Research Of Dual-loop Robust Controller Based On Multi-mode Transition For Unmanned Helicopter

With the development of the science and technology, the unmanned helicopter has been playing an increasing role in military and civilian special operations because of its unique flight characteristics, small size, light weight, and low cost. On the base of the autonomous flight control system, it can complete the tasks that the fixed-wing aircraft can not be competent to accomplish, such as cable inspection, anti–terrorism investigation, disaster inspection, etc. Therefore, it has a very important practical significance in research and development of the autonomous unmanned helicopter flight control system. The main content of this subject is to do the research of dual-loop robust control algorithms based on multi-mode transition for unmanned helicopter, and develop a flight test platform for attitude control.Firstly, an analysis is given to prove the existence of static instability and severe coupling between the channels of unmanned helicopter MIMO linear models provided in literature. Refer to the theory of the robust control and internal/external loop control systems, dual-loop robust control algorithms based on multi-mode transition is proposed. A loop-shaping method is used to design the internal controller to achieve demanded performance which described in ADS-33E-PRF, such as decoupling between 3D angle and vertical velocity channels, bandwidth, static and dynamic ACAH response. It can also provide a robust stability margin to overcome the uncertainty caused by the perturbation of the internal model system. Mixed sensitivity optimization algorithm is introduced to design the external loop controller to achieve vertical and horizontal velocity control and altitude control, and the structure of a lower-order controller is given. The conditions are discussed in achieving multi-mode switching control in multi-modal system. Under the expected assumptions, a fuzzy-based"soft-switch"strategy is proposed on implementation of multi-modal transition control.The algorithm is verified by simulation, and obtain the desired control performance.Secondly, a set of unmanned helicopter flight attitude control test platform is designed. Taking into account of the system reliability and scalability, the system architecture of the test platform 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, with Windows XP system software and Visual C++ 6.0 application software for development. The onboard upper computer should transmit instruction signals and monitoring data with onboard lower computer by serial communication, store data and retransmit data to ground station by WLAN. The ground station should receive and store data transmitted by WLAN from the onboard upper computer. The onboard lower computer board is designed and developed autonomously. According to the system requirement, an architecture of"DSP+CPLD"is proposed, and then the IDE, for example the CCS and QuartusⅡ,should be included for application development. The application software in the onboard lower computer should mainly contain resolving the IMU navigation attitude, tracking attitude by control algorithm, generating the servo drive PWM waveform and switching manual / automatic control. After the completion of platform development, it is considered to transplant the platform onto the"Thunder Tiger 90"prototype helicopter model. And then the indoor and outdoor flight experiments have been done to test the performance of the whole control system. It turns out to fulfill practicality and feasibility on the attitude control by analyzing image data and control data recorded in the flight test.