Passive Robust Control for Internet-Based Time-Delay Switching Systems

The Internet is playing an important role in information retrieval, exchange, and applications. Internet-based control, a new type of control systems, is characterized as globally remote monitoring and adjustment of plants over the Internet. In recent years, Internet-based control systems have gained considerable attention in science and engineering [1-6], since they provide a new and convenient unified framework for system control and practical applications. Examples include intelligent home environments, windmill and solar power stations, small-scale hydroelectric power stations, and other highly geographically distributed devices, as well as tele-manufacturing, tele-surgery, and tele-control of spacecrafts. Internet-based control is an interesting and challenging topic. One of the major challenges in Internet-based control systems is how to deal with the Internet transmission delay. The existing approaches of overcoming network transmission delay mainly focus on designing a model based time-delay compensator or a state observer to reduce the effect of the transmission delay. Being distinct from the existing approaches, literatures (7–9) have been investigating the overcoming of the Internet time-delay from the control system architecture angle, including introducing a tolerant time to the fixed sampling interval to potentially maximize the possibility of succeeding the transmission on time. Most recently, a dual-rate control scheme for Internet-based control systems has been proposed in literature (10). A two-level hierarchy was used in the dual-rate control scheme. At the lower level a local controller which is implemented to control the plant at a higher frequency to stabilize the plant and guarantee the plant being under control even the network communication is lost for a long time. At the higher level a remote controller is employed to remotely regulate the desirable reference at a lower frequency to reduce the communication load and increase the possibility of receiving data over the Internet on time. The local and the remote controller are composed of some modes, which mode is enabled due to the time and state of the network. The mode may changes at instant time k, k ∈ {N+} and at each instant time only one mode of the controller is enabled. A typical dual-rate control scheme is demonstrated in a process control rig (7; 8) and has shown a great potential to over Internet time-delay and bring this new generation of control systems into industries. However, since the time-delay is variable and the uncertainty of the process parameters is unavoidable, a dual-rate Internet-based control system may be unstable for certain control intervals. The interest in the stability of Passive Robust Control for Internet-Based Time-Delay Switching Systems 21