A Practical Approach for Designing Fault-Tolerant Position Controllers in Hydraulic Actuators: Methodology and Experimental Validation

Design of fault-tolerant controllers (FTC) for hydraulic actuators is one of the challenges in the area of fluid power systems. In real applications, it is not possible to model or measure some faults accurately. For example, an accurate model for the actuator internal leakage has not been well-established. To prevent the actuator malfunctioning due to the faults (e.g., the internal leakage), there is a need for designing a fault-tolerant control system. In this paper, a methodology is proposed to design an FTC for the hydraulic actuators using experimental data only. In the proposed design procedure, there is no need for either having a prior knowledge about the system and fault models or measuring and detecting the fault during the experiments. The methodology is based on introducing synthetic errors into the hydraulic actuator that is otherwise operating in the healthy mode. Synthetic errors are used to emulate the effect of the fault on the system response. The wavelet transform (WT) is utilized to quantify the effect of the synthetic errors on the error between the desired and actual displacement data. Results of the wavelet analysis are then employed for designing a fractional-order proportional-integral-derivative (FOPID) controller tolerant to the fault. The proposed approach is exemplified with the design of a controller tolerant to the internal leakage. Several experiments are conducted to verify the efficacy of the FOPID-based FTC. The experimental results prove that the proposed methodology works well for the hydraulic actuation system experiencing the internal leakage.