System Parameter Identification for a Quadrotor UAV by Frequency Domain Method

Without runways and the complex "cross swash plate" mechanical device, quadrotor can both take off vertically and achieve fast maneuvers. As a quite unstable and under-actuated system, to get an accurate bare-airframe model of the studied quadrotor is the key for flight control design. In this paper, the frequency domain system parameter identification method is utilized to obtain the state-space model of a quadrotor. Firstly, the theoretical analysis is conducted to acquire the nonlinear model for the quadrotor. Then, the nonlinear model is linearized, which is divided into four categories by different basic motions as: roll-axis, pitch-axis, yaw-axis, and altitude. After that, CIFER^® is chosen to identify the parameters of four categories. Finally, with the low value of the Cramer–Rao (CR) bounds below 20%, it is concluded that the frequency response of the identified model can fit in the real flight data very well, and an accurate bare-airframe model is obtained.