A Comparison between Zero Steady State Compensators and Optimal Control Regulators in a 4WS vehicle

This paper discusses about a LQR controller as optimal regulator, which is suited for state variable regulation and tracking as a full state feed back controller, Zero side slip (ZSS) and zero yaw rate (ZYR) compensators. ZSS and ZYR are controllers that force the linear system to regulate the steady state response of side slip state variable (have linear relation with lateral velocity) and yaw rate state variable respectively in linear model. As dynamic models, a 2 DOF linear handling model with yaw rate and lateral velocity variables is used as controller model, and a 3 DOF nonlinear model with yaw rate, lateral velocity and roll variables and CALSPAN tire coefficients is proposed for simulations.

Results show that in spite of LQR controller, which yields suitable results in both linear and nonlinear models and both regulation and tracking strategies, zero steady state compensators (ZSS and ZYR) could not yield acceptable results in nonlinear model that simulates real response of vehicle; in addition not to have flexible nature (like LQR) to perform a multi purpose control strategies.