Robust control for high-speed crafts using QFT and eigenstructure assignment

In this work, the problem of stabilisation of a high-speed craft with coupled dynamics is addressed. The action of the actuators to control the longitudinal dynamics (heave and pitch modes) produces a coupling in the transversal dynamics (roll mode), and vice versa. A combination of quantitative feedback theory (QFT) robust methodology and eigenstructure assignment (EA) methods is used to control the coupled system on a high-speed craft. The multi-input multi-output (MIMO) problem is firstly handled with the EA technique in order to decouple the dynamics, which results in three single-input single-output (SISO) systems to solve with QFT design. Dynamic responses of roll, pitch and heave modes of the entire fast ferry system are analysed at different sea states and angles of incidence. Time-domain simulations and frequency-domain performance analyses provide satisfactory results. It is shown that the combined EA/QFT technique is a feasible and very suitable robust method that can accomplish decoupling and damped responses and consequently a reduction in the motion sickness.