Design of a direct current controller for magnetorheological semi-active suspensions with nonlinear constraints

In the application of magnetorheological (MR) semi-active suspensions, the target damping force calculated using the controller must be realised by an MR damper. This requires the target damping force first to be converted into a corresponding drive current. However, owing to the nonlinearity of MR dampers, the drive current based on the target damping force cannot be accurately tracked, which could worsen the control performance. To avoid this situation, this study proposed a gain scheduling control method based on a linear parameter-varying (LPV) model of MR semi-active suspensions. First, based on the nonlinear model of MR semi-active suspension, an LPV model with constraints used as varying parameters was established using convex decomposition. Then, an LPV controller was designed with a convex polytope structure using the linear matrix inequality technique. A system with this controller can achieve H∞ performance. The simulation results showed that the drive current directly obtained with the LPV controller can better utilise the effective region of the MR damper. Consequently, this controller yields smoother current control quantities and lower computational costs while guaranteeing the performance.