[Abstract] This ventilation and dust removal system is a temperature-controlled dust removal device配套的温控尘除装置 for a 500km/h high-speed pantograph-catenary relationship test bench in a high-speed pantograph-catenary relationship laboratory. Its control effect directly affects the normal operation of the high-speed pantograph-catenary relationship test bench. This paper details the automatic control scheme of the dust removal system based on actual control requirements.
Keywords: High-speed pantograph-catenary ventilation and dust removal automatic control PLC
1. System Overview
The entire dust removal system uses a Siemens S7-300 PLC as its control core, employs advanced Schneider frequency converters to control the fans, and utilizes the widely used PROFIBUS bus for communication with each frequency converter. The monitoring computer adopts an Ethernet architecture, providing an interface for the construction of an internal information network. Through an advanced, high-speed, and stable network platform, and with its excellent and comprehensive design, the entire system provides a technologically advanced, safe, reliable, easy-to-operate, easy-to-maintain, and highly expandable control system for the high-speed pantograph-catenary relationship test bench.
1.1 System Design Objectives
Based on the characteristics and requirements of this project, the design goal of this system is to make the system advanced, secure, reliable, scalable, operable, maintainable, and economical.
Advanced
The system adopts Siemens' advanced PLC and Schneider Electric's latest ATV71 series frequency converter, and uses PROFIBUS fieldbus and Ethernet network communication. It features a user-friendly operating interface that provides a clear and intuitive reflection of the equipment status, allowing operators to understand the operating status of the controlled equipment. In addition, the system has comprehensive alarm, prompt, and diagnostic functions.
Safety and reliability
The safe, reliable, and stable operation of the control system is the most basic requirement of an electrical control system. To ensure the system's reliability, the following measures are taken: First, advanced and mature technologies are adopted, such as PLC control, fieldbus, and network technology; second, high-quality domestic and international products are used, such as those from Siemens, Schneider Electric, and Jinzhong Muller; third, the monitoring system employs multi-level password access control to ensure secure system operation; and fourth, the control system's control methods are both independent and centralized. When the host computer malfunctions, manual operation can be performed on-site to ensure the normal operation of all equipment.
Scalability
The system should have good scalability, allowing for expansion as needed in the future without altering the overall system structure. This design incorporates certain scalability features.
Operability
The system can be centrally controlled or operated, and can also be operated in a distributed, stand-alone manner, facilitating installation, debugging, operation, and maintenance. The system is easy to operate, with an intuitive and user-friendly interface.
Maintainability
During project design and construction, construction was carried out in accordance with specifications, with clear signage, labeling, and numbering; the system has real-time fault diagnosis function, which can accurately and promptly display and locate faults; in equipment selection, universal equipment was selected as much as possible, and the programming configuration structure was clear, easy to read and check, and easy to maintain.
Economic practicality
While ensuring advanced technology, reliable quality, and complete functionality, the design aims to achieve the best performance-price ratio through reasonable configuration. Future technological developments should also be considered in the design, allowing for future upgrades and replacements of the system's hardware and software, facilitating the selection of spare parts, and enabling convenient expansion.
1.2 Design Reference Standards
The technical standards and specifications, product standards and specifications, and engineering standards and specifications involved in the implementation of this system include:
GA/T75-94 Security Engineering Procedures and Requirements
GB50093-2002 Standard for Construction and Acceptance of Automation Instrumentation Engineering
GBJ63-90 Design Code for Electrical Measuring Instruments in Electrical Installations
GB7251.3-1997 "Design Code for Low-Voltage Switchgear and Controlgear Assemblies"
GB50169-2006 Code for Construction and Acceptance of Grounding Devices in Electrical Installations
GB2054-96 Code for Construction and Acceptance of Low-Voltage Electrical Equipment in Electrical Installations
GB/T50328-2001 Standard for Filing and Organizing Construction Project Documents
2 System Overall Design
Figure 1 System Overall Structure Diagram
The entire ventilation and dust removal system consists of four layers: the equipment layer, the PLC control layer, the monitoring layer, and the information management layer.
The main controllable objects at the equipment level include: ventilation fans, outdoor dust removal equipment, air conditioning units, and ventilation and dust removal ducts.
