[Abstract] Energy consumption is a significant and controllable component of a company's product costs, and reducing energy consumption is a crucial way for companies to lower costs. This article introduces the application of Siemens PLC and fieldbus in the energy monitoring and management system of a cigarette factory, detailing the system's hardware and software design, as well as the communication network connection.
I. Project Overview
Energy consumption is a significant and controllable component of a company's product costs, and reducing energy consumption is a crucial way for companies to lower costs. The tobacco industry has always been a major energy consumer. With the large-scale introduction of advanced foreign technologies and complete sets of equipment, cigarette production has evolved from slow, manual production to high-speed, fully automated production, leading to ever-increasing energy demands. Therefore, reducing energy consumption and rationally allocating energy will directly improve production efficiency. General Tobacco Group Co., Ltd., established in 1993 and located in Jinan, Shandong Province, is a diversified, cross-regional, cross-industry, and cross-border enterprise group with tobacco as its core business. Its core enterprise, Jinan Cigarette Factory, possesses the world's most advanced cigarette equipment and industry technology center. The company currently has over 5,000 employees and total assets of 7.3 billion yuan, and is one of the 36 key enterprises in the national tobacco industry.
This energy monitoring system is mainly used to monitor, statistically analyze, report, and print energy consumption data for various departments of the Jinan Cigarette Factory. The main monitoring parameters include electricity, water, steam, and compressed air for all departments throughout the factory.
II. System Introduction
This system comprises a three-tiered energy monitoring and management system consisting of the Energy Statistics Office, the Boiler Operation Room, and the Equipment Management Department. Sensors distributed throughout the plant collect parameters from 233 points, including steam, compressed air, water, and electricity, and transmit them to the server. The Boiler Operation Room and Equipment Management Department are responsible for real-time parameter and equipment monitoring. The Energy Statistics Office displays real-time data, provides daily and monthly cumulative energy consumption data, allows queries of daily, monthly, and time-period cumulative data, and prints reports. The Statistics Office's energy monitoring and evaluation procedures complete various performance assessments for each shift, statistically analyze the input and output of the plant's energy supply departments and the energy consumption of energy-using units, and perform cost accounting, providing a reliable basis for improving the plant's energy management and utilization.
This system uses Siemens' Simatic S7-400 CPU414-2DP and S7-300 CPU314 as the CPU master station. The 400 PLC master station is configured with nine ET200M substations. The CPU414-2DP integrates MPI and PROFIBUS-DP communication ports. Each substation connects to the 400 PLC master station via PROFIBUS-DP, minimizing hardware costs while ensuring data acquisition performance requirements. The 400 PLC master station communicates with the host computer via the MPI interface. The 300 PLC master station also communicates with the host computer via the MPI interface. SimaticWinCC is used as the host monitoring software, and VB6.0 is used to edit the energy monitoring and evaluation program for the statistics office.
The system list is as follows:
III. Control System Composition
1. System structure: The system configuration is shown in Figure 1.
Figure 1. Energy Management and Monitoring System Diagram
This system is divided into three main parts: a supervisory control center, a PLC master station, and PLC slave stations. The supervisory control center consists of one server and three client computers. The server is integrated into the enterprise network, making client expansion exceptionally easy and simple: just connect the computer to the local area network and perform simple configurations to use it as a client computer. The 400 PLC master station connects to the server via the MPI protocol. MPI can be used at both the unit and field levels, allowing for very economical connection of a small number of stations. The 400 master station and its slave stations are connected via PROFIBUS DP. This networking method minimizes hardware costs while ensuring data acquisition performance requirements. The data acquisition process is roughly as follows: the output signals from the field sensors are collected by the signal templates at each station, converted into corresponding digital signals, and then sent to the 400 PLC master station via the communication module. The 400 PLC master station performs various calculations and processes on the data from each station as required and then transmits it to the server via the MPI network. Data is transferred between the client computers and the server via OPC.
2. Software Design
The PLC master station and PLC slave station of this system are programmed using STEP7 to realize the initial processing of process data by the PLC; the host computer monitoring uses SIMATIC WinCC to write server software (WinCCServer) and client software (WinCCClient) to realize real-time data display, daily and monthly cumulative display of energy consumption, query of daily, monthly and time period data of cumulative amount, and report printing; the energy monitoring and evaluation program of the statistics office is written in Visual Basic 6.0 to complete the various indicator assessment tasks of the shift.
