| Summary: | 博士 === 國立交通大學 === 電控工程研究所 === 99 === Real-time network control applications have increasingly gained attentions due to the rapid development of data communication network technologies. Network systems can be conveniently and systematically maintained in industrial applications. The networked control system (NCS), which simply interconnects all sensors, actuators, and controllers through the network, is promising in the future development of industrial technologies with low integration cost. However, NCS also leads to unavoidable problems in time delays that seriously degrade control performance and stability. The characteristics of network-induced delays may be in constant, bounded, random, or unpredictable natures depending on the network protocols, nodes, software, and hardware. In this study, there are two approaches proposed for NCS design under significantly varied time delays. In the first approach, on-line estimation of the delay time is developed by processing the on-line measurement of the round-trip time (RTT) between two nodes in real network environments. Three related controllers are thus developed: (1) the adaptive Smith predictor control scheme for significantly varied time delay, (2) the robust NCS design for bounded variation of time delay and disturbance, and (3) the multi-rate design under the condition of wireless network congestion.
The second approach is proposed as the model-free perfect delay compensation (PDC) scheme. This scheme effectively deals with network-induced delays requiring neither the delay time information nor the plant model. NCS with PDC is thus simply equivalent to the original closed-loop system with an additional pure time delay and it is designed without concerning the network. Therefore, the well-designed controller can be directly implemented on a network and its stability can be guaranteed without being affected by the varied time delay. The proposed approaches have been successfully applied to remote control systems under significantly time-varying delay to control an AC servo motor. Provided experimental results have further proven that both SISO and MIMO systems can be directly implemented in networking systems by including the proposed PDC to maintain its original feedback-loop characteristics.
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