Compensation for transmission delays in an ethernet-based control network using variable-horizon predictive control

Distributed control networks encounter nondeterministic delays in data communication between sensors, actuators, and controllers, including direct-feedback control and higher level supervisor control. This paper presents a novel strategy, which extends the Generalized Predictive Control (GPC) algorithm to compensate for these data-transmission delays. Communication lines between sensors to controller and controller to actuators are considered. The present strategy incorporates a minimum-effort estimator to estimate missing or delayed sensor data and a variable-horizon adaptive GPC controller to predict the required future control efforts to drive the plant to track a desired reference trajectory. Action buffers are introduced at the actuators to sequence the future control efforts. A parallel objective of this paper is to investigate the suitability of the Ethernet network, which is cost-effective and widely deployed for implementing networked control systems. An Ethernet-based client-server control architecture is developed. The developed scheme is implemented on the dual-axis hydraulic position system of an industrial fish-processing machine.