A nonlinear quarter-car active suspension design based on feedback linearisation and H∞ control

The nonlinear behaviour of suspension elements is substantial when the vehicles experience large road disturbances. These nonlinearities lead to performance deterioration of active suspension systems, which in turn degrades ride comfort, road holding and road handling. Standard control trends on the active suspension count on linear models to benefit from the well established linear control theory, while neglecting the nonlinear dynamics of the suspension systems. In this study, the quarter-car model has a nonlinear suspension spring with a hysteretic nature. The presented design is based on the combination of feedback linearisation (FBL) and H∞ controller. This approach is selected to take in consideration the nonlinear behaviour of the suspension system, while maintaining the opportunity to conduct the linear control theory. The main objective is maximising the ride comfort while keeping the suspension stroke, tyre dynamic load, and actuator force bounded. To assess the efficiency of the proposed design, simulations are performed on two types of road disturbances. The time and frequency domain simulations show the superiority of the proposed feedback controller in providing ride comfort in comparison with the passive suspension system. Moreover, the proposed design guarantees an agreement between the ride comfort and the other design constraints.