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Electrified Integrated Kinetic Energy Storage
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Doktorand, Uppsala Universitet. (Svänghjulsgruppen)ORCID iD: 0000-0002-5736-5700
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 [en]
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: urn:nbn:se:uu:diva-319622ISBN: 978-91-554-9891-7 (print)OAI: oai:DiVA.org:uu-319622DiVA: diva2:1087343
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
List of papers
1. 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
2. Sliding Mode 4-Quadrant DCDC Converter for a Flywheel Application
Open this publication in new window or tab >>Sliding Mode 4-Quadrant DCDC Converter for a Flywheel Application
2013 (English)In: Control Engineering Practice, ISSN 0967-0661, Vol. 21, no 4, 473-482 p.Article in journal (Refereed) Published
Abstract [en]

A sliding mode control system for a 4-quadrant DCDC converter was designed and a low voltage prototype was constructed. The target application is a flywheel based all-electric driveline. Important qualities are current and voltage control, bidirectionality, and stability for a broad input voltage range, focusing on a smooth transition between operating quadrants. The control decisions were based entirely on the latest available measurements, implying that no memory needs reinitializing when changing quadrant. The boost control was based on a topology specific current source approximation. The control was found to be parameter invariant, regardless of high input/output dynamics variance.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-157065 (URN)10.1016/j.conengprac.2012.12.012 (DOI)000316036500012 ()
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2017-04-06Bibliographically approved
3. 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: 2017-08-24
4. Magnetic Modeling and Measurement of Forces Between Permanent Magnet Rings used as Passive Magnetic Bearings
Open this publication in new window or tab >>Magnetic Modeling and Measurement of Forces Between Permanent Magnet Rings used as Passive Magnetic Bearings
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2013 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Rio de Janeiro, Brazil: , 2013
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-212880 (URN)
Conference
1st Brazilian Workshop on Magnetic Bearings, BWMB 2013
Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2017-08-24
5. 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
6. 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: 2017-04-06Bibliographically approved
7. High Speed Flywheels for Vehicular Applications
Open this publication in new window or tab >>High Speed Flywheels for Vehicular Applications
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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
8. Flywheel Energy Storage for Automotive Applications
Open this publication in new window or tab >>Flywheel Energy Storage for Automotive Applications
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2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 10, 10636-10663 p.Article, review/survey (Refereed) Published
Abstract [en]

A review of flywheel energy storage technology was made, with a special focus on the progress in automotive applications. We found that there are at least 26 university research groups and 27 companies contributing to flywheel technology development. Flywheels are seen to excel in high-power applications, placing them closer in functionality to supercapacitors than to batteries. Examples of flywheels optimized for vehicular applications were found with a specific power of 5.5 kW/kg and a specific energy of 3.5 Wh/kg. Another flywheel system had 3.15 kW/kg and 6.4 Wh/kg, which can be compared to a state-of-the-art supercapacitor vehicular system with 1.7 kW/kg and 2.3 Wh/kg, respectively. Flywheel energy storage is reaching maturity, with 500 flywheel power buffer systems being deployed for London buses (resulting in fuel savings of over 20%), 400 flywheels in operation for grid frequency regulation and many hundreds more installed for uninterruptible power supply (UPS) applications. The industry estimates the mass-production cost of a specific consumer-car flywheel system to be 2000 USD. For regular cars, this system has been shown to save 35% fuel in the U.S. Federal Test Procedure (FTP) drive cycle.

Keyword
flywheel; kinetic energy storage; energy storage
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-268572 (URN)10.3390/en81010636 (DOI)000364230500004 ()
Funder
StandUp
Available from: 2015-12-08 Created: 2015-12-08 Last updated: 2017-04-06Bibliographically approved
9. Eddy Currents in a Passive Magnetic Axial Thrust Bearing for a Flywheel Energy Storage System
Open this publication in new window or tab >>Eddy Currents in a Passive Magnetic Axial Thrust Bearing for a Flywheel Energy Storage System
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(English)In: International journal of applied electromagnetics and mechanics, ISSN 1383-5416, E-ISSN 1875-8800Article in journal (Refereed) In press
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-317880 (URN)
Available from: 2017-03-21 Created: 2017-03-21 Last updated: 2017-08-24
10. Reluctance Machine for a Hollow Cylinder Flywheel
Open this publication in new window or tab >>Reluctance Machine for a Hollow Cylinder Flywheel
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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
11. Eigen frequency and damping in a passive magnetic bearing system
Open this publication in new window or tab >>Eigen frequency and damping in a passive magnetic bearing system
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2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A complete passive magnetic bearing system, consisting in a Permanent Magnet radial bearing and a Superconductive Magnetic Bearing has been simulated and constructed. The forces in both types of magnetic bearings are not linear. The non-linear behavior has been implemented in a FEM model and compared with linear models. A spin down test has been conducted to the built system and the Eigen frequencies have been recorded. The Eigen frequencies calculated with and without the non-linear behavior implemented in the model are very similar.

Keyword
Flywheel, Permanent Magnet Bearing, Superconductive Magnetic Bearing, Eigen frequencies, Passive Bearings, Numerical Analysis, FEM
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-305350 (URN)
Conference
15th International Symposium on Magnetic Bearings (ISMB15), 3-6 August 2016. Kitakyushu Japan
Available from: 2016-10-14 Created: 2016-10-14 Last updated: 2017-04-06Bibliographically approved
12. Fast Optimization Methodology for Press-fitted Composite Hollow Cylinder Flywheel Energy Storage
Open this publication in new window or tab >>Fast Optimization Methodology for Press-fitted Composite Hollow Cylinder Flywheel Energy Storage
(English)In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085Article in journal (Refereed) Submitted
Abstract [en]

An optimization strategy for a hollow flywheel energy storage is presented. Several press-fitted shells of anisotropic materials (such as carbon composites) are studied by an analytical model based on a plane stress assumption. The optimization target is stored energy. The optimizer constraints (which were evaluated at full and zero charge level, respectively) were based on strain-based models for fatigue life of composites, and stress-based fatigue life models for high-strength aluminum. A compiled library was built within the scope of this work, and used to run a robust global grid-search optimizing method. The analytical model was compared against a finite element method solution, and the (single-core) library was seen to be at least 5 orders of magnitude faster. 

Keyword
flywheel energy storage, optimization, fatigue
National Category
Applied Mechanics
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-319521 (URN)
Funder
StandUp
Available from: 2017-04-05 Created: 2017-04-05 Last updated: 2017-04-06
13. 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: 2017-10-08

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