A study on the position control of hydraulic cylinder driven by hydraulic transformer using disturbance observer

A hydraulic cylinder drive using a hydraulic transformer, which is considered as secondary controlled unit, is studied here. Using hydraulic transformer for driving a hydraulic cylinder should avoid energy loss via controlled valves and get benefit from recovery of the load potential. Position control, an important issue of the cylinder control is investigated in this paper. To obtain robust position control in spite of external load disturbance and variation of parameters in the system, a two degree of freedom robust controller based on disturbance observer is designed. The controller includes a mixed - sensitivity H_infinin controller and a high order disturbance observer. Weights for controller synthesis and filter in the disturbance observer are fixed in their structure but vary in values of the coefficients. Genetic algorithm is used to tune parameters of the weights and time constants of the filter. In this manner, a controller with its structure based on robust analysis and parameters depended on performance of nominal plant is design. Simulation results indicate that the system guarantees the robustness with external load disturbance, variation in parameters and sensor noise.