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Modeling for control of centrifugal compressors
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Downsizing and turbocharging of engines provide a way to meet increasing demands for efficiency and performance in the automotive industry. An engine design is a result of compromises, e.g. the selection of charging system, and the trend is to reduce these compromises by increasing system complexity. Models have come to play a central role to handle this rise in complexity, and are used for simulation, system optimization and control synthesis. The models should describe the entire operating range, be capable of extrapolation, be easily parameterizable, and wide cover a range of applications.

A novel compressor model is developed which, in addition to the nominal operation, also covers surge, choke and operation at pressure ratios less than one. The model is based on data from more than 300 compressor maps, measurements from engine test stands, and a surge test stand. The general knowledge gained from the in-depth analysis is condensed in the model equations. The model can be automatically parametrized using a compressor map, is based on static functions for low computational cost, and is shown to extrapolate low speed compressor operation well. Furthermore, it is shown to be applicable to compressors of different size, ranging from small car applications to large heavy duty vehicles. Compressor restriction operation is modeled down to a standstill compressor, and shown to agree well with gas stand measurements. Further, the analysis contributes with new knowledge and models for choking pressure ratio and flow.

A method to automatically determine a turbo map, when the turbo is installed on an engine in an engine test stand is developed. The method can be used to validate manufacturer maps or expand the region covered in a map. An analysis of the limits that an engine installation imposes on the reachable points in the compressor map is performed. The addition of a throttle before the compressor is suggested to increase the reachable map region, and an engine and test cell control structure that can be used to automate the measurements is proposed. Two methods that compensate for the deviation between measured and desired speeds, are proposed and investigated. A gas stand map is compared to the map generated in the engine test stand, and a generally good agreement results.

An experimental analysis of the applicability of the commonly used correction factors, used for estimating compressor performance when the inlet conditions deviate from nominal, is performed. Correction factors are vital, to e.g. estimate turbocharger performance for driving at high altitude or to characterize second stage compressor performance, where the variations in inlet conditions are large. Measurements from an engine test stand and a gas stand show a small but clearly measurable trend, with decreasing compressor pressure ratio for decreasing compressor inlet pressure, for points with equal corrected shaft speed and corrected mass flow. A method that enables measurements to be analyzed with modified corrections is developed. As a result, an adjusted shaft speed correction quantity is proposed, incorporating also the inlet pressure in the shaft speed correction.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 68 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1516
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-91384ISBN: 978-91-7519-626-8 (print)OAI: oai:DiVA.org:liu-91384DiVA: diva2:617415
Public defence
2013-05-24, Visionen, B-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2013-05-13Bibliographically approved
List of papers
1. Time to Surge Concept and Surge Control for Acceleration Performance
Open this publication in new window or tab >>Time to Surge Concept and Surge Control for Acceleration Performance
2008 (English)In: Proceedings of the 17th IFAC World Congress, 2008 / [ed] Chung, Myung Jin; Misra, Pradeep, International Federation of Automatic Control (IFAC) , 2008, 2063-2068 p.Conference paper, Published paper (Refereed)
Abstract [en]

Surge is a dangerous instability that can occur in compressors. It is avoided using a valve that reduces the compressor pressure. The control of this valve is important for the compressor safety but it also has a direct influence on the acceleration performance. Compressor surge control is investigated by first studying the surge phenomenon in detail. Experimental data from a dynamic compressor flow test bench and surge cycles measured on an engine is used to tune and validate a model capable of describing surge. A concept time to surge is introduced and a sensitivity analysis is performed to isolate the important characteristics that influence surge transients in an engine. It is pointed out that the controller clearly benefits from a feed-forward term due to the small time frames associated with the transition to surge. In the next step this knowledge is used in the design of a novel surge controller. This surge controller is then compared to two other controllers and it is shown that it avoids surge and improves the acceleration performance by delivering both higher engine torque and turbo shaft speed after a gear change.

Place, publisher, year, edition, pages
International Federation of Automatic Control (IFAC), 2008
Keyword
automobile powertrains, engine control, compressor, turbo, system modeling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-50768 (URN)10.3182/20080706-5-KR-1001.00350 (DOI)978-3-902661-00-5 (ISBN)
Conference
IFAC World Congress, July 6-11, Seuol, Korea
Available from: 2013-04-09 Created: 2009-10-14 Last updated: 2013-05-07Bibliographically approved
2. Engine Test Bench Turbo Mapping
Open this publication in new window or tab >>Engine Test Bench Turbo Mapping
2010 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A method for determining turbocharger performance on installations in an engine test bench is developed and investigated. The focus is on the mapping of compressor performance but some attention is also given to the turbine mapping. An analysis of the limits that an engine installation imposes on the reachable points in the compressor map is performed, in particular it shows what corrected flows and pressure ratios can be reached and what these limitations depend on. To be able to span over a larger  region of the corrected flow a throttle before the compressor is suggested and this is also verified in the test bench.

Turbocharger mapping is a time consuming process and there is a need for a systematic process that can be executed automatically. An engine and test cell control structure that can be used to automate and monitor the measurements by controlling the system to the desired operating points is also proposed.

In experiments, used for constructing the compressor speed lines, it is virtually impossible to control the turbocharger to the exact corrected speed that is postulated by the speed line. To overcome this two methods that compensate for the deviation between measured speed and the desired speed are proposed and investigated. Detailed data from a gas stand is used to evaluate the measurements compared to those that are generated in the engine test cell installation. The agreements are generally good but there is more noise in the engine data and there are also some small systematic deviations.

