Output feedback H ∞ / GH 2 control for in-wheel motor driven semi-active suspensions with nonlinear constraints

The increased unsprung mass in In-Wheel Motor (IWM) driven semi-active suspension systems leads to degraded handling stability and ride comfort. In this paper, an output feedback H _∞ / generalized H₂ (GH₂) control strategy is proposed for semi-active suspensions equipped with Magneto-Rheological (MR) dampers to attenuate vertical vibration. The H_∞ norm is used to evaluate the closed-loop performance, while the GH₂ norm is applied to limit hard constraints of the system. A major challenge arises from the dissipative characteristic of the MR damper, which introduces nonlinear constraints that complicate optimal control design and limit performance improvements. To address this issue, the allowable damping force range of the MR damper is identified through MTS850 testbed experiments. Subsequently, a piecewise controller is designed to approximate the nonlinear constraint as piecewise constant bounds. The effectiveness of the proposed control strategy has been validated by simulation results.