Alternative robust control strategies for disturbance rejection in fluid power systems

When a number of actuators or motors are operated from a single hydraulic supply their performance is subject to both pressure and load disturbances. The controller on each consumer unit must therefore be capable of ensuring robust performance in the face of these disturbances. It must also accommodate the inherent nonlinearities associated with hydraulic equipment. This paper is an interim report on an on-going study of alternative strategies for the robust control of nonlinear systems. It describes two alternative strategies, one based on a linear design route using the H_∞ loop shaping technique, and the other using self-organising fuzzy logic in which a fuzzy controller automatically adjusts its rules as system characteristics change. Comparisons are made between the two approaches. The representative experimental system is a loaded variable displacement axial cylinder motor supplied from a laboratory ring main via a servovalve. Controllers are implemented digitally on a PC. Rig test results are included