Constraint-following control design for active suspension systems

We formulate the control problem of active suspension systems (ASSs) that are underactuated as constraint-following. The objective is to drive the system to follow a series of servo constraints or control goals which include both equality constraint of the reference trajectory and inequality constraint of the boundary restriction on the sprung mass displacement. The equality constraints may be holonomic or nonholonomic. The control design is implemented in two steps. First, a constraint-following control (CFC) is applied to drive ASSs to follow equality constraints, under the premise of ignoring inequality constraints. No auxiliary variables or pseudo variables are required for the control design. Second, diffeomorphism is employed to integrate inequality constraints into equality constraints, by which a novel CFC is proposed to deal with both equality and inequality constraints. The effectiveness of the proposed approach is demonstrated by rigorous proof. Furthermore, we investigate an ASS control problem in which the equality constraint is determined by the skyhook model, and the inequality contraint of the sprung mass displacement is determined by the suspension deflection and the tire dynamic displacement. Experimental and numerical simulation results on this case are presented for demonstrations. (C) 2020 Elsevier Ltd. All rights reserved.