Mode switching control of independent metering fluid power systems

An independent metering system (IMS) realizes the decoupling of the meter-in and meter-out orifices. The energy efficiency of the hydraulic system can be effectively improved by switching between different operational modes. However, the tracking accuracy of the IMS mode-switching system is difficult to ensure, which can easily lead to instability in the hydraulic system. In view of this, this paper proposes a mode switching controller based on an IMS. First, the K-filters theory is innovatively applied to the mode switching hydraulic system to estimate unmeasurable state variables of a system accurately. In addition, fuzzy logic systems (FLSs) are applied to handle the unmodeled errors and disturbances in the mechanical system dynamics model and hydraulic system. Further, aiming at the stability and trajectory tracking problems in the mode switching control (MSC) process of an IMS, the average dwell time (ADT) stability analysis method is applied to the mode switching hydraulic system to construct a set of switching rules to make the closed-loop switching system stable. Moreover, based on the prescribed performance control (PPC) theory, all state errors of a hydraulic system are guaranteed to reach the performance function constraint boundary at the specified time. Also, a dynamic surface control (DSC) technique is used to avoid the explosion of computational complexity caused by iterative differentiation inherent in the traditional backstepping method. Finally, the feasibility and effectiveness of the proposed method are verified by simulation, and experiments are carried out on mini-excavators. The results show that the designed controller can not only ensure the tracking accuracy, but also effectively suppress the instability of the hydraulic system caused by MSC.