Research On Control Network Scheduling Problems In Safety Critical DCS

The control network scheduling problem is a key issue in the design of safety critical DCS (SCDCS). Compared to non-safety critical DCS, the control network scheduling in SCDCS is designed to meet the need for additional constraints and ensure the credibility of the system. On the basis of discussion to the research status and development trend of control network scheduling, thispaper study with the precondition of control network scheduling design------network transmissioncycle, network scheduling methods with the isolation of anti-crisis and the dynamic real-time scheduling of CAN networks, so as to meet the requirements of control performance, real-time demand and safety technology. The main research results are as follows:(1) The characteristics of safety-critical systems, distributed control system and control network are summarized, and the research status and development trend of control network scheduling problem is analyzed. Some problems in the strategy and the optimal design of network scheduling are indicated. It is proposed that a control network scheduling system should meet the control performance, real-time demand and safety technology, and many other constraints.(2) For a multi-loop SCDCS with multiple input and output, a method to determine network transmission scheduling cycle based on control and integrated design is proposed. This method uses relative error of state to describe the control performance of the loop, and establishes its function expression. The sufficient conditions for loop asymptotic stability and specified stability are derived by using Lyapunov theory and matrix measure properties respectively. On the bases, formulas for MATI are established.(3) The time isolation mechanism which is similar to safety kernel technology is introduced into the control network scheduling, and the open network scheduling framework with anti-segregation mechanism is proposed. Through the analysis of this scheduling framework, a 3-layer real-time scheduling model is established. In view of the rotary-type non-preemptive EDF algorithm in the model, the determinant conditions of schedulability is derived. On this basis, the determinant condition of schedulability in the entire hierarchical scheduling is put forward and a detailed proof is given. The method to get time parameters in the network scheduling is proposed by using this determinant condition.(4) The formulas about the worst transmission time of the CAN message in the ideal and the actual conditions are derived. The influence of random jitter of transmission in CAN network to the TIM network scheduling method is analyzed. In order to reduce this harmful effect, the feedback scheduling is introduced into the network scheduling, and the fuzzy feedback EDF scheduling (FFC-EDF) frame is built. The control mechanism of fuzzy controller and the linear mapping approach from output variable to scheduling parameter is given. The FFC-EDF scheduling with multiple network segment structure is analyzed, and the network segment optimization model based on graph division and its niche self-adaptive genetic algorithm are given later.