Control Strategy for a Hardware in the Loop Test Bench

This paper presents a control concept for a hardware-in-the-loop test rig. The aim is to develop optimized control concepts for aircraft fatigue tests, without risking component damage. The test rig simulates a mechanical structure´s response on a force-controlled axis through two servohydraulic axes. Since speed and position have a significant influence on the force control, both must be controlled as precisely as possible and independently of the force control. Classic single-loop PID controllers are not sufficient in this case. Therefore, a control concept consisting of a position controller and a velocity feedforward control using a characteristic map for partial linearization of the controlled system is proposed. The performance of the controller is compared with a single-loop PID control through step tests, and its influence on system dynamics is analyzed. The results show that the proposed control concept leads to better control behavior without noticeable overshooting compared to the PID control. The use of a characteristic map for load pressure correction also simplifies the mapping of non-linear behavior of hydraulic valves and determination of suitable parameters for feedback only considering information usually available from data-sheets.