering
all subsystems below. Summary of the
overall power budget and efficiencies.
Presentation: A high-level description of the facility’s
electrical system. This should identify each individual
subsystem and highlight common elements. You should
include a summary of the facility’s overall power budget,
and an exterior CAD render adopted and enhanced from
assignment 1.
Water intake (abstraction)
1 person
Power and control of the system.
Handle system inputs which may include
matter, energy and information flows as
identified from assignment 1 functional flow
analyses.
Control energy supply to match energy
consumption.
Report: A description of your design. The simscape model
should include the power source, converter and model
the load. Control elements of the model should be
implemented in the simulink domain. You should report
average energy efficiency of your simulation in normal
use.
Pre-Treatment Process
(screening and filtration)= 1
person
Desalination Process
(hybrid technologies) - 2 persons
Lighting - 1 person
Environment (temperature,
heating & humidity)
1 person
Table 1 Summary of electrical work.
IDP2 Challenge 2022/23: Future Hybrid Desalination Facility March 2023
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The number of people in your group will determine who does what:
• 6 people: Complete all work and 2 desalination processes.
• 5 people: Complete all work and 1 desalination process.
• 4 people: Omit environment
• 3 people: Omit lighting.
Groups of 3 people or lower may be disbanded/merged with other groups depending on the time remaining.
2 MODEL BASED DESIGN
To create your discipline-specific digital twin, you’’ll tackle your
challenge by developing Model-Based Design (MBD) approach.
MBD requires modelling and simulation of the structure as a cyber-
physical system.
Your model defines and observes system inputs and outputs. By
specifying these, you can experiment with electrical circuits to
supply power to empirically determine model parameters such as
component values like resistance, capacitance, inductance, voltages
and currents- a “what-if Analysis”. As your confidence grows you
can add more realistic details to it.
Modelling and simulation is conducted in Simscape which is
part of the Matlab/Simulink environment. It’s an industry
standard tool enabling you to build cyber-physical systems
considering multiple physical domains. Although you’’ll focus
on one physical domain – electrical - you might consider other
physical domains such as mechanical (rotation or translation),
thermal, magnetic, gas and hydraulic. To be a competent
electrical engineer, gaining an appreciation other physical
domain is a must; in the real world an electrical system always coexists with other physical domains.
Digital twin development can facilitate detailed virtual prototypes, generating detailed design and
implementation/fabrication plans, and helping with maintenance. This is part of the industry 4.0 revolution.
Figure 2 Example of a Simscape model
Figure 1 Model Based Design Concept from [2]
IDP2 Challenge 2022/23: Future Hybrid Desalination Facility March 2023
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3 GUIDANCE ON COMPLETING THE DESIGN
3.1 GROUP WORK PHASES
You’ll conduct three work phases to reach a final detail design:
1) Overall design (week 7) – A review of the overall facility based on Assignment 1.
2) Individual designs (weeks 7, 8, 9) – Attend structured lectures and learn Simscape.
3) Implement/Build (weeks 9, 10, 11) – Complete your individual detailed Simscape electrical designs and
present the overall system.
Section 7 contains week-by-week guidance of the minimum tasks you’ll do during assignment 2. Your group is
assigned an academic mentor, who you should meet each week. Your mentor is responsible for approving you to
proceed to the next phase by checking that you have completed the work to date using the “stage-gate” process.
4 OTHER ELECTRICAL ENGINEERING MODULES
You are encouraged to use knowledge from other electrical engineering modules to help refine your design. These
include Mechatronic system design – motor drives and control; power Electronics - converter design, and Control
Systems. Some of the basics for these subjects are covered in the IDP2 lectures as they relate to using Simscape, but
not the detailed theory.
5 SUMMARY
You’ll form new discipline-specific groups in semester 2 and produce individual electrical detail design reports in the
second semester. You will combine them as a group to present an overall electrical design.
6 RECOMMENDED READING DURING RESEARCH PHASE:
Herzog, H. J. (2018). Carbon capture. MIT Press: This provides a good overview to set the scene as used in
assignment 1: https://ebookcentral.proquest.com/lib/bham/detail.action?docID=5496104
Any power electronics, energy control books written in the last 2 decades could inform your power designs. This field
is relatively stable and mature.
Mohan, Undeland and Robbin, Power Electronics: Converters Applications and Design, 2003.
El-Sharkawi, Electrical Energy - An Introduction, CRC Press, 2005.
Shepherd, Hully and Liang, Power electronics and motor control second edition, Cambridge University Press, 2000.
G. Reed, B. Grainger, A. Sparacino and Z. Mao, “Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice,”
IEEE Power and Energy Magazine, vol. 10, no. 6, pp. 70-79, 2012.
R. Aarenstrup, Managing Model-Based Design, CreateSpace Independent Publishing Platform, 2015.
IDP2 Challenge 2022/23: Future Hybrid Desalination Facility March 2023
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7 WEEK-BY-WEEK TASK GUIDANCE FOR ASSIGNMENT 2 DETAIL DESIGN
Week Tasks
7 Monday 11am
FORM GROUP
MEET MENTOR
a. Find your new group on Canvas.
b. Attend introduction lecture
c. Complete “hopes and fears” exercise in the lab.
d. Discuss your Belbin roles discovered in semester 1.
e. Set-up group communication channels.
f. Nominate ONE willing person who will be responsible for coordinating the group (in terms
of meeting together and compiling contributions) – the “Group coordinator”, who is also
responsible for contacting your academic mentor on behalf of the group to resolve any
issues or enquiries. Group members should support the coordinator by providing their
individual contribution in time and form, as requested for the final assignment.
g. The group coordinator should allocate a group member to lead each of the following design
areas of challenge and themselves. Your group should try to meet your academic mentor
every week during the timetabled sessions.
h. Each group member should present their concept design from assignment 1 to the rest of
their group and systematically agree a concept design for the group to take forward to
produce detailed designs.
i. Download and study the Assignment 2 report template now – this should help you
understand what is required.
7-9 CONCEPT
DESIGN
MEET MENTOR
a. Attend all lectures and labs to learn Simscape
b. Meet group to determine common elements between the individual detail designs.
c. Meet mentor once a week.
10-11
IMPLEMENTATION
PREPARE
ASSIGNMENT 2
a. You should complete your designs during these weeks.
b. Each group member should focus on their allocated design.
c. Together the group should complete the presentation including final CAD render.
d. The group should meet regularly to ensure the various individual systems fit together to
create an overall system.
12
ASSIGNMENT 2
a. Submit assignment 2 group presentation and individual report.
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8 ASSIGNMENT 2 SUBMISSION (DETAIL DESIGN REPORTS + GROUP PRESENTATION)
The detail design comprises of a presentation and a written report. The presentation covers the overall design, and
the reports output each of the sub-systems in detail separately. There are two submissions:
• A group presentation (maximum 10 minutes) outlining how you arrived at your final design from the
Assignment 1 candidates, a CAD rendering of its exterior structure, a summary of the entire electrical system
and its overall performance considering all subsystems. The group report is worth 20% of the final mark and
marks will equally allocated across all participating group members.
