1. Introduction
In recent years, with the continuous increase in nonlinear loads such as electric motors and transformers, a large amount of reactive power needs to be supplied to these devices during operation; otherwise, the grid voltage will drop and the power quality will deteriorate. At the same time, the unreasonable distribution of reactive power will also increase line losses and reduce the economic efficiency of power system operation. Therefore, reactive power compensation is needed to improve system imbalance and increase the load power factor.
Because many high-voltage static var generators operate in harsh environments, they often require unattended operation and high reliability. At the same time, it is also necessary to ensure safe and convenient real-time monitoring and control of the power grid operation. Therefore, many sites use host computer background monitoring devices to monitor the operation status.
LabVIEW is a fully functional virtual instrument software development environment, but it is also a powerful programming language. Because LabVIEW uses a flowchart-based graphical programming approach, it is also known as the G language (graphical language). Its key features include program debugging tools such as breakpoint settings, single-step debugging, and data probes, making it comparable to any other high-level language in terms of functionality and application flexibility. Furthermore, it comes with a large number of built-in function libraries, including those for data acquisition, GPIB, serial port control, data analysis, data display and data storage, as well as function icons. Users can directly call these functions, avoiding the tedious process of writing their own programs. Moreover, as an open industry standard, LabVIEW provides drivers for various interface buses and commonly used instruments, making it a universal software development platform.
2. Structure and Function of High-Voltage Static Var Generator
A high-voltage static var generator (SVG), also known as a STATCOM, works by using high-power, switchable electronic devices (such as IGBTs) to form a self-commutated bridge circuit. This circuit is connected in parallel to the power grid via reactors. By appropriately adjusting the amplitude and phase of the AC output voltage of the bridge circuit, or by directly controlling its AC current, the circuit can absorb or generate reactive current to meet requirements, thus achieving dynamic reactive power compensation. The device mainly consists of a switch cabinet, reactor cabinet, power unit cabinet, and control cabinet.
3. System Structure of the Host Computer System
The host computer monitoring system of this system consists of an SVG external communication interface, a serial port connection cable, a serial port converter, an industrial control computer (including a monitor), and monitoring software. The system structure is shown in Figure 1.
Figure 1 System structure diagram
In an SVG (Static Var Generator), the PLC primarily handles system logic checks, parameter reading and writing, and data querying. It exchanges data with the host computer via its external interface (SVG uses RS485; the PC needs to convert it to RS232 for data exchange). Data is processed, displayed, and stored using LabVIEW software. It displays real-time module information and operating status, records fault information, and allows querying of historical data. It can also perform operational status analysis and generate power quality analysis reports.
4. LabVIEW host computer implementation of the SVG monitoring system
Programs developed using LabVIEW are all called VIs (Virtual Instruments), and their default file extension is .vi. All VI development includes two parts: a front panel and a block diagram. The front panel of an SVG monitoring system includes the main interface, module information and fiber optic information query interface, fault query and event logging, parameter settings, and SVG running data. The block diagram mainly includes the configuration and connection of switch points, the storage and triggering of fault records, and the querying of event records. The front panel consists of input controls and display controls, which are the input and output ports of the VI. Users can directly operate the system and query data through this panel. The block diagram is constructed from graphical objects to form the source code as typically seen. The block diagram (similar to a flowchart) corresponds to lines of text in a text-based programming language; in fact, the block diagram is executable code.
4.1 System Monitoring Front Panel
(1) Main interface:
Figure 2 shows the main interface of the system, including system voltage, system current, reactive power, and module bus voltage. This interface allows users to start and stop the SVG (Static Var Generator) and view its primary system status. The "Standby - Charging - Ready - Running - Discharging" sequence displays the current SVG operation steps in real time. Users can use the data displayed on this interface to determine the operating status of the power grid, system, and modules. The operation buttons at the top of the front panel allow users to access the corresponding sub-interfaces.
Figure 2 Main Interface
(2) Module information and fiber optic information query interface
Figure (3) shows the module information and fiber optic information query interface, which mainly displays the module information and fiber optic communication information of the system during operation. Bits 0-7 of the system data bits correspond to the following status information: module normal, module bypass, input phase loss, module undervoltage, module overheating, drive failure, module overvoltage, and communication failure. The fiber optic communication status display corresponds one-to-one with its actual position. If module 1 of phase A has a communication failure, the corresponding indicator light will turn red to display the fault.
Figure 3 Module information and fiber optic information query cross-section
(3) Fault query and event logging interface
Figure (4) shows the system fault information in real time through the fault query and event log interface. The fault log is used to query and display the system operation and fault information history.
Figure 4 Fault Query and Event Log Interface
(4) Parameter setting and SVG running data interface
Figure (5) Parameter setting and SVG operation data interface is mainly used to set and query the parameter values of SVG, and at the same time, it displays the data such as PCC voltage, system voltage, system current, device reactive power, and ambient temperature in real time.
Figure 5 Parameter settings and SVG running data interface
4.2 System Monitoring Communication Configuration
OPC was proposed to standardize the software interfaces between devices and applications from different vendors, simplifying data exchange. While NI LabVIEW software can communicate with other systems in many ways, using NIOPC Server to communicate with SVG will significantly shorten the programming cycle and improve system stability and security.
(1) Configure NIOPCServer: Select the communication driver, set communication parameters, add devices, add variables, etc. (see Figure 6). After completing the above configuration, you can start the OPC Quick Client. If the configuration is successful, you can read the data in the system in real time in the OPC Client window (see Figure 7).
Figure 6 NIOPCServer Configuration
Figure 7 NI Quick Client
(2) Connect LabVIEW to the OPC tag by creating an I/O server.
(3) Establish shared variables for I/O server connection to OPC tag
(4) Using OPC tag data
4.3 System Monitoring Program Flowchart
After completing the system communication configuration, you only need to match the variables in the block diagram with the controls on the front panel to display the data from the SVG system in real time on the front panel.
Event logging and querying in the system can be easily accomplished by using the DatabaseConnectivity toolkit in NI LabVIEW and its encapsulated VIs to save and query historical events.
Figure 8. Preservation of Historical Events
Figure 9 Historical Events Query
5. Conclusion
This LabVIEW-based monitoring system for SVG devices, combined with NI OPC Server and the Database Connectivity Toolkit (DCT) provided by NI, offers ease of program development, high flexibility, and scalability. The stable operation of this monitoring system in real-world scenarios also demonstrates its high level of security and reliability. Furthermore, it facilitates the maintenance and operation of SVG devices for engineers.
