IJFP-2018-0015 - Robust Control Design for an Inlet Metering Velocity Control System of a Linear Hydraulic Actuator

Abstract

In this paper, we consider a hydraulic system in which the velocity is controlled using an inlet-metered pump. The flow of the inlet-metered pump is controlled using an inlet metering valve that is placed upstream from a fixed displacement check valve pump. Placing the valve upstream from the pump reduces the energy losses across the valve. The multiplicative uncertainty associated with uncertain parameters in an inlet metering velocity control system is studied. Six parameters are considered in the uncertainty analysis. Four of the parameters are related to the valve dynamics which are the natural frequency, the damping ratio, the static gain, and the time delay. The other two parameters are the discharge coefficient and the fluid bulk modulus. Performance requirements for the system are described in the frequency domain. Frequency domain analysis is used to determine if the closed-loop velocity control system has robust performance. The time response of the nominal system with PID and H∞ controllers were found to be similar. The H∞ controller was found to have the advantages of robust performance when considering the parametric uncertainty while not requiring integral control as in the PID control system. The PID system did not achieve robust performance.