• An individual report prepared by each person. The individual report is worth 80% of the final mark. Marks
are allocated to each group member individually. A template for the report can be downloaded from canvas.
Group presentation
The online presentation should summarise the key highlights of your design. There should be one slide for the
overall design and 1 slide for each individual design, plus front and back matter. The person responsible for each
subsection should ideally present that slide. Any diagrams you use should match those included in your reports. It is
recommended that you use PowerPoint 365 to create your slides and add the audio narration within PowerPoint
itself. This can be done a slide-by-slide basis facilitating rerecording. Once your presentation is complete, you should
export the presentation as a video file for uploading to canvas including narrations. The presentation should be no
longer than 10 minutes.
Further instructions on creating audio narrations for slides and timing transitions in PowerPoint for Microsoft 365
are given here:
https://support.office.com/en-us/article/Add-or-delete-audio-in-your-PowerPoint-presentation-c3b2a9fd-2547-
41d9-9182-3dfaa58f1316?ui=en-US&rs=en-US&ad=US
https://support.office.com/en-us/article/Record-a-slide-show-with-narration-and-slide-timings-0b9502c6-5f6c-
40ae-b1e7-e47d8741161c
Once you have completed your presentation in PowerPoint, convert to video using Export->Create a Video. Ensure
that you check HD Quality (720p) and “Use Recorded Timings and Narrations”. Upload your video to canvas to
submit your assignment. A statement of contribution will be required for the group presentation to identify non-
contributing members which can be provided as the final slide.
Report
Each individual report for a recycle stream should contain a description of your simulation, which convinces other
engineers it’s fit for purpose. You should use these headings:
• Technical summary: A qualitative description which includes a coherent description which incorporates any
enhancement positions reached.
• The simulation model diagram(s). The electrical model should compile, and the notation should be correct with
meaningful names given to components. Any enhancement positions you have reached should be clear e.g. the
model may incorporate other physical domains including mechanical and thermal domains, and Simulink domain
for control.
• The simulation results. These should be graphs conveying source/load and efficiency/loss characteristics. In
addition to electrical inputs and outputs, those from other domains such as mechanical and thermal can be
included as applicable.
• Appendix (separate upload): To support your report you should also upload your simulations models as an
appendix in a zip file, for inspection to validate any claims that you make in the report.
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Individual Marks
You’ll receive marks and feedback on your individual report submission and group presentation separately.
Benchmark statement of expectation:
The following outlines an example of what an excellent and a failing submission would include. These are indicative,
and the final assessment will take account of other aspects and further academic judgment. Thus, these should only
be used as an indication of what an excellent and a poor submission would include:
An excellent submission: The qualitative description of your simscape model sells them to other engineers and
conforms to the required report structure. All desired positions are met, and at least one advanced position. The
specification details are thorough and, where applicable, evidenced from the simulation results. The simulation model
is technically accomplished with good structure and labelling allowing the casual viewer to understand its intricacies.
The inputs, model and outputs are non-idealised reflecting real-world performance estimation. The model is
submitted as a digital appendix, compiles, and produces all the simulation results in the report automatically. The
group presentation is accomplished and suitable for industry-standard exhibition purposes.
A poor submission: It is unclear that the necessary knowledge to complete the challenge is learned. The report
structure is flawed, none of the desired positions are attempted, and the simscape model is also missing or
incomplete adding very little to that given to you in labs. The specification details are incorrect and not evidenced by
simulation. The simulation model is poor and difficult to comprehend by the casual viewer with unclear or no
labelling. There is little relationship to real-world application or challenge. The individual group member did not
contribute to the presentation and/or the presentation is poor and low quality.
Example of an excellent submission for the individual report:
Note that this submission is for a slightly different assignment (a datasheet not report for a single subsystem), so
some details such as formatting are not relevant. Details have been blurred out to prevent plagiarism opportunities.
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9 TIMETABLE FOR LECTURES AND LABS
Week Lectures (Monday) Labs (Thursday)
7: (13/3)
Introduction/
Generation
EE Lecture 1: Introduction to Simscape and Model-
Based Design
Describe the process of model-based design.
Identify the different domains and their roles in a
physical system. Utilise the concept of cross- and
through- variables when interfacing between
domains. The use of simscape for model-based
design.
EE Lecture 2: Generation
Introduction to the concept of power generation
and its realisation in simscape. Identify and select
power sources. Design a DC Power Generator.
Design a AC Power Generator
Introduction to Semester 2.
Hope and Fears exercise.
Evaluation of the groups candidate concepts
designs from Assignment 1 and agreement of
the hybrid model for Assignment 2.
Running Simscape
Lab 1: Introduction to Simscape
Introduction to Simscape. You will model a
simple electrical circuit, monitor
voltage/current values and consider the
thermal domain.
8: (20/3)
Conversion
EE Lecture 3: Conversion
Introduction to the concept of power conversion.
Identify and select power converters and storage
systems. Understand the role of switches and their
benefits in a converter. Design a Converter: single-
phase and 3-phase Inverter, Rectifier, AC-AC
transformers.
EE Lecture 4: Motors and Actuation
Describe and Identify actuators in complex
systems such as motors, valves and hydraulic
pumps. Describe and Identify the different
applications for Linear and Rotary Actuation.
Design of DC and AC motors
Lab 2: Generation
You will learn how to model simple power
generation functions in matlab and how you
can visualise the output in both the electrical
and mechanical domain
Lab 3: Conversion
You will learn how to model simple power
conversion circuits in simscape which provide
a basis for your own design in week 7-10.
Easter
Holiday
9: 24/4
Control
EE Lecture 5: Control (released in week 8)
Understand the concept of signals and
open/closed loop control in an Electrical system.
Lab 4: Control (released in week 8)
You critically appraise some of the in-built
examples in simscape of power conversion
and control in preparation for your own
design work in weeks 9-11.
Lab 5: Analysis (release week 8)
You will explore how you are going to design
your own circuit and analyse it to determine
energy efficiency in weeks 9-10.
10: 1/5
11: 8/5
No lecture on 1/5 but labs run as normal. Weeks 10-11 for students to work on own
designs with PGTA support for submitting
assignment 2.
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10 SIMSCAPE MODELLING AND SIMULATION GUIDANCE:
This will become clearer once lectures are complete but provides additional information to you:
Foundation work: Before you attempt your individual simscape design, you should complete the structured lectures
and labs to get you up to speed, and you should become more familiar with the challenge and the electrical
subsystems that require powering. Otherwise, you will get confused. Don’t try to model the whole system
realistically straight away because it won’t probably work. Instead, start with simple component models; understand
simple component operation; develop a simple system. Then validate the simple system: anticipate the expected
system output; verify that output matches expectation. If happy, add one enhancement then repeat the validation
steps. If unhappy,go back to your previous version (which you should have saved separately!) and try again.
