The Analysis Of Network-Induced Delay And Algorithm Design On Wireless Networked Control System

A great deal of attention has recently been focused on a class of wireless networked control systems (WiNCS) where the control loops are closed through wireless communication networks. This family of systems is an integration of plants, sensors, controllers, actuators and wireless communication networks of certain local field. It aims to ensure data transmission and coordination manipulation among spatially distributed and mobile components. Compared with conventional point-to-point control systems and wired networked control systems, the advantages of WiNCS based on the control, network, radio frequency communication and computer technology are the elimination of wiring, lower install cost, greater mobility as well as greater agility and robustness in diagnosis and maintenance. Because of these distinctive benefits, these WiNCS are uesd in various fields, such as automotive, mobile robotics, advanced aircraft, mechanical and process control, and so on. The WiNCS becomes a hotspot in the control field.However, the introduction of wireless communication networks in the control loops makes the analysis and design of WiNCS complex. The requirements of stable feedback control with wireless network are not yet satisfied duo to random network-induced delays, higher bit-error, jitter, packet losses as well as limited communication bandwidth.In this dissertation, the WiNCS in the frame of modern control theory and radio frequency communication theory are studied through experimental methods for a class of WiNCS built around wireless sensor networks (WSN). With an aim to improve the stability of closed-loop WiNCS and decrease the impact of the network-induced delay on closed-loop WiNCS, the novel algorithms compensated the network-induced delay are presented from the viewpoint of control and wireless networks.The main research works are as follows:1. Based on the IEEE 802.15.4/Zigbee protocols stack, a novel prototype testbed is designed and used to study the WiNCS and WSN. The testbed can help to develop a thorough understanding of WiNCS and to verify the validity of the research results in this dissertation, also serves as a very useful tool for theoretical researchers on networked control, real-time scheduling and routing algorithm.2. For the WiNCS based on the IEEE 802.15.4/Zigbee communication protocols stack, the different time delay components of the total round-trip time delay in this WiNCS are identified. The experimental studies on a WiNCS prototype testbed are used to analyze the impact of the various factors on the total round-trip time delay. The results indicate the need for compromise between the selected sampling period, routing, condition of the channel, quality of the radio frequency signal and the network's throughput.3. The novel simplified fuzzy control algorithm is proposed based the Takagi-Sugeno fuzzy model and applied in networked brushless direct current motor control system built on the WSN. The experimental results are used to analyze the impact of the wireless networks on closed-loop control system. Based on the analysis results, the simplified fuzzy control algorithm are improved in order to compensate the random network-induce delay.4. For a class of WiNCS with random network-induce delay, the new fuzzy model are presented based the Takagi-Sugeno fuzzy model, in which the random network-induce delay acted as the premise variable. Based on the fuzzy model, it simplifies the fuzzy model through searching the dominant fuzzy sub-system related to the real-time input variables, then the stabilizing problem is studied for a class of WiNCS based the above model simplified algorithm, the conditions of stabilizing closed-system are derived and the stabilizing fuzzy state feedback controller is designed through Lyapunov stability analysis theory and linear matrix inequality respectively.5. For a class of WiNCS based on the multi-hopping radio frequency communication technology, the number of hops necessary for data packets to reach their destinations is variable and affects the network-induced delay. To deal with these variable time delay, an LQR output feedback control scheme is introduced based on the client-server architecture. Because of the controller parameters adjusted according to the number of the hops, the closed-loop WiNCS can be converted into the switched control system, then the conditions of stabilizing closed-system are derived and the parameter optimal procedure of the controller is introduced through Lyapunov stability analysis theory, linear matrix inequality and the result of literatures respectively.6. From the viewpoint of the wireless networks, the sources of network-induced delay are identified for a class of WiNCS built on the WSN. Because the routing severely affect the total round-trip time delay in this WiNCS, a novel routing algorithm that can minimize the total round-trip time delay is proposed, the detailed implementation of the algorithm is introduced.Finally, we summarized the dissertation and suggested some open problems in theory and application.