A packet-based dual-rate PID control strategy for a slow-rate sensing Networked Control System

摘要

This paper introduces a packet-based dual-rate control strategy to facetime-varying network-induced delays, packet dropouts and packet disorder in aNetworked Control System. Slow-rate sensing enables to achieve energy saving byreducing network load. In addition, choosing a slower sensing period than thelongest round-trip time delay can avoid packet disorder. On the other hand, aslow-rate sensing usually degrades control performance in a conventionalcontrol framework. Therefore, including dual-rate control techniques can beuseful to maintain the desired performance, since the controller is able togenerate a fast-rate control signal from a slow-rate sensing signal. Adual-rate PID controller is used, which can be split into two parts: aslow-rate PI controller is located at the remote side (with no permanentcommunication to the plant) and a fast-rate PD controller, at the local side(close to the plant, sensor, and inside the actuator, which can offer a lowcomputation power). In addition, at the remote side, where a powerfulcomputation device is located, a prediction stage is included in order togenerate the packet of future, estimated slow-rate control actions to be sentto the local side. At this side, these actions are converted to fast-rate onesand used when a packet does not arrive due to the network-induced delay or dueto occurring dropouts. The control proposal is able to reach the nominal(no-dropout, no-delay) performance despite the existence of time-varying delaysand packet dropouts. Via real-time control for a Cartesian robot, resultsclearly reveal the superiority of the control approach compared to a previousauthors\' proposal, where the time-varying delays are faced by means of a gainscheduling control strategy.