Robust fault diagnosis of an electro-hydrostatic actuator using the novel dynamic second-order SVSF and IMM strategy

This paper introduces a new robust fault detection and identification (FDI) structure applied to an electro-hydrostatic actuator (EHA) experimental setup. This FDI structure consists of the dynamic second-order smooth variable structure filter (Dynamic second-SVSF) and the interacting multiple model (IMM) strategy. The dynamic second-order smooth variable structure filter (SVSF) is a new robust-state estimation method that benefits from the robustness and chattering suppression properties of second-order sliding mode systems. It produces robust-state estimation by preserving the first and secondorder sliding conditions such that the measurement error and its first difference are pushed towards zero. Moreover, the EHA prototype works under two different operational regimes that are the normal EHA mode and the faulty EHA mode. The faulty EHA setup contains two types of faults, namely friction and internal leakage. The FDI structure contains a bank of dynamic second-order SVSFs estimating state variables based on these models. The IMM strategy combines these filters in parallel and determines the particular operating regime based on the system models and the input-output data. Experimental results demonstrate superior performance in terms of accuracy, robustness, and smoothness of state estimates.