| 1. |
- Härkegård, Ola, 1947-, et al.
(author)
-
Flight Control Design using Backstepping
- 2000
-
Reports (other academic/artistic)abstract
- Today the prevailing nonlinear design method for aircraft flight control is feedback linearization. This paper presents a new method to deal with the nonlinear aerodynamic forces and moments acting on the aircraft: backstepping. Specifically, we derive backstepping control laws for angle of attack and sideslip control that requireless knowledge of the lift and side forces compared to feedback linearization designs. The control laws are made adaptive to errors in the aerodynamic moment coefficients using nonlinear observer techniques.
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| 2. |
- Andersson, Magnus, et al.
(author)
-
A Simulation and Animation Tool for Studying Multivariable Control
- 2002
-
In: Proceedings of the 15th IFAC World Congress. - 9783902661746 ; , s. 1432-1432
-
Conference paper (peer-reviewed)abstract
- A simulation and animation tool for education in multivariable control is presented. The purpose of the tool is to support studies of various aspects of multivariable dynamical systems and design of multivariable feedback control systems. Different ways to use this kind of tool in control education are also presented and discussed.
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| 3. |
- Bergman, Kristoffer, 1990-, et al.
(author)
-
An Optimization-Based Receding Horizon Trajectory Planning Algorithm
- 2020
-
In: IFAC-PapersOnLine. - : ELSEVIER. - 2405-8963. ; , s. 15550-15557
-
Conference paper (peer-reviewed)abstract
- This paper presents an optimization-based receding horizon trajectory planning algorithm for dynamical systems operating in unstructured and cluttered environments. The proposed approach is a two-step procedure that uses a motion planning algorithm in a first step to efficiently find a feasible, but possibly suboptimal, nominal solution to the trajectory planning problem where in particular the combinatorial aspects of the problem are solved. The resulting nominal trajectory is then improved in a second optimization-based receding horizon planning step which performs local trajectory refinement over a sliding time window. In the second step, the nominal trajectory is used in a novel way to both represent a terminal manifold and obtain an upper bound on the cost-to-go online. This enables the possibility to provide theoretical guarantees in terms of recursive feasibility, objective function value, and convergence to the desired terminal state. The established theoretical guarantees and the performance of the proposed algorithm are verified in a set of challenging trajectory planning scenarios for a truck and trailer system.
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| 4. |
- Bergman, Kristoffer, 1990-
(author)
-
Exploiting Direct Optimal Control for Motion Planning in Unstructured Environments
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- During the last decades, motion planning for autonomous systems has become an important area of research. The high interest is not the least due to the development of systems such as self-driving cars, unmanned aerial vehicles and robotic manipulators. The objective in optimal motion planning problems is to find feasible motion plans that also optimize a performance measure. From a control perspective, the problem is an instance of an optimal control problem. This thesis addresses optimal motion planning problems for complex dynamical systems that operate in unstructured environments, where no prior reference such as road-lane information is available. Some example scenarios are autonomous docking of vessels in harbors and autonomous parking of self-driving tractor-trailer vehicles at loading sites. The focus is to develop optimal motion planning algorithms that can reliably be applied to these types of problems. This is achieved by combining recent ideas from automatic control, numerical optimization and robotics.The first contribution is a systematic approach for computing local solutions to motion planning problems in challenging unstructured environments. The solutions are computed by combining homotopy methods and direct optimal control techniques. The general principle is to define a homotopy that transforms, or preferably relaxes, the original problem to an easily solved problem. The approach is demonstrated in motion planning problems in 2D and 3D environments, where the presented method outperforms a state-of-the-art asymptotically optimal motion planner based on random sampling.The second contribution is an optimization-based framework for automatic generation of motion primitives for lattice-based motion planners. Given a family of systems, the user only needs to specify which principle types of motions that are relevant for the considered system family. Based on the selected principle motions and a selected system instance, the framework computes a library of motion primitives by simultaneously optimizing the motions and the terminal states.The final contribution of this thesis is a motion planning framework that combines the strengths of sampling-based planners with direct optimal control in a novel way. The sampling-based planner is applied to the problem in a first step using a discretized search space, where the system dynamics and objective function are chosen to coincide with those used in a second step based on optimal control. This combination ensures that the sampling-based motion planner provides a feasible motion plan which is highly suitable as warm-start to the optimal control step. Furthermore, the second step is modified such that it also can be applied in a receding-horizon fashion, where the proposed combination of methods is used to provide theoretical guarantees in terms of recursive feasibility, worst-case objective function value and convergence to the terminal state. The proposed motion planning framework is successfully applied to several problems in challenging unstructured environments for tractor-trailer vehicles. The framework is also applied and tailored for maritime navigation for vessels in archipelagos and harbors, where it is able to compute energy-efficient trajectories which complies with the international regulations for preventing collisions at sea.