Essential: open-loop, large-signal idealised simulation: Start with a simple, single component-level power converter
for one electrical subsystem to determine the overall basic topology and choice of component values for a general
estimated ideal (non-variable) source and load conditions e.g. driving a single speed ideal DC motor or an AC
induction motor. The simulation objectives will be to obtain current and voltage waveforms to verify that the circuit
behaves properly and measure the efficiencies to produce a data specification for your ideal circuit. Once you have
achieved the idealised simulation, you are free to take your design in a variety of directions to produce a more
complex model. Some suggested ideas are:
Desired: introduce control signals via simulink (closing the loop) Develop a small signal model and controller design.
This could be to either control the structure itself or the electrical circuit e.g. power converter.
Desired: add other physical domains: You can develop your model to generate less idealised system loads and
circuit behaviours. This may include cooling/heating, adjustable motor speeds, considering the inertia and
dampening and so on.
Optional: refine the electrical circuit domain model: You can refine your design to improve efficiencies and
protection. This will include the use of filtering and possibly the addition of circuit protection: preventative
protection guaranteeing against voltage and current surges using snubber circuits and abuse protection through
using opto-isolation. Enhancements you may wish to consider for your circuit include current limitation, isolation,
frequency jitter, energy standard compliance, protections such as open circuit, overcurrent, overvoltage, thermal
cut-out, under voltage, zero load, and electrical isolation.
Very optional: visualise the load: You can import CAD models of the structures and animate them from your
electrical/mechanical simscape simulation using the Simulink 3D animation software. This may only be suitable for
circuits powering mechanical loads.
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Figure 4 Ideal switch
11 SUPPLEMENTARY LECTURE NOTES:
Note that these are provided to you as well as the lectures to provide some background context and references.
Power– A brief Introduction
In essence, the key to designing a power processor is the
switching converter circuit. A power converter must be
designed dependent on the source and load
requirements. These come from mechanical actuators
and structural loads.
Your power circuit will typically convert a power source
voltage and current to those required by a mechanical
actuator and/or or an electrical subsystem. Your power
circuit designs should provide their best performances at
specific loading conditions, which could be either
electrical, hydraulic or pneumatic motors. In the
electrical domain, loading conditions are expressed
fundamentally in terms of current and voltage, and
variations in loading conditions are efficiently dealt with
by continual adjustment of voltage and frequency.
However, a full appreciation of loading will require you to
understand the mechanical rotational and translational domains. In the rotational domain, you need to consider the
Angular velocity and torque. Likewise, in the translational domain you need to consider the translational velocity and
force.
Switches – A key component in power conversion
Electrical equipment is no longer directly powered from the grid: voltages and frequencies are
conditioned to their application using power converters. Conversion allows for efficiency
increases over ranges of operating conditions, for example electric motor speed control and
breaking. A key component in circuit design to achieve this is the use of switches.
There are two types of power electronic devices to realise switching – single component and
hybrid component. Single components include diodes, transistors, MoSFETs and thyristors.
These solid-state devices are not ideal switches in practice, and while iterating your design
you’’ll need to account for their non-ideal characteristics.
Hybrid components are combinations of single components which achieve better performance.
E.g. notably The Darlington Transistor (DT) provides higher current gains, The Insulated Gate
Bipolar Transistor (IGBT) provides high current voltage controlled switching, and the Static
Induction Transistor (SIT) provides higher power, frequency and breakdown voltages.
In ideal conditions, the switching is instantaneous - there is no voltage drop across the switch when on, there is no
current through the switch when off, the voltage withstand capability (insulation) is infinite when off, the current
handling capability is infinite when on, and power handling is infinite. As you iterate your design through simulation,
you can observe and develop an understanding as to why these assumptions are not correct in physical devices, and
how they could affect your results.
Some elements to consider when selecting single and hybrid components for your design include the conduction
losses (on-state voltage and on-state resistance), operating frequency (switching times and energy loss), power
handling (voltage and current ratings), device control (control circuit power), current handling (temperature
coefficient).
Figure 3 Example of a Power converter system [4]
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Converters – Types available and design trade-offs
To do power conversion, switching circuits use hybrid and single component
combinations according to type (AC or DC), voltage, and frequency. There are four
basic converter types. These are: Rectifiers (AC->DC) Converters (DC->DC),
Inverters (DC->AC) and Regulators (AC->AC). The DC may be regulated (i.e.
constant amplitude) or be adjustable. The AC may have constant or adjustable
frequency and adjustable amplitude. Power flow is generally one-way from source
to load, although some applications regarding renewable energy may reverse this.
AC/DC converters (rectifiers) typically must provide a regulated output – i.e. the voltage should vary within specific
tolerances given variations in input voltages and output current loads which is achieved using feedback control and
switched semiconductor devices rather than simple devices such as diodes. It is desirable for the output to be
electrically isolated from the input and this is achieved using a high-frequency isolation transformer. There may be
multiple outputs required for the system with different load characteristics. Most commonly, a three-phase bridge
rectifier circuits are used in industrial power electronics where a 3-phase generator is loaded with a full-wave bridge
rectifier.
Input voltage variations come from disturbances on the power line which can be simulated. These include
overvoltage cause by drops in loads, under voltage/brownout caused by increases in loads, outage/blackout, voltage
spikes, chopped waveforms, harmonics, and electromagnetic interference. Although most of these are out of scope
for this module, you may wish to consider the use of battery back-ups in your circuit.
You must make the correct choice of switch for your specific conversion application, starting with the maximum
voltage and current ratings and switching frequency (slew rate). As you iterate your design, other factors you may
consider include ruggedness under possible abuses (over voltage and current surge), triggering ease, cost and
availability, incidental dissipation, need for circuit protection and heat dissipation e.g. the use of snubbers.
You can design and simulate at the single-component, hybrid component or converter level. However, it’s
recommended that if you initially start with simple power converter circuits made with single components,
optionally progressing to hybrid components and then to the built-in blocks.
Transformers – for voltage steeping and isolation
Like the switch, the transformer is a key part of conversion. It is used to step-up or step-down AC voltages
throughout the power transmission network: Transmission transformer enable low current, high voltage
transmission (up to 1MV) of electricity across distribution lines. Distribution transformers step down the voltage
further (up to 100s KV) followed by service transformers which will be located near domestic loads to step down to
residential levels (110-240V). Typically for large scale industrial machinery you will have access to a distribution
transformer and access voltages higher than those at residential level. In addition, your circuit will require smaller
transformers to step-down voltage and provide impedance matching, filtering and electrical isolation.
The basic transformer consists of a minimum of 2 isolated windings wrapped around an iron core which provides a
magnetic flux path. The difference in the number of windings provides the voltage ratios. In addition to voltage
ratio, each transformer is specified by its apparent power. To make your designs more realistic you may wish to
progress from a single-phase transformer to a three-phase transformer which has a three-legged core with each leg
representing one phase. In practice, there are internal losses in transformers due to parasitic losses such as
resistance and inductance of windows. Typically, this means that the turn ratio and voltage ratio are not equal.
