Model-based control of the flying helicopter simulator: evaluating and optimizing the feedback controller

Abstract

The numerical evaluation and optimization of the feedback controller parameters of the model-based control implemented in the flying helicopter simulator is subject of this paper. The German Aerospace Center operates this helicopter as a flying testbed for numerous applications, e.g., pilot assistance and in-flight simulation. Initially, the elements of the model-based control are presented. A genetic algorithm and the Nelder-Mead simplex method used for optimization are described. Two simple objective functions to rate parameter sets in the time domain are presented, and a Simulink Ò model of the helicopter dynamics and the controller structure are used to find optimized sets. The first function, called ''Delta Rating'', consists of a normalized integral of the absolute error between commanded and measured states. The second function incorporates the Delta Rating, but is enhanced by a penalty on overshoots. The controllers found are further evaluated using a frequency domain approach consisting of a weighted sum of the differences in amplitude and phase, also considering the coherence at the corresponding frequency. Apart from the Simulink Ò model, a ground-based simulator is used to evaluate the standard and the optimized controllers.Keywords Model-based control Á Two-degree-of-freedom control Á Flying helicopter simulator Á In-flight simulation Á Genetic algorithm Á Nelder-Mead simplex Abbreviations AC, RC, TC Attitude, rate, translational rate command DLR Deutsches Zentrum für Luft-und Raumfahrt/German Aerospace Center DR Delta Rating FB, FF Feedback, feedforward controller FHS Flying helicopter simulator IAE Integrated absolute error MBCS Model-based control system MIMO Multiple input multiple output SISO Single input single output A, B, C, D State-space representation matrices (standard form) b Sideslip angle [°] C(s) Transfer function matrix of feedback controller d Disturbance vector d p Pilot inputs (% deflection) d lon , d lat Longitudinal, lateral cyclic pilot control (% deflection) d ped , d col Pedal and collective pilot control (% deflection) G(s) Transfer function matrix I Identity matrix J Objective function J ave Objective function in frequency domain, weighting amplitude and phase difference J

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