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Analysis and control of a hybrid vehicle powered by free-piston energy converter
KTH, School of Electrical Engineering (EES).
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The introduction of hybrid powertrains has made it possible to utilise unconventional engines as primary power units in vehicles. The free-piston energy converter (FPEC) is such an engine. It is a combination of a free-piston combustion engine and a linear electrical machine. The main features of this configuration are high efficiency and a rapid transient response.

In this thesis the free-piston energy converter as part of a hybrid powertrain is studied. One issue of the FPEC is the generation of pulsating power due to the reciprocating motion of the translator. These pulsations affect the components in the powertrain. However, it is shown that these pulsations can be handled by a normal sized DC-link capacitor bank. In addition, two approaches to reduce these pulsations are suggested: the first approach is using generator force control and the second approach is based on phase-shifted operation of two FPEC units. The latter approach results in higher frequency and lower amplitude of the pulsations, which reduce the capacitor losses.

The FPEC start-up requirements are analysed and by choosing the correct amplitude of the generator force during start-up the energy consumption can be minimised.

The performance gain of utilising the FPEC in a medium sized series hybrid electric vehicle (SHEV) is also studied. An FPEC model suitable for vehicle simulation is developed and a series hybrid powertrain, with the same performance as the Toyota Prius, is dimensioned and modelled.

Optimisation is utilised to find a lower limit on the SHEV's fuel consumption for a given drivecycle. In addition, three power management control strategies for the FPEC system are investigated: two load-following strategies using one and two FPEC units respectively and one strategy based on the ideas of an equivalent consumption minimisation (ECM) proposed earlier in the literature.

The results show a significant decrease in fuel consumption, compared to a diesel-generator powered SHEV, just by replacing the diesel-generator with an FPEC. This result is improved even more by using two FPEC units to generate the propulsion power, as this increases the efficiency at low loads. The ECM control strategy does not reduce the fuel consumption compared to the load-following strategies but gives a better utilisation of the available power sources.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 111 p.
Series
Trita-EE, ISSN 1653-5146 ; 2006:047
Keyword [en]
free-piston energy converter, FPEC, series hybrid electric vehicle, SHEV, power management, energy management, powertrain evaluation, equivalent consumption minimisation, ECMS, linear engine
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4189ISBN: 91-7178-485-3 (print)OAI: oai:DiVA.org:kth-4189DiVA: diva2:11141
Presentation
2006-11-27, H1, Teknikringen 33, Stockholm, 15:00
Opponent
Supervisors
Note
QC 20101116Available from: 2006-11-27 Created: 2006-11-27 Last updated: 2010-11-16Bibliographically approved
List of papers
1. Minimizing power pulsations in a free piston energy converter
Open this publication in new window or tab >>Minimizing power pulsations in a free piston energy converter
2005 (English)In: 2005 European Conference on Power Electronics and Applications, 2005Conference paper, Published paper (Refereed)
Abstract [en]

A Free Piston Energy Converter (FPEC) is a combination of a linear combustion engine and a linear electrical machine. This type of converter has many potential advantages like high efficiency, low fuel consumption and low emissions, which make it suitable for a series hybrid vehicle. However, the generated power pulsates due to the reciprocating motion of the translator. This paper presents a comparative study on how different generator force profiles affect the electric power pulsations produced by the FPEC. In addition, the influence of these profiles on translator motion and the needed power converter current is investigated. A dynamic free piston model is used for the investigation. Results show that the generator force profile has a major impact on the power pulsation amplitude and peak current demand. Thus the chosen force profile will affect dimensioning of power converter, electrical machine and energy storage. Furthermore, loading the translator heavily in the beginning or end of the stroke seems to affect the peak translator velocity more than evenly distributed load profiles.

Keyword
Converter machine interactions, Distributed power, Emerging technology, Energy converters for HEV, Generation of electrical energy, Hybrid Electric Vehicle (HEV), Linear drive
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6429 (URN)2-s2.0-33947636523 (Scopus ID)978-907581508-5 (ISBN)
Conference
2005 European Conference on Power Electronics and Applications; Dresden; 11 September 2005 through 14 September 2005
Note
QC 20101116Available from: 2006-11-27 Created: 2006-11-27 Last updated: 2010-11-16Bibliographically approved
2. Operational strategies for a free piston energy converter
Open this publication in new window or tab >>Operational strategies for a free piston energy converter
2005 (English)In: Proceedings of the Fifth International Symposium on Linear Drives for Industry Applications (LDIA05), 2005Conference paper, Published paper (Refereed)
Abstract [en]

This paper investigates how the losses in a Free Piston Energy Converter during start, stop and idling affects energy consumption and required power from the supply system. Simulation results indicate that the electrical machine efficiency is the most critical factor during start. Moreover, by choosing the correct amplitude of the starting force, energy consumption during start can be reduced. When it comes to idling, friction is the most significant loss factor. Nevertheless, by compensating the mechanical loss for short time intervals using the generator force, the reciprocating motion can be kept alive for a rapid start without major energy consumption.

Keyword
energy conversion, hybrid vehicle, Free Piston Energy Converter, auxiliary power unit, energy, power, HCCI
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6430 (URN)
Conference
Fifth International Symposium on Linear Drives for Industry Applications (LDIA05), Kobe-Awaji, Japan, September 2005
Note
QC 20101116Available from: 2006-11-27 Created: 2006-11-27 Last updated: 2010-11-16Bibliographically approved
3. Performance of a Series Hybrid Electric Vehicle with a Free-Piston Energy Converter
Open this publication in new window or tab >>Performance of a Series Hybrid Electric Vehicle with a Free-Piston Energy Converter
2006 (English)In: 2006 IEEE VEHICLE POWER AND PROPULSION CONFERENCE, NEW YORK, NY: IEEE , 2006, 108-113 p.Conference paper, Published paper (Refereed)
Abstract [en]

The free-piston energy converter (FPEC), consists of an internal combustion engine and a linear electrical machine. It is characterised by high efficiency and rapid transient response, which makes it suitable for hybrid electric vehicles. In this paper we investigate the performance gain of utilising the FPEC in a medium sized series hybrid electric vehicle (SHEV), compared to a conventional diesel-generator. First, we utilise optimisation to find a lower limit on the SHEVs fuel consumption for a given drive cycle. In addition, we develop a control strategy based on the ideas of an equivalent consumption minimisation (ECM) proposed earlier in the literature. The results show a potential decrease in fuel consumption of up to 19% compared to a diesel-generator SHEV. The ECM control strategy behaves as desired, and a 13% reduction of fuel consumption compared to a traditional load-following strategy is achieved.

Place, publisher, year, edition, pages
NEW YORK, NY: IEEE, 2006
Keyword
hybrid electric vehicles, internal combustion engines, linear machines, power convertors, transient response
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-6431 (URN)10.1109/VPPC.2006.364342 (DOI)000253928200020 ()2-s2.0-81455137509 (Scopus ID)978-1-4244-0158-1 (ISBN)
Conference
IEEE Vehicle Power and Propulsion Conference (VPPC). Windsor, ENGLAND. SEP 06-08, 2006
Note
QC 20101116 QC 20111007Available from: 2006-11-27 Created: 2006-11-27 Last updated: 2011-10-10Bibliographically approved

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