Other types of transformers you may come across include Multi-winding transformers and Autotransformers, the
latter which allow variations in voltage ratios. These should be considered advanced topics and are purely optional.
Figure 5 Power Converters are either
Inverters or Rectifiers
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Energy Efficiency – a key optimisation parameter
The key design factor that you should consider when producing your power circuit designs are to minimise the
amount of wasted and dissipated energy. This typically occurs when components operate in their active states when
they don’t need to. A key strategy to accomplish this is to operate transistors as on/off switches which are switched
at high frequency. The selection of frequency is a trade-off between transistor switching costs (Incidental dissipation)
and requirements of other components such as, for example in AC-AC regulation, a transformer to provide electrical
isolation and filters to reduce ripple.
Control – to ensure power efficiency and performance adherence
You may come across control in two areas of IDP: the power conversion system and the control of the mechanical
actuators. You are not required to develop detailed control schemes for either, but you should be aware of this
distinction and consider the control schemes as separate entities.
A modern power electronics circuit will include a control scheme to bring about efficiencies. The control modifies the
conversion circuit to account for variations in source and load in response to some feedback from the circuit itself
i.e. a reference signal. Control is a large aspect of power electronic design and the control signals are increasingly
generated in software before digital to analogue conversion, and generated in isolation from the power circuits for
reliability reasons. You should consult your other modules if you wish to introduce control elements into your
design.
Circuit protection – an added refinement to your power circuit
Circuit protection can be considered in terms of both preventative detection and abuse protection. Preventative
detection is to stop secondary device ratings from being exceeded e.g. excess voltages and current surges can be
mitigated with snubber circuits. Abuse protection aims to handle external faults i.e. source and load fault conditions.
Common conditions are protection from overcurrent using hall plates for rapid detection to switch off, and
protection from overvoltage via crowbar circuits. Many modern switches have these functions incorporated, and you
add these to your circuits once basic operation is established.
Power sources – Incorporate knowledge about the power network into your design
You should understand the power source specification when designing your circuit – i.e. the power network. It
consists of 3 systems: generation, transmission, and distribution. The power plants convert energy resources such as
cola/oil/gas, hydro and nuclear, from chemical, mechanical, or atomic energy respectively, into electrical energy
using generators. Transformers are used to step-up voltage to reduce current for long transmission at typically 220-
1200kV, and to step-down to industrial and residential applications.
By considering different power plant sources, you can assess the environmental impact of your design. E.g. If your
energy source is a Hydroelectric Dam, its size and water velocity for the required power output. For Thermal Heat,
amount of coal, mass of nuclear material, area solar panels, and wind turbine size blade power.
The most likely source for your system will be AC. You should be familiar with AC current: waveforms, RMS, Phase
shifts, Phasors, Complex impedance and power (active, reactive and complex). Three phase AC systems are the
norm. They have advantages in that they can generate rotating magnetic fields enabling motors can rotate without
extra controls and they are also 3 times more powerful in terms of generation, transmission and reliability than
single phase systems. You should be familiar with 3 Phase powers and summing the powers of each phase in a 3-
phase circuit to calculate overall power.
Mechanical Domain: Motors/ Drives – The AC Induction Motor and DC motor.
When designing your power electronics circuit, you must gain a good understanding of your load- for example, a
dual-action electro-mechanical converter – a motor. Motors convert electrical energy to mechanical energy and are
key to “making big things move”. The simplest motor for this in terms of power electronics design would be a DC
motor. It has two basic components: field windings mounted on a tube (stator) and armature windings mounted on
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a rotor. It is supplied with a rectified voltage and current from an AC source. The DC motor is well established
technology, requiring simple power converters and control systems with a wide speed range and a fast response.
More common than DC motors in industrial applications due to its reliability and efficiency is the Rotating AC
Induction Motor. It comprises of windings mounted symmetrically inside a hollow metal tube (stator). The 3-phased
balanced voltage applied to these windings creates 3 magnetic fields whose flux rotates the rotor - mounted in the
centre of stator - and its shaft – on which the load is connected. The power of the motor – a function of input
voltages, current, winding, core and rotational losses, is expressed as its output torque and rotor speed. An induction
motor will have key operating points to consider when starting up, to reach a steady-state operating region of
constant motor speed and a torque matched to the load torque.
Another common induction motor you could consider is the wheeled linear induction motor. This performs a similar
manner to the rotating induction motor with the primary difference being that the stator and rotor are flat; the rotor
is fixed, and the magnetic flux propels the mechanical body housing the stator; railway trains are the common
application with the rotor being the track.
Once you have a basic, single speed DC or AC induction motor drive simulated you could consider whether to make
the speed adjustable/variable although this is a purely optional feature. Adjusting DC motor speed is by changing
voltage or current supplied. Motor speed control for induction motors is via several control schemes. These can be
considered either slip control, where voltage and impedance is varied, or frequency control (cyclo-converters and
DC-Link inverters). There are other motors that can be considered for variable speed control such as AC synchronous
motors, however the single speed DC motor and AC Induction motor should be your primary consideration.
Motors are part of most but not all load types. If your load requires a motor, you will need to consider the Torque-
Speed characteristics of your load i.e. what is the required torque for the speed you require to move your load.
Several other factors could be considered when choosing the motor. These include the speed range, efficiency
(input/output power ration), speed regulation (speed reduction due to torque increase), controllability, braking
requirements, reliability, power-to-weight ratio, power factor, load factor and duty cycle, supply variation effect.
References
[1] Mohan, Undeland and Robbin, Power Electronics: Converters Applications and Design, 2003.
[2] El-Sharkawi, Electrical Energy - An Introduction, CRC Press, 2005.
[3] Shepherd, Hully and Liang, Power electronics and motor control second edition, Cambridge University Press,
2000.
[4] G. Reed, B. Grainger, A. Sparacino and Z. Mao, “Ship to Grid: Medium-Voltage DC Concepts in Theory and
Practice,” IEEE Power and Energy Magazine, vol. 10, no. 6, pp. 70-79, 2012.
[5] R. Aarenstrup, Managing Model-Based Design, CreateSpace Independent Publishing Platform, 2015.
1
Future Hybrid Desalination Facility
The electrical engineer’s assignment 2 challenge specification
1. INTRODUCTION TO ASSIGNMENT 2
For assignment 1 you completed a group challenge to help solve the problem of water security- a concept design for
a future hybrid desalination facility which filters sea water to produce fresh drinking water. Your facility’s concept
design passed the water through several processing stages: intake, pre-treatment (screening and filtration),
desalination (hybrid technologies), post treatment (disinfection), freshwater storage and brine disposal. You also
considered the whole project’s structure and energy efficiency.
In assignment 2 you will work together in groups to produce a discipline-specific detailed design. There are separate
groups for mechanical, electrical, and civil disciplines. Consequently, you will be working with different people. You
will follow the same process as assignment 1: complete the stage-gate process, be assigned an academic mentor,
and divide the work to work on individual subsystems. You’ll come together to discuss common elements between
systems and to develop an overall model. The detailed design will be assessed by assignment 2.