(1) PLC Master Program: This program includes 6 OB blocks, 20 FC blocks, and 15 DB blocks. It processes the data of compressed air, steam, electricity, and water collected on-site (including steam flow compensation and steam temperature calculation), and records the cumulative amount of each variable. The flowchart of the master program (organization block OB1) is as follows:
Figure 3 Flowchart of the main program (organization block OB1)
(2) Host computer WinCC program: Based on the customer's requirements, a user-friendly host computer interface was developed using WinCC. See the figure below:
Figure 2. Compressed air distribution interface of the host computer.
3. Selection of Energy Monitoring and Assessment Procedure Design Scheme by the Statistical Office
The energy monitoring and assessment program is an application developed using VB6.0 , installed on the client machine of the statistics office. It performs monthly performance evaluations of various departments and determines bonuses accordingly. The program needs to record changes in over 70 quantities from the boiler room, air compressor station, sheet metal workshop, and main power distribution room, and perform corresponding data processing to assess workers in each department and shift. It also needs to calculate production costs and print detailed monthly reports, making the workload very large. In practice, the following solutions were used to implement communication between the program and its service.
(1) Option 1: Develop an OPC client application using VB6.0 and use the program to communicate with the server.
Disadvantages: The client program does not have a robust fault tolerance and fault diagnosis function. When the server experiences a brief error, the OPC connection is interrupted, causing a system crash.
(2) Option 2: Add a diagnostic program to the client to determine whether the server is faulty by continuously connecting to the server. If the server is not in normal condition, restart the system software to realize fault diagnosis and handling.
Disadvantages: Frequent connection and disconnection between the client and the server results in high consumption of server resources.
(3) Option 3: OPC communication is divided into two parts: the first part is to develop a small WinCC client application on the client machine and use the OPC interface integrated in WinCC to transmit data between the server and the client machine; the second part is to develop an OPC client application using VB6.0 to enable the program to communicate with WinCC on the client machine.
Advantages: It uses the OPC interface integrated within WinCC for data transmission between the server and the client, which has good stability and more complete fault diagnosis and handling, completely avoiding system crashes.
(4) Scheme selection: In view of the advantages and disadvantages of the above schemes, the third scheme is selected. As shown in Figure 3.
Figure 3 Schematic diagram of Scheme 3
IV. Functions Performed by the Control System
1. Main functions of the system
This system is primarily used to collect and statistically calculate four parameters—steam, compressed air, water, and electricity—from various production workshops, providing data for production planning. Specific functions are as follows:
(1) Real-time display: This system includes five working condition diagrams that display production parameters in real time, including the overall system working condition diagram, the yarn making workshop working condition diagram, the winding and packaging workshop working condition diagram, the energy and power workshop working condition diagram, and the non-production department working condition diagram.
(2) Status curve: Displays the status curve of the data collected in each workshop, including the instantaneous change trend of the data collected in the total amount, the yarn making workshop, the winding and packaging workshop, the energy and power and non-production departments.
(3) Statistical calculation: Organize, statistically analyze, and generate an 8-hour database and a daily database from the data in the current half-hour database of each department to be assessed.
(4) Statistical reports: Display the data from each department in the required reports.
(5) Parameter settings: Set the parameters used in this system, including: shift parameters, shift table, password settings and curve parameter settings.
2. Technical challenges in the project
Users need to record and process changes in over 70 quantities from the boiler room, air compressor station, sheet metal workshop, and main power distribution room, requiring various complex report outputs: daily, ten-day, monthly, quarterly, and annual reports. Furthermore, the report formats differ, making implementation in WinCC quite complex. Therefore, VB's flexible and convenient report creation capabilities were considered. In the chosen solution, WinCC Client plays a unique role; it acts as the client for WinCC Server, but as the server for the energy management software.
V. Conclusion
This system has been put into use and operates reliably and stably, improving the reliability, accuracy, and calculation precision of data, and reducing losses caused by human error and inaccuracies. It has also significantly saved manpower, reduced the computational burden on operators, and achieved good social and economic benefits.
