An Adaptive Attitude Controller Of An Unmanned Helicopter Based On A Nonlinear Model

With the development of science and technology, unmanned helicopter is playing an increasingly important role in the field of military and civilian use due to the characteristics of small size, light weight, low cost and unique flying features. The expansion of application scope puts forward higher requirements to the attitude control of unmanned helicopter. Traditional linear attitude control schemes design linear attitude controllers based on a linear model. These schemes ignore the nonlinear and strong coupling features of unmanned helicopter, therefore can only adjust the attitude of the unmanned helicopter near balance point. Aiming at this problem, scholars try to use nonlinear control methods such as feedback linearization, sliding mode control, and backstepping control to design nonlinear attitude controllers of unmanned helicopter. These nonlinear controllers overcome the deficiency of the linear ones. Nonetheless they are complex and difficult to be applied in actual system. Considering these factors, this article is aimed at studying a nonlinear attitude controller of unmanned helicopter with simple structure and high realizability. In order to realize the proposed controller, this article developes a flight control system of unmanned helicopter.Firstly, this article designs an adaptive attitude controller with small caculation amount and high realizability. This controller overcomes the deficiency of all the above control methods. In addition, it can eliminate attitude control error and keep the global asymptotic stability under the influence of external disturbance. According to the response rate difference, the attitude controller of unmanned helicopter is divided into inner and outer loops. Inner-loop controller is used to control the main rotor flapping angle by using linear open-loop control. Outer-loop attitude controller introduces an adaptive control strategy for compensating disturbance. The global asymptotic stability of the closed-loop system is rigorously proved by Lyapunov techniques. By simulation comparison, the adaptive controller can eliminate steady offset of attitude control, keep global asymptotic stability and implement large angle maneuver accurately.Secondly, a flight control system is designed in order to realise the propsed controller. Taking into account of the system reliability and scalability, the system architecture of the flight system is ?onboard lower computer – onboard upper computer – ground station?. The onboard upper computer is composed of embedded computer which contains PC104 plus module and WIFI module. The onboard upper computer should store flight data and work as the communication repeater between on-board lower computer andground station.The ground station should transmit instruction signals and monitoring flight data. The onboard lower computer board is designed and developed autonomously. The architecture of the onboard lower computer is ?DSP+FPGA?. The DSP is used to realise the proposed controller and the FPGA is used to realize sensor signal acquisition, manual /automatic switching, servo drive and ground station communication. Because of the reasonable task assignment, the designed flight control system has strong computing power, good real-time and high flexibility, providing a good hardware and software basis for realizing the proposed adaptive attitude controller.