Research On The Scheduling Algorithm Of Networked Control System Based On CAN Bus

NCS, Networked Control System, is a sort of distributed Real-Time Feedback Control System, in which data transmission and exchange among sensor, controller and actuator proceed by network. Each control loop performance of NCS is not only dependent on the control algorithm, but the shared resource allocation and scheduling. Because each loop shares the network resource and each node need to compete the network access right to send data preferentially, a series of problems such as induced time delay, packet loss and network congestion and so on, can be caused. In order to distribute network resource equitably, network scheduling emerges to solve these problems as data collision and information conflict at the time of multiple objects access to network. Through studying the CAN-based typical dynamic and static algorithm influence on the system performance, the paper introduces the concept of the dynamic feedback scheduler and eventually puts forward an advanced mixed scheduling algorithm combining dynamic with static algorithm. The main work is concluded as follows:First of all, the concept, development and characteristics of NCS, including the basic problems existing in network scheduling, are introduced in detail. Then CAN bus protocol is explained systematically. In the following, the simulation toolbox TrueTime used for modeling and simulation is stated. Then the thesis takes NCS with single control loop for example, showing the usage way of the toolbox.Secondly, CAN-based typical dynamic and static algorithm are analyzed and studied in depth, and the dynamic scheduling algorithm as EDF and static scheduling algorithm as RM influence on the system performance is studied with emphasis. The models of NCS with three control loops and four control loops are set up with TrueTime, and the merits and demerits of the two algorithms are compared by the simulation results, which indicate that the two has no significant difference at the high network rate and with light load. However, at heavy load, EDF shows the obvious scheduling advantages.Finally, combining dynamic algorithm merits with static algorithm merits and based on MTS algorithm, an advanced mixed scheduling algorithm (EMTS, Enhanced-MTS) is proposed. The feedback scheduler, Emergency Data Node and Interference Node are added into the NCS with three control loops, and the improvement on the system performance by the scheduler is verified through comparing the simulation results of MTS and EMTS. Moreover, that the advanced strategy can overcome the shortage of prior algorithm, such as low network utilization and high scheduling expense, is to be proved. Meanwhile, it can also improve the dynamic and stable control performance of the system.