Position control of an electro-hydraulic servo system based on improved Smith predictor

For some electro-hydraulic servo system with long pipelines, the dynamic characteristic and time delay property of the pipeline will have a great impact on system performancs and can not be ignored. Based on a two-port network model and linear friction model, the general mathematical model of electro-hydraulic servo position control system including pipeline effect was established. The derived high order mathematical model was simplified into a second-order model with time delay in frequency domain, which increases its use value. For the problem of system time delay, the traditional Smith predictor is ineffective for model mismatch, and an improved Smith predictor was designed by combining the Smith predictor with the sliding mode control. Furthermore, the two methods was compared by simulation. The results show that the improved Smith predictor has better control quality and robustness property than the standard Smith predictor.