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Flywheel in an all-electric propulsion system
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Svänghjul)ORCID iD: 0000-0002-4350-5194
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Energy storage is a crucial condition for both transportation purposes and for the use of electricity. Flywheels can be used as actual energy storage but also as power handling device. Their high power capacity compared to other means of storing electric energy makes them very convenient for smoothing power transients. These occur frequently in vehicles but also in the electric grid. In both these areas there is a lot to gain by reducing the power transients and irregularities.

The research conducted at Uppsala university and described in this thesis is focused on an all-electric propulsion system based on an electric flywheel with double stator windings. The flywheel is inserted in between the main energy storage (assumed to be a battery) and the traction motor in an electric vehicle. This system has been evaluated by simulations in a Matlab model, comparing two otherwise identical drivelines, one with and one without a flywheel.

The flywheel is shown to have several advantages for an all-electric propulsion system for a vehicle. The maximum power from the battery decreases more than ten times as the flywheel absorbs and supplies all the high power fluxes occuring at acceleration and braking. The battery delivers a low and almost constant power to the flywheel. The amount of batteries needed decreases whereas the battery lifetime and efficiency increases. Another benefit the flywheel configuration brings is a higher energy efficiency and hence less need for cooling.

The model has also been used to evaluate the flywheel functionality for an electric grid application. The power from renewable intermittent energy sources such as wave, wind and current power can be smoothened by the flywheel, making these energy sources more efficient and thereby competitive with a remaining high power quality in the electric grid.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2011. , 50 p.
Series
Licentiate Thesis, Division of Electricity, Department of Engineering Sciences, ISSN 0349-8352
Keyword [en]
Flywheel, electric vehicle, hybrid vehicle, power management, energy storage
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-222030OAI: oai:DiVA.org:uu-222030DiVA: diva2:710589
Presentation
2011-06-10, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-04-09 Created: 2014-04-07 Last updated: 2014-04-09Bibliographically approved
List of papers
1. Losses in Axial-Flux Permanent-Magnet Coreless Flywheel Energy Storage Systems
Open this publication in new window or tab >>Losses in Axial-Flux Permanent-Magnet Coreless Flywheel Energy Storage Systems
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2008 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Vilamoura, Portugal: , 2008
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113430 (URN)
Conference
18th International Conference on Electrical Machines
Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2016-04-12Bibliographically approved
2. Design Parameters Calculation of a Novel Driveline for Electric Vehicles
Open this publication in new window or tab >>Design Parameters Calculation of a Novel Driveline for Electric Vehicles
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2009 (English)In: World Electric Vehicle Journal, ISSN 2032-6653, Vol. 3Article in journal (Refereed) Published
Abstract [en]

A driveline for electric vehicles is presented. The propulsion system is operated at a higher voltage than the primary energy source. The batteries selected as the primary energy source deliver power to the vehicle through a motor-generator wounded with two electrically isolated sets of windings, named Two Voltage Level Machine (TVLM). The dynamic behaviour of a vehicle operating according to a standard drive cycle is studied. Parameters of the driveline such as power rates and size of the flywheel are obtained by optimization. A description of the performance of a TVLM is also presented through its equivalent circuit and the control of the machine. Special attention to the system losses is presented. A scale prototype has been constructed and tested under a drive cycle, demonstrating the system performance of the system.

Keyword
Flywheel, Electric driveline, Regenerative braking, Simulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113157 (URN)ISSN 2032-6653 (ISBN)
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2016-04-14Bibliographically approved
3. A Double Wound Flywheel System under Standard Drive Cycles: Simulations and Experiments
Open this publication in new window or tab >>A Double Wound Flywheel System under Standard Drive Cycles: Simulations and Experiments
2010 (English)In: International Journal of Emerging Electric Power Systems, ISSN 1553-779X, Vol. 11, no 4, Article 6.- p.Article in journal (Refereed) Published
Abstract [en]