1 DETAIL DESIGN (ASSIGNMENT 2) - ELECTRICAL: “THE BRAIN”
You’re allocated to a new electrical engineers-only group. You’ll probably come from different assignment 1 groups.
As a result, you’ll have worked on a different assignment 1 concept designs. Your first task will be to pick one of
these concept designs that your new group should adopt for everything you do in assignment 2.
Each group member will produce a discipline-specific detail design and contribute to a group presentation. As an
electrical engineer, you’ll consider simulation of the energy use of the facility– how energy is converted and
controlled in the system. You’ll take the chosen assignment 1 concept design and develop a “digital twin”.
Civil engineers provide expertise in building. Mechanical engineers are experts in designing physical assets. You’ll
provide expertise to power and control loads in throughout the facility by supplying voltages and currents. Your
simulations should focus on matching the power source input(s) to the output(s).
Each person should focus on one part of the facility. A guiding design principle for your individual system and the
overall system is to make it as realistic as possible and maximise energy efficiency. To encourage creativity, many of
the design requirements are open-ended. Table 1 summarises the task
System Requirements Assignment 2
Whole energy system and
structure - All people
Summary of the electrical system covering
all subsystems below. Summary of the
overall power budget and efficiencies.
Presentation: A high-level description of the facility’s
electrical system. This should identify each individual
subsystem and highlight common elements. You should
include a summary of the facility’s overall power budget,
and an exterior CAD render adopted and enhanced from
assignment 1.
Water intake (abstraction)
1 person
Power and control of the system.
Handle system inputs which may include
matter, energy and information flows as
identified from assignment 1 functional flow
analyses.
Control energy supply to match energy
consumption.
Report: A description of your design. The simscape model
should include the power source, converter and model
the load. Control elements of the model should be
implemented in the simulink domain. You should report
average energy efficiency of your simulation in normal
use.
Pre-Treatment Process
(screening and filtration)= 1
person
Desalination Process
(hybrid technologies) - 2 persons
Lighting - 1 person
Environment (temperature,
heating & humidity)
1 person
Table 1 Summary of electrical work.
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The number of people in your group will determine who does what:
• 6 people: Complete all work and 2 desalination processes.
• 5 people: Complete all work and 1 desalination process.
• 4 people: Omit environment
• 3 people: Omit lighting.
Groups of 3 people or lower may be disbanded/merged with other groups depending on the time remaining.
2 MODEL BASED DESIGN
To create your discipline-specific digital twin, you’’ll tackle your
challenge by developing Model-Based Design (MBD) approach.
MBD requires modelling and simulation of the structure as a cyber-
physical system.
Your model defines and observes system inputs and outputs. By
specifying these, you can experiment with electrical circuits to
supply power to empirically determine model parameters such as
component values like resistance, capacitance, inductance, voltages
and currents- a “what-if Analysis”. As your confidence grows you
can add more realistic details to it.
Modelling and simulation is conducted in Simscape which is
part of the Matlab/Simulink environment. It’s an industry
standard tool enabling you to build cyber-physical systems
considering multiple physical domains. Although you’’ll focus
on one physical domain – electrical - you might consider other
physical domains such as mechanical (rotation or translation),
thermal, magnetic, gas and hydraulic. To be a competent
electrical engineer, gaining an appreciation other physical
domain is a must; in the real world an electrical system always coexists with other physical domains.
Digital twin development can facilitate detailed virtual prototypes, generating detailed design and
implementation/fabrication plans, and helping with maintenance. This is part of the industry 4.0 revolution.
Figure 2 Example of a Simscape model
Figure 1 Model Based Design Concept from [2]
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3 GUIDANCE ON COMPLETING THE DESIGN
3.1 GROUP WORK PHASES
You’ll conduct three work phases to reach a final detail design:
1) Overall design (week 7) – A review of the overall facility based on Assignment 1.
2) Individual designs (weeks 7, 8, 9) – Attend structured lectures and learn Simscape.
3) Implement/Build (weeks 9, 10, 11) – Complete your individual detailed Simscape electrical designs and
present the overall system.
Section 7 contains week-by-week guidance of the minimum tasks you’ll do during assignment 2. Your group is
assigned an academic mentor, who you should meet each week. Your mentor is responsible for approving you to
proceed to the next phase by checking that you have completed the work to date using the “stage-gate” process.
4 OTHER ELECTRICAL ENGINEERING MODULES
You are encouraged to use knowledge from other electrical engineering modules to help refine your design. These
include Mechatronic system design – motor drives and control; power Electronics - converter design, and Control
Systems. Some of the basics for these subjects are covered in the IDP2 lectures as they relate to using Simscape, but
not the detailed theory.
5 SUMMARY
You’ll form new discipline-specific groups in semester 2 and produce individual electrical detail design reports in the
second semester. You will combine them as a group to present an overall electrical design.
6 RECOMMENDED READING DURING RESEARCH PHASE:
Herzog, H. J. (2018). Carbon capture. MIT Press: This provides a good overview to set the scene as used in
assignment 1: https://ebookcentral.proquest.com/lib/bham/detail.action?docID=5496104
Any power electronics, energy control books written in the last 2 decades could inform your power designs. This field
is relatively stable and mature.
Mohan, Undeland and Robbin, Power Electronics: Converters Applications and Design, 2003.
El-Sharkawi, Electrical Energy - An Introduction, CRC Press, 2005.
Shepherd, Hully and Liang, Power electronics and motor control second edition, Cambridge University Press, 2000.
G. Reed, B. Grainger, A. Sparacino and Z. Mao, “Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice,”
IEEE Power and Energy Magazine, vol. 10, no. 6, pp. 70-79, 2012.
R. Aarenstrup, Managing Model-Based Design, CreateSpace Independent Publishing Platform, 2015.
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7 WEEK-BY-WEEK TASK GUIDANCE FOR ASSIGNMENT 2 DETAIL DESIGN
Week Tasks
7 Monday 11am
FORM GROUP
MEET MENTOR
a. Find your new group on Canvas.
b. Attend introduction lecture
c. Complete “hopes and fears” exercise in the lab.
d. Discuss your Belbin roles discovered in semester 1.
e. Set-up group communication channels.
f. Nominate ONE willing person who will be responsible for coordinating the group (in terms
of meeting together and compiling contributions) – the “Group coordinator”, who is also
responsible for contacting your academic mentor on behalf of the group to resolve any
issues or enquiries. Group members should support the coordinator by providing their
individual contribution in time and form, as requested for the final assignment.
g. The group coordinator should allocate a group member to lead each of the following design
areas of challenge and themselves. Your group should try to meet your academic mentor
every week during the timetabled sessions.
h. Each group member should present their concept design from assignment 1 to the rest of
their group and systematically agree a concept design for the group to take forward to
produce detailed designs.
i. Download and study the Assignment 2 report template now – this should help you
understand what is required.
7-9 CONCEPT
DESIGN
MEET MENTOR
a. Attend all lectures and labs to learn Simscape
b. Meet group to determine common elements between the individual detail designs.
c. Meet mentor once a week.
