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Power Control Systems in a Flywheel based All-Electric Driveline
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. (Energy Storage)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Flywheel systems are attractive in hybrid and electric vehicles due to their ability to handle power during acceleration and braking. The combination of a flywheel device with a battery source has several advantages such as high peak power capacity, high energy density and reduction in the number of charge/discharge cycles of the battery.

A flywheel based all-electric driveline is investigated in this thesis. The novelty of the system consists in the use of a double wound flywheel machine, which divides the system in two different power levels. Due to this configuration, the system becomes efficient and can handle the power developed during fast dynamical processes.

The complete driveline consists of three main components: the battery, the flywheel machine and the wheel motor. The High-Power (HP) side of the driveline connects the flywheel machine to the wheel motor, whereas the Low-Power (LP) side connects the flywheel machine to the battery. The connections of different components of the system are made electrically through power converter devices.

The present thesis focuses on the electrical converters and control strategies used in the flywheel based all-electric driveline. The control of power converters is responsible for the logic and functionality of the driveline, being a challenging step within this project.

Different power converter topologies have been investigated: a DC/DC plus a DC/AC converter on the LP side, and an AC/DC/AC converter on the HP side. The design and assembly of the power electronics and their control scheme have been successfully implemented. Different control strategies have been suggested and a complete scaled driveline has been assembled and tested based on previous simulation results.

Results have confirmed the functionality of the driveline, where smoothed output power has been obtained from the battery, whereas the flywheel handles power transients on the traction side. An average efficiency of about 87% (battery to wheels) has been obtained. The power converter systems have been shown to be efficient and robust, with control strategies able to handle the peak energy flow in the system. A regenerative braking strategy has been simulated and a wheel-to-wheel efficiency of about 80% has been estimated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 102 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 844
Keyword [en]
Flywheels, batteries, electric vehicles, control systems, power electronics, electric machines, efficiency.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-157074ISBN: 978-91-554-8133-9 (print)OAI: oai:DiVA.org:uu-157074DiVA: diva2:434755
Public defence
2011-09-30, Polhemsalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2011-09-09 Created: 2011-08-15 Last updated: 2011-11-03Bibliographically approved
List of papers
1. Battery Recharging Issue for a Two-Power-Level Flywheel System
Open this publication in new window or tab >>Battery Recharging Issue for a Two-Power-Level Flywheel System
2010 (English)In: Journal of Electrical and Computer Engineering, ISSN 2090-0147, E-ISSN 2090-0155, Vol. 2010, 470525- p.Article in journal (Refereed) Published
Abstract [en]

A novel battery recharging system for an all-electric driveline comprising a flywheel with a permanent magnet double wound synchronous machine (motor/generator) is presented. The double winding enables two voltage levels and two different power levels. This topology supersedes other all-electric drivelines. The battery operates in a low-power regime supplying the average power whereas the flywheel delivers and absorbs power peaks, which are up to a higher order of magnitude. The topology presents new challenges for the power conversion system, which is the focus of this investigation. The main challenge is the control of the power flow to the battery when the vehicle is parked despite the decay of the flywheel machine voltage; which is dependent on its charge state, that is, rotational speed. The design and simulation of an unidirectional DC/DC buck/boost converter for a variable rotational speed flywheel is presented. Conventional power electronic converters are used in a new application, which can maintain a constant current or voltage on the battery side. Successful PI current control has been implemented and simulated, together with the complete closed loop system.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-140342 (URN)10.1155/2010/470525 (DOI)
Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2017-12-11Bibliographically approved
2. 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
3. Battery discharging power control in a double-wound flywheel system applied to electric vehicles
Open this publication in new window or tab >>Battery discharging power control in a double-wound flywheel system applied to electric vehicles
2011 (English)In: International Journal of Emerging Electric Power Systems, ISSN 2194-5756, E-ISSN 1553-779X, Vol. 12, no 1, 1-15 p.Article in journal (Refereed) Published
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-157073 (URN)10.2202/1553-779X.2674 (DOI)
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2017-12-08Bibliographically approved
4. 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
5. Study on doubly fed flywheel machine based driveline withan AC/DC/AC converter
Open this publication in new window or tab >>Study on doubly fed flywheel machine based driveline withan AC/DC/AC converter
Show others...
2012 (English)In: IET Electrical Systems in Transportation, ISSN print 2042-9738; online 2042-9746, Vol. 2, no 2, 51-57 p.Article in journal (Refereed) Published
Abstract [en]

