| 1. |
- Härkegård, Ola, 1947-, et al.
(författare)
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Flight Control Design using Backstepping
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)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.
(författare)
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A Simulation and Animation Tool for Studying Multivariable Control
- 2002
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Ingår i: Proceedings of the 15th IFAC World Congress. - 9783902661746 ; , s. 1432-1432
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Konferensbidrag (refereegranskat)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. |
- Edström, Krister, et al.
(författare)
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Algorithmic, Physically based Mode Initialization when Simulating Hybrid Systems
- 2002
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Ingår i: 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
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Gerdin, Markus, 1977-, et al.
(författare)
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Parameter Estimation in Linear Differential-Algebraic Equations
- 2003
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Ingår i: Proceedings of the 13th IFAC Symposium on System Identification. - Linköping : Linköping University Electronic Press. - 9780080437095 ; , s. 1530-
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Konferensbidrag (refereegranskat)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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| 5. |
- Glad, Torkel, 1947-
(författare)
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A Differential Algebra Representation of the RGA
- 2000
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Ingår i: Proceedings of the 14th International Symposium on Mathematical Theory of Networks and Systems. - Linköping : Linköping University Electronic Press. ; , s. 169-178
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Konferensbidrag (refereegranskat)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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| 6. |
- Glad, Torkel, 1947-, et al.
(författare)
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Aircraft Pitch Attitude Control using Backstepping
- 2000
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Ingår i: Proceedings of Reglermöte 2000. - Linköping : Linköping University Electronic Press. ; , s. 143-148
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 7. |
- Glad, Torkel, et al.
(författare)
-
Backstepping Control of a Rigid Body
- 2004
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Rapport (övrigt vetenskapligt/konstnärligt)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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| 8. |
- Glad, Torkel, 1947-, et al.
(författare)
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Bounds on the Response Time under Control Constraints
- 2001
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Ingår i: Automatica. - : Elsevier. - 0005-1098 .- 1873-2836. ; 37:12, s. 2073-2076
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Glad, Torkel, 1947-, et al.
(författare)
-
Flight Control Design using Backstepping
- 2001
-
Ingår i: Proceedings of the 5th IFAC Symposium Nonlinear Control Systems. ; , s. 259-264
-
Konferensbidrag (refereegranskat)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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| 10. |
- Glad, Torkel, 1947-, et al.
(författare)
-
Robustness Guarantees for Linear Control Designs with an Estimated Nonlinear Model Error Model
- 2004
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Ingår i: International Journal of Robust and Nonlinear Control. - Linköping : John Wiley & Sons. - 1049-8923 .- 1099-1239. ; 14:11, s. 959-970
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Tidskriftsartikel (refereegranskat)abstract
- Much attention in robust identification and control has been focused on linear low order models approximating high order linear systems. We consider the more realistic situation with a linear model approximating a nonlinear system. We describe how a nonlinear model error model can be developed, that allows a complete linear design process that results in a closed loop system with performance robustness guarantees (in terms of gain from disturbance to output) against the nonlinear error. Clearly the design can be successful only if the linear model is a reasonably good approximation of the system. A particular aspect of the design process is to define a workable definition of 'practical stability' for robust control design, with possible non-linear model errors. We use affine norms for that purpose.
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| 11. |
- Glad, Torkel, 1947-
(författare)
-
Step Responses of Nonlinear Non-Minimum Phase Systems
- 2004
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Ingår i: Proceedings of the 6th IFAC Symposium on Nonlinear Control Systems. - Linköping : Linköping University Electronic Press. - 9780080443034
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Konferensbidrag (refereegranskat)abstract
- For nonlinear systems, instability of the zero dynamics is known to correspond to the non-minimum phase property of linear systems. For linear systems it is also known that non-minimum phase is associated with certain step response behavior e.g. the initial direction of the step response is opposite to the final value. The corresponding step response properties of nonlinear systems are investigated in this contribution. It is also investigated whether a certain nonlinear canonical form gives insight into the relation between step response and non-minimum phase behavior.
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| 12. |
- Glad, Torkel, 1947-, et al.
