Nonlinear cascade control of high-response proportional solenoid valve based on an extended disturbance observer

With the gradually increasing usage of high-response proportional solenoid valve in the middle- and high-end electronic hydraulic system, to possess a superior performance controller is always most important for high-response proportional solenoid valve. Thus, many novel nonlinear control algorithms, such as sliding mode control and adaptive robust control, are researched and applied to high-response proportional solenoid valve. However, the strict condition of full-state feedback usually cannot be met, since there are no velocity and acceleration measurements available in high-response proportional solenoid valve. Therefore, we proposed an extended disturbance observer to observe the velocity of the high-response proportional solenoid valve’s spool assembly at first. Or rather, the extended disturbance observer is designed to observe the disturbances in the model of high-response proportional solenoid valve and the velocity is also obtained as a by-product. And then, a nonlinear cascade controller based on the extended disturbance observer is designed. The proposed extended disturbance observer is driven by both the estimation error and the virtual input discrepancy of nonlinear cascade controller. The nonlinear cascade controller is designed by utilizing backstepping technique. The stability of the overall closed-loop system is proved according to the Lyapunov theory. As a comparison, a desired compensation nonlinear cascade controller is also applied to the same high-response proportional solenoid valve. The experiment results demonstrate that the proposed nonlinear cascade controller based on extended disturbance observer has an excellent performance under multiple working conditions. Even when the supply pressure has severe fluctuations, the nonlinear cascade controller based on extended disturbance observer can still maintain high performance.