| 1. |
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Control of Complex Systems
- 2001
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Editorial collection (other academic/artistic)abstract
- The world of artificial systems is reaching hitherto undreamed-of levels of complexity. Surface traffic, electricity distribution, mobile communications, etc., demonstrate that problems are arising that are beyond classical scientific or engineering knowledge. In order that our ability to control such systems should not be hindered by lack of comprehension, there is an on-going effort to understand them. This book is an example of the types of approach that European researchers are using to tackle problems derived from systems' complexity. It has grown out of activities in the Control of Complex Systems (COSY) research program the goals of which are to promote multi-disciplinary activity leading to a deeper understanding and further development of control technologies for complex systems and if possible, to develop the theory underlying such systems. The material in this book represents a selection of the results of the COSY program and is organised as a collection of essays of varying nature: surveys of essential areas, discussion of specific problems, case studies, and benchmark problems. Topics covered include: Modelling complex physical systems; Passivity-based control of non-linear systems; Aspects of fault identification and fault tolerance; Control design; Learning control; Satellite attitude control. Complex systems appear in many different fields and for this reason this book should be of interest to scientists, researchers and industrial engineers with a broad spectrum of experience.
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| 2. |
- Gelso, Esteban, 1977, et al.
(author)
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Structural analysis extended with active fault isolation - methods and algorithms
- 2009
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In: 7th IFAC Symposium on Fault Detection, Supervision and Safety of Technical Processes SAFEPROCESS.
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Conference paper (peer-reviewed)abstract
- Isolability of faults is a key issue in fault diagnosis whether the aim is maintenance or active fault-tolerant control. It is often encountered that while faults are detectable, they are only group-wise isolable from a usual diagnostic point of view. However, active injection of test signals on system inputs can considerably enhance fault isolability. This paper investigates this possibility of active fault isolation from a structural point of view. While such extension of the structural analysis approach was suggested earlier, algorithms and case studies were needed to explore this theory. The paper develops algorithms for investigation of the possibilities of activestructural isolation and it offers illustrative examples and a larger case study to explore the properties of active structural isolability ideas.
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| 3. |
- Nielsen, Kraen Vodder, et al.
(author)
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Adaptive Observer for Nonlinearly Parameterized Hammerstein System With Sensor Delay-Applied to Ship Emissions Reduction
- 2018
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In: IEEE Transactions on Control Systems Technology. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1063-6536 .- 1558-0865. ; 26:4, s. 1508-1515
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Journal article (peer-reviewed)abstract
- Taking offspring in a problem of ship emission reduction by exhaust gas recirculation control for large diesel engines, an underlying generic estimation challenge is formulated as a problem of joint state and parameter estimation for a class of multiple-input single-output Hammerstein systems with first-order dynamics, sensor delay, and a bounded time-varying parameter in the nonlinear part. This brief suggests a novel scheme for this estimation problem that guarantees exponential convergence to an interval that depends on the sensitivity of the system. The system is allowed to be nonlinear, parameterized, and time dependent, which are characteristics of the industrial problem we study. The approach requires the input nonlinearity to be a sector nonlinearity in the time-varying parameter. Salient features of the approach include simplicity of design and implementation. The efficacy of the adaptive observer is shown on simulated cases, on tests with a large diesel engine on test bed, and on tests with a container vessel.
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| 4. |
- Nielsen, Kraen Vodder, et al.
(author)
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Marine diesel engine control to meet emission requirements and maintain maneuverability
- 2018
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In: Control Engineering Practice. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0967-0661 .- 1873-6939. ; 76, s. 12-21
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Journal article (peer-reviewed)abstract
- International shipping has been reported to account for 13% of global NOx emissions and 2.1% of global green house gas emissions. Recent restrictions of NOx emissions from marine vessels have led to the development of exhaust gas recirculation (EGR) for large two-stroke diesel engines. Meanwhile, the same engines have been downsized and derated to optimize fuel efficiency. The smaller engines reduce the possible vessel acceleration, and to counteract this, the engine controller must be improved to fully utilize the physical potential of the engine. A fuel index limiter based on air/fuel ratio was recently developed (Turbo, 2016), but as it does not account for EGR, accelerations lead to excessive exhaust smoke formation which could damage the engine when recirculated. This paper presents two methods for extending a fuel index limiter function to EGR engines. The methods are validated through simulations with a mean-value engine model and on a vessel operating at sea. Validation tests compare combinations of the two index limiter methods, using either traditional PI control for the EGR loop or the recently developed fast adaptive feedforward EGR control (Nielsen et al., 2017a). The experiments show that the extended limiters reduce exhaust smoke formation during acceleration to a minimum, and that the suggested limiter, combined with adaptive feedforward EGR control, is able to maintain full engine acceleration capability. Sea tests with engine speed steps from 35 to 50 RPM, made peak exhaust opacity increase by only 5% points when using the proposed limiter, whereas it increased 70% points without the limiter.