(författare)
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Structural Identifiability : Tools and Applications
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The paper deals with the application of identifiability criteria to mean-value models of turbocharged IC engines. A way of reducing such models to linear regressions using differential algebra is presented. The conditions of global identifiability and persistent excitation are formulated in explicit form for a given set of sensors. It is accompanied with a technique for reducing the set of sensors required for the engine identification. The software tools required are outlined and their complexity is discussed.
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| 13. |
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| 14. |
- Glad, Torkel, 1947-, et al.
(författare)
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The Gröbner Basis Method in Control Theory : An Overview
- 2002
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Ingår i: Proceedings of the 15th IFAC World Congress. - 9783902661746 ; , s. 906-906
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Konferensbidrag (refereegranskat)abstract
- The paper discusses the usefulness of Gröbner bases methods in a variety of control problems for a class of polynomial systems. Polynomial systems are described by difference or differential equations in which the transition map or vectorfield are polynomials. Gröbner bases methods are useful in both the analysis and the design of polynomial control systems.
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| 15. |
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| 16. |
- Hansson, Anders, et al.
(författare)
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Stability Analysis of Nonlinear Systems using Frozen Stationary Linearization
- 2004
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Ingår i: Proceedings of the 2004 American Control Conference. - 0780383354 ; , s. 424-428
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Konferensbidrag (refereegranskat)abstract
- This work discusses how to compute stability regions for nonlinear systems with slowly varying parameters using frozen stationary linearization. It is shown that larger stability regions can be obtained as compared to traditional approaches using recent stability results for linear parameter-varying systems.
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| 17. |
- Hansson, Anders, et al.
(författare)
-
Stability Analysis of Nonlinear Systems using Frozen Stationary Linearization
- 2003
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This work discusses how to compute stability regions for nonlinear systems with slowly varying parameters using frozen stationary linearization. It is shown that larger stability regions can be obtained as compared to traditional approaches using recent stability results for linear parameter-varying systems.
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| 18. |
- Härkegård, Ola, et al.
(författare)
-
A Backstepping Design for Flight Path Angle Control
- 2000
-
Ingår i: Proceedings of the 39th IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 0780366387 ; , s. 3570-3575
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Konferensbidrag (refereegranskat)abstract
- A nonlinear approach to flight path angle control is presented. Using backstepping, a globally stabilizing control law is derived. Although the nonlinear nature of the lift force is considered, the pitching moment to be produced is only linear in the measured states. Thus, the resulting control law is much simpler than if feedback linearization had been used. The free parameters that spring from the backstepping design are used to achieve a desired linear behavior around the operating point.
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| 19. |
- Härkegård, Ola, et al.
(författare)
-
Backstepping Control of a Rigid Body
- 2002
-
Ingår i: Proceedings of the 41st IEEE Conference on Decision and Control. - 0780375165 ; , s. 3944-3945 vol.4
-
Konferensbidrag (refereegranskat)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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| 20. |
- Härkegård, Ola, et al.
(författare)
-
Control of Systems with Input Nonlinearities and Uncertainties : An Adaptive Approach
- 2001
-
Ingår i: Proceedings of the 2001 European Control Conference. - 9789727520473 ; , s. 1912-1917
-
Konferensbidrag (refereegranskat)abstract
- Although many of todays nonlinear control design algorithms assume the system dynamics to be affine in the control input, this often does not hold in practice. A remedy for this is to instead design acontrol law in terms of some other entity that satisfies the structural assumptions of the design method. In this contribution we discuss how to realize such a virtual control law in terms of the actual control variable. Given a nominal static invertible model of the mapping between the two, the true mapping is assumed to differ from the model by a constant bias. Two ways of how to estimate this bias on-line and use it for feedback are proposed. One of them corresponds to adaptive backstepping, the other one is an observer based approach. In both cases we investigate how to guarantee closed loop stability when the estimate is used for feedback.
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| 21. |
- Härkegård, Ola, et al.
