A solution to gain loss in hybrid integrator-gain systems

Hybrid integrator-gain systems (HIGS) are non-linear control elements that are designed to primarily operate as integrators in so-called integrator mode. Switching to gain mode occurs only when needed to keep sign equivalence between the input and output signals of the control element, thereby aiming for phase advantages. In order to guarantee the integrator mode to be the primary mode of operation, in this paper a combined pre- and post-filtering approach is studied. Such an approach offers a solution to the problem of gain loss that occurs when the HIGS switches too often between its modes. Typically, this happens in the presence of dominant high-frequency contributions in the input to the HIGS. Along the discussion on pre- and post-filtering, measurement results are presented from a high-performance industrial stage system.