Analysis And Research Of The Scheduling Algorithm Of Networked Control System Based On CAN Fieldbus

When a traditional feedback control system is closed via network, which is a sort of completely distributed, networked and real-time feedback control system, then the control system is called Networked Control System (NCS). Differed from the common network system, messages transmitted in the NCS have the distinct characteristic of short data length, short transmission period and high real-time. Because in the NCS physical medium is shared by all the nodes, each node having message to transmit must win the privilege of access to the medium. For these reasons the network communication should be scheduled and managed. The scheduling algorithm of NCS in CAN field bus is researched in the thesis based on the survey and analysis of the scheduling theory of NCS in several years.First, aiming at the distribution of NCS, specially the multi-master system such as CAN, there is no unified network clock, so the scheduling and management are affected. In the thesis based on the posteriori agreement from the point of reducing the message for clock synchronization and improving the precision and accuracy of network clock synchronization, the phase-decoupled algorithm is proposed. When applying the algorithm to NCS, the message for synchronization will be reduced from n2+2n to 3n.Second, based on the analysis of the problems of applying EDF algorithm to CAN, the corresponding solutions are researched. Founded on the basic EDF algorithm, the logarithmic quantization of message deadline that can solve the problem of mapping the deadline to priority is proposed. Because of the simple implementation of DM and the flexibility and the high resource utilization of EDF, a new enhanced EDF algorithm is put forward, which solves the low resource utilization of DM and the high excess resource wasting of EDF.Finally, grounded on the EEDF algorithm the feedback control real-time scheduling algorithm for NCS is proposed. In the paper the proposed algorithm aiming at the characteristic of NCS the performance index relating to the message deadline is used as adjuster. In the meanwhile based on the analysis of control theory and real-time scheduling, the general feedback scheduling model is built and established and as the basis for the future research.