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Automated Production Technologies and Measurement Systems for Ferrite Magnetized Linear Generators
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Vågkraft)ORCID iD: 0000-0001-8315-5523
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

The interest in breaking the historical dependence on fossil energy and begin moving towards more renewable energy sources is rising worldwide. This is largely due to uncertainties in the future supply of fossil fuels and the rising concerns about humanity’s role in the currently ongoing climate changes. One renewable energy source is ocean waves and Uppsala University has since the early 2000s been performing active research in this area. The Uppsala wave energy concept is centered on developing linear generators coupled to point absorbing buoys, with the generator situated on the seabed and connected to the buoy on the sea surface via a steel wire. The motion of the buoy then transfers energy to the generator, where it is converted into electricity and sent to shore for delivery into the electrical grid.

This thesis will mainly focus on the development and evaluation of technologies used to automate the manufacturing of the translator, a central part of the linear generator, using industrial robotics. The translator is a 3 m high and 0.8 m wide three sided structure with an aluminum pipe at its center. The structure consists of alternating layers of steel plates (pole-shoes) and ferrite magnets, with a total of 72 layers per side. To perform experiments on translator assembly and production, a robot cell (centered on an IRB6650S industrial robot) complimented with relevant tools, equipment and security measures, has been designed and constructed. The mounting of the pole-shoes on the central pipe, using the industrial robot, proved to be the most challenging task to solve. However, by implementing a precise work-piece orientation calibration system, combined with selective compliance robot tools, the task could be performed with mounting speeds of up to 50 mm/s. Although progress has been made, much work still remains before fully automated translator assembly is a reality.

A secondary topic of this thesis is the development of stand-alone measurement systems to be used in the linear generator, once it has been deployed on the seabed. The main requirements of such a measurement system is robustness, resistance to electrical noise, and power efficiency. If possible the system should also be portable and easy to use. This was solved by developing a custom measurement circuit, based on industry standard 4–20 mA current signals, combined with a portable submersible logging unit. The latest iteration of the system is small enough to be deployed and retrieved by one person, and can collect data for 10 weeks before running out of batteries. Future work in this area should focus on increasing the usability of the system.

The third and final topic of this thesis is a short discussion of an engineering approach to kinetic energy storage, in the form of high-speed composite flywheels, and the design of two different prototypes of such flywheels. Both designs gave important insights to the research group, but a few crucial design faults unfortunately made it impossible to evaluate the full potential of the two designs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 79 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1573
Keyword [en]
industrial robotics, automation, self-sensing, calibration, ferrite, linear generator, wave energy, offshore, measurements, electronics, kinetic energy storage, reluctance motor
National Category
Robotics Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-330866ISBN: 978-91-513-0095-5 (print)OAI: oai:DiVA.org:uu-330866DiVA: diva2:1147784
Public defence
2017-11-24, Polhemsalen, Lägerhyddsvägen 1, 752 37 Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-11-02 Created: 2017-10-08 Last updated: 2017-11-02
List of papers
1. Self-Sensing Electromagnets for Robotic Tooling Systems: Combining Sensor and Actuator
Open this publication in new window or tab >>Self-Sensing Electromagnets for Robotic Tooling Systems: Combining Sensor and Actuator
2016 (English)In: Machines, ISSN 2075-1702, Vol. 4, no 3, 16Article in journal (Refereed) Published
Abstract [en]

A low-cost method, which integrates distance sensing functionality into a switched electromagnet by using a hybrid switching mode and current ripple measurements, is proposed. The electromagnet is controlled by a micro-controller via a MOSFET H bridge, utilizing a comparator-based current control. Additionally, a method for calculating the inductance of the electromagnet and approximating the magnetic contact between the electromagnet and its target is also presented. The resulting tool is attached to an industrial robot, and the system performance using this setup is evaluated. Distance sensing in the range of 0 mm to 5.2 mm is demonstrated. It is also shown that the relation between magnetic contact, coil current and calculated inductance can be reduced to a predictive look-up table, enabling the quality of the magnetic contact to be estimated using minimal computational effort.