Place, publisher, year, edition, pages
SAE International, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-64337 (URN)10.4271/2010-01-1232 (DOI)
Conference
SAE 2010 World Congress, April 13-15, Detroit, Michigan, USA
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2013-05-07
3. Investigation of compressor correction quantities for automotive applications
Open this publication in new window or tab >>Investigation of compressor correction quantities for automotive applications
2012 (English)In: International Journal of Engine Research, ISSN 1468-0874, Vol. 13, no 6, 588-606 p.Article in journal (Other academic) Published
Abstract [en]

Turbo performance is represented using maps, measured for one set of inlet conditions. Corrections are then applied to scale the performance to other inlet conditions. A turbo compressor for automotive applications experiences large variations in inlet conditions, and the use of two stage charging increases these variations. The variations are the motivation for analyzing the correction quantities and their validity. The corrections reveals a novel surge avoidance strategy, where the result is that a reduction in inlet pressure increases the surge margin for eight maps studied. The method to investigate the applicability of the strategy is general.

An experimental analysis of the applicability of the commonly used correction factors, used when estimating compressor performance for varying inlet conditions, is presented. The experimental campaign uses measurements from an engine test cell and from a gas stand, and shows a small, but clearly measurable trend, with decreasing compressor  pressure ratio for decreasing compressor inlet pressure. A method is  developed, enabling measurements to be analyzed with modified corrections.

An adjusted shaft speed correction quantity is proposed, incorporating also the inlet pressure in the shaft speed correction. The resulting decrease in high altitude engine performance, due to compressor limitations, are quantified and shows a reduction in altitude of 200 – 600 m, for when engine torque has to be reduced to due limited compressor operation.

Place, publisher, year, edition, pages
SAGE Publications (UK and US) / Professional Engineering Publishing (Institution of Mechanical Engineers), 2012
Keyword
Experimental analysis; map; inlet conditions; speed line; measurements
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-64340 (URN)10.1177/1468087412439018 (DOI)000311831200004 ()
Available from: 2011-01-19 Created: 2011-01-19 Last updated: 2013-05-07Bibliographically approved
4. A surge and choke capable compressor flow model: Validation and extrapolation capability
Open this publication in new window or tab >>A surge and choke capable compressor flow model: Validation and extrapolation capability
2013 (English)In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 21, no 12, 1871-1883 p.Article in journal (Refereed) Published
Abstract [en]

Increasingly stringent emissions legislation combined with consumer performance demand, have created the need for complex automotive engines. The control of these complex system rely heavily on control oriented models. Models capable of describing all operating modes of the systems are beneficial, and the models should be easily parametrized and enable extrapolation. A large database of automotive compressor maps is characterized, and used to develop, validate and automatically parametrize a compressor flow model capable of describing reversed flow, normal operation and choke. Measurement data from both an engine test stand, and a surge test stand, is used to parametrize and validate the surge capability of the model. The model is shown to describe all modes of operation with good performance, and also to be able to extrapolate to small turbo speeds. The extrapolation capability is important, since compressor maps are shown to lack information for low speeds, even though they frequently operate there in an engine installation.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-92090 (URN)10.1016/j.conengprac.2013.07.005 (DOI)000329017200023 ()
Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2017-12-06Bibliographically approved
5. Measurement, analysis and modeling of compressor flow for low pressure ratios
Open this publication in new window or tab >>Measurement, analysis and modeling of compressor flow for low pressure ratios
2016 (English)In: International journal of engine research, ISSN 1468-0874, Vol. 17, no 2, 153-168 p.Article in journal (Other academic) Published
Abstract [en]

Increasingly stringent emissions legislation combined with consumer performance demands, have driven the development of downsized engines with complex turbocharger arrangements. To handle the complexity model-based methods have become a standard tool, and these methods need models that are capable of describing all operating modes of the systems. The models should also be easily parametrized and enable extrapolation. Both single and multiple stage turbo systems can operate with a pressure drop over their compressors, both stationary and transient. The focus here is to develop models that can describe centrifugal compressors that operate both in normal region and restriction region from standstill to maximum speed. The modeling results rely on an analysis of 305 automotive compressor maps, whereof five contain measured restriction operation, and two contain measured standstill characteristic. A standstill compressor is shown to choke at a pressure ratio of approximately 0.5, and the corresponding choking corrected mass flow being approximately 50% of the compressor maximum flow capacity. Both choking pressure ratio and flow are then shown to increase with corrected speed, and the choking pressure ratio is shown to occur at pressure ratios larger than unity for higher speeds. Simple empirical models are proposed and shown to be able to describe high flow and pressure ratios down to choking conditions well. A novel compressor flow model is proposed and validated to capture the high flow asymptote well, for speeds from standstill up to maximum.

Place, publisher, year, edition, pages
Sage Publications, 2016
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-92091 (URN)10.1177/1468087414562456 (DOI)000368815100001 ()
Note

Funding agencies: Vinnova Industry Excellence Center: LINK-SIC Linkoping Center for Sensor Informatics and Control

Vid tiden för disputation förelåg publikationen endast som manuskript

Available from: 2013-05-07 Created: 2013-05-07 Last updated: 2016-02-23Bibliographically approved

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