Nonlinear damping in vehicle lateral control: theory and experiment

The sensor and actuator limits in real-world control systems imposes unavoidable tradeoffs between performance and the size of the operating region. When linear control design techniques are used, these limits are either neglected or accounted for by lowering the gains of the controller. The former results in severe reduction of the operating region, while the latter yields low performance. These tradeoffs can often be mitigated by using a nonlinear control strategy, in which nonlinear terms are intentionally introduced in order to implement different design objectives in different operating regions. In this paper, nonlinear damping is utilized as a design tool in lateral control of automated vehicles. Design considerations of the vehicle lateral controller include lateral tracking errors, passenger ride quality and reference/sensing system characteristics. It is shown that the intentionally introduced nonlinear damping term in the feedback loop possesses several favorable design features in the lateral control system. Experimental results using a full scale automated vehicle show that passenger comfort can be enhanced for small errors by significantly reducing the original controller gains, while at the same time achieving the same level of maximum lateral tracking errors.