PID controller with feed forward estimation used for fault tolerant control of hydraulic system

The paper stresses on the designing and implementation of a nonlinear offline feed forward controller in association with a PID controller as a fault tolerant control measure for a closed loop hydraulic system. An off-line nonlinear feed forward control with proportional pressure relief valve (PRV) loading on the loading pump has been developed using the subsystem models without taking into considerations the oil compressibility, valve dynamics and leakages associated with various components of the hydraulic circuit. A PID feedback has been utilized in real-time to deal with the unmodeled features and the modelling approximations. The characteristics of the speed response are significantly influenced by the disturbances related to external torque, change in the input magnitude as well as system parameters like inertia load and supply pressure. The real-time control showed that the experimental and predicted closed–loop control performances justify each other quite well. Hence, the PID gains were estimated quite effectively with the help of the developed simulation tool here. The control model produced good agreement between the demanded and real-time speed response for various loading conditions such as step load, sinusoidal load, variable load, triangular load etc.