Abstract: Gain – scheduled H ∞ controller is controller is designed for electrohydraulic force servo system with time –varying flexible load. Gain – scheduled H ∞ control requires that system state –space matrices depend affinely on the vector of time – varying parameters, and the system is a slow time – varying one. The form of gain – scheduled H ∞ controller can be conditioned by real – time value of these parameters in order to satisfy the requirement performance of different time. The methodology presented is applied in hydraulic automatic cyclic triaxial equipment with earthquake wave input (cyclic triaxial). The simulation results show the validity on improving the performance of cyclic triaxial with large parameter – varying load.

Key words: Electrohydraulic force servo system, Gain – scheduled H ∞ control, Linear matrix inequality