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Control of EGR and VGT for Emission Control and Pumping Work Minimization in Diesel Engines
Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, The Institute of Technology.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Legislators steadily increase the demands on lowered emissions from heavy duty vehicles. To meet these demands it is necessary to integrate technologies like Exhaust Gas Recirculation (EGR) and Variable Geometry Turbochargers (VGT) together with advanced control systems. Control structures are proposed and investigated for coordinated control of EGR valve and VGT position in heavy duty diesel engines. Main control goals are to fulfill the legislated emission levels, to reduce the fuel consumption, and to fulfill safe operation of the turbocharger. These goals are achieved through regulation of normalized oxygen/fuel ratio and intake manifold EGR-fraction. These are chosen as main performance variables since they are strongly coupled to the emissions. To design successful control structures, a mean value model of a diesel engine is developed and validated. The intended applications of the model are system analysis, simulation, and development of model-based control systems. Dynamic validations show that the proposed model captures the essential system properties, i.e. non-minimum phase behaviors and sign reversals. A first control structure consisting of PID controllers and min/max-selectors is developed based on a system analysis of the model. A key characteristic behind this structure is that oxygen/fuel ratio is controlled by the EGR-valve and EGR-fraction by the VGT-position, in order to handle a sign reversal in the system from VGT to oxygen/fuel ratio. This structure also minimizes the pumping work by opening the EGR-valve and the VGT as much as possible while achieving the control objectives for oxygen/fuel ratio and EGR-fraction. For efficient calibration an automatic controller tuning method is developed. The controller objectives are captured by a cost function, that is evaluated utilizing a method choosing representative transients. Experiments in an engine test cell show that the controller achieves all the control objectives and that the current production controller has at least 26% higher pumping losses compared to the proposed controller. In a second control structure, a non-linear compensator is used in an inner loop for handling non-linear effects. This compensator is a non-linear state dependent input transformation. PID controllers and selectors are used in an outer loop similar to the first control structure. Experimental validations of the second control structure show that it handles nonlinear effects, and that it reduces EGR-errors but increases the pumping losses compared to the first control structure. Substantial experimental evaluations in engine test cells show that both these structures are good controller candidates. In conclusion, validated modeling, system analysis, tuning methodology, experimental evaluation of transient response, and complete ETC-cycles give a firm foundation for deployment of these controllers in the important area of coordinated EGR and VGT control.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2009. , 230 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1256
National Category
Control Engineering
Identifiers
URN: urn:nbn:se:liu:diva-18484ISBN: 978-91-7393-611-8 (print)OAI: oai:DiVA.org:liu-18484DiVA: diva2:219874
Public defence
2009-06-12, Visionen, B-huset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2009-05-29 Created: 2009-05-28 Last updated: 2009-05-29Bibliographically approved
List of papers
1. Modeling of a Diesel Engine with VGT and EGR capturing Sign Reversal and Non-minimum Phase Behaviors
Open this publication in new window or tab >>Modeling of a Diesel Engine with VGT and EGR capturing Sign Reversal and Non-minimum Phase Behaviors
2009 (English)Report (Other academic)
Abstract [en]

A mean value model of a diesel engine with VGT and EGR is developed and validated. The intended model applications are system analysis, simulation, and development of model-based control systems. The goal is to construct a model that describes the dynamics in the manifold pressures, turbocharger, EGR, and actuators with few states in order to have short simulation times. Therefore the model has only eight states: intake and exhaust manifold pressures, oxygen mass fraction in the intake and exhaust manifold, turbocharger speed, and three states describing the actuator dynamics. The model is more complex than e.g. the third order model in [12] that only describes the pressure and turbocharger dynamics, but it is considerably less complex than a GT-POWER model or a Ricardo WAVE model. Many models in the literature, that approximately have the same complexity as the model proposed here, use three states for each control volume in order to describe the temperature dynamics. However, the model proposed here uses only two states for each manifold. Model extensions are investigated showing that inclusion of temperature states and pressure drop over the intercooler only have minor effects on the dynamic behavior and does not improve the model quality. Therefore, these extensions are not included in the proposed model. Model equations and tuning methods are described for each subsystem in the model. In order to have a low number of tuning parameters, flows and efficiencies are modeled using physical relationships and parametric models instead of look-up tables. To tune and validate the model, stationary and dynamic measurements have been performed in an engine laboratory at Scania CV AB. Static and dynamic validations of the entire model using dynamic experimental data show that the mean relative errors are 12.7 % or lower for all measured variables. The validations also show that the proposed model captures the essential system properties, i.e. a non-minimum phase behavior in the channel EGR-valve to intake manifold pressure and a non-minimum phase behavior, an overshoot, and a sign reversal in the channel VGT to compressor mass flow.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 56 p.
Series
LiTH-ISY-R, ISSN 1400-3902 ; 2882
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-18333 (URN)LiTH-ISY-R-2882 (ISRN)
Note

When citing this work, it is recommended that the citation is the improved and extended work, published in the peer-reviewed article Johan Wahlstr¨om and Lars Eriksson, Modeling diesel engines with a variable-geometry turbocharger and exhaust gas recirculation by optimization of model parameters for capturing non-linear system dynamics, Proceedings of the Institution of Mechanical Engineers, Part D, Journal of Automobile Engineering, Volume 225, Issue 7, July 2011, http://dx.doi.org/10.1177/0954407011398177.

