Adaptive fault tolerant control for hydraulic actuators

Sudden or incipient faults can lead to a degradation in plant performance, impairment of important functions and eventual loss of safety. Thus, the diagnosis and accommodation of incipient faults in dynamical systems is important to meet performance and reliability requirements. This paper outlines a fault tolerant control algorithm for a hydraulic actuator with a faulty piston seal. An experimental setup capable of simulating different kinds of faults observed in hydraulic systems is constructed. A detailed nonlinear model of the experimental setup is developed and validated. A robust nonlinear control strategy is developed for position control of the actuator. A nonlinear stochastic parameter estimation algorithm is also developed and its effectiveness in estimating leakage faults is demonstrated. The nonlinear control strategy is then improved upon by adapting based on the online fault estimate. The experimental results demonstrate the effectiveness of the adaptive fault tolerant control strategy by maintaining a position tracking error below .2mm compared to simple robust control for which the error increases to .5mm as the fault size increases.