Research And Application Of Distributed Self-organization Sequence Control System

As the expansion of the scale and the growth of the complexity of industrial production, the distributed structure is adopted in more and more control system. Besides that, the scale of the application of wireless technology in industrial field has been enlarged constantly in recent years. Given these trends, a distributed self-organization sequence control system (DSSCS) is proposed and discussions and research are carried out in-depth. In DSSCS, the resource of computation, memory and communication is utilized to not only execute the sequence control logic in a distributed manner, but also generate the control logic automatically. It improves the level of automation of the system and bears positive significance for the development of industrial automation.For the realization of DSSCS is based on wireless network, the delay and bit error in wireless transmission may lead the system to generating totally wrong control command, resulting in serious consequences. So related mechanisms have to be designed to reduce the influence caused by delay and bit error and the controllability and stabilizability of the system should be also guaranteed. In addition, for the traditional manner of configuration is of inefficiency and fallibility, to improve the configuration efficiency of DSSCS, the generation of control logic in self-organization manner which is production-oriented is designed. Around the above critical problems in the realization of DSSCS, the theoretical research results and innovative points achieved in this paper are summarized as follows:1. A Distributed Self-organization Sequence Control System (DSSCS) is proposed. There is no centralized controller in DSSCS and the control logic is totally dispersed into the wireless control nodes in field, executing the control tasks in a distributed manner. Besides that, the system can generate the control logic in a self-organization manner, so that the control logic can be generated automatically without artificial configuration. Compared to the traditional sequence control system, DSSCS has distinct advantage, such as the centralized fault is eliminated by adopting distributed structure, lots of cable is saved by using wireless network for signal transmission and the configuration efficiency is improved through the manner of self-organized generation of control logic.2. Analyzing the performance of DSSCS affected by delay and bit error in wireless transmission and designing the mechanisms reducing the influence. The deterministic and stochastic Petri net and temporal Petri net are combined to model the work process of DSSCS with the complexed marking introduced. The delay in wireless transmission is presented by the transition with randomly distributed firing time and the occurrence of bit error is simulated by the probabilistic firing between the conflicted transitions. To make sure that the states of the system are transferred according to the given sequence steps, temporal logic equations are introduced to determine the firing condition of other conflicted transitions in DSSCS. Based on the derived model, the possible states and their durations can be analyzed, so that it can be confirmed whether the operation of the system meets the requirement of the given steps. Considering the bit error in transmission, the method of state restriction is proposed to improve the probability that the system operates correctly, meanwhile the deviation compensation is presented to minimize the deviation of the duration of the states. And the simulation results are also presented to show the improvement.3. Using Boolean control network to build the control model of DSSCS, with semi-tensor product introduced, the state incidence matrix of the system is obtained to analyze the controllability and stabilizability of DSSCS affected by bit error and delay. In the analysis, the problem of the altered states caused by bit error is transformed as that the control nodes choose different structure matrices and different state incidence matrices of the system will be derived. And the system states with delay are decomposed into different state transition paths according to the value of delay. Based on the possible structure matrices and the length of the longest path, the criteria of the controllability and stabilizability of DSSCS affected by bit error and delay can be derived. Besides that, by using semi-tensor product, the self-organized generation of control logic which is production-oriented is proposed. So, the distributed control nodes can automatically generate the structure matrices which denote the corresponding control logics through the operation based on production process, forming an organized sequence control system with cooperative control. Moreover, the control nodes can automatically maintain the distributed control logics in the situation that the nodes are replaced.4. DSSCS based on wireless network is applied for the sequence control of ultrafiltration system of chemical water treatment in power plant. According to the requirement of practical production, the overall framework is constructed and several functions are designed, such as information sharing, control logic generation in self-organized manner, distributed control, hierarchical diagnosis and real-time supervision with the low-power design for wireless network considered, to realize a DSSCS with safety, reliability and low-power dissipation. In addition, the design principles of the hardware and software of wireless DI/O modules and base station are presented. And the application of DSSCS in the field is exhibited.