Gertjan Looye

Design of Robust Dynamic Inversion Control Laws using Multi-Objective Optimization

The design of robust attitude control laws for a civil aircraft with nonlinear dynamic inversion and multiobjective optimization is discussed. Dynamic inversion is a methodology that achieves linearization and decoupled command responses of the closedloop system via inverse model equations in the feedback loop. Using a linear outer loop controller the desired dynamic behavior is imposed. For tuning the free controller parameters, multi-objective optimization is used. The required robustness is achieved via a multi-model approach, as well as local robustness measures (e.g. gain and phase margins) as optimization criteria. As a new approach, not only the linear controller gains are optimized, but also physical parameters in the inverse model that are considered uncertain in the design model. The resulting control laws are used as inner loops of an autoland system, which was assessed for JAR-AWO requirements and successfully ∞ight tested.

Symbolic and numerical software tools for LFT-based low order uncertainty modeling

One of the main difficulties in applying modern control theories for designing robust controllers for linear uncertain plants is the lack of adequate models describing structured physical model uncertainties. We present a systematic approach for the generation of uncertainty models described by linear fractional transformations (LFTs) and report on recently developed symbolic and numerical software to assist the generation of low order LFT-based uncertainty models. The kernel of the symbolic software is a Maple library for generation and manipulation of LFT models. Additional numerical tools for order reduction of LFT models are based on MATLAB and FORTRAN implementations of numerically reliable algorithms. Three examples of uncertainty modeling of aircraft dynamics illustrate the capabilities of the new software to solve high order uncertainty modeling problems.

Object-oriented computational model building of aircraft flight dynamics and systems

Abstract For economic reasons aircraft performance is pushed towards its physical limitations. As far as flight control is concerned, a thorough investigation of flight system dynamics is required, i.e., covering the interaction between flight dynamics (including airframe structural flexibility) and flight systems (consisting of actuators/motivators and controls). Computational handling of this interaction is best taken into account if a comprehensive simulation model is available within a common computer processable description. This paper describes the computational model building of such a multidisciplinary non-linear aircraft simulation model for the design and validation of flight control systems. The approach has been validated in several projects and is demonstrated in this contribution by various views on a common example. The object-oriented, equation-based software package Dymola is used as the modelling environment.

Design of Autoland Controller Functions with Multiobjective Optimization

The application of multiobjective optimization to the design of longitudinal automatic-landing control laws for a civil aircraft is discussed. The control laws consist of a stability and command augmentation, a speed/flight path tracking, a glide-slope guidance, and a flare function. Mulitobjective optimization is used to synthesize the free parameters in these controller functions. Performance criteria are thereby computed from linear as well as nonlinear analysis. Robustness to uncertain and varying parameters is addressed via linear robustness criteria and via statisticle criteria computed from online Monte Carlo analysis. For each controller function, an optimization problem setup is defined. Starting with the inner loops, the synthesis is sequentially expanded with each of these setups eventually leading to simultaneous optimization of all controller functions. In this way, dynamic interactions between controller components are accounted for, and inner loops can be compromised such that these can be used in combination with different outer loop functions. This reduces controller complexity while providing good overall control system performance.

Application of an Optimization-based Design Process for Robust Autoland Control Laws

The design of a robust autoland con- troller using an optimization based design process is described. A modular controller architecture is de- veloped flrst. Inner loops are based on Dynamic In- version, speed and longitudinal path tracking loops are based on the Total Energy Control System. Functions for lateral path tracking, ILS guidance, ∞are and runway alignment are based on classical PID structures. The free parameters in the con- troller functions are tuned using multi-objective op- timization. Performance criteria are directly derived from the imposed design requirements and com- puted from linear or nonlinear analysis (e.g. eigen- values, simulations). Robustness is addressed via a multi-model approach, via optimization criteria (e.g. gain/phase margins), and, as a new contribution, via statistical criteria computed from on-line Monte- Carlo analysis. The design process and selected ar- chitecture have been applied to a wide-body as well as a small passenger aircraft to demonstrate con- troller robustness and e-ciency of the process. In both cases, JAR-AWO speciflcations had to be met. ⁄ Research Engineer, PhD candidate y Research Engineer, PhD z Research Engineer, DLR-Braunschweig, Institute for ∞ight system dynamics Copyright c ∞2001 by the German Aerospace Center DLR (Deutsches Zentrum fur Luft- und Raumfahrt e.V.). Pub- lished by the American Institute of Aeronautics and Astro- nautics, Inc., with permission. The latter design was successfully ∞ight tested.

