Higher-Harmonic-Control Algorithm for Helicopter Vibration Reduction Revisited

The higher-harmonic-control (HHC) algorithm is examined from a control theory perspective. A brief review of the history and variants of HHC is given, followed by a careful development of the algorithm. An analytic convergence and robustness analysis is then performed. Online identification with the adaptive variant of the algorithm is also addressed. A new version of the algorithm, relaxed HHC, is introduced and shown to have beneficial robustness properties. Some numerical results comparing these variants of the HHC algorithm applied to helicopter vibration reduction are also presented. The results presented unify and extend previous work on the higher-harmonic-control algorithm.