Keyword
electromagnet, distance measurement, self-sensing, robotic-tool, current control, current ripple, H bridge, micro-controller
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-305436 (URN)10.3390/machines4030016 (DOI)000401524100003 ()
Funder
VINNOVA
Available from: 2016-10-18 Created: 2016-10-18 Last updated: 2017-10-08Bibliographically approved
2. Automated Mounting of Pole-Shoe Wedges in Linear Wave Power Generators-Using Industrial Robotics and Proximity Sensors
Open this publication in new window or tab >>Automated Mounting of Pole-Shoe Wedges in Linear Wave Power Generators-Using Industrial Robotics and Proximity Sensors
2017 (English)In: MACHINES, ISSN 2075-1702, Vol. 5, no 1, 10Article in journal (Refereed) Published
Abstract [en]

A system for automatic mounting of high tolerance wedges inside a wave power linear generator is proposed. As for any renewable energy concept utilising numerous smaller generation units, minimising the production cost per unit is vital for commercialization. The linear generator in question uses self-locking wedges, which are challenging to mount using industrial robots due to the high tolerances used, and because of the fact that any angular error remaining after calibration risks damaging the equipment. Using two types of probes, mechanical touch probes and inductive proximity sensors, combined with a flexible robot tool and iterative calibration routines, an automatic mounting system that overcomes the challenges of high tolerance wedge mounting is presented. The system is experimentally verified to work at mounting speeds of up to 50mms(-1), and calibration accuracies of 0.25mm and 0.1 degrees are achieved. The use of a flexible robot tool, able to move freely in one Cartesian plane, was found to be essential for making the system work.

Place, publisher, year, edition, pages
MDPI AG, 2017
Keyword
automated production, wave power, robotics, calibration, sensors, wedges, linear-generator, touch probe
National Category
Environmental Engineering
Identifiers
urn:nbn:se:uu:diva-324353 (URN)10.3390/machines5010010 (DOI)000401524900009 ()
Funder
VINNOVA
Available from: 2017-06-14 Created: 2017-06-14 Last updated: 2017-10-08Bibliographically approved
3. Preparing the Uppsala University wave energy converter generator for large-scale production
Open this publication in new window or tab >>Preparing the Uppsala University wave energy converter generator for large-scale production
Show others...
2014 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Halifax, Canada: , 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-237554 (URN)
Conference
5th International Conference on Ocean Energy
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2017-10-08
4. Offshore Measurement System for WavePower: Using Current Loop Feedback
Open this publication in new window or tab >>Offshore Measurement System for WavePower: Using Current Loop Feedback
2016 (English)In: Electronics, ISSN 2079-9292, Vol. 5, no 4, 86Article in journal (Refereed) Published
Abstract [en]

This paper presents the design and testing of a measurement system for wave powergenerators. The work is part of a project to build a robust and cheap measurement system for offshoremonitoring of wave power farms. Due to the harsh offshore environment, low accessibility andhigh cost for installation and maintenance, it is of key importance to minimize power consumption,complexity and cost of each measurement unit. For the first prototype, the objective was to measurevoltage, current and translator position inside the linear wave power generator. For this, twoprinted circuit boards (PCBs) were developed, using a two wire current loop transmitter setup.They were tested separately and in a three phase setup inside a wave power generator duringonshore tests. To ensure stability, speed and accuracy in the signal transfer, the PCBs were tested forlinearity, frequency response and step response. In addition, power consumption was measured,for operational time evaluation. Results show good agreement between expected and measuredperformance, with an input range of ±1560 V and ±420 A for alternating current measurements anda bandwidth of 10 kHz and 7 kHz, for voltage and current measurements, respectively. The powerconsumption was measured to 0.5 W for each measurement unit, at 24 V feed.

