| Networked Control Systems(NCS) are the computer control systems which are closed by digital network. NCS which integrate computer, communication and automatic control provide several advantages, such as higher reliability, less connecting wires, robust anti-jamming and open communication protocol. However, there exist many problems in application, such as network induced delay, packet dropout and network security. In order to deal with network induced delay and packet dropout, this thesis focuses the research on works as follows:First, NCS' background, basic concept, merits and shortcomings are introduced. A survey of NCS research works is given.Second, the characteristics of network induced delay and packet dropout are analyzed, including the causes, combinations and behaviors. The degradation caused by delay and packet dropout is showed via theory analysis and simulation.Third, in order to deal with delay and packet dropout, an improved algorithm for network is proposed as Measured Delay based DMC algorithm. In this algorithm, when the actuator node cannot receive the data on time, the predictive output sequence and control increment sequence are used for open-loop control, which avoids the actuator's not operating. When the control data arrives at actuator, the control increment value is selected from the sequence based on the measured delay, and used to switch the NCS to closed-loop control. The effectiveness of this algorithm is validated via simulation in Matlab.With the lack of experimental platform in network, the Ethemet Networked Motion Control Open Platform is implemented. The platform consists of a PMSM with Ethernet interface, a controller based on PC which is equipped with many control algorithms, a network monitor providing real-time output of system, and network disturbers adjusting network load. Finally, the availability of Measured Delay based DMC in the actual network is proved based on the platform. |
