From the history and trend of China's railway development, the proportion of electrified railway in the road network will be larger and larger, and the impact on the public power grid will be more and more serious. Therefore, the establishment and implementation of power quality monitoring and analysis is an important technical means to improve power quality. Developing a new power quality parameter monitoring system to effectively monitor power quality parameters is of great significance to ensure the safety, economy and reliability of power system operation.
At present, portable power quality monitor is still used for power quality measurement in most parts of China. Due to the single measurement index, continuous monitoring and high measurement labor intensity, the instrument can not meet the needs of power quality management. With the rapid development of digital measurement technology, computer technology and network communication technology, some domestic scientific research institutes have carried out the research of power quality remote monitoring system. Computer remote on-line monitoring can continuously monitor multiple points and assist management, so it can overcome the defects of traditional manual monitoring methods. In this paper, the application of virtual instrument technology to power quality monitoring system also has the above advantages, and it is more convenient to realize.
1. Overall system structure
The electrified railway power quality parameter monitoring system based on virtual instrument must also have three functional modules of the traditional monitoring system, namely data acquisition module '); " onmouseout="hide_ bk_ about(); " href=" http://www.ck365.cn " target="_ blank "> data acquisition module, data analysis and processing module and result display module. The data acquisition module is still completed by the traditional acquisition hardware. The difference is that the data analysis and processing module is completely realized by the computer software. This part of the function is not limited by the hardware, and the module can be added and modified at any time according to the needs of users. This advantage is unmatched by the traditional instrument. The software part of the power quality parameter monitoring system studied in this paper is the core. As long as the hardware part converts the voltage and current signals of the monitoring points into digital signals with minimum distortion through the signal conditioner and data acquisition card, the other tasks (such as windowing, filtering, data processing and statistical analysis, data remote transmission, display and printing, etc.) will be completely handed over to the software for processing.
The hardware of the system consists of sensor, signal conditioning module, data acquisition card and computer. Its hardware structure is shown in Figure 1.
The software development environment of this system is LabVIEW, which is a virtual instrument software development tool based on G language launched by American NI company. For a virtual instrument system, software is the key and soul, and hardware is only used to solve the input and output of signals.
2. Overall design idea of the system
The functions of the electrified railway power quality parameter monitoring system based on virtual instrument technology include the simultaneous measurement of different parameters such as effective value of voltage and current, voltage deviation, grid frequency, frequency deviation, three-phase imbalance, harmonic content and flicker. Therefore, this design adopts the modular method, each functional module completes the corresponding function, and finally completes the system design through integration. The biggest advantage of adopting module structure is high efficiency. Because modules can share data and call each other, they can achieve very high overall efficiency by flexibly organizing each module. If you need to upgrade a function of the module, you only need to rewrite the corresponding module without changing the whole software structure. When system functions need to be added, only corresponding software function modules need to be added.
The modules of power quality measurement mainly include data acquisition module, RMS measurement module, voltage deviation measurement module, frequency measurement module, frequency deviation measurement module, three-phase imbalance measurement module, power measurement module, harmonic measurement module and flicker measurement module. The RMS measurement module, voltage deviation measurement module, frequency measurement, frequency deviation measurement and three-phase imbalance measurement module can be integrated into one module, i.e. volt ampere measurement module. Its system function is shown in Figure 2.