Keyword
wave power; conditional monitoring; PCB; current loop; measurement system
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-313258 (URN)10.3390/electronics5040086 (DOI)000392387600008 ()
Available from: 2017-01-18 Created: 2017-01-18 Last updated: 2017-10-08Bibliographically approved
5. Portable Data Acquisition Systemfor Offshore Applications
Open this publication in new window or tab >>Portable Data Acquisition Systemfor Offshore Applications
(English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Refereed) Submitted
Abstract [en]

In the development of ocean energy technologies, full scale sea trials has proven expensive and challenging. Asa contribution to the development of flexible, reliable and affordable measurement systems for such sea trials, thispaper presents and evaluates a portable data acquisition system. The system is battery powered and consists of asensor system and a logger unit, where the logger and battery is placed in a retrievable pressure vessel. Sensor outputis carried with 4-20 mA current signals between sensor system and logger. The custom logger is programmable andoffers many options to apply different logging schedules and to limit the sensor system power supply accordingly.Evaluation show that the system implemented offers 5-22 weeks of 1 kHz, 16 bit monitoring of 16 signals, dependingon chosen logging schedule. Suggestions are also given for how to raise the operation time to up to 50 weeks.Although lacking the sophistication of a full signal infrastructure, the system offers a cheap and flexible option forwhen and where such infrastructure is no available.

Keyword
Data Acquisition, Ocean Energy, Wave Power, Logger, Offshore Measurments
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-329827 (URN)
Available from: 2017-09-21 Created: 2017-09-21 Last updated: 2017-10-08
6. Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters
Open this publication in new window or tab >>Nearshore Tests of the Tidal Compensation System for Point-Absorbing Wave Energy Converters
2015 (English)In: Energies, ISSN 1996-1073, Vol. 8, no 4, 3272-3291 p.Article in journal (Refereed) Published
Abstract [en]

The power production of the linear generator wave energy converter developed at Uppsala University is affected by variations of mean sea level. The reason is that these variations change the distance between the point absorber located on the surface and the linear generator located on the seabed. This shifts the average position of the translator with respect to the center of the stator, thereby reducing the generator output power. A device mounted on the point absorber that compensates for tides of small range by regulating the length of the connection line between the buoy at the surface and the linear generator has been constructed and tested. This paper describes the electro-mechanical, measurement, communication and control systems installed on the buoy and shows the results obtained before its connection to the generator. The adjustment of the line was achieved through a linear actuator, which shortens the line during low tides and vice versa. The motor that drives the mechanical device was activated remotely via SMS. The measurement system that was mounted on the buoy consisted of current and voltage sensors, accelerometers, strain gauges and inductive and laser sensors. The data collected were transferred via Internet to a Dropbox server. As described within the paper, after the calibration of the sensors, the buoy was assembled and tested in the waters of Lysekil harbor, a few kilometers from the Uppsala University research site. Moreover, the performance of the sensors, the motion of the mechanical device, the power consumption, the current control strategy and the communication system are discussed.

National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-255300 (URN)10.3390/en8043272 (DOI)000353963400045 ()
Available from: 2015-06-18 Created: 2015-06-15 Last updated: 2017-10-08Bibliographically approved
7. Control System for Compensator of Mean Sea Level Variations at the Lysekil Research Site
Open this publication in new window or tab >>Control System for Compensator of Mean Sea Level Variations at the Lysekil Research Site
2014 (English)Conference paper, Published paper (Other academic)
Place, publisher, year, edition, pages
Japan, Tokyo: , 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-237524 (URN)
Conference
2nd Asian Wave and Tidal Energy Conference
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2017-10-08
8. Reluctance Machine for a Hollow Cylinder Flywheel
Open this publication in new window or tab >>Reluctance Machine for a Hollow Cylinder Flywheel
Show others...
2017 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 3, 316Article in journal (Refereed) Published
Abstract [en]

A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have a shaft and spokes and is predicted to store 181 Wh/kg at ultimate tensile strength (UTS) according to simulations. The novel SRM is an axial flux machine, chosen due to its robustness and tolerance for high strain. The computed maximum tip speed of the motor at UTS is 1050 m/s . A small-scale proof-of-concept electric machine prototype has been constructed, and the machine inductance has been estimated from measurements of voltage and current and compared against results from analytical models and finite element analysis (FEA). The prototype measurements were used to simulate operation during maximal speed for a comparison towards other high-speed electric machines, in terms of tip speed and power. The mechanical design of the flywheel was performed with an analytical formulation assuming planar stress in concentric shells of orthotropic (unidirectionally circumferentially wound) carbon composites. The analytical approach was verified with 3D FEA in terms of stress and strain.