The main controller uses the Siemens S7300 series CPU315-2PN/DP, which comes with one DP port and one Ethernet port. The DP port communicates with the frequency converter, while the Ethernet port is mainly reserved for commissioning.
The monitoring computer is equipped with a CP5611 board and communicates with the field PLC via PROFIBUS. Remote hosts can access and control the monitoring computer via a web-based interface.
The hot backup computer is synchronized with the monitoring computer. When the monitoring computer stops running due to an unexpected situation, the hot backup computer can be put into use immediately to avoid affecting the system control effect.
The server is mainly responsible for storing the parameters required for the experiment. Important data is stored on the monitoring computer and simultaneously uploaded to the server. The data on the monitoring computer has a limited lifespan, while the data on the server can be stored indefinitely for historical query and retrieval.
2.1 System Control Method
There are two control methods: "local/remote control" and "manual/automatic control".
The PLC cabinet is equipped with a "local/remote control" switch. When the switch is set to "local", the PLC controls all devices within the system; when the switch is set to "remote control", the monitoring computer can directly control the local devices within the system.
Each individual device is equipped with a "manual/automatic" switch on the electrical control cabinet. When the switch is set to "automatic," the PLC program automatically controls the equipment; when the switch is set to "manual," the equipment is manually controlled by the operator. This ensures that the power equipment can continue to operate normally even if the PLC malfunctions.
For equipment with a power rating of 7.5KW or higher, soft start or frequency converter control should be used. For equipment with a power rating of less than 7.5KW, direct start should be used. For equipment requiring soft start, direct control via I/O contacts should be used; for equipment controlled by frequency converters, network control should be used.
2.2 Fan frequency conversion control
The air conditioning units, ventilation fans, and dust removal fans are controlled by frequency converters. The frequency converters selected are from the Schneider ATV71 series, equipped with PROFIBUS-DP interface cards. These cards connect to the S7315-2PN/DP control system, allowing real-time monitoring of fan start/stop control, operating status, and data such as voltage, current, and power. Since the fans are controlled by frequency converters, AC contactors are no longer used, and corresponding circuit breakers are provided. A changeover switch is installed at the fan site for easy manual operation and maintenance.
2.3 Dust Removal System
The dust collection unit's fan and ash discharge valve work together to complete the system's dust removal. Whenever the main dust collector fan motor starts or stops, the corresponding ash discharge motor also starts simultaneously, with a slight delay in its operation. The ash discharge valve operates in both directions; a changeover switch is installed on-site to isolate the main power circuit, facilitating safe equipment maintenance.
2.4 Functions implemented by the monitoring computer
2.4.1 Graphical Monitoring System
●Dust removal system process diagram
The experimental procedure section displays the real-time dynamic operating status of the dust collector fan, ash discharge valve, ventilation fan, and air conditioning unit. It can monitor all parameters during equipment operation, as well as the status of motors and valves, and provides audible and visual alarms. Operators can operate the system using a mouse. The color-coded display of operating parameters clearly indicates their status (normal, alarm). The procedure section allows direct access to the operating screens of specific control loops and the equipment operation program control screen.
● Summary display of running data
The equipment operation data summary table lists the real-time status of various parameters of the equipment operation, providing a comprehensive overview of the operation of each control loop and data monitoring loop. It displays the measured values, setpoints, and outputs of each control loop. The changing background color of specific parameters indicates the operating status (normal, alarm) of each equipment parameter.
●Control screen
The control screen displays the specific status of each control element. In this section, operators can see the operating status of each control loop, the curve running time, and the upper and lower alarm limits. Engineers can also use this section to modify the control parameters, range, alarm thresholds, process curves, etc., of the control loops.
●Data trend chart screen
Trend data reflects the operating parameters of dust collectors and other equipment in the form of curves. Multiple curves can be displayed simultaneously on the same screen, making it easy to find relevant quantities. It also has a local area zoom-in/zoom-out function.