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| 5. |
- Bergman, Kristoffer, 1990-
(author)
-
On Motion Planning Using Numerical Optimal Control
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- During the last decades, motion planning for autonomous systems has become an important area of research. The high interest is not the least due to the development of systems such as self-driving cars, unmanned aerial vehicles and robotic manipulators. In this thesis, the objective is not only to find feasible solutions to a motion planning problem, but solutions that also optimize some kind of performance measure. From a control perspective, the resulting problem is an instance of an optimal control problem. In this thesis, the focus is to further develop optimal control algorithms such that they be can used to obtain improved solutions to motion planning problems. This is achieved by combining ideas from automatic control, numerical optimization and robotics.First, a systematic approach for computing local solutions to motion planning problems in challenging environments is presented. The solutions are computed by combining homotopy methods and numerical optimal control techniques. The general principle is to define a homotopy that transforms, or preferably relaxes, the original problem to an easily solved problem. The approach is demonstrated in motion planning problems in 2D and 3D environments, where the presented method outperforms both a state-of-the-art numerical optimal control method based on standard initialization strategies and a state-of-the-art optimizing sampling-based planner based on random sampling.Second, a framework for automatically generating motion primitives for lattice-based motion planners is proposed. Given a family of systems, the user only needs to specify which principle types of motions that are relevant for the considered system family. Based on the selected principle motions and a selected system instance, the algorithm not only automatically optimizes the motions connecting pre-defined boundary conditions, but also simultaneously optimizes the terminal state constraints as well. In addition to handling static a priori known system parameters such as platform dimensions, the framework also allows for fast automatic re-optimization of motion primitives if the system parameters change while the system is in use. Furthermore, the proposed framework is extended to also allow for an optimization of discretization parameters, that are are used by the lattice-based motion planner to define a state-space discretization. This enables an optimized selection of these parameters for a specific system instance.Finally, a unified optimization-based path planning approach to efficiently compute locally optimal solutions to advanced path planning problems is presented. The main idea is to combine the strengths of sampling-based path planners and numerical optimal control. The lattice-based path planner is applied to the problem in a first step using a discretized search space, where system dynamics and objective function are chosen to coincide with those used in a second numerical optimal control step. This novel tight combination of a sampling-based path planner and numerical optimal control makes, in a structured way, benefit of the former method’s ability to solve combinatorial parts of the problem and the latter method’s ability to obtain locally optimal solutions not constrained to a discretized search space. The proposed approach is shown in several practically relevant path planning problems to provide improvements in terms of computation time, numerical reliability, and objective function value.
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| 6. |
- Brannmark, Cecilia, et al.
(author)
-
Mass and Information Feedbacks through Receptor Endocytosis Govern Insulin Signaling as Revealed Using a Parameter-free Modeling Framework
- 2010
-
In: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 285:26, s. 20171-20179
-
Journal article (peer-reviewed)abstract
- Insulin and other hormones control target cells through a network of signal-mediating molecules. Such networks are extremely complex due to multiple feedback loops in combination with redundancy, shared signal mediators, and cross-talk between signal pathways. We present a novel framework that integrates experimental work and mathematical modeling to quantitatively characterize the role and relation between coexisting submechanisms in complex signaling networks. The approach is independent of knowing or uniquely estimating model parameters because it only relies on (i) rejections and (ii) core predictions (uniquely identified properties in unidentifiable models). The power of our approach is demonstrated through numerous iterations between experiments, model-based data analyses, and theoretical predictions to characterize the relative role of co-existing feedbacks governing insulin signaling. We examined phosphorylation of the insulin receptor and insulin receptor substrate-1 and endocytosis of the receptor in response to various different experimental perturbations in primary human adipocytes. The analysis revealed that receptor endocytosis is necessary for two identified feedback mechanisms involving mass and information transfer, respectively. Experimental findings indicate that interfering with the feedback may substantially increase overall signaling strength, suggesting novel therapeutic targets for insulin resistance and type 2 diabetes. Because the central observations are present in other signaling networks, our results may indicate a general mechanism in hormonal control.