10-11
IMPLEMENTATION
PREPARE
ASSIGNMENT 2
a. You should complete your designs during these weeks.
b. Each group member should focus on their allocated design.
c. Together the group should complete the presentation including final CAD render.
d. The group should meet regularly to ensure the various individual systems fit together to
create an overall system.
12
ASSIGNMENT 2
a. Submit assignment 2 group presentation and individual report.
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8 ASSIGNMENT 2 SUBMISSION (DETAIL DESIGN REPORTS + GROUP PRESENTATION)
The detail design comprises of a presentation and a written report. The presentation covers the overall design, and
the reports output each of the sub-systems in detail separately. There are two submissions:
• A group presentation (maximum 10 minutes) outlining how you arrived at your final design from the
Assignment 1 candidates, a CAD rendering of its exterior structure, a summary of the entire electrical system
and its overall performance considering all subsystems. The group report is worth 20% of the final mark and
marks will equally allocated across all participating group members.
• An individual report prepared by each person. The individual report is worth 80% of the final mark. Marks
are allocated to each group member individually. A template for the report can be downloaded from canvas.
Group presentation
The online presentation should summarise the key highlights of your design. There should be one slide for the
overall design and 1 slide for each individual design, plus front and back matter. The person responsible for each
subsection should ideally present that slide. Any diagrams you use should match those included in your reports. It is
recommended that you use PowerPoint 365 to create your slides and add the audio narration within PowerPoint
itself. This can be done a slide-by-slide basis facilitating rerecording. Once your presentation is complete, you should
export the presentation as a video file for uploading to canvas including narrations. The presentation should be no
longer than 10 minutes.
Further instructions on creating audio narrations for slides and timing transitions in PowerPoint for Microsoft 365
are given here:
https://support.office.com/en-us/article/Add-or-delete-audio-in-your-PowerPoint-presentation-c3b2a9fd-2547-
41d9-9182-3dfaa58f1316?ui=en-US&rs=en-US&ad=US
https://support.office.com/en-us/article/Record-a-slide-show-with-narration-and-slide-timings-0b9502c6-5f6c-
40ae-b1e7-e47d8741161c
Once you have completed your presentation in PowerPoint, convert to video using Export->Create a Video. Ensure
that you check HD Quality (720p) and “Use Recorded Timings and Narrations”. Upload your video to canvas to
submit your assignment. A statement of contribution will be required for the group presentation to identify non-
contributing members which can be provided as the final slide.
Report
Each individual report for a recycle stream should contain a description of your simulation, which convinces other
engineers it’s fit for purpose. You should use these headings:
• Technical summary: A qualitative description which includes a coherent description which incorporates any
enhancement positions reached.
• The simulation model diagram(s). The electrical model should compile, and the notation should be correct with
meaningful names given to components. Any enhancement positions you have reached should be clear e.g. the
model may incorporate other physical domains including mechanical and thermal domains, and Simulink domain
for control.
• The simulation results. These should be graphs conveying source/load and efficiency/loss characteristics. In
addition to electrical inputs and outputs, those from other domains such as mechanical and thermal can be
included as applicable.
• Appendix (separate upload): To support your report you should also upload your simulations models as an
appendix in a zip file, for inspection to validate any claims that you make in the report.
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Individual Marks
You’ll receive marks and feedback on your individual report submission and group presentation separately.
Benchmark statement of expectation:
The following outlines an example of what an excellent and a failing submission would include. These are indicative,
and the final assessment will take account of other aspects and further academic judgment. Thus, these should only
be used as an indication of what an excellent and a poor submission would include:
An excellent submission: The qualitative description of your simscape model sells them to other engineers and
conforms to the required report structure. All desired positions are met, and at least one advanced position. The
specification details are thorough and, where applicable, evidenced from the simulation results. The simulation model
is technically accomplished with good structure and labelling allowing the casual viewer to understand its intricacies.
The inputs, model and outputs are non-idealised reflecting real-world performance estimation. The model is
submitted as a digital appendix, compiles, and produces all the simulation results in the report automatically. The
group presentation is accomplished and suitable for industry-standard exhibition purposes.
A poor submission: It is unclear that the necessary knowledge to complete the challenge is learned. The report
structure is flawed, none of the desired positions are attempted, and the simscape model is also missing or
incomplete adding very little to that given to you in labs. The specification details are incorrect and not evidenced by
simulation. The simulation model is poor and difficult to comprehend by the casual viewer with unclear or no
labelling. There is little relationship to real-world application or challenge. The individual group member did not
contribute to the presentation and/or the presentation is poor and low quality.
Example of an excellent submission for the individual report:
Note that this submission is for a slightly different assignment (a datasheet not report for a single subsystem), so
some details such as formatting are not relevant. Details have been blurred out to prevent plagiarism opportunities.
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9 TIMETABLE FOR LECTURES AND LABS
Week Lectures (Monday) Labs (Thursday)
7: (13/3)
Introduction/
Generation
EE Lecture 1: Introduction to Simscape and Model-
Based Design
Describe the process of model-based design.
Identify the different domains and their roles in a
physical system. Utilise the concept of cross- and
through- variables when interfacing between
domains. The use of simscape for model-based
design.
EE Lecture 2: Generation
Introduction to the concept of power generation
and its realisation in simscape. Identify and select
power sources. Design a DC Power Generator.
Design a AC Power Generator
Introduction to Semester 2.
Hope and Fears exercise.
Evaluation of the groups candidate concepts
designs from Assignment 1 and agreement of
the hybrid model for Assignment 2.
Running Simscape
Lab 1: Introduction to Simscape
Introduction to Simscape. You will model a
simple electrical circuit, monitor
voltage/current values and consider the
thermal domain.
8: (20/3)
Conversion
EE Lecture 3: Conversion
Introduction to the concept of power conversion.
Identify and select power converters and storage
systems. Understand the role of switches and their
benefits in a converter. Design a Converter: single-
phase and 3-phase Inverter, Rectifier, AC-AC
transformers.
EE Lecture 4: Motors and Actuation
Describe and Identify actuators in complex
systems such as motors, valves and hydraulic
pumps. Describe and Identify the different
applications for Linear and Rotary Actuation.
Design of DC and AC motors
Lab 2: Generation
You will learn how to model simple power
generation functions in matlab and how you
can visualise the output in both the electrical
and mechanical domain
Lab 3: Conversion
You will learn how to model simple power
conversion circuits in simscape which provide
a basis for your own design in week 7-10.
Easter
Holiday
9: 24/4
Control
EE Lecture 5: Control (released in week 8)
Understand the concept of signals and
open/closed loop control in an Electrical system.
Lab 4: Control (released in week 8)
You critically appraise some of the in-built
examples in simscape of power conversion
and control in preparation for your own
design work in weeks 9-11.
Lab 5: Analysis (release week 8)
You will explore how you are going to design
your own circuit and analyse it to determine
energy efficiency in weeks 9-10.
