1. Introduction PROFIBUS is one of the most successful fieldbuses in industrial control systems and has been widely used. It is a manufacturer-independent, open fieldbus that allows various automation devices to exchange information through the same interface protocol. PROFIBUS-DP (Distributed I/O System) is an optimized module with a high data transfer rate, suitable for communication between the system and external devices, especially for remote I/O systems. It allows for high-speed, periodic, small-batch data communication, making it suitable for time-critical automated control systems. The PROFIBUS-DP fieldbus system enables many field devices (such as PLCs, intelligent transmitters, and frequency converters) to perform bidirectional, multi-information digital communication on the same bus, thus facilitating the interconnection of control and measurement systems from different manufacturers into a communication network. Jinan Iron & Steel Baode Color Plate Co., Ltd. is a large-scale color plate production base with an annual output of 200,000 tons, invested and built by Jinan Iron & Steel Group Corporation in 2003. The curing furnace, thermal oil furnace and coal gas system in the coal gas to hydrogen production line must be pressurized twice by the coal gas pressurizer to meet the production process requirements. The coal gas pressurizer control system adopts the Profibus-DP process fieldbus communication technology scheme. The automation control unit and the frequency converter are products from different manufacturers, namely Siemens S7-300 PLC and ABB ACS600 frequency converter. 2 System Configuration and Communication Protocol (1) System Configuration This system uses relevant products from Siemens and ABB to realize the communication and control principle of the all-digital AC speed regulation system in the Profibus-DP network. The attached figure is the network configuration diagram of the Profibus-DP network of this system, in which the PLC is Siemens SIMATIC S7-315-2DP, the frequency converter is ACS600 series, and NPBA-12 is the communication adapter matched with the frequency converter. The programming software is STEP7 V5.2 software, which is used to program the S7-300 PLC and configure and communicate with the Profibus-DP network. The upper computer screen operation uses WinCC5.1 for screen programming and operation, and the communication with the PLC is via Ethernet. (2) Communication Protocol In this system, when the S7-300 PLC is the master station and the frequency converter is the slave station, the master station sends the running instructions to the frequency converter and receives the signals of the running status and fault alarm status fed back by the frequency converter. The frequency converter is connected to the NPBA-12 communication adapter module and connected to the Profibus-DP network as a slave station, receiving control from the master station SIMATIC S7-315-2DP. The NPBA-12 communication adapter module stores the process data received from the Profibus-DP network into the bidirectional RAM. Each word is addressed. The bidirectional RAM at the frequency converter end can be sorted by the addressed parameters to write control words, set values ​​or read actual values, diagnostic information and other parameters to the frequency converter. From a software perspective, the core of a frequency converter fieldbus control system is the fieldbus communication protocol. The Profibus-DP communication protocol's data telegram structure is divided into a protocol header, network data, and a protocol layer. Network data, or PPO, includes parameter values ​​(PKW) and process data (PZD). PKW parameters are function codes defined during frequency converter operation; PZD parameters are input/output values ​​during frequency converter operation, such as frequency setpoint, speed feedback, and current feedback. Profibus-DP has two types of network PPOs: one without PKW but with 2 or 6 words of PZD; the other with PKW and 2, 6, or 10 words of PZD. This classification of network data aims to accomplish different tasks; the transmission of PKW and PZD do not interfere with each other and operate independently, allowing the frequency converter to operate according to the instructions of the higher-level automation system. 3 STEP7 Project System Configuration and Communication Programming (1) Use STEP7V5.2 configuration software to enter Hardware Configure to complete the hardware configuration of S7-300 PLC; (2) Select S7-315-2DP as the master station system, import the GSD (device database) file of NPBA-12 into the STEP7 programming environment, configure NPBA-12 to the DP network with S7-315-2DP as the master station, and select the PPO type to be used. This design uses PPO4 and sets the station network address. In the Profibus structure of the variable frequency drive, the ABB inverter uses the Profibus-DP communication module (NPBA-12) for data transmission, which is mainly periodic: the host reads the input information from the slave station and sends the output information back to the slave station. Therefore, it is necessary to call two system function blocks SFC14 and SFC15 in the PLC main program to read and write these data to realize the communication control of the inverter; (3) Establish a data block in the main PLC program for data communication of the inverter; establish a variable table for observing the real-time communication effect. 4 Inverter operation settings After the inverter and PLC are connected to the network using the Profibus-DP fieldbus, in addition to programming in the PLC automation system, appropriate parameter settings should also be made on each inverter. After the communication cable is connected, start the inverter and complete the communication parameters of the inverter. 4.1 Basic settings (1) 51.01—Module type, this parameter displays the module model detected by the drive. Its parameter value cannot be adjusted by the user. If this parameter is not defined, communication cannot be established between the module and the drive. (2) 51.02—This parameter selects the communication protocol. “0” means Profibus-DP communication protocol is selected. (3) 51.03—This parameter is the PPO type selected for Profibus connection. “3” means PPO4, but the PPO type on the inverter should be consistent with the PPO type configured on the PLC. (4) 51.04—This parameter is used to define the device address number, that is, the station address of the inverter. Each device on the Profibus connection must have a unique address. In this design, the two inverters are station 2 and station 3 respectively. [1] 4.2 Connection of process parameters The process parameter interconnection completes the definition and connection of the corresponding parameters between the NPBA-12 dual-port RAM connector and the inverter, including the connection from the master station (PLC) to the inverter and the connection from the inverter to the master station (PLC). Set the following connection parameters on the inverter. (1) PZD values ​​sent from PLC to the frequency converter of the drive unit: PZD1—control word, such as control commands for starting, stopping, and emergency stopping of the frequency converter; PZD2—frequency setting value of the frequency converter. (2) PZD values ​​sent from the frequency converter of the drive unit to PLC: PZD1—status word, such as alarm, fault, and other frequency converter operating status; PZD2—actual speed value, actual current value, etc. of the frequency converter. 5 Conclusion After the frequency converter control system adopted the Profibus-DP fieldbus control mode, not only was the overall system highly reliable and easy to operate, but it could also be flexibly modified according to process needs. After the system was applied at Jinan Iron and Steel Baode Color Plate Co., Ltd., the operating effect was good, providing a successful model for the future automation equipment (network communication between different manufacturers) of the head office. [b][align=center]For details, please click: Fieldbus Communication Technology between Siemens PLC and ABB Frequency Converter[/align][/b]