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| 7. |
- Chen, Ke Wang, et al.
(author)
-
Estimation of the Primary Current in a Saturated Transformer
- 1991
-
In: Proceedings of the 30th IEEE Conference on Decision and Control. - Linköping : Linköping University. - 0780304500 ; , s. 2363-2365 vol.3
-
Conference paper (peer-reviewed)abstract
- It is pointed out that, when a current in a power system is measured using a transformer, the measurement can be distorted by transformer saturation. The authors examine two methods of estimating the primary current from the secondary in the presence of saturation. The first is based on an extended Kalman filter, while the second is based on an off-line Gauss-Newton method
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| 8. |
- Edström, Krister, et al.
(author)
-
Algorithmic, Physically based Mode Initialization when Simulating Hybrid Systems
- 2002
-
In: Proceedings of the Institution of mechanical engineers. Part I, journal of systems and control engineering. - : SAGE Publications. - 0959-6518 .- 2041-3041. ; 216:I1, s. 65-72
-
Journal article (peer-reviewed)abstract
- In the simulation of hybrid systems, discontinuities can appear at mode changes. An algorithm is presented that gives initial values for the continuous state variables in a new mode. The algorithm is based on a switched bond graph representation of the system, and it handles discontinuities introduced by a changed number of state variables at a mode change. The algorithm is obtained by integrating the bond graph relations over the mode change and assuming that the physical variables are bounded. This gives a relation between the variables before and after the mode change. It is proved here that the equations for the new initial conditions are solvable. The algorithm is related to a singular perturbation theory by replacing the discontinuity by a fast continuous change. The action is considered of a single switch and the corresponding continuous change, tuned by a single parameter. By letting this parameter tend to zero, the same initial state values are achieved as those derived by the presented algorithm. The algorithm is also related to physical principles such as charge conservation.
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| 9. |
- Fliess, M, et al.
(author)
-
An Algebraic Approach to Linear and Nonlinear Control
- 1993
-
In: Essays on Control. - Boston ; Basel : Birkhäuser. - 0817636706 - 3764336706 ; , s. 223--267
-
Book chapter (peer-reviewed)abstract
- The analysis and design of control systems has been greatly influenced by the mathematical tools being used. Maxwell introduced linear differential equations in the 1860’s. Nyquist, Bode and others started the systematic use of tranfer functions, utilizing complex analysis in the 1930’s. Kalman brought forward state space analysis around 1960. For nonlinear systems, differential geometric concepts have been of great value recently. We will argue here that algebraic methods can be very useful for both linear and nonlinear systems. To give some motivation we will begin by looking at a few examples.
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| 10. |
- Fliess, Michel, et al.
(author)
-
An Algebraic Approach to Linear and Nonlinear Control
- 1994
-
Reports (other academic/artistic)abstract
- The analysis and design of control systems has been greatly influenced by the mathematical tools being used. Maxwell introduced linear differential equations in the 1860’s. Nyquist, Bode and others started the systematic use of tranfer functions, utilizing complex analysis in the 1930’s. Kalman brought forward state space analysis around 1960. For nonlinear systems, differential geometric concepts have been of great value recently. We will argue here that algebraic methods can be very useful for both linear and nonlinear systems. To give some motivation we will begin by looking at a few examples.
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| 11. |
- Forsman, Krister, et al.
(author)
-
Constructive Algebra and Control Theory
- 1993
-
In: Proceedings of the 1993 International Symposium on The Mathematical Theory of Networks and Systems. - Linköping : Linköping University. - 9783055016615 ; , s. 149-152
-
Reports (other academic/artistic)
|
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| 12. |
|
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| 13. |
- Gerdin, Markus, et al.
(author)
-
Global Identifiability of Complex Models, Constructed from Simple Submodels
- 2007
-
In: Modeling, Estimation and Control. - Linköping : Linköping University Electronic Press. - 9783540735694 ; , s. 123-133
-
Reports (other academic/artistic)abstract
- It is a typical situation in modern modeling that a total model is built up from simpler submodels, or modules, for example residing in a model library. The total model could be quite complex, while the modules are well understood and analysed. A procedure to decide global parameter identifiability for such a collection of model equations of differential-algebraic nature is suggested. It is shown how to make use of the natural modularization of the model structure. Basically, global identifiability is obtained if and only if each module is identifiable, and the connecting signals can be retrieved from the external signals, without knowledge of the values of the parameters.
