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Nonlinear Position and Attitude Control of a Twin Coaxial Helicopter

Shafiee, Morteza | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45344 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Salarieh, Hassan; Alasti, Aria
  7. Abstract:
  8. Coaxial helicopters are one of the kinds of helicopters that have two main rotors spinning opposite to each other. These helicopters have no tail rotor and their size varies from very small (about 100 grams) to large (manned). The widespread use of helicopters justifies controller design for them.
    In this research, at first step coaxial helicopter is controlled with two linear control methods. In many control problems linear control responds to the diverse needs. In addition it has good robustness in situations like uncertainties, disturbances, noise etc. For this purpose, nonlinear dynamic model of helicopter is used in the beginning. This model is linearized around hover condition to use EESA (Entire Eigen Structure Assignment) algorithm for designing a MIMO linear controller. Linearized model has pure integrators on position and yaw angle that causes outputs track step reference inputs. After designing MIMO controller, a structure based on PID controller is suggested. PID is a SISO controller so the model should be analyzed to comprehend which input Influence on specific output. By this analysis, four SISO controllers are designed for four inputs.
    Although linear control is a good approach for some problems but they usually work properly only in small vicinity around local operating point thus after designing linear controllers next step is nonlinear controller design. Backstepping and INDI (Incremental Nonlinear Dynamic Inversion) are two method that nonlinear controller are designed with them.
    In simulations, two maneuvers are used. The first one is a point to point displacement and the second is an 8 shape maneuver. In both of them the yaw angel is not constant. Results of simulations for first maneuver show that all controllers except MIMO controller have fast and acceptable responses. Although closed loop model with MIMO controller is stable but its Response in this maneuver is slowest one. Because of Consideration of nonlinear part of model nonlinear controllers have better performance in second maneuver which is a complex and time-varying maneuver.
    Robustness tests are simulated for analyzing performance of controller in some situations like existence of uncertainties and noise. As expected PID controller is winner of this tests and its performance is affected slightly because it is not a full model based controller. After this controller nonlinear controllers have acceptable response in most tests and MIMO linear controller is the worst in robustness tests
  9. Keywords:
  10. Nonlinear Control ; Backstepping Algorithm ; Coaxial Helicopter ; Helicopter Dynamic ; Incremental Nonlinear Dynamic Inversion Cntroller

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