Open-closed-loop iterative learning control for hydraulically driven fatigue test machine of insulators

To simulate large loading and intensive vibration in fatigue experiments for insulators, the hydraulically driven fatigue test machine is researched in the present study, because it has the advantages of large power, fast response and high precision. An open-closed-loop proportional-derivative (PD)-type iterative learning control (ILC) scheme is designed for control of this fatigue test machine to obtain ideal vibration performance. Firstly, the hydraulic scheme and control principle are introduced, including static and dynamic control subsystems, and then the actual fatigue test machine based on such principles is described. The mathematical model of the electro-hydraulic servo load system is built, which shows that this system is completely different from traditional hydraulic position-control systems, and indicates that with conventional proportional-integral-derivative (PID) control it is difficult to achieve a satisfactory result. Therefore an open-closed-loop PD-type ILC method has been designed and applied to the fatigue test machine to achieve the high-precision control for dynamic force with repetitive regularity. This control method is simulated and experimented fully, and it is compared with PID control, open-loop and closed-loop ILCs. The experimental results have verified the correctness and feasibility of the hydraulic scheme and control principle, as well as the superiority of the open-closed-loop PD-type ILC. The fatigue test machine based on electro-hydraulic principles and the open-closed-loop ILC discussed in the present study have been applied to fatigue experiments for a serial of the compound insulators and gave an ideal performance, with specifications of 150KN maximum static force, 20KN maximum dynamic force, 0.5KN force control precision and 100Hz maximum dynamic frequency.