introduction
In recent years, with the expansion of my country's industrial scale and the continuous development of science and technology, more and more enterprises and users have adopted advanced equipment with good performance and high efficiency, but which is sensitive to changes in power supply characteristics. Many new electrical devices inject various electromagnetic interferences into the power system during operation, and the harm and impact on the safe operation of the power system and the normal operation of user equipment are constantly increasing, making power quality pollution of the power system increasingly serious. Power quality is directly related to the overall efficiency of the national economy. Therefore, in-depth research on power quality has very important practical significance.
Power quality issues not only affect the power grid but also people's lives and production, directly impacting national economic benefits. Power quality monitoring is fundamental to power quality control. Therefore, in-depth research on power quality is of paramount importance. Power dispatching departments face increasingly urgent requirements for real-time monitoring and analysis of power quality.
Currently, the power quality detection methods used in my country have many problems: poor real-time performance, limited monitoring indicators, large workload, and low efficiency. This paper proposes a power quality monitoring and analysis system based on virtual instrument (VI) technology and network communication technology. This system overcomes the shortcomings of conventional testing systems, such as limited functionality and complex upgrades. It enriches the system's functions, improves measurement accuracy, accelerates data acquisition, and enhances automation. This enables relevant departments of the power system to monitor power quality in real time and propose optimal solutions for grid management.
1. Introduction to LabVIEW
Virtual instrument technology originated in the United States in the 1980s with a virtual instrument development platform software developed by NI Corporation. Its key feature is that it primarily implements the functions of traditional instruments through software. Based on the concept of graphical programming, unlike traditional instruments, LabVIEW allows for easy modification of instrument functions and generally avoids component damage or aging issues. The software development platform for virtual instruments in this system uses LabVIEW, a laboratory virtual instrument development platform based on the graphical programming language. It mainly consists of a front panel, block diagram programs, and numerous nodes, making it easy to design user-friendly interactive interfaces. When combined with a dedicated DAQ card, LabVIEW facilitates data acquisition, analysis, storage, and display. Because the software provides numerous data analysis and processing nodes, as well as commonly used algorithm nodes, and can interface with MATLAB and C languages, it significantly shortens instrument development time. Furthermore, with the increasing reliance of modern industry on networks, LabVIEW's Communication sub-template contains numerous nodes implementing network functions, making it easy to build local area networks, thus holding an important position in the measurement and control fields.
2. Main Calculation Methods for Power Quality Indicators
Because power systems contain a large number of diverse loads, especially nonlinear loads such as inductive and capacitive loads, the originally qualified electrical energy can be "polluted," causing a decline in power grid quality. To address this, my country's State Administration for Technical Supervision has issued five national standards for evaluating the quality of electrical energy: voltage deviation, system frequency, three-phase imbalance, total harmonic distortion (THD), and voltage fluctuation and flicker.
(1) Effective values of voltage and current
Based on the definitions of the effective value and average power of a periodic continuous function, calculations are performed in the continuous time domain as follows:
This paper designs an online power quality monitoring and analysis system, which fully utilizes the characteristics of virtual instrument technology in the field of measurement and control, as well as its user-friendly human-computer interface. Hardware-wise, it employs voltage sensors, a DAQ data acquisition board, and a PC for data acquisition. Software-wise, it utilizes the LabVIEW virtual instrument software to create an interface and implement functional modules for data acquisition, calculation, reporting, and alarms, thus realizing the monitoring and analysis of power quality indicators. The system developed using virtual instruments can shorten the development cycle of the power quality monitoring system, reduce system costs, and improve system performance. Testing has shown that the system operates with high stability and has significant practical value.
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