Fuzzy Adaptive Backstepping Control For Active Suspension Systems

In this thesis,under the framework of adaptive backstepping control design and fuzzy control theory,fuzzy adaptive control methods and the corresponding closed-loop system stability analysis problems are investigated for several classes of nonlinear vehicle active suspension systems.The main works as follows:(1)For a class of nonlinear fourth-order vehicle active suspension systems with actuator bias fault,the fault-tolerant control problem is studied.Since this kind active suspension system contains two identical controllers in the second and fourth equations,the “algebraic-loop” problem will occur by using traditional backstepping control technology.In the establish the equivalent actuator.Fuzzy logic system and Nussbaum gain function are used to solve the problems unknown functions and actuator bias fault,respectively.Based on the adaptive backstepping control design technology,a fuzzy adaptive fault tolerant control design method is proposed,and this method can effectively avoid the “algebraic-loop” problem.The stability of the control system is proved by Lyapunov stability theory.The effectiveness of the proposed fault tolerant control method is further verified by simulation results.(2)For a class of nonlinear vehicle active suspension systems with electromagnetic actuator,the fuzzy adaptive control design problem is studied.In the control design,the fuzzy logic system is used to approximate the unknown nonlinear functions,and a fuzzy adaptive control design method is proposed,based on the backstepping control design technology.The stability of closed-loop system is proved by Lyapunov stability theory.The effectiveness of the proposed fuzzy adaptive control method is further verified by simulation results.(3)For a class of nonlinear vehicle active suspension systems with permanent magnet motors,the fuzzy adaptive fault-tolerant control problem is investigated.In the control design,the fuzzy logic systems are used to approximate the unknown nonlinear functions and sudden-change fault.Lyapunov-Krasovskii functional theory is adopted to solve the problem of unknown time-varying delay of body dynamics in the active suspension system,and a fuzzy adaptive control design method is proposed,based on the backstepping control design technology.It is proved that the proposed control approach can guarantee all the signals of the closed-loop system are semi-global uniform ultimate boundedness.The effectiveness of the proposed fuzzy adaptive control method is further verified by simulation results.