10: 1/5
11: 8/5
No lecture on 1/5 but labs run as normal. Weeks 10-11 for students to work on own
designs with PGTA support for submitting
assignment 2.
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10 SIMSCAPE MODELLING AND SIMULATION GUIDANCE:
This will become clearer once lectures are complete but provides additional information to you:
Foundation work: Before you attempt your individual simscape design, you should complete the structured lectures
and labs to get you up to speed, and you should become more familiar with the challenge and the electrical
subsystems that require powering. Otherwise, you will get confused. Don’t try to model the whole system
realistically straight away because it won’t probably work. Instead, start with simple component models; understand
simple component operation; develop a simple system. Then validate the simple system: anticipate the expected
system output; verify that output matches expectation. If happy, add one enhancement then repeat the validation
steps. If unhappy,go back to your previous version (which you should have saved separately!) and try again.
Essential: open-loop, large-signal idealised simulation: Start with a simple, single component-level power converter
for one electrical subsystem to determine the overall basic topology and choice of component values for a general
estimated ideal (non-variable) source and load conditions e.g. driving a single speed ideal DC motor or an AC
induction motor. The simulation objectives will be to obtain current and voltage waveforms to verify that the circuit
behaves properly and measure the efficiencies to produce a data specification for your ideal circuit. Once you have
achieved the idealised simulation, you are free to take your design in a variety of directions to produce a more
complex model. Some suggested ideas are:
Desired: introduce control signals via simulink (closing the loop) Develop a small signal model and controller design.
This could be to either control the structure itself or the electrical circuit e.g. power converter.
Desired: add other physical domains: You can develop your model to generate less idealised system loads and
circuit behaviours. This may include cooling/heating, adjustable motor speeds, considering the inertia and
dampening and so on.
Optional: refine the electrical circuit domain model: You can refine your design to improve efficiencies and
protection. This will include the use of filtering and possibly the addition of circuit protection: preventative
protection guaranteeing against voltage and current surges using snubber circuits and abuse protection through
using opto-isolation. Enhancements you may wish to consider for your circuit include current limitation, isolation,
frequency jitter, energy standard compliance, protections such as open circuit, overcurrent, overvoltage, thermal
cut-out, under voltage, zero load, and electrical isolation.
Very optional: visualise the load: You can import CAD models of the structures and animate them from your
electrical/mechanical simscape simulation using the Simulink 3D animation software. This may only be suitable for
circuits powering mechanical loads.
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Figure 4 Ideal switch
11 SUPPLEMENTARY LECTURE NOTES:
Note that these are provided to you as well as the lectures to provide some background context and references.
Power– A brief Introduction
In essence, the key to designing a power processor is the
switching converter circuit. A power converter must be
designed dependent on the source and load
requirements. These come from mechanical actuators
and structural loads.
Your power circuit will typically convert a power source
voltage and current to those required by a mechanical
actuator and/or or an electrical subsystem. Your power
circuit designs should provide their best performances at
specific loading conditions, which could be either
electrical, hydraulic or pneumatic motors. In the
electrical domain, loading conditions are expressed
fundamentally in terms of current and voltage, and
variations in loading conditions are efficiently dealt with
by continual adjustment of voltage and frequency.
However, a full appreciation of loading will require you to
understand the mechanical rotational and translational domains. In the rotational domain, you need to consider the
Angular velocity and torque. Likewise, in the translational domain you need to consider the translational velocity and
force.
Switches – A key component in power conversion
Electrical equipment is no longer directly powered from the grid: voltages and frequencies are
conditioned to their application using power converters. Conversion allows for efficiency
increases over ranges of operating conditions, for example electric motor speed control and
breaking. A key component in circuit design to achieve this is the use of switches.
There are two types of power electronic devices to realise switching – single component and
hybrid component. Single components include diodes, transistors, MoSFETs and thyristors.
These solid-state devices are not ideal switches in practice, and while iterating your design
you’’ll need to account for their non-ideal characteristics.
Hybrid components are combinations of single components which achieve better performance.
E.g. notably The Darlington Transistor (DT) provides higher current gains, The Insulated Gate
Bipolar Transistor (IGBT) provides high current voltage controlled switching, and the Static
Induction Transistor (SIT) provides higher power, frequency and breakdown voltages.
In ideal conditions, the switching is instantaneous - there is no voltage drop across the switch when on, there is no
current through the switch when off, the voltage withstand capability (insulation) is infinite when off, the current
handling capability is infinite when on, and power handling is infinite. As you iterate your design through simulation,
you can observe and develop an understanding as to why these assumptions are not correct in physical devices, and
how they could affect your results.
Some elements to consider when selecting single and hybrid components for your design include the conduction
losses (on-state voltage and on-state resistance), operating frequency (switching times and energy loss), power
handling (voltage and current ratings), device control (control circuit power), current handling (temperature
coefficient).
Figure 3 Example of a Power converter system [4]
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Converters – Types available and design trade-offs
To do power conversion, switching circuits use hybrid and single component
combinations according to type (AC or DC), voltage, and frequency. There are four
basic converter types. These are: Rectifiers (AC->DC) Converters (DC->DC),
Inverters (DC->AC) and Regulators (AC->AC). The DC may be regulated (i.e.
constant amplitude) or be adjustable. The AC may have constant or adjustable
frequency and adjustable amplitude. Power flow is generally one-way from source
to load, although some applications regarding renewable energy may reverse this.
AC/DC converters (rectifiers) typically must provide a regulated output – i.e. the voltage should vary within specific
tolerances given variations in input voltages and output current loads which is achieved using feedback control and
switched semiconductor devices rather than simple devices such as diodes. It is desirable for the output to be
electrically isolated from the input and this is achieved using a high-frequency isolation transformer. There may be
multiple outputs required for the system with different load characteristics. Most commonly, a three-phase bridge
rectifier circuits are used in industrial power electronics where a 3-phase generator is loaded with a full-wave bridge
rectifier.
Input voltage variations come from disturbances on the power line which can be simulated. These include
overvoltage cause by drops in loads, under voltage/brownout caused by increases in loads, outage/blackout, voltage
spikes, chopped waveforms, harmonics, and electromagnetic interference. Although most of these are out of scope
for this module, you may wish to consider the use of battery back-ups in your circuit.
You must make the correct choice of switch for your specific conversion application, starting with the maximum
voltage and current ratings and switching frequency (slew rate). As you iterate your design, other factors you may
consider include ruggedness under possible abuses (over voltage and current surge), triggering ease, cost and
availability, incidental dissipation, need for circuit protection and heat dissipation e.g. the use of snubbers.
You can design and simulate at the single-component, hybrid component or converter level. However, it’s
recommended that if you initially start with simple power converter circuits made with single components,
optionally progressing to hybrid components and then to the built-in blocks.
