PROFIBUS is one of the most successful fieldbuses in industrial control systems and is 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 automation control systems. The PROFIBUS-DP fieldbus system enables many field devices (such as PLCs, intelligent transmitters, and frequency converters) to perform bidirectional, multi-message 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 Steel Plate Co., Ltd. is a large-scale color steel plate production base with an annual output of 200,000 tons, invested and built by Jinan Iron & Steel Group Corporation in 2003. Its production line's curing furnace, thermal oil furnace, and coal gas system in the coal gas-to-hydrogen production line require secondary pressurization of the coal gas via a coal gas compressor to meet production process requirements. The coal gas compressor control system adopts...
Using the Profibus-DP process fieldbus communication technology solution, the automation control unit and the frequency converter are products from different manufacturers, namely Siemens' S7-300 PLC and ABB's ACS600 frequency converter.
2 System Configuration and Communication Protocol
(1) System Configuration
This system utilizes products from Siemens and ABB to implement the communication and control principles of a fully digital AC speed control system within a Profibus-DP network. The attached diagram shows the network configuration of the Profibus-DP network for this system. The PLC is a Siemens SIMATIC S7-315-2DP, the frequency converter is an ACS600 series, and the NPBA-12 is the communication adapter配套 with the frequency converter. The programming software is STEP7V5.2 , used for programming the S7-300 PLC and configuring the Profibus-DP network. The host computer interface is operated using WinCC5.1 for screen programming and operation, and communication with the PLC is via Ethernet.
(2) Communication Protocol
In this system, when the S7-300 PLC acts as the master station and the frequency converter acts as the slave station, the master station transmits operating commands to the frequency converter and simultaneously receives operating status and fault alarm signals from the frequency converter. The frequency converter is connected to the NPBA-12 communication adapter module and enters 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 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.
3STEP7 Project System Configuration and Communication Programming
(1) Use STEP7V5.2 configuration software to enter HardwareConfigure 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 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 frequency converter uses the Profibus-DP communication module (NPBA-12) for data transmission, which is mainly periodic: the master station 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 to the frequency converter;
(3) Create a data block in the main PLC program for data communication with the frequency converter; create a variable table for observing the real-time communication effect.
4. Inverter Operation Settings
After the frequency converter and PLC are connected to form a network using the Profibus-DP fieldbus, in addition to programming in the PLC automation system, appropriate parameter settings must also be made on each frequency converter.
After connecting the communication cable, start the frequency converter and complete the communication parameters of the frequency converter.
4.1 Basic Settings
(1) 51.01 — Module type. This parameter displays the module model detected by the transmission device. Its parameter value cannot be adjusted by the user. If this parameter is not defined, communication cannot be established between the module and the transmission.
(2) 51.02 — This parameter selects the communication protocol. “0” means Profibus-DP communication protocol is selected.
(3) 51.03 — This parameter is for Profibu
The PPO type selected for the s connection is "3" for PPO4, but the PPO type on the frequency converter 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 frequency converter. Each device on the Profibus connection must have a unique address. In this design, the two frequency converters 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 frequency converter, including two parts: the connection from the master station (PLC) to the frequency converter and the connection from the frequency converter to the master station (PLC). Set the following connection parameters on the frequency converter.
(1) PZD value sent from PLC to the frequency converter of the drive device
PZD1—Control word, such as control commands for the inverter's start enable, stop, and emergency stop;
PZD2 — Frequency setting value of the frequency converter.
(2) PZD value sent from the frequency converter of the drive device to the PLC
PZD1 — Status word, such as alarm, fault, and other inverter operating status;
PZD2—actual speed and current values of the frequency converter.
5. Conclusion
After adopting the Profibus-DP fieldbus control mode, the frequency converter control system not only boasts high reliability and ease of operation, but also allows for flexible functional modifications based on process requirements. The system has demonstrated excellent performance since its application at Jinan Iron & Steel Baode Color Plate Co., Ltd., providing a successful model for future automation equipment (network communication between different manufacturers) within the head office.