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| 5. |
- Svärd, Carl, 1981-
(author)
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Residual Generation Methods for Fault Diagnosis with Automotive Applications
- 2009
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Licentiate thesis (other academic/artistic)abstract
- The problem of fault diagnosis consists of detecting and isolating faults present in a system. As technical systems become more and more complex and the demands for safety, reliability and environmental friendliness are rising, fault diagnosis is becoming increasingly important. One example is automotive systems, where fault diagnosis is a necessity for low emissions, high safety, high vehicle uptime, and efficient repair and maintenance.One approach to fault diagnosis, providing potentially good performance and in which the need for additional hardware is minimal, is model-based fault diagnosis with residuals. A residual is a signal that is zero when the system under diagnosis is fault-free, and non-zero when particular faults are present in the system. Residuals are typically generated by using a mathematical model of the system and measurements from sensors and actuators. This process is referred to as residual generation.The main contributions in this thesis are two novel methods for residual generation. In both methods, systems described by Differential-Algebraic Equation (DAE) models are considered. Such models appear in a large class of technical systems, for example automotive systems. The first method consider observer-based residual generation for linear DAE-models. This method places no restrictions on the model, such as e.g. observability or regularity, in comparison with other previous methods. If the faults of interest can be detected in the system, the output from the design method is a residual generator, in state-space form, that is sensitive to the faults of interest. The method is iterative and relies on constant matrix operations, such as e.g. null-space calculations and equivalence transformations.In the second method, non-linear DAE-models are considered. The proposed method belongs to a class of methods, in this thesis referred to as sequential residual generation, which has shown to be successful for real applications. This method enables simultaneous use of integral and derivative causality, and is able to handle equation sets corresponding to algebraic and differential loops in a systematic manner. It relies on a formal framework for computing unknown variables in the model according to a computation sequence, in which the analytical properties of the equations in the model as well as the available tools for equation solving are taken into account. The method is successfully applied to complex models of an automotive diesel engine and a hydraulic braking system.
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| 6. |
- Vodder Nielsen, Kraen, et al.
(author)
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Adaptive feedforward control of exhaust recirculation in large diesel engines
- 2017
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In: Control Engineering Practice. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0967-0661 .- 1873-6939. ; 65, s. 26-35
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Journal article (peer-reviewed)abstract
- Environmental concern has led the International Maritime Organization to restrict NOx emissions from marine diesel engines. Exhaust gas recirculation (EGR) systems have been introduced in order to comply to the new standards. Traditional fixed-gain feedback methods are not able to control the EGR system adequately in engine loading transients so alternative methods are needed. This paper presents the design, convergence proofs and experimental validation of an adaptive feedforward controller that significantly improves the performance in loading transients. First the control concept is generalized to a class of first order Hammerstein systems with sensor delay and exponentially converging bounds of the control error are proven analytically. It is then shown how to apply the method to the EGR system of a two-stroke crosshead diesel engine. The controller is validated by closed loop simulation with a mean-value engine model, on an engine test bed and on a vessel operating at sea. A significant reduction of smoke formation during loading transients is observed both visually and with an opacity sensor. (C) 2017 Elsevier Ltd. All rights reserved.
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| 7. |
- Vodder Nielsen, Kraen, et al.
(author)
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Control-Oriented Model of Molar Scavenge Oxygen Fraction for Exhaust Recirculation in Large Diesel Engines
- 2017
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In: Journal of Dynamic Systems Measurement, and Control. - : ASME. - 0022-0434 .- 1528-9028. ; 139:2
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Journal article (peer-reviewed)abstract
- Exhaust gas recirculation (EGR) systems have been introduced to large marine engines in order to reduce NOx formation. Adequate modeling for control design is one of the bottlenecks to design EGR control that also meets emission requirements during transient loading conditions. This paper therefore focuses on deriving and validating a mean-value model of a large two-stroke crosshead diesel engine with EGR. The model introduces a number of amendments and extensions to previous, complex models and shows in theory and practice that a simplified nonlinear model captures all essential dynamics that is needed for EGR control. Our approach is to isolate and reduce the gas composition part of the more complex models using nonlinear model reduction techniques. The result is a control-oriented model (COM) of the oxygen fraction in the scavenge manifold with three molar flows being inputs to the COM, and it is shown how these flows are estimated from signals that are commonly available. The COM is validated by first comparing the output to a simulation of the full model, then by comparing with measurement series from two engines. The control-oriented nonlinear model is shown to be able to replicate the behavior of the scavenge oxygen fraction well over the entire envelope of load and blower speed range that are relevant for EGR. The simplicity of the new model makes it suitable for observer and control design, which are essential steps to meet the emission requirements for marine diesel engines that take effect from 2016.
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