Research On Modeling Of A Quadrotor Aircraft Based On System Identification

The flight control system is an important equipment to increase the safety and stability of a rotorcraft.Flight dynamics model is an important basis for flight control system design.However,due to the complexity of a rotorcraft,it is difficult to obtain a flight dynamics model with high confidence based on conventional theoretical modeling techniques.The system identification is an effective tool to increase the accuracy of the rotorcraft flight dynamics model.In order to solve the difficulties in applying conventional identification methods to rotorcraft flight dynamics modeling,this thesis did research on frequency domain system identification which is applicable for rotorcraft modeling.Firstly,the linear flight dynamics model was built based on a sample rotorcraft.The stability augmented flight control law was also designed.Then the simulation test platform was established in MATLAB/Simulink environment and the simulated flight test was performed.Secondly,an improved frequency domain non-parametric identification method based on chirp-z transform,window optimization and MIMO system decoupling technique was established in this thesis.Identification and verification were conducted based on the sample rotorcraft.The results show that the frequency response function calculation accuracy of rotorcrafts such coupled system is increased base on this method.Then,a frequency domain state space model parameter identification method composes of least square algorithm and frequency domain output error algorithm was established.Identification and verification to the sample rotorcraft were conducted.At the meantime,a comparative study between this thesis' s method and current time domain methods was also performed.The results indicate that the frequency domain method established in this thesis' s method has higher efficiency,accuracy and better numerical stability.Moreover,the identified model in this thesis has better physical meaning.Finally,a quadrotor flight test platform was built and several flight tests were carried out.A comprehensive flight test data analysis and processing was conducted to guarantee the quality of the data.Non-parametric identification and state space model parameter identification of the quadrotor aircraft were implemented.Verification of the identified model was performed.The results indicate that the methods developed in this thesis are able to identify the frequency response characteristics and state space model of the quadrotor aircraft and can be easily applied in engineering.