Keyword
flywheel energy storage, hollow cylinder flywheel, reluctance machine, high-speed machines
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-317875 (URN)10.3390/en10030316 (DOI)000398736700056 ()
Available from: 2017-03-21 Created: 2017-03-21 Last updated: 2017-10-08Bibliographically approved
9. High-Speed Kinetic Energy Buffer: Optimization of Composite Shell and Magnetic Bearings
Open this publication in new window or tab >>High-Speed Kinetic Energy Buffer: Optimization of Composite Shell and Magnetic Bearings
2014 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, Vol. 61, no 6, 3012-3021 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents the design and optimization of a high-speed (30 000 r/min) kinetic energy storage system. The purpose of the device is to function as an energy buffer storing up to 867 Wh, primarily for utility vehicles in urban traffic. The rotor comprises a solid composite shell of carbon and glass fibers in an epoxy matrix, constructed in one curing. The shell is optimized using a combined analytical and numerical approach. The radial stress in the shell is kept compressive by integrating the electric machine, thereby avoiding delamination. Radial centering is achieved through eight active electromagnetic actuators. The actuator geometry is optimized using a direct coupling between SolidWorks, Comsol, and Matlab for maximum force over resistive loss for a given current density. The optimization results in a system with 300% higher current stiffness than the reference geometry with constant flux area, at the expense of 33% higher power loss. The actuators are driven by semipassive H bridges and controlled by an FPGA. Current control at 20 kHz with a noise of less than 5 mA (95% CI) is achieved, allowing position control at 4 kHz to be implemented.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212101 (URN)10.1109/TIE.2013.2259782 (DOI)000329055300039 ()
Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2017-10-08Bibliographically approved
10. Spin-down Losses and Vibration Analysis of a Flywheel Energy Storage System
Open this publication in new window or tab >>Spin-down Losses and Vibration Analysis of a Flywheel Energy Storage System
(English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073Article in journal (Refereed) Submitted
Abstract [en]

An integrated flywheel prototype designed to store 868 W h at 30 000 rpm with a novel radial flux core-less electric machine was constructed. The rotor was suspended contactlessly on active radial magnetic bearings and passive axial magnetic bearings. This paper describes the system in detail. The rotor was found to be weakly damped (even at standstill) and the magnetic bearings were used to specifically compensate particular eigenfrequencies. The levitation system was then used to experimentally evaluate the vibrations of the rotor, and compared to FEM studies. Spin-down tests were conducted to evaluate levitation system performance. 

Keyword
flywheel energy storage, spin-down losses, vibrations
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-319522 (URN)
Funder
StandUp
Available from: 2017-04-06 Created: 2017-04-06 Last updated: 2017-11-20
11. High Speed Flywheels for Vehicular Applications
Open this publication in new window or tab >>High Speed Flywheels for Vehicular Applications
Show others...
2014 (English)In: 14th International Symposium on Magnetic Bearings, Linz, Austria, 2014Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Linz, Austria: , 2014
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-237547 (URN)
Conference
14th International Symposium on Magnetic Bearings
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2017-10-08
12. A Method for Calibrating Work-Piece Orientation: Using a Dual-Axis MEMS Inclinometer
Open this publication in new window or tab >>A Method for Calibrating Work-Piece Orientation: Using a Dual-Axis MEMS Inclinometer
(English)In: Robotics and Computer-Integrated Manufacturing, ISSN 0736-5845, E-ISSN 1879-2537Article in journal (Refereed) Submitted
Abstract [en]

An accelerometer based alignment system designed to align robotic tools and work-pieces in a Cartesian coordinate system is presented, with potential applications within the automated production industry. An overview of the underlying theory, used hardware, micro-controller implementation and performed experiments is presented. The developed theoretical model and prototype hardware is veried against both simulations and experiments, evaluating their performance and practical limitations. For a set of 2000 random initial misalignments with an amplitude in the range of 0° to 10°, the system achieved an alignment accuracy with a 3-sigma bound of 0.023° in the XY plane and 0.14° along the Z-axis. On average the used robot needed 20.86 s to align the used tool to stated accuracy.

National Category
Robotics
Identifiers
urn:nbn:se:uu:diva-330869 (URN)
Available from: 2017-10-05 Created: 2017-10-05 Last updated: 2017-10-15

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