A Discrete-Time Feedforward-Feedback Compensator for Real-Time Hybrid Simulation

Real-Time Hybrid simulation (RTHS) is a powerful experimental technique which provides engineers the opportunity of performing cost-effective dynamic tests for large or full scale structures. To carry out a successful RTHS test, the time delay, which is mostly associated with the servo-hydraulic actuator dynamics, needs to be reduced by an appropriate compensator. Model-based feedforward compensators are designed based on the dynamic model of the plant, including both the servo-hydraulic actuator and the specimen attached to it. This dynamic model may not represent the plant accurately during the RTHS, especially when the specimen behaves nonlinearly during the test. As a result, the feedforward compensator/controller which is designed based on this plant model may not work effectively. In this paper, a discrete time feedback controller is introduced, in addition to the feedforward compensator, to provide robustness to the delay compensation. Both numerical and experimental studies will be conducted. The performance of this feedforward-feedback compensator is evaluated through the actuator time delay and the relative Root-Mean-Square (RMS) error between the desired and measured actuator displacement.