The combination of a flywheel device with a battery source has several advantages, such as high-peak power capacity, high energy density and reduction in the number of charging/discharging cycles in the battery. The flywheel system investigated here uses a double-wound flywheel motor/generator to divide the system into two different voltage/power levels. An AC/DC/AC converter is used to connect the high-power windings of the flywheel machine to the traction motor. The control strategy of the AC/DC/AC converter is discussed. The simulations of the complete system are carried out using Simulink and are compared with the experimental results, obtained from a scaled experimental test set-up. Simulations and experimental results show good agreement, where the designed controllers have managed to keep the different controlled signals almost equal to their reference values. Unity power factor and low distortion has been obtained in the flywheel voltage and current. The average efficiency of the driveline during a simple drive cycle has been obtained, being approximately 87%. A theoretical calculation, based on the real parameters of the system, was made, and it showed good agreement with the simulation and experimental results.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-157061 (URN)10.1049/iet-est.2011.0040 (DOI)
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2013-03-07Bibliographically approved
6. Controlling a permanent-magnet motor using PWM converter in flywheel energy storage systems
Open this publication in new window or tab >>Controlling a permanent-magnet motor using PWM converter in flywheel energy storage systems
2008 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Orlando, USA: , 2008
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113426 (URN)
Conference
34th Annual Conference of the IEEE Industrial Electronics Society (IECON-2008)
Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2016-04-12Bibliographically approved
7. Power electronics and control of two-voltage-level flywheel based all-electric driveline
Open this publication in new window or tab >>Power electronics and control of two-voltage-level flywheel based all-electric driveline
2011 (English)In: Proceedings of the IEEE International Symposium on Industrial Electronics, IEEE conference proceedings, 2011, 1659-1665 p.Conference paper, Published paper (Refereed)
Abstract [en]

A novel all-electric driveline comprising a flywheel with a permanent magnet doubly wound synchronous motor/generator is presented. The flywheel machine with a double set of windings divides the system in two voltage levels: a low voltage/power level, which is connected to the main energy storage source (e. g. battery) and a high voltage/power level, which is connected to the traction machine. A DC/DC + DC/AC converter makes the connection between the battery and the flywheel low voltage windings. An AC/DC/AC converter connects the flywheel high voltage windings to the wheel machine. A complete simulation of the system has been made in Simulink. Vector control based speed regulators have been designed and successfully simulated. DC link voltage control has been achieved by using synchronous rectification. Power estimation has been used during regenerative braking in order to charge the flywheel with the power generated from the vehicle speed reduction. Simulations have verified the functionality of the proposed system.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2011
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-157064 (URN)10.1109/ISIE.2011.5984410 (DOI)000297160600262 ()978-1-4244-9312-8 (ISBN)
Conference
2011 IEEE International Symposium on Industrial Electronics, Gdansk University of Technology Gdańsk, Poland 27 - 30 June, 2011
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2016-04-19Bibliographically approved
8. 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
Show others...
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
9. 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, E-ISSN 1873-6939, 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: 2017-12-08Bibliographically approved
10. 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
Show others...
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
11. Implementation and control of an AC/DC/AC converter for double wound flywheel application
Open this publication in new window or tab >>Implementation and control of an AC/DC/AC converter for double wound flywheel application
Show others...
2011 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-157067 (URN)
Conference
Proceedings of the IEEE International Conference on Control and Automation
Available from: 2011-08-15 Created: 2011-08-15 Last updated: 2016-04-20

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