Input saturation and disturbances often exist in hydraulic systems, reducing internal state stability and tracking response performances of the system as well as complicating the design of advanced non‐linear controllers. A practical method named active disturbance rejection controller is proposed by backstepping method for full‐state constrained hydraulic systems to constrain tracking errors in the desired boundaries and deal with input saturation as well as disturbances. To achieve the previously mentioned objectives, the disturbance compensation strategy and dynamic auxiliary systems are integrated into the barrier Lyapunov theory for the first time. It is proved that all states of hydraulic systems are kept within the ultimate boundaries with satisfactory dynamic performance and high steady‐state accuracy. In addition, when disturbances are constants, asymptotic tracking is theoretically achieved. The performance of the control strategy is verified by experimental results.

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An active rear steering and direct yaw moment (ARS-DYC) coordination control is conducted on the basis of nonlinear fuzzy observation to improve yaw and roll stability control of vehicles under extreme conditions. First, a Takagi–Sugeno (T-S) model of yaw and roll motion is established, and tire nonlinearity at emergency steering is approximated with sector domain. A nonlinear fuzzy observation model is established on the basis of the extended Kalman filter (EKF) to observe the sideslip angle, yaw rate, and roll state accurately under extreme conditions in real time. Second, an improved ideal yaw reference model under the T-S framework is constructed in accordance with the effect of yaw rate on roll stability, and the feedforward control of roll stability is achieved through yaw motion tracking. A fuzzy sliding mode controller is designed on the basis of nonlinear fuzzy observation considering tire sideslip stiffness and actuator constraints, and the coordinated control strategy of layered sliding mode surface for yaw and roll is constructed. Finally, the parameters of sub-sliding mode surface are adjusted with the 4-wire phase plane stability domain, the main sliding mode surface parameters are adjusted following the roll stability index, and the stability of the fuzzy sliding mode controller is proven in the Lyapunov framework. A hardware-in-loop simulation test is established with Carsim-Labview software, and results show that the proposed controller significantly enhances the yaw and roll stability of vehicles under the extreme steering process, due to the accuracy of nonlinear dynamic observation and the flexibility of layered sliding surface coordinated control.

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