Some practical improvements of sliding-mode control for servo-solenoid valve

The sliding-mode (SLM) control for a servo-solenoid valve (SSV) has been employed before to achieve better performance compared to traditional PID control. However, there still exists some improvement potential for the previous SLM control, such as the static accuracy, the response to ramp or sinusoidal input, and the extra cost of sensors to get full-state feedback. Through effective analysis, this paper develops four practical improvements for the SLM control of a SSV, which can obviously achieve better control performance and not increase the implementation difficulties from the existing controllers. Specifically, the modeling, identification, and the standard SLM control strategy for SSVs are introduced first. The improvements of the SLM control include: the integral element is used to eliminate steady-state error; the tracking control strategies by the velocity feedforward are developed to enhance the trajectory tracking ability; the switch of power supply is employed to improve dynamic response; and the circuit modification of linear variable differential transformer (LVDT) is designed to obtain displacement, velocity, and acceleration signals together. The experiments are carried out and the results reveal that the transient and steady-state performances of SSVs are significantly improved by these improvements to the SLM control.