Available from: 2009-05-28 Created: 2009-05-19 Last updated: 2014-10-08Bibliographically approved
2. System analysis of a Diesel Engine with VGT and EGR
Open this publication in new window or tab >>System analysis of a Diesel Engine with VGT and EGR
2009 (English)Report (Other academic)
Abstract [en]

A system analysis of a diesel engine with VGT and EGR is performed in order to obtain insight into a VGT and EGR control problem where the goal is to control the performance variables oxygen fuel ratio and EGR-fraction using the VGT actuator and the EGR actuator. Step responses over the entire operating region show that the channels VGT to oxygen fuel ratio, EGR-valve to oxygen fuel ratio, and VGT to EGR-fraction have non-minimum phase behaviors and sign reversals. The fundamental physical explanation of these system properties is that the system consists of two dynamic effects that interact: a fast pressure dynamics in the manifolds and a slow turbocharger dynamics. It is shown that the engine frequently operates in operating points where the non-minimum phase behaviors and sign reversals occur for the channels VGT to oxygen fuel ratio and VGT to EGR-fraction, and consequently, it is important to consider these properties in a control design. Further, an analysis of zeros for linearized multiple input multiple output models of the engine shows that they are non-minimum phase over the complete operating region. A mapping of the performance variables oxygen fuel ratio and EGR-fraction and the relative gain array show that the system from EGR-valve and VGT to oxygen fuel ratio and EGR-fraction is strongly coupled in a large operating region. It is also illustrated that the pumping losses decrease with increasing EGR-valve and VGT opening for almost the complete operating region.

Publisher
39 p.
Series
LiTH-ISY-R, ISSN 1400-3902 ; 2881
Keyword
diesel engine, VGT, EGR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-18334 (URN)LiTH-ISY-R-2881 (ISRN)
Available from: 2009-05-28 Created: 2009-05-19 Last updated: 2014-10-08Bibliographically approved
3. EGR-VGT Control and Tuning for Pumping Work Minimization and Emission Control
Open this publication in new window or tab >>EGR-VGT Control and Tuning for Pumping Work Minimization and Emission Control
2010 (English)In: IEEE Transactions on Control Systems Technology, ISSN 1063-6536, E-ISSN 1558-0865, Vol. 18, no 4, 993-1003 p.Article in journal (Refereed) Published
Abstract [en]

A control structure is proposed and investigated for coordinatedcontrol of EGR valve and VGT position in heavy duty diesel engines.Main control goals are to fulfill the legislated emission levels, toreduce the fuel consumption, and to fulfill safe operation of theturbocharger. These goals are achieved through regulation ofnormalized oxygen/fuel ratio and intake manifoldEGR-fraction. These are chosen both as main performance variables andfeedback variables since they contain information about when it ispossible to decrease the fuel consumption by minimizing the pumpingwork. Based on this a novel and simple pumping work minimizationstrategy is developed.The proposed performance variables are also strongly coupled to theemissions which makes it easier to adjust set-points, e.g. dependingon measured emissions during an emission calibration process, since itis more straightforward than control of manifold pressure and air massflow. Further, internally the controller is structured to handle thedifferent control objectives. Controller tuning is important forperformance but can be time consuming and to meet this end a method isdeveloped where the controller objectives are captured in a costfunction, which makes automatic tuning possible even though objectivesare conflicting. Performance trade-offs are necessary and areillustrated on the European Transient Cycle. The proposed controlleris validated in an engine test cell, where it is experimentallydemonstrated that the controller achieves all the control objectivesand that the current production controller has at least 26% higherpumping losses compared to the proposed controller.

