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  • 1.
    Glad, Torkel
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Aircraft Pitch Attitude Control using Backstepping2000In: Proceedings of Reglermöte 2000, 2000, p. 143-148Conference paper (Other academic)
    Abstract [en]

    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.

  • 2.
    Glad, Torkel
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Backstepping Control of a Rigid Body2004Report (Other academic)
    Abstract [en]

    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.

  • 3.
    Glad, Torkel
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Flight Control Design using Backstepping2001In: Proceedings of the 5th IFAC Symposium Nonlinear Control Systems, 2001, p. 259-264Conference paper (Refereed)
    Abstract [en]

    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.

  • 4.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Backstepping and control allocation with applications to flight control2003Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In this thesis we study a number of nonlinear control problems motivated by their appearance in flight control. The results are presented in a general framework and can also be applied to other areas. The two main topics are backstepping and control allocation.

    Backstepping is a nonlinear control design method that provides an alternative to feedback linearization. Here, backstepping is used to derive robust linear control laws for two nonlinear systems, related to angle of attack control and flight path angle control, respectively. The resulting control laws require less modeling information than corresponding designs based on feedback linearization, and achieve global stability in cases where feedback linearization can only be performed locally. Further, a method for backstepping control of a rigid body is developed, based on a vector description of the dynamics. We also discuss how to augment an existing nonlinear controller to suppress constant input disturbances. Two methods, based on adaptive backstepping and nonlinear observer design, are proposed.

    Control allocation deals with actuator utilization for overactuated systems. In this thesis we pose the control allocation problem as a constrained least squares problem to account for actuator position and rate constraints. Efficient solvers based on active set methods are developed with similar complexity to existing, approximate, pseudoinverse methods. A method for dynamic control allocation is also proposed which enables a frequency dependent control distribution among the actuators to be designed. Further, the relationship between control allocation and linear quadratic control is investigated. It is shown that under certain circumstances, the two techniques give the same freedom in distributing the control effort among the actuators. An advantage of control allocation, however, is that since the actuator constraints are considered, the control capabilities of the actuator suite can be fully exploited.

  • 5.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Backstepping Designs for Aircraft Control - What is there to Gain?2001In: Proceedings of the Third Conference on Computer Science and Systems Engineering, 2001, p. 201-205Conference paper (Other academic)
    Abstract [en]

    Aircraft flight control design is traditionally based on linear control theory, due to the existing wealth of tools for linear design and analysis. However, in order to achieve tactical advantages, modern fighter aircraft strive towards performing maneuvers outside the region where the dynamics of flight are linear, and the need for nonlinear tools arises. In this paper, backstepping is proposed as a possible framework for nonlinear flight control design. Its capabilities of handling five major issues - stability, performance, robustness, saturation, and disturbance attenuation - are investigated.

  • 6.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Backstepping Designs for Aircraft Control - What is there to Gain?2001Report (Other academic)
    Abstract [en]

    Aircraft flight control design is traditionally based on linear control theory, due to the existing wealth of tools for linear design and analysis. However, in order to achieve tactical advantages, modern fighter aircraft strive towards performing maneuvers outside the region where the dynamics of flight are linear, and the need for nonlinear tools arises. In this paper, backstepping is proposed as a possible framework for nonlinear flight control design. Its capabilities of handling five major issues - stability, performance, robustness, saturation, and disturbance attenuation - are investigated.

  • 7.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Dynamic Control Allocation for Overactuated Aircraft2002In: Proceedings of Reglermöte 2002, 2002, p. 211-216Conference paper (Other academic)
    Abstract [en]

    Aircraft control allocation deals with the problem of distributing a given aerodynamic moment demand among an available, redundant set of control surfaces. Most existing methods for control allocation are static in the sense that resulting control distribution only depends on the current moment demand. In this paper we propose a method for dynamic control allocation, in which the relationship between the moment demand and the resulting control distribution is dynamic. In the non saturated case, the resulting control distribution is determined by a first order linear filter which can be assigned different properties at different frequencies. The main advantage of the method is that it allows the user to design the transient and steady state control distributions separately. The control allocation problem is posed as a constrained quadratic programming problem which allows for automatic redistribution of the control effort when one actuator saturates in position or in rate.

  • 8.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Dynamic Control Allocation using Constrained Quadratic Programming2002In: Proceedings of the 2002 AIAA Guidance, Navigation, and Control Conference and Exhibit, 2002Conference paper (Refereed)
    Abstract [en]

    Control allocation deals with the problem of distributing a given control demand among an available set of actuators. Most existing methods are static in the sense that the resulting control distribution depends only on the current control demand. In this paper we propose a method for dynamic control allocation, in which the resulting control distribution also depends on the distribution in the previous sampling instant. The method extends the traditional generalized inverse method by also penalizing the individual actuator rates. Its main feature is that it allows for different control distributions during the transient phase of a maneuver and during trimmed flight. The control allocation problem is posed as a constrained quadratic programming problem which provides automatic redistribution of the control effort when one actuator saturates inposition or in rate. When no saturations occur, the resulting control distribution coincides with the control demand fed through a linear filter which can be assigned different frequency characteristics for different actuators.