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| 14. |
- Gerdin, Markus, 1977-, et al.
(author)
-
On Identifiability of Object-Oriented Models
- 2006
-
In: Proceedings of the 14th IFAC Symposium on System Identification. - 9783902661029 ; , s. 820-825
-
Conference paper (peer-reviewed)abstract
- When estimating unknown parameters, it is important that the model is identifiable so that the parameters can be estimated uniquely. For nonlinear differential-algebraic equation models with polynomial equations, a differential algebra approach to examine identifiability is available. This approach can be slow, so the present paper describes how this method can be modularized for object-oriented models. A characteristic set of equations is computed for components in model libraries, and stored together with the components. When an object-oriented model is built using such models, identifiability can be examined using the stored equations.
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| 15. |
- Gerdin, Markus, et al.
(author)
-
On Identifiability of Object-Oriented Models
- 2005
-
Reports (other academic/artistic)abstract
- When estimating unknown parameters, it is important that the model is identifiable so that the parameters can be estimated uniquely. For nonlinear differential-algebraic equation models with polynomial equations, a differential algebra approach to examine identifiability is available. This approach can be slow, so the present paper describes how this method can be modularized for object-oriented models. A characteristic set of equations is computed for components in model libraries, and stored together with the components. When an object-oriented model is built using such models, identifiability can be examined using the stored equations.
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| 16. |
- Gerdin, Markus, 1977-, et al.
(author)
-
On Parameter and State Estimation for Linear Differential-Algebraic Equations
- 2007
-
In: Automatica. - Linköping : Elsevier. - 0005-1098 .- 1873-2836. ; 43:3, s. 416-425
-
Journal article (peer-reviewed)abstract
- The current demand for more complex models has initiated a shift away from state-space models towards models described by differential-algebraic equations (DAEs). These models arise as the natural product of object-oriented modeling languages, such as Modelica. However, the mathematics of DAEs is somewhat more involved than the standard state-space theory. The aim of this work is to present a well-posed description of a linear stochastic differential-algebraic equation and more importantly explain how well-posed estimation problems can be formed. We will consider both the system identification problem and the state estimation problem. Besides providing the necessary theory we will also explain how the procedures can be implemented by means of efficient numerical methods.
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| 17. |
- Gerdin, Markus, 1977-, et al.
(author)
-
Parameter Estimation in Linear Differential-Algebraic Equations
- 2003
-
In: Proceedings of the 13th IFAC Symposium on System Identification. - Linköping : Linköping University Electronic Press. - 9780080437095 ; , s. 1530-
-
Conference paper (peer-reviewed)abstract
- This report describes how parameter estimation can be performed in linear DAE systems. Both time domain and frequency domain identification are examined. The results are exemplified on a small system. A potential application for the algorithms is to make parameter estimation in models generated by a modeling language like Modelica.
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| 18. |
- Gerdin, Markus, 1977-, et al.
(author)
-
Well-Posedness of Filtering Problems for Stochastic Linear DAE Models
- 2005
-
In: Proceedings of the 44th IEEE Conference on Decision and Control and European Control Conference. - Linköping : Linköping University Electronic Press. - 0780395670 ; , s. 350-355
-
Conference paper (peer-reviewed)abstract
- Modern modeling tools often give descriptor or DAE models, i.e., models consisting of a mixture of differential and algebraic relationships. The introduction of stochastic signals into such models in connection with filtering problems raises several questions of well-posedness. The main problem is that the system equations may contain hidden relationships affecting variables defined as white noise. The result might be that certain physical variables get infinite variance or contain formal differentiations of white noise. The paper gives conditions for well-posedness in terms of certain subspaces defined by the system matrices.
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| 19. |
- Germundsson, Roger, et al.
