Disturbance Mitigation in Quadcopter Altitude and Attitude Control

Though different sophisticated control techniques have been suggested for quadcopters, contemporary commercial quadcopters still tend to use variants of the traditional Proportional Integral Derivative (PID) control. This paper focusses on quadcopter control schemes with disturbance rejection features to attenuate disturbances. Conventional Disturbance Observer (DOB) based control and the so-named Extended State Observer (ESO) based Active Disturbance Rejection Control (ADRC), which also provide some degree of robustness w.r.t. parameter variations are considered. This paper introduces and characterizes a novel Linear Parameter Varying (LPV) disturbance observer to improve the cross-channel disturbance mitigation performance. Performance of the controllers are evaluated for additive disturbances in the altitude and attitude channels as well as for cross channel disturbances with the help of case studies after ensuring level playing field in terms of actuator amplitude. Some interesting findings are (i) DOB based control is seen to be efficient in eliminating the effects of additive disturbances, (ii) performance of the conventional DOB based controllers to mitigate cross channel disturbance can be substantially improved using the LPV based DOB, (iii) disturbance rejection performance using DOB is seen to be at par or better compared to the ESO based ADRC.