2.4.2. Alarm and Accident Handling
Timely alarm: Conduct inspections on the status of relevant components and equipment such as dust removal fans, ventilation fans, and air conditioning units, and compare them with preset values in a timely manner. Once the value approaches the preset value, an audible and visual alarm signal will be issued immediately to ensure the safe operation of the system.
Alarm and accident reporting records alarm status and important events during equipment operation, enabling better investigation and analysis of accident causes in the production process. All reports can be printed in real time via a printer.
The alarm report form includes: serial number, alarm item, normal value, alarm value, alarm time, confirmation time, and clearance time;
The accident report form includes: serial number, accident details, time of occurrence, time of confirmation, and time of recovery;
2.4.3. System Management Functions
● Diagnostic functions
When the system is running, it can automatically diagnose hardware faults. When the computer detects an abnormality in a certain circuit of the system and it cannot be restored to normal within a certain period of time, the system automatically issues an alarm signal and displays the location and type of the abnormality. This facilitates operators in accurately identifying the location of the fault and promptly handling and eliminating it, preventing the escalation of the accident.
●Parameter settings and system management
Engineers can configure and modify specific system parameters through system functions to better maintain the system's normal operation. This section allows for password settings and tiered operation based on user requirements to prevent human error and potential losses.
●Production Reports
It automatically generates various daily, monthly, and annual reports, and offers flexible and convenient printing options.
●Equipment management function
The system can collect statistics on fault information and equipment runtime. It accumulates the running time of major motors, such as dust collector fans and ventilation fans, facilitating preventative maintenance for equipment management.
2.4.4. Record Storage
It can print reports, compare curves, and print curves based on real-time operating data of dust collectors, ventilation fans, etc.; it can also save historical data of operating conditions of dust collectors, ventilation fans, etc., and selectively print historical data and curves.
2.5 The ventilation and dust removal system communicates with the test control system and forms an interlock.
This ventilation and dust removal system provides external interfaces including Ethernet and OPC, both of which facilitate communication with the test control system. If the test control system is developed using visual programming software, the configuration software can be added as a control component within the visual software, and its properties, events, and methods can be called to achieve communication with the ventilation and dust removal monitoring system. If the test control system is developed using configuration software, OPC communication can be used to achieve data interaction between the two.
In the ventilation and dust removal system, a system normal flag is set in the main PLC program, which serves as a self-test result signal. The parameters for setting the flag include the real-time temperature value in the test pit, the communication status between the air conditioning unit controller and the main PLC, the operating status of each motor, the temperature of the contact wire and pantograph, and the air pressure in the pit. These parameters are processed by the PLC program to obtain a system normal operation flag. The flag signal is periodically transmitted to the test control system, which uses this signal as the basis for starting and stopping.
The monitoring software configures alarm tags, including the pit temperature, pit air pressure, pit dust concentration, outlet dust concentration, contact wire temperature, pantograph temperature, wind speed in the contact wire and pantograph contactor friction zone, operating status of each motor, and air conditioning unit operating status. It provides both audible alarms and alarm bar notifications. Alarm notifications include the abnormal signal name and type, abnormal signal location, current value, and signal description. After a successful self-test and normal system startup, if an abnormality occurs in the ventilation and dust removal system, its monitoring system transmits the abnormal signal alarm bar display to the test control system. The test system then stops the experiment according to the set steps based on the fault signal. A list of safety signals is shown in Table 1.
3. System Hardware Configuration
3.1 Server
Because the server plays a critical role in the system, a highly reliable model must be selected to ensure continuous 24/7 operation (UPS should be provided), while also possessing high performance to meet its real-time requirements. A Dell server will be selected as the database server.
3.2 Monitoring Computer
The monitoring unit is used by dispatchers to issue monitoring commands, display the operating status of the ventilation and dust removal system, and perform functions such as monitoring data retrieval, statistical analysis, audible and visual alarms, and sending control commands. A DELL industrial computer was selected.
3.3 Network Equipment Configuration
Cisco switch with 8 100M Ethernet ports
Ethernet NIC 10/100Base-TX
3.4 UPS Power Supply
To increase system reliability and accommodate network expansion, this system is equipped with a UPS power supply that supports a 2-hour delay. This allows staff to quickly shut down the system in the event of a sudden power outage.
