To handle different perspectives of unstructured uncertainties, two robust control techniques on the basis of a universal model\nare studied in this paper. Rather than building a model only applicable to a specific small-scale multi rotor helicopter (MHeli),\nthe paper proposes a modeling technique to develop a universal model-framework. Particularly, it is straightforward to apply the\nuniversal model to a certain MHeli because the contribution and allocation matrix is proposed in the model-framework. Based on\nthe model uncertainties, the load perturbation of the rotor is the primary focus due to its indispensable importance in the tracking\nperformance. In contrast to the common methods, it is proposed to take this unstructured uncertainty in that external disturbance\nand designs disturbance observer (DOB). In addition, a class of lead-compensator is specifically designed as for compensating\nphase lag induced by DOB. Compared with H? loop-shaping, greater robust tracking performance on rejecting load perturbation\ncould be achieved as a trade off between robust stability and tracking performance which is successfully avoided with DOB-based\ncontrol strategy.
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