With the rapid development and implementation of Internet technologies, well-designed/tuned controllers obtained from control design without network are desired, which can be further realized in remote control systems directly. Theoretically, available networked control system (NCS) designs are developed with a known system model and time delay. However, the nature of network-induced delay is unpredictable, which depends on network protocol and hardware, and available design approaches usually become impractical in real concerns. The study presents an NCS structure with the proposed perfect delay compensation (PDC) scheme, which is constructed with modified butterfly elements to deal with unknown delay effects without system model and delay information. Both analytical and simulation results prove that the proposed model-free PDC scheme effectively compensates for the unknown network-induced delays. Furthermore, the proposed PDC is carried out using Ethernet, and a well-tuned PI controller for the AC servo motor was directly networked to the remote control system. Experimental results indicate that the proposed PDC renders satisfactory and desirable design results in real NCS applications.
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