Nonlinear Modeling And Control System Design Of Small-scale Unmanned Helicopter

The small-scale unmanned helicopter has considerable potential in both military and civil areas, due to its compact size, light weight, low cost, high maneuverability and ability to vertically take off and land. This dissertation focuses on the research of nonlinear modeling and control method of a small-scale unmanned helicopter. The ultimate goal is to develop an autonomous flight control system which can maximize the performance of the small-scale helicopter as well as guarantees the flight safety, and to prepare for the intelligent aerial platform in the future. The main contributions of the dissertation is as follows:(1) A small-scale Unmanned Aerial Vehicle(UAV) helicopter experimental system is developed based on a Raptor 90 hobby helicopter. Firstly, the system framework is introduced, which consists of the RC model helicopter, onboard avionics system, ground station, and vibration isolator. To avoid the effect of noises, an efficient sensor data processing algorithm and an integrated navigation algorithm are designed and implemented on the onboard avionics, which can provide some necessary states for identification and control design.(2) A nonlinear model of the small-scale helicopter is systematically derived and a comprehensive method for parameter determination is presented. The nonlinear model is developed on the basis of the Newton-Euler equation and blade element theory. For simplification, the yaw dynamics is derived including the Angular Vector Control System(AVCS). Considering the global search ability and strong robustness of the genetic algorithm, a new adaptive genetic algorithm is proposed to identify the model parameters, and a comprehensive method for parameter determination is proposed. Finally, on the basis of the input-output data collected from actual flight experiments and the parameter determination method, the parameters of the nonlinear model are determined.(3) The flight envelop and flying quality of the small-scale helicopter are studied,which provide guidance for the controller design. Considering the characteristics of the small-scale helicopter, the operational flight envelop, which is defined by the operational velocities, operational accelerations and operational angular rates, is firstly analyzed.Then, ADS-33 is introduced and tailored; and some indexes, such as bandwidth–phase delay, quickness, and settle time, are selected to judge the flying quality. Finally, the reference models for each channel are designed based on the flight envelop and flying quality indexes.(4) The attitude control method is studied and realized. The importance of the flapping dynamics for attitude control is firstly analyzed. The roll and pitch control problems considering and not considering the flapping dynamics are then studied, respectively. For the case of disregarding the flapping dynamics, the flapping motion can be treated as a steady process, and the rotation dynamics can be expressed as a first-order model; to compensate for the disregarded dynamics and external disturbances, a roll and pitch robust controller is designed based on extended state observer. For the case of considering the flapping dynamics, a state transformation is introduced to avoid using flapping angles feedback, because the flapping angles cannot be directly measured. Two roll and pitch controllers are proposed on the basis of extended state observer and sliding mode control.Next, considering the AVCS as a inner loop angular rate controller, a heading controller is designed and realized.(5) A position controller is designed. Firstly, the position controller is divided into height controller and horizontal position controller on the basis of model structure analysis. Then, the height controller and horizontal position controller is designed, respectively.The height controller is designed by dynamic inversion method incorporating with extended state observer, the extended state observer is used to estimate the disturbances. The horizontal position controller is designed based on the inner loop roll and pitch controller.Compared with the traditional controller design, acceleration feedback compensation is used to eliminate the effect of the disregarded force terms and disturbances.