Study On Application Of Smith Fuzzy Control In Networked Control Systems

In the networked control systems, the transmission of information between nodes is completed through the network. The transmission of measurement signal or control signal between system components(sensors, controllers and actuators) is also realized through the network channel. Networked control system has completely distributed strueture and is the closed-loop control system composed of the network channel and network nodes. Sensors, controllers, actuators and the network channel the networked form control systems in a proper way which has advantage in transmission speed of signal and real-time performance of system. Users in different space can coordinate with each other and share information. Although there are many advantages for network control, the networked control system also has some problems that can influence performance of system seriously, such as packet losses and disorder of packets time sequence caused by multi-packet transmission and network time delay, etc. Among these problems, compensation of network time delay has attracted considerable attention. The network transmission delay can influence dynamic and static performance of system seriously, such as increase of overshoot and settling time. Excessive time delay will even lead to loss of stability. How to realize compensation of network time delay is drawing more and more attention of experts and scholars.In this paper, generation, composition and influence on NCS stability of time delay are analyzed. According to Smith predictive control scheme based on the controlled object, three improved design methods of Smith predictor are proposed. Considering that the changes of network time delay and the controlled object parameters will make it difficult for Smith predictor to achieve satisfying results and that fuzzy controller can make up for the deficiency of Smith predictor. Based on fuzzy adaptive PID control and Smith predictive control, advantages of the two control strategies are combined to analyze and design an improved controller.Finally, the simulation and contrast for control quality of controllers designed under MATLAB are done. The simulation results show that the closed loop control system have better robustness and control performance when the control strategy of fuzzy Smith predictive time delay compensation based on recursive least squares identification online is adopted.