Research On Modeling And Control Algorithm For Unmanned Coaxial Rotor Helicopter

Unmanned helicopter has great potential for the application of platforms in environmental monitoring, agriculture mechanization, geological exploration, logistics and military fields. Comparing fixed-wing UAV, it has advantages in the fixed point, precise and detailed tasks with unique hover and low-speed flight. Unmanned helicopter with coaxial rotor configuration has great potential for practical application in high speed, long endurance and high lift. It has re-aroused the enthusiasm and commitment of researchers. However, there are problems in late start, low investment and weak research base at domestic. The existed coaxial rotor helicopters were totally imported from the Soviet Union. There is a great deal of technical problems encountered in the upgrading process. Especially, there is a serious deficiency research in modeling and flight control. A huge gap has been constructed when comparing with the same type of helicopter at abroad. Therefore, it is extremely necessary and urgent to conduct research of modeling and control of unmanned coaxial rotor helicopter.In this paper, relying on the "National High Technology Research and Development Program(863 Program)"- "intelligent unmanned helicopter with a heavy load for Geophysical dedicated development"(2013AA063903), modeling and control algorithm of unmanned coaxial rotor helicopter was implemented. This study will provide guidance on the design theory for carrying, transformation and upgradation of unmanned coaxial rotor helicopter. It will also make up for the lack of flight control algorithm of unmanned coaxial rotor helicopter and provide theoretical and technical support to improve system stability and efficiency when nonlinear model, strong coupling and multi uncertainties happen in the helicopter. Through this study, it will shorten the development time of project and reduce the cost of a prototype. It also lays a solid foundation for high-speed, high load and high mobility compound coaxial rotor helicopter.In modeling, researchers have mostly focused on the coaxial rotor aerodynamic performance analysis and optimization design at home and abroad. There lacks of complete and systematization in modeling prototype. In the meantime, the nonlinear, high uncertainty and strong coupling between the upper and lower rotors increase the difficulty of modeling an unmanned coaxial-rotor helicopter. In flight control, PID, robust, and adaptive neural network algorithm have been successfully applied in single rotor helicopter. However, there is a lack of the research about flight control algorithms of unmanned coaxial rotor helicopter. Most of control algorithms are difficult to ensure a high level of flight performance and robustness stability for unmanned coaxial rotor helicopter with high complexity, uncertainty and multiple strong coupling. In addition, flight control system not only includes the control algorithm, but also flight control strategy, control structure and algorithm engineering implementation.The main contents are as followed:(1) For the lack of a complete unmanned coaxial rotor helicopter model, modularization method was adopted to systematical model an unmanned coaxial rotor helicopter. The methodology includes modeling component, trim calculation of dynamic equation, non-linear equations linearization and stability analyzes. Rationalization check was conducted to analysis parameters based on experience parameters of rotorcraft. Finally, the whole parametric unmanned coaxial rotor helicopter was constructed and a systematic modularization methods and rationalization check process were formatted.(2) As for the problem that there is a lack of the research about flight control algorithms of unmanned coaxial rotor helicopter with nonlinear, high complexity and high flying uncertainty, H_? loop shaping was proposed to apply to flight controller design. Based on singular value response analysis and RGA(relative gain arrangement) principle, a flight control strategy for unmanned coaxial rotor helicopter was proposed. The implementation process was derived. Then the flight controller was achieved. Finally, simulations prove that the closed-loop system has ability to ensure robust stability under uncertainties interference while the controller has good decoupling and step response.(3) As for high controller order and inflexible regulating of H_? shaping loop control, we proposed a low order and flexible H_? shaping loop algorithm based on linear matrix inequality. The stability conditions are derived. Then, attitude subsystem of the model was selected as a plant to design controller. Finally, simulations were implemented to prove the effectiveness of the proposed algorithm in reducing order of the controller and flexible design performance when comparing H_? shaping loop.(4) As for the problem that multiple-input multiple output control controller of unmanned coaxial rotor helicopter would be designed and implemented for engineering application. Typical unmanned helicopter flight control structures were analyzed and summarized. Then, based on the singular value responses, we proposed a "double layers with three modules" flight control structures. Simulations results were compared among the H_? shaping loop control, H_? shaping loop control based on LMI and the proposed method. In the meanwhile, it was also implemented to compare with step responses of the full-order structure with H_? shaping loop controller. Therefore, subsystem has flexibility to choose the appropriate control algorithm. Finally, under the requirements of performance, robust stability and ease of implementation, H_? shaping loop control was selected as the control law of the inner layer and the proposed algorithm was selected as the outer layer flight control system.(5) In the flight control test platform. Through the actually modeling, assembling and commissioning of single rotor helicopter and quadrotor, the quadrotor was finally selected as test platform to reduce risk and cost. Then, dynamical characteristic of quadrotor was analyzed under the hover condition. Finally, the platform was conducted to flight test and demonstrated the ability of testing control algorithm.Innovations are as followed:(1) Based on a modularization design concept, unmanned coaxial rotor helicopter dynamics model was systematic constructed. The methodology includes modeling component, trim calculation of dynamic equation, non-linear equations linearization and stability analyzes. Parameters verification was designed reasonably. Unmanned coaxial rotor helicopter prototype was constructed.(2) H_? shaping loop control was proposed to apply to control unmanned coaxial rotor helicopter. The controller has ability to keep robust stability under nonlinear part and high uncertainty interference.(3) A low order and parametric H_? shaping loop control is proposed based on LMI. This method effectively reduces the controller order and improves flexibility performance design under unknown uncertainties interference.(4) A "double layers with three modules" is proposed for flight control structure of unmanned coaxial rotor helicopter. It not only is achieved that a satisfied results in the stability margin, decoupling, rise-time, overshoot and settle-time, but also the main coupling characteristic is still existed and the complexity of engineering applications is reduced. It also provides an easy way for controller design of subsystem to flexibility choose the appropriate control algorithms under the constraints such as flight performance, robustness stability and control law implementation.