(author)
-
A Unified Constructive Study of Linear, Nonlinear and Discrete Event Systems
- 1995
-
Reports (other academic/artistic)abstract
- Starting from the behavioral point of view a system is defined by its set of behaviors. In discrete time this is a relation over D N and hence a very infinite object. A model is a relation over D N for some finite N that can be extended to a behavior. Furthermore properties of a system is defined in terms of its behavior. Starting from a constructive point of view we need to be able to represent and manipulate systems. A natural choice is to use some a constructive model, i.e. one that can be finitely represented and manipulated. We will consider four such classes of models: polynomial and linear relations over finite and infinite fields. There are a number of restrictions on the geometric (or behavioral) operations that are possible for each of these classes and still remain within the class. If we want to interpret our models as systems and analyze system properties, then several properties become impossible to compute. Some examples: The set of reachable states for a polynomial model over an infinite field is in general impossible to compute. It may converge to be fractal. The set of reacable states ik steps or less in a linear model cannot be represented as a linear set in general.
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| 20. |
- Glad, Torkel, 1947-
(author)
-
A Differential Algebra Representation of the RGA
- 2000
-
In: Proceedings of the 14th International Symposium on Mathematical Theory of Networks and Systems. - Linköping : Linköping University Electronic Press. ; , s. 169-178
-
Conference paper (peer-reviewed)abstract
- Extentions of the RGA (relative gain array) technique to nonlinear systems are considered. The steady-state properties are given by an array of nonlinear functions. It is shown that the corresponding dynamic description can be calculated using a reduction algorithm from differential algebra.
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| 21. |
- Glad, Torkel, 1947-, et al.
(author)
-
A Multiplier Method with Automatic Limitation of Penalty Growth
- 1979
-
In: Mathematical programming. - : Springer. - 0025-5610 .- 1436-4646. ; 17:1, s. 140-155
-
Journal article (peer-reviewed)abstract
- This paper presents a multiplier method for solving optimization problems with equality and inequality constraints. The method realizes all the good features that were foreseen by R. Fletcher for this type of algorithm in the past, but which suffers from none of the drawbacks of the earlier attempts.
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| 22. |
- Glad, Torkel, 1947-, et al.
(author)
-
Aircraft Pitch Attitude Control using Backstepping
- 2000
-
In: Proceedings of Reglermöte 2000. - Linköping : Linköping University Electronic Press. ; , s. 143-148
-
Conference paper (other academic/artistic)abstract
- A nonlinear approach to the automatic pitch attitude control problem for a generic fighter aircraft is presented. A nonlinear model describing the longitudinal equations of motion in strict feedback form is derived. Backstepping is utilized for the construction of a globally stabilizing controller with a number of free design parameters. Two tuning schemes are proposed based on the desired locally linear controller properties. The controller is evaluated using the HIRM fighter aircraft model.
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| 23. |
|
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| 24. |
|
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| 25. |
|
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| 26. |
- Glad, Torkel, 1947-
(author)
-
Analysis of Actuator Cross Coupling in Aircraft
- 1998
-
In: Proceedings of the 1998 Conference on Mathematical Theory of Networks and Systems. ; , s. 1019-1022
-
Conference paper (peer-reviewed)abstract
- When several control signals share the same physical actuators, actuator saturation has the effect of giving coupling between control loops which are otherwise decoupled. This effect occurs e.g. in aircraft control where the elevator and aileron functions often use the same physical control surfaces. The effect is particularly important when one of the loops is open loop unstable. The paper consider the effects on the stabilizable region of cross coupling with another control loop. To give further insight simple optimal control problems are considered.
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| 27. |
- Glad, Torkel, 1947-
(author)
-
Analysis of Actuator Cross Coupling in Aircraft
- 1999
-
Reports (other academic/artistic)abstract
- When several control signals share the same physical actuators, actuator saturation has the effect of giving coupling between control loops which are otherwise decoupled. This effect occurs e.g. in aircraft control where the elevator and aileron functions often use the same physical control surfaces. The effect is particularly important when one of the loops is open loop unstable. The paper consider the effects on the stabilizable region of cross coupling with another control loop. To give further insight simple optimal control problems are considered.
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| 28. |
- Glad, Torkel, et al.
(author)
-
Backstepping Control of a Rigid Body
- 2004
-
Reports (other academic/artistic)abstract
- A method for backstepping control of rigid body motion is proposed. The control variables are torques and the force along the axis of motion. The proposed control law and lyapunov function guarantee asymptotic stability from all initial values except one singular point.
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| 29. |
- Glad, Torkel, 1947-, et al.
