Design of a Multivariable Helicopter Flight Control System for Handling Qualities Enhancement (original) (raw)
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Implementation of Controller Design for an Unmanned Aerial Vehicle Helicopter
The overall objective with this paper is to evaluate a method for designing nonlinear controllers in aircrafts with concern in robustness against modeling insecurities and also to minimize the design effort. The later objective is of great importance since there exists, in the industry, an ambition to automatize the design for as far extend as possible. The nonlinear method, State Dependent Riccati Equation (SDRE), used in this work is a nonlinear version of classic LQ design and both are evaluated and compared for a few flying conditions. Also another nonlinear control method is tested. LQ and SDRE show equal performance during both looping and more complicated maneuvers, such as high angle of attack wind-vector roll. Further it is possible to automatize the LQ design as well as it is possible for SDRE. Still SDRE is preferable since it will always be somewhat more accurate than LQ. A Monte Carlo simulation is made on LQ and SDRE showing that the model is robust against relatively large modeling error of 40%.
A mini scale helicopter exhibits not only increased sensitivity to control inputs and disturbances, but also higher bandwidth of its dynamics. These properties make model helicopters, as a flying robot, more difficult to control. The dynamics model accuracy will determine the performance of the designed controller. It is attractive in this regards to have a controller that can accommodate the unmodeled dynamics or parameter changes and perform well in such situations. Coefficient Diagram Method (CDM) is chosen as the candidate to synthesize such a controller due to its simplicity and convenience in demonstrating integrated performance measures including equivalent time constant, stability indices and robustness. In this study, CDM is implemented for a design of multivariable controller for a small scale helicopter during hover and cruise flight. In the synthesis of MIMO CDM, good design common sense based on hands-on experience is necessary. The low level controller algorithm is designed as part of hybrid supervisory control architecture to be implemented on an onboard computer system. Its feasibility and performance are evaluated based on its robustness, desired time domain system responses and compliance to hard-real time requirements.