Robust harmonic control for helicopter vibration attenuation

Higher Harmonic Control (HHC) has been considered for many years a valid approach for the design and the implementation of active rotor control laws aiming at the attenuation of helicopter vibration and noise and at the improvement of rotor performance. Its implementation requires knowledge of the frequency response relating the control input to the output measurements at the disturbance frequency (a multiple of the rotor angular frequency). An offline identification can be performed to this aim, but unfortunately, when the information is uncertain or when the plant is subject to change, instability can occur. While this is usually handled in the literature by resorting to adaptive schemes, in this paper this issue is dealt with by designing a robust controller obtained by integrating model uncertainty directly in the design process.