Cascade tuning for nonlinear position control of an electrohydraulic actuator

The nonlinear position control of an electrohydraulic actuator is approached by using two control structures. The first is a direct near IO linearization of the system model with piston position as output. The second is a cascade controller with a near IO linearizing pressure force controller as an inner-loop to a feedback plus feed forward outer-loop position controller. It is shown in this paper that the two control structures are theoretically equivalent. Furthermore, the equivalence is exploited to extract a simple, physically intuitive, tuning procedure for the gains of the two controller structures. This is particularly significant for the near IO linearizing position controller whose gains lack a physically tractable interpretation that guides their selection.