Abstract: The load of hydraulic operation control system in giant hydraulic press is analyzed. The conclusion is that the load is the transient change of the opening force of distribution valve spool occurring in the control process, and the change range is great, thereby affecting the robustness and control accuracy of the control system. Based on the characteristic of the load, a PID-H∞ closed-loop cascade control strategy is put forward. The transient load is regarded as disturbing signal of the control system. The controller is designed and the mathematic model is established. The control strategy is applied in 300 MN die forging hydraulic press. Simulation and comparison of single PID control and PID-H∞ compound control are carried out. The simulation results and practical applications show that the PID-H∞closed-loop cascade control is better than the single PID control in suppressing the disturbance effect of transient load and in improving the robustness and control accuracy of the system.

Key words: H∞ control, Hydraulic press, Operation system, PID control, Robust control, dissimilar metals, friction stir spot welding, intermetallic compound, Zn interlayer