Nonlinear cascade control based on an integral separated disturbance observer of proportional poppet valve

The large flow rate proportional poppet valve (PPV) finds widespread use in high-power hydraulic systems. However, the indispensable dead-zone nonlinearity that guarantees the safe shut-off of the PPV will cause a tracking lag when a command goes outside the dead-zone. The lag should be properly solved in a controller, which is a highlight of this study. Simultaneously, achieving high tracking precision in a PPV is necessary to meet the demands of advanced hydraulic systems. In this study, a practical nonlinear controller based on an integral separated disturbance observer is proposed to improve the performance of a PPV. In particular, the lag could be alleviated and the high tracking precision achieved simultaneously by enabling or disabling a disturbance observer in the proposed controller. A separation coefficient is proposed for the disturbance observer to detach the integral action from the controller and avert the deep input saturation of the pilot stage. Additionally, the command filtering technology is applied to the nonlinear controller to improve its interference resisting capacity in the industrial environment. The stability and effectiveness of the proposed controller are proved in theory and verified by experiments.