3.5 PLC Section
The PLC is the core of this control system. All input and output quantities during the control process must be processed by the PLC, and the actions of all relays are completed by the output control of the PLC.
This design selects the Siemens S7-300 PLC from Germany. Siemens is a world-renowned company with over 150 years of history, and PLCs are one of its key products. In various PLC application fields worldwide, Siemens PLCs rank among the top in terms of market share, quality, and brand recognition. Therefore, choosing a Siemens PLC is a strong guarantee for the reliable operation of the project.
The S7-300 is a modular, medium-sized PLC system designed to meet the needs of applications with medium performance requirements. Its modular design, fanless structure, ease of distribution, and user-friendliness make the S7-300 a convenient and economical solution for various medium-scale control tasks.
The S7-300 programmable controller features a modular design. Various individual modules can be extensively combined.
The S7-300 system mainly consists of: a central processing unit (CPU), a signal module (SM), a communication processor (CP), a function module (FM), a load power supply module (PS), an interface module (IM), and a SIMATIC M7 automation computer. The SIMATIC M7-300 is suitable for general applications, with high electromagnetic compatibility and strong vibration resistance, giving it the highest adaptability to industrial environments. Its temperature range is from 0°C to 60°C, and under special conditions, it can reach -25°C to 60°C, exhibiting stronger resistance to vibration and contamination.
3.6 List of Main Equipment for Ventilation and Dust Removal System
3.7 List of Main Equipment for Refrigeration Units
4 System Software Design
4.1 Operating System
Products conforming to IEEE and ANSI standards should be selected. The selected operating system is as follows:
The server operating system uses Microsoft Windows 2003 Server, which has the following characteristics:
Able to be closely connected to the Internet
When running busy web servers, terminal services, e-commerce, and VPN solutions, incoming communication is distributed across numerous server clusters using network load balancing; performance is enhanced by leveraging state-of-the-art server hardware, achieving up to 8-way SMP and up to 8GB of RAM; and the full potential of the Internet is fully realized through reliable integration of Internet services, high-performance websites, and applications.
Improve reliability
Two-node, highly reliable cluster services ensure that critical applications function normally and on demand; network load balancing redistributes web workloads on failed servers; an improved core architecture provides design enhancements to improve system uptime; and segmented upgrade support reduces planned downtime required for maintenance or upgrades, including upgrades from Windows NT 4.0 clusters.
More user-friendly and manageable
Clusters can be remotely managed from the Cluster Manager and NLB script command interface on any networked Windows 2000 system; Cluster Services clusters can be accessed and managed as ActiveDirectory objects.
The best choice for new equipment
It utilizes the latest server hardware, including up to 8-way SMP using Intel and Profusion chips and architectures, and 8GB of RAM using Intel's Physical Address Extension (PAE).
The monitoring and management machines use Microsoft Windows 2000 Professional as their operating system.
4.2 Configuration software WINCC
WinCC is a world-leading industrial control software jointly developed by Siemens and Microsoft, utilizing cutting-edge automation technologies. WinCC stands for Windows Control Center. It is a powerful and fully open monitoring system suitable for both small-scale, simple process monitoring applications and complex applications. In any situation, WinCC can generate a beautiful and user-friendly human-machine interface, enabling operators to clearly manage and optimize production processes.
WINCC possesses almost all the functions of advanced human-computer interface products, and its integrated functions include:
The graphics system is used to freely configure the screen and operate entirely through graphical objects, which have dynamic attributes and can be configured online.
Alarm information system – records, stores, and displays events, allows for free selection of information categories, display methods, and reports, and is very easy to operate.
Variable archiving—receives, records, and compresses measurements for curve and chart display and further editing functions.
Reporting system --- Users can freely choose certain report formats and output user reports based on information operations and current document data according to time sequence or event triggering.
Data processing – Editing the actions of graphical objects using the C language and a C compiler.
Standard interface – Access the SYBASE database for configuration and process data via ODBC and SQL.
Application Programming Interface (API) – Allows users to write standard applications that can be used to extend the basic functionality of WinCC.
In addition, WinCC offers a variety of optional software packages. For example, the Communication Development Kit (CDK) allows users to develop communication software for connecting the data manager to any target system.
