Abstract: This paper designs a distributed control system for pulverized coal preparation based on PROFIBUS fieldbus using configurable programming technology. This system integrates the advantages of programmable logic controllers (PLCs), distributed control systems (DCS), and fuzzy control algorithms, ensuring stable and reliable operation after commissioning. It is simple and convenient to operate, improving productivity and product quality. Furthermore, it provides strong practical guidance for the design of other preparation control systems. Keywords: Fieldbus; Programmable Logic Controller; Distributed Control System; Fuzzy Control 1 Introduction Pulverized coal preparation is one of the most important links in cement production equipment. Its task is to safely process raw coal into pulverized coal that meets requirements, and then transport the prepared pulverized coal to the pulverized coal silo for storage, thus providing fuel for the cement production process. Due to the large inertia, pure time delay, and nonlinearity of the pulverized coal preparation process, and the complex and variable production conditions, it is impossible to establish an accurate mathematical model of the system. Therefore, traditional control strategies are difficult to achieve satisfactory control results. Fuzzy control, however, can achieve good control results for model-less complex control objects like pulverized coal preparation. Meanwhile, due to the geographically dispersed equipment in the pulverized coal preparation system, utilizing fieldbus technology for distributed control of the entire production line can achieve twice the result with half the effort in order to improve productivity and increase system reliability. 2. Process Flow The process flow of the pulverized coal preparation system is shown in Figure 1. [align=center]Figure 1 Process Flow Diagram of Pulverized Coal Preparation System[/align] Raw coal is lifted from the coal yard by an elevator and sent to the raw coal silo. After being measured by a load sensor inside the silo, it is fed into the coal mill by a disc feeder. Inside the mill, the raw coal is dried and ground by hot air supplied by a hot air blower, and then sent to a dynamic classifier. Unqualified coarse powder is returned to the mill head for re-grinding, while fine powder enters the pulverized coal dust collector. The pulverized coal collected by the dust collector is sent to the pulverized coal silo equipped with a load sensor via a bidirectional screw conveyor, and finally, after being measured by a rotor weighing scale, it is sent to the kiln head. 3 System Design The system design adopts a hierarchical distributed open structure, utilizing PROFIBUS-DP fieldbus, DCS configuration, and PLC control technologies to form a distributed control system with decentralized control and centralized management. Functionally, it is divided into three levels: the bottom PLC control level, the intermediate communication level, and the upper management and remote network monitoring level. The system structure diagram is shown in Figure 2. [align=center] Figure 2 System Structure Diagram[/align] 3.1 Hardware Design The bottom PLC control level consists of three S7-300 PLCs (slave stations), mainly responsible for acquiring field data and controlling field instruments, actuators, and frequency converters. The PLCs communicate with the intermediate communication master station through a master-slave network. Each PLC is an independent control slave station, capable of performing control tasks such as data acquisition, fault diagnosis, and equipment control. Furthermore, it can automatically enter local control mode in case of a fault in the master station or transmission line. Based on the bottom PLC control level, a communication processing master station and a data server are set up, connected via PROFIBUS-DP fieldbus. The communication processing master station, as the master station in the master-slave network, has bus control rights. The data server manages the database of the entire system and acts as a router between the fieldbus and Ethernet. The upper-level management and remote network monitoring level consists of an operator station computer connected to the data server via Ethernet to share data and information. Information from the data server is sent to the operator station via Ethernet, where the operator station performs data processing, diagnosis, and fault alarms, and displays the process flow, historical curves, real-time curves, alarm screens, etc. in real time. The operator station also performs the functions of a network server, transmitting production data via the Internet to achieve networked remote browsing. 3.2 Software Design 3.2.1 Software Design of the Bottom-Level PLC Control Level According to the requirements of the coal powder preparation process, the main flowchart of the control program of the bottom-level PLC control level is shown in Figure 3. [align=center] Figure 3 Bottom-Level PLC Control Level Main Program Flowchart[/align] The load control of the coal mill is achieved by using fuzzy control based on factors such as the elevator, mill noise, and powder return amount. The input variables of the fuzzy controller are the material return error e[sub]h[/sub], the grinding noise error e[sub]m[/sub], and the power error e[sub]σ[/sub], and the output variable is the control variable u. The fuzzy subsets of the input variables are as follows: e[sub]h[/sub] has 5 levels: {negative large, negative small, zero, positive small, positive large}, denoted as {NB, NS, ZO, PS, PB}; e[sub]m[/sub] has 5 levels: {negative large, negative small, zero, positive small, positive large}, denoted as {NB, NS, ZO, PS, PB}; e[sub]σ[/sub] has 5 levels: {negative large, negative small, zero, positive small, positive large}, denoted as {NB, NS, ZO, PS, PB}. The fuzzy subset of the output variable is: u has 5 levels: {negative large, negative small, zero, positive small, positive large}, denoted as {NB, NS, ZO, PS, PB}. The corresponding membership functions e[sub]h[/sub], e[sub]m[/sub], and e[sub]σ[/sub] are trapezoidal functions, and u is a Gaussian function. The weighted average method is used for defuzzification. 3.2.2 The software design of the master station and data server adopts a structured approach, dividing the master station software into: an initialization module, a communication module, and a fault diagnosis module. The initialization module mainly assigns initial values ​​to the input storage area and image area each time the PLC starts, completing the initialization of the S7-300. The master station communicates with the slave station through CP342-5 using "periodic I/O mode". The programming idea of ​​the fault diagnosis module is to use the rack fault organization block OB86 in the S7-300. Fault diagnosis is performed by checking the values ​​of temporary variables in this organization block. The program flow is shown in Figure 4. [align=center] Figure 4 Fault Diagnosis Program Flowchart[/align] 3.2.3 Software Design of the Operator Station The operator station is developed using the MCGS 5.1 general version industrial control configuration software from Beijing Kunlun Tongtai Company. It can realize real-time display of field signals, adjustment of control parameters, saving of important historical data, display of multiple curves, signal alarms, and report printing, etc. According to the control requirements of the process and equipment, a series of operator station interfaces were developed, including the startup interface, main process flow interface (Figure 5), group startup interface (Figure 6), startup debugging interface, alarm interface, real-time curve interface, historical curve interface, and event record and report interface, etc. [align=center] Figure 5 Main Process Flowchart[/align] [align=center] Figure 6 Group Startup Interface[/align] The entire system software has strong self-diagnosis, redundancy and error correction functions, and the communication equipment has strong fault tolerance; the system has good scalability, and the standardized network TCP/IP protocol and SQL database are conducive to high-level interconnection of the system. 4 Conclusion This system adopts the configuration control concept, the PROFIBUS fieldbus control method, and combines the advantages of PLC and DCS. It not only overcomes many shortcomings in the traditional coal powder preparation control system and improves production efficiency and product quality, but also expands the interconnection, interoperability and interoperability of the system, which is very popular among users. References [1] Yang Xianhui. Fieldbus Technology and Its Application. Beijing: Tsinghua University Press, 1999. [2] Guo Zongren. Programmable Controller and Its Communication Network Technology. Beijing: People's Posts and Telecommunications Press, 1999.