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Kinetic Energy Storage and Magnetic Bearings: for Vehicular Applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
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 [en]
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: urn:nbn:se:uu:diva-212106ISBN: 978-91-554-8825-3 (print)OAI: oai:DiVA.org:uu-212106DiVA: diva2:676303
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
List of papers
1. Prototype of electric driveline with magnetically levitated double wound motor
Open this publication in new window or tab >>Prototype of electric driveline with magnetically levitated double wound motor
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2010 (English)In: Electrical Machines (ICEM), 2010 XIX International Conference on, 2010Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the ongoing work of constructing a complete driveline for an electric road vehicle, using a flywheel as auxiliary energy storage. The flywheel energy storage system (FESS) is connected in series between the main energy storage (batteries) and the wheel motor of the vehicle, allowing the batteries to deliver power to the system in an optimized way, while at the same time making efficient use of regenerative braking. A double wound permanent magnet electric machine is used to electrically separate the two sides. In order to minimize losses, the machine has a double rotor configuration and is suspended with magnetic bearings. A bench test set-up is being constructed to investigate the properties of this system in detail. This set-up will achieve a level of power and energy close to that of a full scale system. This will allow measurements of complete drive cycles to be performed, improving the understanding of the constituting components and optimization of the complete system.

Keyword
electric drives, flywheels, magnetic bearings, permanent magnet machines, regenerative braking, road vehicles, auxiliary energy storage, double rotor configuration, double wound permanent magnet electric machine, electric driveline, electric road vehicle, flywheel energy storage system, magnetically levitated double wound motor, wheel motor
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-140370 (URN)
Conference
International Conference on Electrical Machines, ICEM
Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2016-04-18Bibliographically approved
2. Magnetic bearings in kinetic energy storage systems for vehicular applications
Open this publication in new window or tab >>Magnetic bearings in kinetic energy storage systems for vehicular applications
2011 (English)In: Journal of Electrical Systems, ISSN 1112-5209, Vol. 7, no 2, 225-236 p.Article in journal (Refereed) Published
Abstract [en]

The rotating Kinetic Energy Storage System (KESS) is suitable as temporary energy storage in electric vehicles due to its insensitivity to the number of charge-discharge cycles and its relatively high specific energy. The size and weight of the KESS for a given amount of stored energy are minimized by decreasing the moment of inertia of the rotor and increasing its speed. A small and fast rotor has the additional benefit of reducing the induced gyroscopic moments as the vehicle turns. The very high resulting rotational speed makes the magnetic bearing an essential component of the system, with the Active Magnetic Bearing (AMB) being the most common implementation. The complexity and cost of an AMB can be reduced by integration with the electric machine, resulting in a bearingless and sensorless electric machine. This review article describes the usage of magnetic bearings for FESS in vehicular applications.

Keyword
Magnetic bearing, FESS, flywheel, energy storage, electric vehicle
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-165038 (URN)
Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2017-12-08Bibliographically approved
3. Prototype of Kinetic Energy Storage System for Electrified Utility Vehicles in Urban Traffic
Open this publication in new window or tab >>Prototype of Kinetic Energy Storage System for Electrified Utility Vehicles in Urban Traffic
2012 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Arlington, Virginia, USA: , 2012
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-190197 (URN)
Conference
13th International Symposium on Magnetic Bearings
Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2017-04-06
4. On the Efficiency of a Two-Power-Level Flywheel-Based All-Electric Driveline
Open this publication in new window or tab >>On the Efficiency of a Two-Power-Level Flywheel-Based All-Electric Driveline
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2012 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 5, no 8, 2794-2817 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents experimental results on an innovative electric driveline employing a kinetic energy storage device as energy buffer. A conceptual division of losses in the system was created, separating the complete system into three parts according to their function. This conceptualization of the system yielded a meaningful definition of the concept of efficiency. Additionally, a thorough theoretical framework for the prediction of losses associated with energy storage and transfer in the system was developed. A large number of spin-down tests at varying pressure levels were performed. A separation of the measured data into the different physical processes responsible for power loss was achieved from the corresponding dependence on rotational velocity. This comparison yielded an estimate of the perpendicular resistivity of the stranded copper conductor of 2.5 x 10(-8) +/- 3.5 x 10(-9). Further, power and energy were measured system-wide during operation, and an analysis of the losses was performed. The analytical solution was able to reproduce the measured distribution of losses in the system to an accuracy of 4.7% (95% CI). It was found that the losses attributed to the function of kinetic energy storage in the system amounted to between 45% and 65%, depending on usage.

Keyword
kinetic energy storage, flywheel, electric machine, driveline, electric vehicle, losses
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-182543 (URN)10.3390/en5082794 (DOI)000308241500011 ()
Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2017-12-07Bibliographically approved
5. A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings
Open this publication in new window or tab >>A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings
2014 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 9, 8101809Article in journal (Refereed) Published
Abstract [en]

Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-212105 (URN)10.1109/TMAG.2014.2321104 (DOI)000343036900019 ()
Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2017-12-06Bibliographically approved
6. Passive Axial Thrust Bearing for a Flywheel Energy Storage System
Open this publication in new window or tab >>Passive Axial Thrust Bearing for a Flywheel Energy Storage System
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2013 (English)Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212104 (URN)
Conference
The 1st Brazilian Workshop on Magnetic Bearings
Available from: 2013-12-05 Created: 2013-12-05 Last updated: 2017-10-24
7. 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, 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.

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: 2017-12-06Bibliographically approved

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Citation style
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Output format
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