Study on the compensation control of electro

Nonlinear variable load is one of the most important factors affecting the tracking performance and the robustness in electro-hydraulic servo force loading systems, which causes a great output distortion in the practical systems. An electro-hydraulic servo force loading system of the dynamic triaxial apparatus is used as a typical example to study the nonlinear variable parameter compensation. The external load in the sand liquefaction experiment of the dynamic triaxial apparatus usually goes through three different phases: the linear, the transitional and the nonlinear, where the nonlinear phase has a great impact on the precision of the experiment. In this article, a state-space model of the dynamic triaxial apparatus is established, and a proportional plus derivative–type iterative learning control method is designed to compensate its nonlinear variable load. The simulation and the experiment have been conducted. The results indicate that the control strategy proposed in this article is valid, and the tracking performance and the robustness of the dynamic triaxial apparatus in nonlinear variable load condition have been remarkably improved