  • 9.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Dynamic Control Allocation using Constrained Quadratic Programming2004Report (Other academic)
    Abstract [en]

    Control allocation deals with the problem of distributing a given control demand among an available set of actuators. Most existing methods are static in the sense that the resulting control distribution depends only on the current control demand. In this paper we propose a method for dynamic control allocation, in which the resulting control distribution also depends on the distribution in the previous sampling instant. The method extends the traditional generalized inverse method by also penalizing the individual actuator rates. Its main feature is that it allows for different control distributions during the transient phase of a maneuver and during trimmed flight. The control allocation problem is posed as a constrained quadratic programming problem which provides automatic redistribution of the control effort when one actuator saturates inposition or in rate. When no saturations occur, the resulting control distribution coincides with the control demand fed through a linear filter which can be assigned different frequency characteristics for different actuators.

  • 10.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Dynamic Control Allocation using Constrained Quadratic Programming2004In: Journal of Guidance Control and Dynamics, ISSN 0731-5090, E-ISSN 1533-3884, Vol. 27, no 6, p. 1028-1034Article in journal (Refereed)
    Abstract [en]

    Control allocation deals with the problem of distributing a given control demand among an available set of actuators. Most existing methods are static in the sense that the resulting control distribution depends only on the current control demand. In this paper we propose a method for dynamic control allocation, in which the resulting control distribution also depends on the distribution in the previous sampling instant. The method extends regular quadratic-programming control allocation by also penalizing the actuator rates. This leads to a frequency-dependent control distribution, which can be designed to, for example, account for different actuator bandwidths. The control allocation problem is posed as a constrained quadratic program, which provides automatic redistribution of the control effort when one actuator saturates in position or in rate. When no saturations occur, the resulting control distribution coincides with the control demand fed through a linear filter.

  • 11.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Efficient Active Set Algorithms for Solving Constrained Least Squares Problems in Aircraft Control Allocation2002In: Proceedings of the 41st IEEE Conference on Decision and Control, 2002, p. 1295-1300 vol.2Conference paper (Refereed)
    Abstract [en]

    In aircraft control, control allocation can be used to distribute the total control effort among the actuators when the number of actuators exceeds the number of controlled variables. The control allocation problem is often posed as a constrained least squares problem to incorporate the actuator position and rate limits. Most proposed methods for real-time implementation, like there distributed pseudoinverse method, only deliver approximate, and sometimes unreliable solutions. In this paper we investigate the use of classical active set methods for control allocation. We develop active set algorithms that always find the optimal control distribution, and show by simulation that the timing requirements are in the same range as for two previously proposed solvers.

  • 12.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Efficient Active Set Algorithms for Solving Constrained Least Squares Problems in Aircraft Control Allocation2002Report (Other academic)
    Abstract [en]

    In aircraft control, control allocation can be used to distribute the total control effort among the actuators when the number of actuators exceeds the number of controlled variables. The control allocation problem is often posed as a constrained least squares problem to incorporate the actuator position and rate limits. Most proposed methods for real-time implementation, like there distributed pseudoinverse method, only deliver approximate, and sometimes unreliable solutions. In this paper we investigate the use of classical active set methods for control allocation. We develop active set algorithms that always find the optimal control distribution, and show by simulation that the timing requirements are in the same range as for two previously proposed solvers.

  • 13.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Longitudinal Aircraft Control using Backstepping1999In: Proceedings of the Second Conference on Computer Science and Systems Engineering, 1999, p. 69-73Conference paper (Other academic)
    Abstract [en]

    Aircraft control constitutes a classical control design challenge. The nonlinear dynamical contributions from the aerodynamics are often dealt with by linearization around one or several working points. This paper addresses the task of global stabilization, considering the longitudinal motions of a combat aircraft. A nonlinear, recursive design technique called backstepping is described and utilized for constructing a control law, which is then used for simulation.

  • 14.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Resolving Actuator Redundancy - Control Allocation vs. Linear Quadratic Control2003In: Proceedings of the 2003 European Control Conference, 2003Conference paper (Refereed)
    Abstract [en]

    When designing control laws for systems with more inputs than controlled variables, one issue to consider is how to deal with actuator redundancy. Two tools for distributing the control effort among a redundant set of actuators are control allocation and linear quadratic control design. In this paper, we investigate the relationship between these two design tools when a quadratic performance index is used for control allocation. We show that for a particular class of linear systems, they give exactly the same design freedom in distributing the control effort among the actuators. The main benefit of using a separate control allocator is that actuator constraints can be considered, which is illustrated with a flight control example.

