A QFT fault-tolerant control for electrohydraulic positioning systems

This paper describes the design and experimental evaluation of a fault-tolerant controller (FTC) for an electrohydraulic servo positioning system. The controller is required to retain the stability of the system under sensor failure or, in the presence of faults in servovalve and supply pump. A mathematical model describing the hydraulic actuator is derived in which sensor failures and component faults are captured as uncertainties in the model parameters. A robust controller is designed, using quantitative feedback theory (QFT), to maintain key properties of the closed-loop system, i.e., stability and disturbance rejection. The designed controller is easy to implement and no online tuning or adaptation is necessary. The feasibility of the controller was evaluated by implementing it on an experimental test rig. Experimental results demonstrate the effectiveness of the controller under abrupt sensor failures or incorrect supply pump pressures.