(author)
-
Bounds on the Response Time under Control Constraints
- 1998
-
In: Proceedings of the 37th IEEE Conference on Decision and Control. - 0780343948 ; , s. 929-930 vol.1
-
Conference paper (peer-reviewed)abstract
- We consider the problem of transferring the output of a linear system from one equilibrium value to another under control amplitude constraint. It is possible to give a simple lower bound on the time required, expressed in the longest time constant, the gain of the system, the change in y and the control bound.
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| 30. |
- Glad, Torkel, 1947-, et al.
(author)
-
Bounds on the Response Time under Control Constraints
- 2001
-
In: Automatica. - : Elsevier. - 0005-1098 .- 1873-2836. ; 37:12, s. 2073-2076
-
Journal article (peer-reviewed)abstract
- We consider the problem of transferring the output of a linear system from one equilibrium value to another under control amplitude constraint. It is possible to give a simple lower bound on the time required, expressed in the longest time constant, the gain of the system, the change in y and the control bound. This theoretical bound appears to be useful as a practical lower bound of the rise time.
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| 31. |
- Glad, Torkel, 1947-
(author)
-
Computing the Settling Time for Nonlinear Step Responses
- 2007
-
In: Proceedings of the 7th IFAC Symposium on Nonlinear Control Systems. - 9783902661289 ; , s. 119-122
-
Conference paper (peer-reviewed)abstract
- The settling time for the step response of a nonlinear system can be computed using the Poincaré-Dulac normal form. It is then possible to use a simple approximate formula, whose error can be estimated. The data needed can all be calculated from the leading coefficients of series expansions of the Poincaré-Dulac transformation and the equilibrium curve.
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| 32. |
- Glad, Torkel, 1947-, et al.
(author)
-
Constructive Algebraic Geometry in Nonlinear Control
- 1990
-
In: Proceedings of the 29th IEEE Conference on Decision and Control. - Linköping : Linköping University. ; , s. 2825-2827
-
Conference paper (peer-reviewed)abstract
- It is shown how Grobner bases can be used to solve some common problems in nonlinear systems theory efficiently. These problems include finding critical levels of local Lyapunov functions and solving the equations that arise in the harmonic balancing method. The methods proposed are illustrated by some concrete examples in which the computer algebra system Maple is used for performing the necessary calculations.
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| 33. |
- Glad, Torkel, 1947-, et al.
(author)
-
Controllers for Amplitude Limited Model Error Models
- 2005
-
In: Proceedings of the 16th IFAC World Congress. - Linköping : Linköping University Electronic Press. - 9783902661753 ; , s. 662-662
-
Conference paper (peer-reviewed)abstract
- In this paper, systems where information about model accuracy is contained in a model error model are considered. The validity of such a model is typically restricted to input signals that are limited in amplitude. It is then natural to require the same amplitude restriction when designing controllers. The resulting implications for controller design are investigated in both the continuous and the discrete time case.
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| 34. |
- Glad, Torkel, 1947-
(author)
-
Deadbeat Control for Nonlinear Systems
- 1988
-
In: Analysis and Control of Nonlinear Systems. - Amsterdam : North-Holland. - 0444704965
-
Book chapter (other academic/artistic)
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| 35. |
|
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| 36. |
- Glad, Torkel, 1947-
(author)
-
Dealing with Inequalities in Polynomial Models
- 2012
-
In: Proceedings of the 16th IFAC Symposium on System Identification. - 9783902823069 ; , s. 936-940
-
Conference paper (peer-reviewed)abstract
- It is described how set membership identification and model rejection for polynomial models can be described using polynomial inequalities and inequations. Using difference algebra methods these problems can be reduced to a form based on so called autoreduced sets. It is shown that these descriptions generalize state space descriptions. It is also discussed how special forms of autoreduced sets can make calculations based on interval methods easier to implement.
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| 37. |
|
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| 38. |
- Glad, Torkel, 1947-
(author)
-
Differential Algebraic Modelling of Nonlinear Systems
- 1990
-
In: Realization and Modelling in System Theory. - Boston ; Basel : Birkhäuser Verlag. - 081763469X - 376433469X - 0817634681 - 9781461280330 ; , s. 97-105
-
Book chapter (other academic/artistic)abstract
- This paper discusses how the concepts of differential algebra can be used in the modelling of physical systems. In particular it is shown that the concepts of ranking and characteristic set can be used to give a structure to the set of physical equations. The characteristic set makes it easy to find the number of inputs and the order of the system. The question of observability can also be investigated using the characteristic set. In particular one can see that the order of an input output differential equation will be the same as the system order if and only if all variables are observable from the output.