Transformers – for voltage steeping and isolation
Like the switch, the transformer is a key part of conversion. It is used to step-up or step-down AC voltages
throughout the power transmission network: Transmission transformer enable low current, high voltage
transmission (up to 1MV) of electricity across distribution lines. Distribution transformers step down the voltage
further (up to 100s KV) followed by service transformers which will be located near domestic loads to step down to
residential levels (110-240V). Typically for large scale industrial machinery you will have access to a distribution
transformer and access voltages higher than those at residential level. In addition, your circuit will require smaller
transformers to step-down voltage and provide impedance matching, filtering and electrical isolation.
The basic transformer consists of a minimum of 2 isolated windings wrapped around an iron core which provides a
magnetic flux path. The difference in the number of windings provides the voltage ratios. In addition to voltage
ratio, each transformer is specified by its apparent power. To make your designs more realistic you may wish to
progress from a single-phase transformer to a three-phase transformer which has a three-legged core with each leg
representing one phase. In practice, there are internal losses in transformers due to parasitic losses such as
resistance and inductance of windows. Typically, this means that the turn ratio and voltage ratio are not equal.
Other types of transformers you may come across include Multi-winding transformers and Autotransformers, the
latter which allow variations in voltage ratios. These should be considered advanced topics and are purely optional.
Figure 5 Power Converters are either
Inverters or Rectifiers
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Energy Efficiency – a key optimisation parameter
The key design factor that you should consider when producing your power circuit designs are to minimise the
amount of wasted and dissipated energy. This typically occurs when components operate in their active states when
they don’t need to. A key strategy to accomplish this is to operate transistors as on/off switches which are switched
at high frequency. The selection of frequency is a trade-off between transistor switching costs (Incidental dissipation)
and requirements of other components such as, for example in AC-AC regulation, a transformer to provide electrical
isolation and filters to reduce ripple.
Control – to ensure power efficiency and performance adherence
You may come across control in two areas of IDP: the power conversion system and the control of the mechanical
actuators. You are not required to develop detailed control schemes for either, but you should be aware of this
distinction and consider the control schemes as separate entities.
A modern power electronics circuit will include a control scheme to bring about efficiencies. The control modifies the
conversion circuit to account for variations in source and load in response to some feedback from the circuit itself
i.e. a reference signal. Control is a large aspect of power electronic design and the control signals are increasingly
generated in software before digital to analogue conversion, and generated in isolation from the power circuits for
reliability reasons. You should consult your other modules if you wish to introduce control elements into your
design.
Circuit protection – an added refinement to your power circuit
Circuit protection can be considered in terms of both preventative detection and abuse protection. Preventative
detection is to stop secondary device ratings from being exceeded e.g. excess voltages and current surges can be
mitigated with snubber circuits. Abuse protection aims to handle external faults i.e. source and load fault conditions.
Common conditions are protection from overcurrent using hall plates for rapid detection to switch off, and
protection from overvoltage via crowbar circuits. Many modern switches have these functions incorporated, and you
add these to your circuits once basic operation is established.
Power sources – Incorporate knowledge about the power network into your design
You should understand the power source specification when designing your circuit – i.e. the power network. It
consists of 3 systems: generation, transmission, and distribution. The power plants convert energy resources such as
cola/oil/gas, hydro and nuclear, from chemical, mechanical, or atomic energy respectively, into electrical energy
using generators. Transformers are used to step-up voltage to reduce current for long transmission at typically 220-
1200kV, and to step-down to industrial and residential applications.
By considering different power plant sources, you can assess the environmental impact of your design. E.g. If your
energy source is a Hydroelectric Dam, its size and water velocity for the required power output. For Thermal Heat,
amount of coal, mass of nuclear material, area solar panels, and wind turbine size blade power.
The most likely source for your system will be AC. You should be familiar with AC current: waveforms, RMS, Phase
shifts, Phasors, Complex impedance and power (active, reactive and complex). Three phase AC systems are the
norm. They have advantages in that they can generate rotating magnetic fields enabling motors can rotate without
extra controls and they are also 3 times more powerful in terms of generation, transmission and reliability than
single phase systems. You should be familiar with 3 Phase powers and summing the powers of each phase in a 3-
phase circuit to calculate overall power.
Mechanical Domain: Motors/ Drives – The AC Induction Motor and DC motor.
When designing your power electronics circuit, you must gain a good understanding of your load- for example, a
dual-action electro-mechanical converter – a motor. Motors convert electrical energy to mechanical energy and are
key to “making big things move”. The simplest motor for this in terms of power electronics design would be a DC
motor. It has two basic components: field windings mounted on a tube (stator) and armature windings mounted on
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a rotor. It is supplied with a rectified voltage and current from an AC source. The DC motor is well established
technology, requiring simple power converters and control systems with a wide speed range and a fast response.
More common than DC motors in industrial applications due to its reliability and efficiency is the Rotating AC
Induction Motor. It comprises of windings mounted symmetrically inside a hollow metal tube (stator). The 3-phased
balanced voltage applied to these windings creates 3 magnetic fields whose flux rotates the rotor - mounted in the
centre of stator - and its shaft – on which the load is connected. The power of the motor – a function of input
voltages, current, winding, core and rotational losses, is expressed as its output torque and rotor speed. An induction
motor will have key operating points to consider when starting up, to reach a steady-state operating region of
constant motor speed and a torque matched to the load torque.
Another common induction motor you could consider is the wheeled linear induction motor. This performs a similar
manner to the rotating induction motor with the primary difference being that the stator and rotor are flat; the rotor
is fixed, and the magnetic flux propels the mechanical body housing the stator; railway trains are the common
application with the rotor being the track.
Once you have a basic, single speed DC or AC induction motor drive simulated you could consider whether to make
the speed adjustable/variable although this is a purely optional feature. Adjusting DC motor speed is by changing
voltage or current supplied. Motor speed control for induction motors is via several control schemes. These can be
considered either slip control, where voltage and impedance is varied, or frequency control (cyclo-converters and
DC-Link inverters). There are other motors that can be considered for variable speed control such as AC synchronous
motors, however the single speed DC motor and AC Induction motor should be your primary consideration.
Motors are part of most but not all load types. If your load requires a motor, you will need to consider the Torque-
Speed characteristics of your load i.e. what is the required torque for the speed you require to move your load.
Several other factors could be considered when choosing the motor. These include the speed range, efficiency
(input/output power ration), speed regulation (speed reduction due to torque increase), controllability, braking
requirements, reliability, power-to-weight ratio, power factor, load factor and duty cycle, supply variation effect.
References
[1] Mohan, Undeland and Robbin, Power Electronics: Converters Applications and Design, 2003.
[2] El-Sharkawi, Electrical Energy - An Introduction, CRC Press, 2005.
[3] Shepherd, Hully and Liang, Power electronics and motor control second edition, Cambridge University Press,
2000.
[4] G. Reed, B. Grainger, A. Sparacino and Z. Mao, “Ship to Grid: Medium-Voltage DC Concepts in Theory and
Practice,” IEEE Power and Energy Magazine, vol. 10, no. 6, pp. 70-79, 2012.
[5] R. Aarenstrup, Managing Model-Based Design, CreateSpace Independent Publishing Platform, 2015.