Keyword
Diesel engine modeling, engine control
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-18336 (URN)10.1109/TCST.2009.2031473 (DOI)000278997400023 ()
Note
©2009 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Johan Wahlström, Lars Eriksson and Lars Nielsen, EGR-VGT Control and Tuning for Pumping Work Minimization and Emission Control, 2010, IEEE Transactions on Control Systems Technology, (18), 4, 993-1003. http://dx.doi.org/10.1109/TCST.2009.2031473 Available from: 2009-05-19 Created: 2009-05-19 Last updated: 2010-08-24Bibliographically approved
4. Controller Tuning based on Transient Selection and Optimization for a Diesel Engine with EGR and VGT
Open this publication in new window or tab >>Controller Tuning based on Transient Selection and Optimization for a Diesel Engine with EGR and VGT
2008 (English)In: Electronic Engine Controls, SAE World Congress & Exhibition, April, Detroit, MI, USA: SAE Technical paper series SP-2159, 2008-01-0985, SAE International , 2008, 2008-01-0985- p.Conference paper, Published paper (Refereed)
Abstract [en]

In modern Diesel engines Exhaust Gas Recirculation (EGR) and Variable Geometry Turbochargers (VGT) have been introduced to meet the new emission requirements. A control structure that coordinates and handles emission limits and low fuel consumption has been developed. This controller has a set of PID controllers with parameters that need to be tuned. To be able to achieve good performance, an optimization based tuning method is developed and tested. In the optimization the control objectives are captured by a cost function. To aid the tuning a systematic method has been developed for selecting representative and significant transients that excite different modes in the controller. The performance is evaluated on the European Transient Cycle. It is demonstrated how weighting factors in the cost function influence control behavior, and that the proposed tuning method gives a significant improvement in control performance compared to standardized tuning methods for PID controllers. Further, the proposed tuning method and the control structure are applied and validated on an engine in a test cell, where it is demonstrated that the control structure achieves all stated control objectives.

Place, publisher, year, edition, pages
SAE International, 2008
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-18341 (URN)10.4271/2008-01-0985 (DOI)978-0-7680-2001-4 (ISBN)
Conference
2008 World Congress; Detroit, MI; United States; 14 April 2008 through 17 April 2008
Available from: 2009-05-19 Created: 2009-05-19 Last updated: 2014-06-02Bibliographically approved
5. Non-linear Compensator for handling non-linear Effects in EGR VGT Diesel Engines
Open this publication in new window or tab >>Non-linear Compensator for handling non-linear Effects in EGR VGT Diesel Engines
2009 (English)Report (Other academic)
Abstract [en]

A non-linear compensator is investigated for handling of non-linear effects in diesel engines. This non-linear compensator is a non-linear state dependent input transformation that is developed by inverting the models for EGR-flow and turbine flow having actuator position as input and flow as output. The non-linear compensator is used in an inner loop in a control structure for coordinated control of EGR-fraction and oxygen/fuel ratio. A stability analysis of the open-loop system with a non-linear compensator shows that it is unstable in a large operating region. This system is stabilized by a control structure that consists of PID controllers and min/max-selectors. The EGR flow and the exhaust manifold pressure are chosen as feedback variables in this structure. Further, the set-points for EGR-fraction and oxygen/fuel ratio are transformed to set-points for the feedback variables. In order to handle model errors in this set-point transformation, an integral action on oxygen/fuel ratio is used in an outer loop. Experimental validations of the proposed control structure show that it handles nonlinear effects, and that it reduces EGR-errors but increases the pumping losses compared to a control structure without non-linear compensator.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 30 p.
Series
LiTH-ISY-R, ISSN 1400-3902 ; 2897
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-18348 (URN)LiTH-ISY-R-2897 (ISRN)
Available from: 2009-05-28 Created: 2009-05-20 Last updated: 2014-10-08Bibliographically approved
6. Robust Nonlinear EGR and VGT Control with Integral Action for Diesel Engines
Open this publication in new window or tab >>Robust Nonlinear EGR and VGT Control with Integral Action for Diesel Engines
2008 (English)In: Proceedings of the 17th IFAC World Congress, Seoul, Korea: The International Federation of Automatic Control , 2008, 2057-2062 p.Conference paper, Published paper (Refereed)
Abstract [en]

A robust non-linear multivariable control design with integral action is proposed and investigated for control of EGR valve and VGT position in heavy duty diesel engines. The main control goal is to regulate oxygen/fuel ratio and intake manifold EGR-fraction. These are chosen as main performance variables since they are strongly coupled to the emissions. A recently developed non-linear control design based on feedback linearization is extended with integral action. The nonlinear controller gives an inner loop with good stability and robustness properties. It is shown that integral action is necessary to handle model errors so that the controller can track the performance variables specified in the outer loop. In particular the control design method utilizes a control Lyapunov function and inverse optimal control, which results in a control law with robustness properties interpretable as gain and phase margins. Furthermore, comparisons by simulation also show that the proposed control design successfully handles non-linear effects.

Place, publisher, year, edition, pages
Seoul, Korea: The International Federation of Automatic Control, 2008
Keyword
Lyapunov function, inverse optimal control
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-18349 (URN)
Available from: 2009-05-20 Created: 2009-05-20 Last updated: 2009-10-14Bibliographically approved

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