WinCC's configuration and archived data are stored in a relational database, and the data can be read using standard tools such as ODBC and SQL. Many standard applications, such as Microsoft Excel, can run in parallel with WinCC, and process data can be loaded via DDE. The operator station software allows for common OCX and ActiveX links. Furthermore, the integrated OPC (OLE for Process Control) server allows process data to be accessed by other applications (OPC clients).
4.3 Programming software STEP7
STEP7 is the standard programming tool for SIEMENS S7-300, S7-400, and M7 series PLCs. It is based on the international standard IEC-1131-3 and is similar to other PLC programming languages based on the IEC standard.
STEP7 runs on Microsoft's Windows platform and is a visual programming tool. Like other Windows applications, it is easy to use, has a user-friendly interface, and integrates seamlessly with Windows. Its basic functions include:
Hardware configuration and parameter settings
Define communication network
Control program development
Test, Start-up, Maintenance
Documents, filing
STEP7 manages user-written programs and data in blocks, allowing for the calling of one block from another, even subroutines, making structured user programs possible. This significantly increases the clarity, understandability, and maintainability of PLC program organization.
4.4 Application Software
To preserve important parameters in the experimental system for a long time, data upload application software was installed on the monitoring computer to upload data from the monitoring computer to the server. The database front-end application development tool used was Visual Studio .net, which integrates development tools such as VB and VC within its software package.
4.5 Backend Database
The database is used to store historical data on system operation parameters, alarm data, equipment operating time, and equipment status change times. Production tasks issued through the human-machine interface and their execution status by the monitoring machine are permanently recorded for future reference.
The database uses popular network-enabled database software and supports open interfaces such as ODBC, DDE, and DLL. We chose SQL Server 2000 for its high cost-performance ratio, with the following features:
Full Web support
SQL Server offers extended database program functionality based on Web standards. Rich support for XML and Internet standards allows you to easily store and retrieve data in XML format using built-in stored procedures. You can also easily insert, update, and delete data using XML updaters.
Easily access data via the web. With SQL Server, you can use HTTP to send queries to the database, perform full-text searches on documents stored in the database, and perform natural language queries via the web.
Powerful and flexible web-based analytics. SQL Server Analysis Services capabilities have been extended to the Internet. You can access and control multidimensional data through a web browser.
Short development cycle
SQL Server is the central hub for data management and analysis in Microsoft .NET Enterprise Server. SQL Server includes tools to accelerate the development process from concept to final delivery.
1. Integrated and scalable analytics services. With SQL Server, you can build end-to-end analytics solutions with integrated tools to create value from your database. Furthermore, you can automate business processes based on analytics results and flexibly retrieve custom result sets from even the most complex calculations.
2. Rapid development, debugging, and data transformation. SQL Server features interactive query tuning and debugging, rapid data movement and transformation from any data source, and the ability to define and use functions in a Transact-SQL manner. You can design and write database applications visually from any Visual Studio tool.
3. Simplified management and adjustment. With SQL Server, you can easily manage databases centrally alongside your enterprise resources. Databases can be easily moved and copied between computers or instances while remaining online.
4.6 PID Function
The proportional action is essentially a linear amplification (reduction) function. Once a sampling deviation occurs, the controller immediately generates a control action proportional to the magnitude of the deviation, causing the controlled variable to change in the direction of reducing the error. The magnitude of this action is measured by the proportional gain Kp. A large Kp results in a fast response and small steady-state error, but may lead to significant overshoot or instability. Conversely, a small Kp results in a slow response, longer settling time, and reduced control accuracy. The integral action acts as a memory, accumulating the error, which helps eliminate steady-state error. However, if the integral action is too strong, it can cause significant overshoot or oscillation, and integral saturation is frequently encountered in practice. The derivative action is mainly used to generate an earlier control action, improving dynamic characteristics, reducing settling time, and making the system easier to stabilize. Appropriate coordination of these three parameters is necessary to achieve a fast, smooth, and accurate transient response. The PID controller schematic is shown in Figure 3.
