Active vibration control in helicopters : the adaptation robustness tradeoff

This study describes the robust and the adaptive strategies as alternatives to the classical LQ controller in the Higher Harmonic Control (HHC) environment for helicopter vibration attenuation. Furthermore, it analyses the tradeoff between the mentioned approaches. Their implementation requires the estimation of the system, which is defined by means of the T-matrix algorithm. Uncertainty in the elements of this T matrix is the responsible of the loss of performance and instability suffered when using an optimal controller. As noticed, robust and adaptive approaches have been proposed in order to overcome this limitation. First of all, the Hinf controller has been considered in the background of robust control and two algorithms for the optimization problem solution have been compared. This controller uses an offline estimation of the T-matrix and it is able to work even when the system includes uncertainty due to changes in flight condition as results will reveal in this study. On the other hand, an online estimation of the T-matrix can be done, known as adaptive controller. It has been proved also its e efectiveness against uncertainty, however, as it will be seen from results, the adaptive controller does not seem to be strictly necessary when it is compared to the robust controller performance.