Design and Performance Evaluation of an Optimal Discrete-Time Feedforward Controller for Servo-Hydraulic Compensation

Abstract

Servo-hydraulic actuators exhibit frequency-dependent variations of amplitude and delay during real-time hybrid simulation (RTHS). Effective compensation techniques to overcome these variations is a crucial component for the successful implementation of RTHS. Most of the existing compensation techniques have demonstrated effective performance under excitations with relatively low frequency bandwidth. To further advance the servo-hydraulic compensation for broader frequency bandwidth, this paper presents the design and performance evaluation of an optimal discrete-time model-based feedforward controller under inputs with broader frequency bandwidth as high as 0–30 Hz. As a compensation technique has not been fully explored in RTHS, the model-based design of discrete-time domain compensation techniques introduces the new technical challenge of inverting nonminimum phase systems. This paper identifies this new challenge by providing detailed supporting derivation, and explains the use of a digital filtering technique—a finite impulse response (FIR) filter—to address this new challenge, and the development process of the proposed FIR compensator using different optimization schemes. Furthermore, this paper demonstrates the compensation performance of the proposed FIR compensator, both numerically and experimentally, under reference inputs with various bandwidths, including bandlimited white noises with frequency bandwidth as high as 0–30 Hz. For comparison purposes, several existing feedforward compensation techniques are also implemented and compared with the proposed FIR compensator. Based on this study, it is found that the proposed FIR compensator technique not only provides excellent compensation performance under various bandwidths, but also offers great flexibility in its formulation by varying the model order with desired compensation performance and computational demands.