Robust Position Control of an Electrohydraulic Actuator With a Faulty Actuator Piston Seal

The development of a fault tolerant control (FTC) strategy to compensate for the degrading effects of fluid leakage across a faulty actuator piston seal in an electrohydraulic positioning system is presented. Due to relatively large variations in the dynamics of the plant, accomplishing the FTC task with a single controller requires a compensator of relatively high gain. Hence, the problem is first reformulated by discretizing the desired range of fault tolerance into a number of distinct levels. Next, a set of low gain local controllers is synthesized via quantitative feedback theory, such that the resulting closed-loop systems all conform to a priori defined performance specifications. Each controller is designed to compensate for a specific level of leakage. A simple switching algorithm is then employed to determine the appropriate control action by scaling each controller’s output based upon an estimate of the leakage level. Experimental results illustrate the ability of the designed FTC scheme to compensate for the degrading effect of the leakage fault.