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Modeling and high accuracy parameter estimates for a friction based electro-hydraulic load simulator

In this paper, a novel friction based electro-hydraulic load simulator (FEHLS) is presented. Although the FEHLS has no extra torque, i.e., no external disturbance, like most of electro-hydraulic servo systems (EHSSs), the FEHLS is a highly nonlinear system always with uncertain parameters, measurement noise, etc. Therefore, the nonlinear mathematical control model of the FEHLS is established. Recently, due to high parameter estimate convergence speed, controller-estimator separability, etc, the indirect adaptive control (IAC) methods are widely implemented. For the IAC, high performance parameter estimator is crucial. Measurement noise will decrease the estimate performance. However, in current literatures, few parameter estimation laws are designed for IAC considered the measurement noise. Therefore, for the FEHLS in the presence of measurement noise, a projection mapping type recursive least-square (RLS) parameter estimation law with low-pass filter is proposed. Besides, the slowly time-varying parameters in the FEHLS are also considered. Based on the FEHLS plant, the simulation is carried out to verify the effectiveness of the proposed parameter estimation law. The simulation results show the proposed law can achieve high precision parameter estimates in the presence of measurement noise and slowly time-varying parameters. The proposed law is then can be applied to synthesize indirect adaptive controllers for the FEHLS in the future.