When the pit temperature in this system is controlled manually via a central control system, the temperature inside the pit must be maintained around the value set by the monitoring center. To achieve this, the system introduces a PID control strategy, as shown in Figure 4. It continuously compares the setpoint and the collected values, using the difference as the input signal. The PID algorithm then controls the actuator, i.e., the air conditioning unit, to ensure the current temperature value closely approximates the setpoint. The entire PID adjustment process achieves the requirements of speed, stability, and accuracy.
Figure 3 PID control of temperature inside the foundation pit
5 System Network
The selection of a reliable network system is crucial for this system. In this solution, the information transmission between the frequency converters and PLCs, as well as between the PLCs and the monitoring computer, utilizes a reliable and fast wired transmission network—PROFIBUS, the European industrial fieldbus network. PROFIBUS, a European standard industrial fieldbus introduced by SIEMENS, is widely used in the control field due to its high data transmission speed, high data transmission reliability, and excellent physical and electrical interface standards. Furthermore, the controllers (PLCs), frequency converters, and other hardware selected in this solution all integrate PROFIBUS interfaces, allowing for convenient and reliable connection into a fieldbus network.
5.1 Definition and Classification of PROFIBUS
PROFIBUS is an abbreviation for Process Fieldbus, an international open fieldbus standard, also known as the EN50170 European standard. Many automation manufacturers worldwide currently provide PROFIBUS interfaces for their equipment. It is widely used in manufacturing automation, process industry automation, and automation in building, transportation, power, and other fields. PROFIBUS is available in three compatible versions based on application characteristics: PROFIBUS-DP, PROFIBUS-FMS, and PROFIBUS-PA.
(1) PROFIBUS-DP: An optimized, high-speed, and inexpensive communication link designed for communication between automatic control systems and device-level distributed I/O. Using a PROFIBUS-DP module can replace expensive 24V or 0-20mA parallel signal lines. Used for high-speed data transmission in distributed control systems.
(2) PROFIBUS-FMS: It solves general communication tasks at the workshop level, provides a large number of communication services, and completes cyclic and non-cyclic communication tasks with medium transmission speed. It is used for general automation control in textile industry, building automation, electrical drive, sensors and actuators, programmable controllers, low-voltage switchgear, etc. It is a token structure, real-time multi-master network.
PROFIBUS is a fieldbus technology used for workshop-level monitoring and data communication and control at the field device level in factory automation. It enables distributed digital control and field communication networks from the field device level to the workshop level, thus providing a feasible solution for achieving comprehensive factory automation and intelligent field devices.
5.2 PROFIBUS Protocol Structure
The PROFIBUS protocol architecture is based on the ISO 7498 international standard, using the Open Systems Interconnection (OSI) model as a reference. This model has seven layers: Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, and Application Layer. Fieldbus adopts a simplified network architecture, featuring a three-layer protocol similar to the OSI model (Physical Layer, Data Link Layer, and Application Layer) or a four-layer protocol further including either a Network Layer or a Transport Layer, without using a Session Layer and a Presentation Layer. Flow control and error control are performed at the Data Link Layer, while reliable message transmission can be performed at either the Data Link Layer or the Application Layer. This fluid architecture ensures fast and efficient data transmission, and the user interface specifies the application functions that users, the system, and different devices can access.
PROFIBUS-DP uses RS485 for transmission, employing shielded twisted-pair cable with a single wire pair. Baud rates range from 9.6 Kbit/s to 19.2 Mbit/s. RS485 operation is easy, and the bus architecture allows for the addition and removal of stations; distributed deployment does not affect the operation of other stations.
6. Conclusion
As an auxiliary system for the normal operation of the high-speed pantograph-catenary interaction test rig, the ventilation and dust removal system is interlocked with the operation of the test rig. The dust removal effect directly affects the accuracy of the test data. This paper elaborates on the process of achieving automatic control of the ventilation and dust removal system from the aspects of hardware, software and control strategies, starting from the control requirements. The whole design concept meets the requirements of distributed control system for decentralized control and centralized management. Its solution has very good reference value for high-speed pantograph-catenary interaction applications.
About the author:
Kong Linghui, male engineer, major research areas: advanced computer control and intelligent systems.
