Nonlinear Control Design for an Active Suspension using Velocity-Based Linearisations

The conflict between ride comfort and safety is well-known for vehicle suspension systems. This work presents a control design concept which tries to ease this conflict for a fully active nonlinear suspension system using velocity-based linearisations. Within the corresponding velocity-based design framework, any nonlinear system can be approximated by a family of local linear subsystems which facilitates classical linear control design and analysis methods. In case of the active suspension system, first two robust linear controllers for good comfort and safety, respectively, are determined by numerical optimization. Then the velocity-based design framework is used to identify an adequate, locally stable way of continuously interpolating between those two controllers with scheduling variables. By that, a nonlinear controller is gained which is aimed at high performance and which avoids unnecessary restrictive slow-variation requirements on the scheduling variables. Finally the nonlinear controller is tested and evaluated in simulations with a realistic quarter-car model of a quad vehicle.