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High-Speed Kinetic Energy Buffer: Optimization of Composite Shell and Magnetic Bearings
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2014 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, 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.

Place, publisher, year, edition, pages
2014. Vol. 61, no 6, 3012-3021 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-212101DOI: 10.1109/TIE.2013.2259782ISI: 000329055300039OAI: oai:DiVA.org:uu-212101DiVA: diva2:676226
Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Kinetic Energy Storage and Magnetic Bearings: for Vehicular Applications
Open this publication in new window or tab >>Kinetic Energy Storage and Magnetic Bearings: for Vehicular Applications
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the main challenges in order to make electric cars competitive with gas-powered cars is in the improvement of the electric power system. Although many of the energy sources currently used in electric vehicles have sufficientlyhigh specific energy, their applicability is limited due to low specific power. It would therefore be advantageous to create a driveline with the main energy storage separated from a smaller energy buffer, designed to have high power capabilities and to withstand frequent and deep discharge cycles. It has been found that rotating kinetic energy storage in flywheels is very well suited for this type of application.

A composite shell, comprising an inner part made of glassfiber and an outer part made of carbonfiber, was analyzed analytically and numerically, designed, and constructed. The shell was fitted onto a metallic rotor using shrinkfitting. The cost of the shell, and the complexity of assembly, was reduced by winding the glass- and carbonfiber consecutively on a mandrel, and curing the complete assembly simultaneously. Thereby, the shell obtained an internal segmentation, without the need for fitting several concentric parts onto each other. The radial stress inside the composite shell was kept compressive thanks to a novel approach of using the permanent magnets of the integrated electric machine to provide radial mechanical load during rotation.

Two thrust bearing units (one upper and one lower) comprising one segmented unit with the permanent magnets in a cylindrical Halbach configuration and one non-segmented unit in a up/down configuration were optimized, constructed and tested. Each thrust bearing unit generated 1040 N of repelling force, and a positive axial stiffness of 169 N/mm at the nominal airgap of 5 mm. 

Two radial active magnetic bearings (one upper and one lower) were optimized, constructed and tested. By parameterizing the shape of the actuators, a numerical optimization of force over resistive loss from the bias currentcould be performed. The optimized shape of the electromagnets was produced by watercutting sheets of laminated steel. A maximum current stiffness of120 N/A at a bias current of 1.5 A was achieved.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 107 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1104
Keyword
flywheel, magnetic bearing, energy storage, electric vehicle
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212106 (URN)978-91-554-8825-3 (ISBN)
Public defence
2014-02-05, sal Å80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 08:15 (English)
Opponent
Supervisors
Available from: 2014-01-14 Created: 2013-12-05 Last updated: 2014-01-24
2. Electrified Integrated Kinetic Energy Storage
Open this publication in new window or tab >>Electrified Integrated Kinetic Energy Storage
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The electric car is a technically efficient driveline, although it is demanding in terms of the primary energy source. Most trips are below 50 km and the mean power required for maintaining speed is quite low, but the system has to be able to both provide long range and high maximum power for acceleration. By separating power and energy handling in a hybrid driveline, the primary energy source, e.g. a battery can be optimised for specific energy (decreasing costs and material usage). Kinetic energy storage in the form of flywheels can handle the short, high power bursts of acceleration and decceleration with high efficiency.

This thesis focuses on the design and construction of flywheels in which an electric machine and a low-loss magnetic suspension are considered an integral part of the composite shell, in an effort to increase specific energy. A method of numerically optimising shrink-fitted composite shells was developed and implemented in software, based on a plane stress assumption, with a grid search optimiser. A composite shell was designed, analysed numerically and constructed, with an integrated permanent magnet synchronous machine. Passive axial lift bearings were optimised, analysed numerically for losses and lift force, and verified with experiments. Active radial electromagnets optimised for high stiffness per ohmic loss were built and analysed in terms of force and stiffness, both numerically and experimentally. Electronics and a high-speed measurement system were designed to drive the magnetic bearings and the electric machine. The control of these systems were implemented in an FPGA, and a notch-filter was designed to suppress eigenfrequencies to achieve levitation of the rotor. The spin-down losses of the flywheel in vacuum were found to be 1.7 W/Wh, evaluated at 1000 rpm.

A novel switched reluctance machine concept was developed for hollow cylinder flywheels. This class of flywheels are shaft-less, in an effort to avoid the shaft-to-rim connection. A small-scale prototype was built and verified to correspond well to analytical and numerical models, by indirect measurement of the inductance through a system identification method.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 93 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1504
Keyword
flywheel energy storage, magnetic bearings, carbon composite
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-319622 (URN)978-91-554-9891-7 (ISBN)
Public defence
2017-06-08, Ång/80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Funder
StandUpSwedish Energy Agency
Available from: 2017-05-15 Created: 2017-04-06 Last updated: 2017-05-16
3. Automated Production Technologies and Measurement Systems for Ferrite Magnetized Linear Generators
Open this publication in new window or tab >>Automated Production Technologies and Measurement Systems for Ferrite Magnetized Linear Generators
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
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
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:nbn:se:uu:diva-330866 (URN)978-91-513-0095-5 (ISBN)
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

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Abrahamsson, JohanHedlund, MagnusKamf, TobiasBernhoff, Hans

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