Design of H ∞ loop-shaping controllers for fluid power systems

Fluid power systems are highly non-linear, making the application of traditional linear feedback control techniques challenging. In this paper, a dual-mode H ∞ control scheme has been proposed and demonstrated to be both feasible and practical for controlling such systems. The plant used is a speed control hydrostatic transmission and the particular H ∞ approach used is loop shaping as suggested by McFarlane and Glover; this, in addition to simplicity, admits a wider class of uncertainties than comparable schemes. The dual-mode controller is surprisingly effective, delivering robust stability over the entire speed range and offering bumpless transfer, wind-up protection and multi-rate sampling at little extra cost, a factor which is crucial in digital implementation. It is shown that, despite some challenges, a successful H ∞ controller need not be of high order.