A Multivariable Nonlinear H_infty Controller for a Laboratory Helicopter

This paper considers the problem of a nonlinear H∞ design for a laboratory twin rotor system. This mechanical device features a highly nonlinear strongly coupled dynamics, which constitutes a challenge for many classical linear control techniques. The approach presented in this paper considers a nonlinear H∞ disturbance rejection procedure on the reduced dynamics of the rotors, including integral terms on the tracking error to cope with persistent disturbances. The resulting controller exhibits the structure of a nonlinear PID, with time-varying constants according to the system dynamics. The methodology has been tested by experimental results using a laboratory helicopter.