Integrated Modelling of an Unmanned High-Altitude Solar-Powered Aircraft for Control Law Design Analysis

Solar-powered high-altitude unmanned platforms are highly optimized and integrated aircraft. In order to account for the complex, multi-physical interactions between their systems, we propose using integrated simulation models throughout the aircraft’s life cycle. Especially small teams with limited ressources should benefit from this approach. In this paper, we describe our approach to an integrated model of the Electric High-Altitude Solar-Powered Aircraft ELHASPA. It includes aspects of the environment, flight mechanics, energy system, and aeroelasticity. Model variants can be derived easily. The relevant parts of the model are described and the model’s application is demonstrated.

Integrated Flight Mechanics and Aeroelastic Aircraft Modeling using Object-Oriented Modeling Techniques

In this paper a software implementation is proposed of integrated flight mechanics / aeroelastic aircraft models, using object-oriented modeling techniques. Model development involves integrating a rigid aircraft simulation model with aeroelastic flutter analysis models. The main application is primary flight control law design, in which most of the criteria are of flight mechanical nature. For this reason, the rigid aircraft model is taken as the basis, while the fidelity of the aeroelastic part may depend on the accuracy required. Object-oriented modeling allows physical objects and phenomena to be implemented one-to-one into software objects, since interconnections can be defined freely (e.g. according to physical interactions like energy flow). This feature facilitates integration of model components from different engineering disciplines. A model compiler generates simulation code by symbolic manipulation of the model equations. The code can be exported to several (simulation) languages. This allows the same model to be used in different engineering environments. We illustrate this feature with a flutter analysis example.

Modular scalable system for operation and testing of UAVs

In this paper we present a system for operation and testing of different UAVs. The system allows easy development and modification of control and mission software. The system is composed of hard- and software modules with a standardized interface. We have been using the system with rotary and fixed wing UAVs with a take-off mass between 10 and 100 kg. For larger platforms the system can be used in a redundant setup. The software modules are integrated in a special real-time framework, which supports execution, scheduling, communication and system monitoring. A modular simulation and control infrastructure allows for flexible, integrated design and analysis of control laws. The code for the computational part of the modules can be generated from Matlab/Simulink-models or from Modelica-models. The system supports debugging, soft- and hardware in the loop simulations, operator training as well as real flight experiments. The main design concepts are explained at hand of our solar powered high altitude platform ELHASPA and the 10 years experience in development and operation will be summarized.

Design and flight testing of nonlinear autoflight control laws

This paper describes the design of an autoflight controller, based upon nonlinear model-based control laws. These control laws include the previously developed concept of Pseudo Control Hedging (PCH). This PCH algorithm adapts the reference model for the system output in case of unachievable commands due to control input saturation. This control algorithm has been applied on a high fidelity simulation model of the VFW-614 ATTAS (Advanced Technologies Testing Aircraft System) laboratory aircraft, where its beneficial influence has been illustrated. Test flights have been performed with ATTAS to evaluate the flight control technique in a relevant environment.

Design and flight testing of manual nonlinear flight control laws

This paper describes the design of a manual flight controller, based upon nonlinear model-based control laws. These control laws include the previously developed concept of Pseudo Control Hedging (PCH). This PCH algorithm adapts the reference model for the system output in case of unachievable commands due to control input saturation. This control algorithm has been applied in the body angular rate control loops of a high fidelity simulation model of the VFW-614 ATTAS (Advanced Technologies Testing Aircraft System) laboratory aircraft, where its beneficial influence has been illustrated. Test flights have been performed with ATTAS to evaluate the flight control technique in a relevant environment.