抄録
This study deals with the application of a Model Reference Adaptive Control (MRAC) theory in discrete time to an electro-hydraulic servo system. MRAC is very useful to control a plant of which parameters are unknown or vary during operation.
An electro-hydraulic servo system is generally a continuous time system. In order to control this system by micro-computer in discrete time, z-transform is used. It should be noted that the plant becomes a non-minimum phase system in discrete time for smaller sampling periods, even if it is a minimum phase system in continuous time, and the plant can no longer be controlled by MRAC in discrete time.
Conditions under which the discrete plant is in non-minimum phase are being investigated. If the sampling period is less than about one half of the natural period of the electro-hydraulic system in continuous time, its discrete system using z-transform becomes a non-minimum phase system.
The output velocity (or state-variable) of the plant is fed back to decrease the natural period. The modified plant is combined with MRAC in discrete time. This indicates that the problem of short sampling time is greatly reduced.
