Application of a model-based two-DOF control structure for enhanced force tracking in a semi-active vehicle suspension

The paper presents a two degrees of freedom (2-dof) structure combining a dynamic feedforward approach with a nonlinear feedback component to control the damper valves' currents of a semi-active suspension system. The concept makes use of a dynamic damper model, which is able to represent the dynamic behavior significantly more accurate than the standard approach, where static damper characteristics are used.While an additional force feedback path is able to enhance force tracking even further, a measurement signal of the realized damper force is not available for control purposes in practice. Hence, a model-based and a signal-based estimation approach are employed. The impact on ride performance caused by the reduced tracking error is studied using three different suspension controllers known from literature. The performance potential of the force tracking controller as well as of the entire control structure is analyzed in simulations and on a quarter-car test rig. No matter which suspension controller is applied and thus independently from the respective control objective, the overall ride performance can be increased due to the enhanced force tracking of the semi-active damper.