(författare)
-
Control of Systems with Input Nonlinearities and Uncertainties : An Adaptive Approach
- 2000
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Although many of todays nonlinear control design algorithms assume the system dynamics to be affine in the control input, this often does not hold in practice. A remedy for this is to instead design acontrol law in terms of some other entity that satisfies the structural assumptions of the design method. In this contribution we discuss how to realize such a virtual control law in terms of the actual control variable. Given a nominal static invertible model of the mapping between the two, the true mapping is assumed to differ from the model by a constant bias. Two ways of how to estimate this bias on-line and use it for feedback are proposed. One of them corresponds to adaptive backstepping, the other one is an observer based approach. In both cases we investigate how to guarantee closed loop stability when the estimate is used for feedback.
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| 22. |
- Härkegård, Ola, et al.
(författare)
-
Resolving Actuator Redundancy - Control Allocation vs. Linear Quadratic Regulation
- 2002
-
Ingår i: Proceedings of the 4th Conference on Computer Science and Systems Engineering. ; , s. 17-21
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One issue to be dealt with when designing flight control laws is how to deal with actuator redundancy. While traditional aircraft use elevator, aileron, and rudder to control the aircraft motion in pitch, roll, and yaw, modern aircraft may have ten or more control surfaces that can be independently controlled. Two tools for distributing the control effect among a set of actuators are linear quadratic regulation and control allocation. In this paper we investigate the relationship between these two design tools and show that in some cases they can be tuned to give the exact same control signal.
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| 23. |
- Ljung, Lennart, 1946-, et al.
(författare)
-
Uncertain LTI-Models for Linear Control Design of Nonlinear Systems
- 2001
-
Ingår i: Proceedings of the 40th IEEE Conference on Decision and Control. - 0780370619 ; , s. 2692-2694 vol.3
-
Konferensbidrag (refereegranskat)abstract
- Much attention in robust identification and control has been focused on linear low order models approximating high order linear systems. We consider the more realistic situation with a linear model approximating a non-linear system. We describe how a linear time invariant (LTI) model with unstructured uncertainty, i.e. a "band" of Nyquist curves can be developed using a non-linear model error model. Applying standard linear robust control design to this uncertain LTI model will lead to a (non-linear) closes loop system with performance robustness guarantees (in terms of gain from disturbances to output) well in line with the objectives of the linear design. Clearly the design can be successful only if the linear model is a reasonable good approximation of the system. A particular aspect of the design process is to define a workable definition of "practical stability" for robust control design, with possibly non-linear model errors. We use affine power norms for that purpose.
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| 24. |
- Schön, Thomas, 1977-, et al.
(författare)
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A Modeling and Filtering Framework for Linear Differential-Algebraic Equations
- 2003
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Ingår i: Proceedings of the 42th IEEE Conference on Decision and Control. - 0780379241 ; , s. 892-897 vol.1
-
Konferensbidrag (refereegranskat)abstract
- General approaches to modeling, for instance using object-oriented software, lead to differential-algebraic equations (DAE). As the name reveals, it is a combination of differential and algebraic equations. For state estimation using observed system inputs and outputs in a stochastic framework similar to Kalman filtering, we need to augment the DAE with stochastic disturbances ("process noise"), whose covariance matrix becomes the tuning parameter. We will determine the subspace of possible causal disturbances based on the linear DAE model. This subspace determines all degrees of freedom in the filter design, and a Kalman filter algorithm is given. We illustrate the design on a system with two interconnected rotating masses.
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| 25. |
- Schön, Thomas, 1977-, et al.
(författare)
-
A Modeling and Filtering Framework for Linear Implicit Systems
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- General approaches to modeling, for instance using object-oriented software, lead to differential algebraic equations (DAE), also called implicit systems. For state estimation using observed system inputs and outputs in a stochastic framework similar to Kalman filtering, we need to augment the DAE with stochastic disturbances (process noise), whose covariance matrix becomes the tuning parameter. We will determine the subspace of possible causal disturbances based on the linear DAE model. This subspace determines all degrees of freedom in the filter design, and a Kalman filter algorithm is given.We illustrate the design on a system with two interconnected rotating masses.
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