Nonlinear Unscented $H_{\infty }$ Suspension and Tracking Control of Mobile Vehicles

In this paper, a new nonlinear q controller synthesis algorithm is applied to suspension and tracking control of a mobile vehicle. It is well known that the traditional H_∞ controller for a linear system consists of a full-state estimate-based linear feedback control law and an H_∞ state estimator. The feedback control law is synthesized by solving an algebraic Riccati equation, whereas the estimator is similar in form to a Kalman filter (KF). The nonlinear controller is obtained by synthesizing a “frozen” or “semifrozen” estimated state optimal control law, replacing the estimator by a nonlinear filter, and obtaining the estimates by applying the unscented transformation. The resulting controller is a nonlinear controller. The results indicate that, in the case of the closed-loop nonlinear H_∞ controller, the estimator tracks the platform position to within 2% of the setpoint. When the H_∞ estimator is combined with methods involving the control law synthesis based on replacing the nonlinear optimal control problem by a sequence of linear optimal control problems, a powerful computational tool may be established for synthesizing control laws for a variety of nonlinear controller synthesis applications.