  • 15.
    Härkegård, Ola
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Resolving Actuator Redundancy - Control Allocation vs. Linear Quadratic Control2004Report (Other academic)
    Abstract [en]

    When designing control laws for systems with more inputs than controlled variables, one issue to consider is how to deal with actuator redundancy. Two tools for distributing the control effort among a redundant set of actuators are control allocation and linear quadratic control design. In this paper, we investigate the relationship between these two design tools when a quadratic performance index is used for control allocation. We show that for a particular class of linear systems, they give exactly the same design freedom in distributing the control effort among the actuators. The main benefit of using a separate control allocator is that actuator constraints can be considered, which is illustrated with a flight control example.

  • 16.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Backstepping Design for Flight Path Angle Control2000In: Proceedings of the 39th IEEE Conference on Decision and Control, 2000, p. 3570-3575Conference paper (Refereed)
    Abstract [en]

    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.

  • 17.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    A Backstepping Design for Flight Path Angle Control2000Report (Other academic)
    Abstract [en]

    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.

  • 18.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Aircraft Pitch Attitude Control using Backstepping2000Report (Other academic)
    Abstract [en]

    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.

  • 19.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Backstepping Control of a Rigid Body2002In: Proceedings of the 41st IEEE Conference on Decision and Control, 2002, p. 3944-3945 vol.4Conference paper (Refereed)
    Abstract [en]

    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.

  • 20.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Control of Systems with Input Nonlinearities and Uncertainties: An Adaptive Approach2001In: Proceedings of the 2001 European Control Conference, 2001, p. 1912-1917Conference paper (Refereed)
    Abstract [en]

    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.

  • 21.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Control of Systems with Input Nonlinearities and Uncertainties: An Adaptive Approach2000Report (Other academic)
    Abstract [en]

    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.

  • 22.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Flight Control Design using Backstepping2000Report (Other academic)
    Abstract [en]

    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.

  • 23.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Resolving Actuator Redundancy - Control Allocation vs. Linear Quadratic Control2004Report (Other academic)
    Abstract [en]

    When designing control laws for systems with more inputs than controlled variables, one issue to consider is how to deal with actuator redundancy. Two tools for distributing the control effort among a redundant set of actuators are control allocation and linear quadratic control design. In this paper, we investigate the relationship between these two design tools when a quadratic performance index is used for control allocation. We show that for a particular class of linear systems, they give exactly the same design freedom in distributing the control effort among the actuators. The main benefit of using a separate control allocator is that actuator constraints can be considered, which is illustrated with a flight control example.

  • 24.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Resolving Actuator Redundancy - Control Allocation vs. Linear Quadratic Regulation2002In: Proceedings of the 4th Conference on Computer Science and Systems Engineering, 2002, p. 17-21Conference paper (Other academic)
    Abstract [en]

    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.

  • 25.
    Härkegård, Ola
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Resolving Actuator Redundancy: Optimal Control vs. Control Allocation2005In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 41, no 1, p. 137-144Article in journal (Refereed)
    Abstract [en]

    This paper considers actuator redundancy management for a class of overactuated nonlinear systems. Two tools for distributing the control effort among a redundant set of actuators are optimal control design and control allocation. In this paper, we investigate the relationship between these two design tools when the performance indexes are quadratic in the control input. We show that for a particular class of nonlinear systems, they give exactly the same design freedom in distributing the control effort among the actuators. Linear quadratic optimal control is contained as a special case. A benefit of using a separate control allocator is that actuator constraints can be considered, which is illustrated with a flight control example.

  • 26.
    Härkegård, Ola
    et al.
    Saab AB, Sweden.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Vector Backstepping Design for Flight Control2007In: Proceedings of the 2007 AIAA Guidance, Navigation, and Control Conference and Exhibit, 2007Conference paper (Other academic)
    Abstract [en]

    A backstepping design for an aircraft described by rigid body dynamics is proposed. The system states are the unit velocity vector and the angular velocity in a body-fixed coordinate system. The result can be viewed as a multi-variable controller for angle of attack, sideslip angle, and velocity vector roll rate. The backstepping design is performed on the rigid body dynamics described on vector form. The resulting controller achieves convergence to a desired state from almost all starting points. Guidelines are given for tuning the controller to affect the characteristics of the short period mode, the roll mode and the dutch roll mode. A coupled high angle of attack, high roll rate maneuver is simulated using a simplified aircraft model to illustrate the design.

1 - 26 of 26
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