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| 39. |
- Glad, Torkel, 1947-
(author)
-
Differential Algebraic Modelling of Nonlinear Systems
- 1989
-
Reports (other academic/artistic)abstract
- This paper discusses how the concepts of differential algebra can be used in the modelling of physical systems. In particular it is shown that the concepts of ranking and characteristic set can be used to give a structure to the set of physical equations. The characteristic set makes it easy to find the number of inputs and the order of the system. The question of observability can also be investigated using the characteristic set. In particular one can see that the order of an input output differential equation will be the same as the system order if and only if all variables are observable from the output.
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| 40. |
- Glad, Torkel, 1947-
(author)
-
Extensions of the RGA Concept to Nonlinear Systems
- 1999
-
In: Proceedings of the 5th European Control Conference. ; , s. 332-
-
Conference paper (peer-reviewed)abstract
- Extentions of the RGA (relative gain array) technique to nonlinear systems are considered. The steady-state properties are given by an array of nonlinear functions. The high frequency properties are characterized by forming the conventional RGA of the decoupling matrix.
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| 41. |
- Glad, Torkel, 1947-, et al.
(author)
-
Flight Control Design using Backstepping
- 2001
-
In: Proceedings of the 5th IFAC Symposium Nonlinear Control Systems. ; , s. 259-264
-
Conference paper (peer-reviewed)abstract
- Today's prevailing nonlinear design method for aircraft flight control is feedback linearization. This paper presents a new method to deal with the nonlinear aerodynamic forces and moments acting on the aircraft: backstepping. Specically, we derive backstepping control laws for angle of attack and sideslip control that require less knowledge of the lift and side forces compared to feedback linearization designs. The control laws are made adaptive to errors in the aerodynamic moment coefficients using nonlinear observer techniques.
|
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| 42. |
|
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| 43. |
|
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| 44. |
- Glad, Torkel, 1947-, et al.
(author)
-
Hamilton-Jacobi Equations for Nonlinear Descriptor Systems
- 2006
-
In: Proceedings of the 2006 American Control Conference. - 1424402107 - 1424402093 ; , s. 1027-1031
-
Conference paper (peer-reviewed)abstract
- Optimal control problems for nonlinear descriptor systems are considered. Anapproach where the descriptor system is conceptually reduced to a state spaceform is compared to an approach where the Hamilton-Jacobi equation is directly formulated for the descriptor system. The two approaches are shown to give essentially the same systems of equations to be solved. A certain unknown function is present only in the second approach but is shown to be computable from the quantities common to both approches.
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| 45. |
- Glad, Torkel, 1947-, et al.
(author)
-
Hamilton-Jacobi Equations for Nonlinear Descriptor Systems
- 2005
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Reports (other academic/artistic)abstract
- Optimal control problems for nonlinear descriptor systems are considered. Anapproach where the descriptor system is conceptually reduced to a state spaceform is compared to an approach where the Hamilton-Jacobi equation is directly formulated for the descriptor system. The two approaches are shown to give essentially the same systems of equations to be solved. A certain unknown function is present only in the second approach but is shown to be computable from the quantities common to both approches.
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| 46. |
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| 47. |
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| 48. |
- Glad, Torkel, 1947-, et al.
(author)
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Identifiability of Turbocharged IC Engine Models
- 1999
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In: Proceedings of the SAE 1999 International Congress & Exposition. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Conference paper (peer-reviewed)abstract
- The paper deals with the problem of identifiability of mean-value models of turbocharged IC engines. A way of reducing such models to linear regressions using differential algebra is presented. The conditions of the global identifiability and the persistent excitation are formulated in explicit form for a given set of sensors. It is accompanied with the discussion how to reduce the set of sensors required for engine identification. As a side product it is shown how to use regressors derived for estimation and/or verification of some static nonlinearities using dynamic test data. The results obtained can be used for both model-based FDI (fault detection and isolation) and engine control purposes but mainly for automatic generation of engine test plans and identification.
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| 49. |
- Glad, Torkel, 1947-, et al.
(author)
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Identifiability with Constraints
- 1999
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Reports (other academic/artistic)abstract
- It is shown that identifiability of very general nonlinear models, described by polynomial implicit differential equations, inequations and inequalities, can be decided algorithmically. An algorithm based on differential algebra and real algebra can perform the calculations.
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| 50. |
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