Research On Fractional-order Control Strategy For Controllable Suspension System

Vehicle suspension system is an important part that is related to ride comfort and running safety. Currently, the passive suspension is widely used in the vehicle, which is difficult to meet requirement of ride comfort and handling stability under the conditions of different driving cycles. The controllable suspension system with control mechanism can effectively solve the above problems. Therefore, the controllable suspension system is the important trend for suspension technology research and development of the modern vehicle.Control strategy not only is an important aspect in the development of on the controllable suspension system, but also is the key guarantee for obtaining excellent performances through controlling the suspension system. Since the end of the last century,form the suspension system model, according the common thread of modern control theories and artificial intelligence control algorithms, people have proposed a lot of suspension control method. However, most of these existed control methods are single form, which has its advantages and disadvantages and can hardly obtain satisfied control effects for complex driving cycles. In recent years, the application of fractional order mathematical theory has become a study hotspot, in which fractional-order control has also become a new trend in the field of automation control. Nowadays, a few of research reports have revealed that the fractional-order control can effectively improve the control performances of vehicle suspension system. Consequently it is a new idea to explore fractional-order control strategies for effective controlling suspension system. In this paper,Aiming at the control problem of nonlinear controllable suspension system, the following two aspects of research work on fractional-order control method of the suspension system are carried out.(1) Controlling nonlinear suspension system via fractional-order PDμ controllerConsidering the nonlinear dynamic model of the 1/4 vehicle suspension system of single DOF, using frequency-domain design method of linear systems and suspension control system performances optimization of integral time squared error(ITSE), a fractional-order PDμ controller is designed out. Because adjustable fractional order parameter is added, fractional-order PDμ controller can not only get better control performance and robustness than integral-order PDμ controller through further reducing the vertical vibration displacement, velocity, and acceleration in the frequency range of the body sensitivity of suspension system, but also can improve the ride comfort of the vehicle.(2) Controlling nonlinear suspension system via a fractional-order sliding mode controllerThe nonlinear suspension and "Ceiling" damping suspension system are chosen as actual model with 2 DOF and reference model respectively. The vertical vibration velocity error and the displacement error between two models are used to construct the fractionalorder sliding mode function. Based on the Lyapunov stability theory and the reach condition of the sliding mode surface, a fractional-order sliding mode controller is designed, in which control parameters including fractional order are obtained by a genetic algorithm according the minimum principle of the defined objective function. Simulation results show that compared with the traditional integral-order sliding mode control method,the fractional-order control strategy of the nonlinear suspension system can further reduce body vertical vibration acceleration, suspension deflections and tire deformation, the better ride comfort and driving safety of vehicle can be achieved.Research results about fractional-order control strategy of the suspension system can provides a novel and useful references for developing controllable suspension system of vehicle.