Flywheel systems are attractive for use in electric vehicles, being able to efficiently handle the large power needed for acceleration and regenerative braking. A double wound flywheel machine, divided in two different voltage levels by the windings, acting like a rotating transformer, is studied. The flywheel stator windings have two sides: a low voltage side connected to the battery and a high voltage side connected to the wheel motor. The load variations on the high voltage side have minimal affect on the low voltage side of the system, in which the speed control of the machine is performed. In this paper the functionality of the system is investigated by means of simulations and experiments. Different standard drive cycles are applied on the high voltage side to assess the effect of load variations in the system as a whole and particularly in the speed control. The response of the speed control system is investigated with computer simulations and experimental verification. The energy storage in the flywheel allows a steady power supply from the battery via the inverter, proving the functionality of the system.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-140340 (URN)10.2202/1553-779X.2487 (DOI)
Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2015-12-08Bibliographically approved
4. 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
5. Flywheel as power handling device in electric and hybrid vehicles
Open this publication in new window or tab >>Flywheel as power handling device in electric and hybrid vehicles
(English)In: International Journal of Vehicular Technology, ISSN 1687-5702, E-ISSN 1687-5710Article in journal (Other academic) Submitted
Abstract [en]

The introduction of electric and hybrid vehicles will make it possible to reduce the negative environmental impact from the transportation sector. The integration of a flywheel as a power handling device would enhance the efficiency of the electric driveline. This article presents a model for a proposed driveline with an integrated flywheel. It also compares the performance for that driveline with that of a driveline without a flywheel by simulating the model performing two different drive cycles, the American FTP 75 and the European NEDC. Simulations show that the integrated flywheel driveline enables higher energy density batteries, decreases total losses, increases the efficiency and lifetime of the battery and also enables an efficient regenerative braking.

Keyword
Flywheel, electric vehicle, power management, energy storage
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-221949 (URN)
Available from: 2014-04-07 Created: 2014-04-07 Last updated: 2017-12-05Bibliographically approved
6. Dynamic stability of an electricity generation system based on renewable energy
Open this publication in new window or tab >>Dynamic stability of an electricity generation system based on renewable energy
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2011 (English)In: Proceedings of CIRED 2011 - the 21st International Conference and Exhibition on Electricity Distribution, CIRED - Congrès International des Réseaux Electriques de Distribution, 2011, 0940- p.Conference paper, Published paper (Refereed)
Abstract [en]

Renewable energy must be stored in order to make itreliable. Flywheels are capable of storing high amounts ofenergy and can also be used as power buffers, due to theirhigh power densities. This paper investigates a way tosmooth the power output from renewable energy converters(wave, wind and marine current) by adding a doublewoundflywheel energy storage to the system. Simulationsshow that a ramp-controlled flywheel energy storage woulddrastically smooth the short time power from a wave energyconverter but not be that appropriate for longer termenergy storage. The power quality enhancement producedby the addition of the flywheel to the system is alsosimulated and discussed.

Place, publisher, year, edition, pages
CIRED - Congrès International des Réseaux Electriques de Distribution, 2011
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-157071 (URN)
Conference
CIRED 2011 - 21st International Conference and Exhibition on Electricity Distribution, June 6-9, Frankfurt am Main, Germany
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2016-04-19
7. Power balance control in an AC/DC/AC converter for regenerative braking in a two-voltage-level flywheel based driveline
Open this publication in new window or tab >>Power balance control in an AC/DC/AC converter for regenerative braking in a two-voltage-level flywheel based driveline
2011 (English)In: International Journal of Vehicular Technology, ISSN 1687-5702, E-ISSN 1687-5710, Vol. 2011, 934023- p.Article in journal (Refereed) Published
Abstract [en]

The integration of a flywheel as a power handling can increase the energy storage capacity and reduce the number of battery charge/discharge cycles. Furthermore, the ability of recovering energy of the vehicle during breaking can increase the system efficiency. The flywheel-based all-electric driveline investigated here has its novelty in the use of a double-wound flywheel motor/generator, which divides the system in two different voltage levels, enhancing the efficiency of the electric driveline. The connection of two AC electrical machines (i.e., the flywheel and the wheel motor) with different and variable operation frequency is challenging. A power matching control applied to an AC/DC/AC converter has been implemented. The AC/DC/AC converter regenerates the electric power converted during braking to the flywheel machine, used here as power handling device. By controlling the power balance, the same hardware can be used for acceleration and braking, providing the reduction of harmonics and robust response. A simulation of the complete system during braking mode has been performed both in Matlab and Simulink, and their results have been compared. The functionality of the proposed control has been shown and discussed, with full regeneration achieved. A round-trip efficiency (wheel to wheel) higher than 80% has been obtained.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-157059 (URN)10.1155/2011/934023 (DOI)
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2017-12-08Bibliographically approved

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