Profibus is one of the most successful fieldbuses in industrial control systems and has been widely used. It is an open fieldbus that does not depend on the manufacturer. A variety of automation devices can exchange information through the same interface protocol. Profibus-DP (Distributed I/O System) is an optimized module with high data transfer rate for communication between the system and external devices. The remote I/O system is especially Suitable. It allows high-speed periodic small-volume data communication for time-critical automated control systems. The Profibus-DP fieldbus system enables many field devices (such as PLCs, smart transmitters, and inverters) to perform bidirectional multi-information digital communication on the same bus, so it is easy to connect to a communication network using control measurement systems produced by different manufacturers. . Jigang Gangde Color Plate Co., Ltd. is a large-scale color plate production base with an annual output of 200,000 tons invested by Jinan Iron and Steel Group Corporation in 2003. The gas system in the curing furnace, heat-conducting oil furnace and gas hydrogen production in the production line must pass the gas. The gas pressurizing machine is subjected to secondary pressurization to meet the production process requirements, and the gas pressurizing machine control system adopts
With Profibus-DP process field bus communication technology scheme, the automation control unit and inverter use different manufacturers' products, respectively adopt Siemens S7-300 PLC and ABB ACS600 inverter.
2 system configuration and communication protocol
(1) System configuration
The system uses the related products of Siemens and ABB to realize the communication and control principle of the full digital AC speed control system in the Profibus-DP network. The figure shows the network configuration diagram of the Profibus-DP network of the system. The PLC is SIMATIC S7-315-2DP from Siemens, the inverter is ACS600 series, and the NPBA-12 is the communication adapter for the inverter. The programming software is STEP7 V5.2 software for programming S7-300 PLCs and configuring and communicating the Profibus-DP network. The upper computer screen operation adopts WinCC5.1 for screen programming and operation, and the PLC communication adopts Ethernet communication mode.
(2) Communication protocol
In this system, when the S7-300 PLC is used as the master station and the inverter is used as the slave station, the master station transmits the running command to the inverter, and receives the signals of the running status and fault alarm status fed back by the inverter. The inverter is connected to the NPBA-12 communication adapter module and connected to the Profibus-DP network as a slave to receive 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, and each word is addressed. The bidirectional RAM on the inverter side can be sorted by the addressed parameters to the inverter. Write control words, set values, or read actual values, diagnostic information, and other parameters.
From the perspective of software, the core content of the inverter fieldbus control system is the communication protocol of the fieldbus. The data telegram structure of the Profibus-DP communication protocol is divided into protocol header, network data and protocol layer. The network data, ie the PPO, includes the parameter value PKW and the process data PZD. The parameter value PKW is some function code to be defined when the inverter is running; the process data PZD is some data values ​​to be input/output during the running of the inverter, such as frequency reference value, speed feedback value and current feedback value. Profibus-DP has two types of network PPO: one is PZD with no PKW and 2 words or 6 words; the other is PZD with PKW and 2 words, 6 words or 10 words. The purpose of classifying network data in this way is to accomplish different tasks, that is, the transmission of PKW and the transmission of PZD do not affect each other, and each works independently, so that the inverter can operate according to the instructions of the upper-level automation system.
3 STEP7 project system configuration and communication programming
(1) Using the STEP7V5.2 configuration software, enter Hardware Configure to complete the S7-300 PLC hardware configuration;
(2) Select S7-315-2DP as the master station system, import the GSD (device database) file of NPBA-12 into the programming environment of STEP7, and configure NPBA-12 to S7-315-2DP as the main station. On the DP network, and selected the type of PPO used, this design uses PPO4 to set the site network address. In the structure of the variable frequency drive Profibus, ABB inverter uses Profibus-DP communication module (NPBA-12) for data transmission, mainly cyclical: 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, and realize the communication control to the inverter;
(3) Create 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 running settings
After the inverter and the PLC application Profibus-DP field bus are connected into a network, in addition to programming in the PLC automation system, appropriate parameter settings must 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 transmission. The parameter value is not user adjustable. If this parameter is not defined, communication between the module and the drive cannot be established.
(2) 51.02—This parameter selects the communication protocol, and “0†is the Profibus-DP communication protocol.
(3) 51.03—This parameter is Profibu
s Connect the selected PPO type, “3†is PPO4, but the PPO type on the inverter should be the same as the PPO type configured on the PLC.
(4) 51.04—This parameter is used to define the device address number, which is the site address of the inverter. Each device on the Profibus link must have a separate address. In this design, the two inverters are stations 2 and 3. [1]
4.2 Connection of process parameters
The process parameter interconnection completes the definition and connection of the corresponding parameters of the NPBA-12 dual port RAM connector and the inverter, including the connection between the master station (PLC) and the inverter and the connection of the inverter to the main station (PLC). Set the following connection parameters on the inverter.
(1) PZD value sent from the PLC to the transmission inverter
PZD1—Control word, such as control commands such as start-up enable, stop, and emergency stop of the inverter;
PZD2—The frequency setting of the inverter.
(2) PZD value sent from the drive inverter to the PLC
PZD1—Status word, such as alarm, fault, etc.
PZD2—The actual speed value of the inverter, the actual value of the current, and so on.
5 Conclusion
After adopting Profibus-DP fieldbus control mode, the inverter control system not only has strong reliability, easy operation, but also flexible function modification according to process requirements. After the application of Jinan Baode Color Plate Co., Ltd., the system has a good running effect and provides a successful model for the future automation equipment of the head office (network communication of different manufacturers).
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