| 1. |
- Eriksson, Lars, 1970-, et al.
(författare)
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Physical Modeling of Turbocharged Engines and Parameter Identification
- 2009. - 1
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Ingår i: Automotive Model Predictive Control. - London : Springer Verlag. - 9781849960700 - 9781849960717 ; , s. 53-71
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Bokkapitel (refereegranskat)abstract
- The common theme in this chapter is physical modeling of engines and the subjects touch three topics in nonlinear engine models and parameter identification. First, a modeling methodology is described. It focuses on the gas and energy flows in engines and covers turbocharged engines. Examples are given where the methodology has been successfully applied, covering naturally aspirated engines and both single and dual stage turbocharged engines. Second, the modeling with the emphasis on models for EGR/VGT equipped diesel engine. The aim is to describe models that capture the essential dynamics and nonlinear behaviors and that are relatively small so that they can be utilized in model predictive control algorithms. Special emphasis is on the selection of the states. The third and last topic is related to parameter identification in gray-box models. A common issue is that parameters with physical interpretation often receive values that lie outside their admissible range during the identification. Regularization is discussed as a solution and methods for choosing the regularization parameter are described and highlighted.
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| 2. |
- Wahlström, Johan, 1978-
(författare)
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Control of EGR and VGT for Emission Control and Pumping Work Minimization in Diesel Engines
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Wahlström, Johan, 1978-
(författare)
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Control of EGR and VGT for emission control and pumping work minimization in diesel engines
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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. A control structure with PID controllers and selectors is 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, compared to manifold pressure or air mass flow, which makes it easy to adjust set-points depending on e.g. measured emissions during an emission calibration process. In addition a mechanism for fuel efficient operation is incorporated in the structure, this is achieved by minimizing the pumping work. To design a successful control structure, 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. Model equations and tuning methods for the model parameters are described for each subsystem in the model. Static and dynamic validations of the entire model show mean relative errors that are less than 12%. Based on a system analysis of the model, a key characteristic behind the control 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. For efficient calibration an automatic controller tuning method is developed. The controller objectives are captured in a cost function, that is evaluated utilizing a method choosing representative transients. The performance is evaluated on the European Transient Cycle. It is demonstrated how the weights in the cost function influence behavior, and that the tuning method is important in order to improve the control performance compared to if only a standard method is used. It is also demonstrated that the controller structure performs well regarding all control objectives. In combination with its efficient tuning, the controller structure thus fulfills all requirements for successful application.
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| 4. |
- Wahlström, Johan, 1978-, et al.
(författare)
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Controller Tuning based on Transient Selection and Optimization for a Diesel Engine with EGR and VGT
- 2008
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Ingår i: Electronic Engine Controls, SAE World Congress & Exhibition, April, Detroit, MI, USA. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 9780768020014 ; , s. 2008-01-0985-
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Wahlström, Johan, 1978-, et al.
(författare)
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EGR-VGT Control and Tuning for Pumping Work Minimization and Emission Control
- 2010
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Ingår i: IEEE Transactions on Control Systems Technology. - 1063-6536 .- 1558-0865. ; 18:4, s. 993-1003
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Wahlström, Johan, 1978-, et al.
(författare)
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Modeling of a diesel engine with intake throttle, VGT, and EGR
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A mean value model of a diesel engine with intake throttle, VGT, and EGR is developed, parameterized, 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 gas flow dynamics includ- ing the dynamics in the intercooler pressure, manifold pressures, turbocharger, EGR, and actuators with few states in order to have short simulation times. An investigation of model complexity and descriptive capabilities is performed, resulting in a model that has only eleven states. To tune and validate the model, stationary and dynamic measurements have been performed in an engine labo- ratory at Scania CV AB. All the model parameters are estimated automatically using weighted least squares optimization of both the sub-models and the com- plete model. Dynamic measurements and simulations show that the proposed model cap- tures the essential system properties, i.e. non-minimum phase behaviors, over- shoots, and sign reversals. Validations of the entire model show that the mean value of all absolute relative errors for all measured outputs are equal to 7.4%. A system analysis of the proposed model 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 lambdaO and EGR-fraction xegr. Step responses over the entire operating region show that the channels VGT to lambdaO, EGR to lambdaO, and VGT to xegr have sign reversals.
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| 7. |
- Wahlström, Johan, 1978-, et al.
(författare)
-
Modeling of a Diesel Engine with VGT and EGR capturing Sign Reversal and Non-minimum Phase Behaviors
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 8. |
- Wahlström, Johan, 1978-, et al.
(författare)
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Modeling of a Diesel Engine with VGT and EGR including Oxygen Mass Fraction
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A mean value model of a diesel engine with VGT and EGR and that includes oxygen mass fraction is developed and validated. The intended model applications are system analysis, simulation, and development of model-based control systems. Model equations and tuning methods are described for each subsystem in the model. In order to decrease the amount of tuning parameters, flows and efficiencies are modeled using physical relationships and parametric models instead of look-up tables. The static models have mean relative errors that are equal to or lower than 6.1%. Static and dynamic validations of the entire model show that the mean relative errors are less than 12%. The validations also show that the proposed model captures the essential system properties, i.e. a non-minimum phase behavior in the transfer function EGR-valve to intake manifold pressure and a non-minimum phase behavior, an overshoot, and a sign reversal in the transfer function VGT to compressor mass flow.
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| 9. |
- Wahlström, Johan, 1978-, et al.
(författare)
-
Non-linear Compensator for handling non-linear Effects in EGR VGT Diesel Engines
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 10. |
- Wahlström, Johan, 1978-, et al.
(författare)
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Nonlinear EGR and VGT Control with Integral Action for Diesel Engines
- 2009
-
Ingår i: <em>2009 IFAC Workshop on Engine and Powertrain Control, Simulation and Modeling</em>. Paris, France.. - : Curran Associates, Inc.. - 9781617380204
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Konferensbidrag (refereegranskat)abstract
- A non-linear multivariable control design with integral action is proposed and investigated for control of Exhaust Gas Recirculation (EGR) and Variable Geometry Turbocharger (VGT) in heavy duty diesel engines. The main control goal is to regulate oxygen/fuel ratio and intake manifold EGR-fraction, and they are specified in an outer loop. These are chosen as main performance variables since they are strongly coupled to the emissions. An existing non-linear control design based on feedback linearization is extended with integral action. In particular the control design method utilizes a control Lyapunov function, inverse optimal control, and a non-linear compensator. Comparisons between different control structures are performed in simulations showing the following four points. Firstly, integral action is necessary to handle model errors so that the controller can track the performance variables specified in the outer loop. Secondly, the proposed control design handles the non-linear effects in the diesel engine that results in less control errors compared to a control structure with PID controllers. Thirdly, it is important to use the non-linear compensator and it is sufficient to use a control structure with PID controllers and a non-linear compensator to handle the non-linear effects. Fourthly, the proposed control design is sensitive to model errors in the EGR and turbine flow model while a control structure with PID controllers and a non-linear compensator handles these model errors.
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