The hottest power quality supervision of electrifi

Design of power quality monitoring system for electrified railway based on LabVIEW

Introduction

from the history and trend of railway development in China, the proportion of electrified railway in the road will be larger and larger, and the impact on public electricity 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 type of 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. Because the measurement index of this instrument is single, it can not be continuously monitored, and the measurement labor intensity is high, it can not well 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 institutions have carried out the research of power quality remote monitoring system. Using computer remote monitoring, it can continuously monitor multiple points and assist in management, so it can overcome the defects of traditional manual monitoring methods. In this paper, the virtual instrument technology should be verified and calibrated is still in the research stage. It also has the above advantages and is convenient to implement in the power quality monitoring system

1 overall structure of the system

the electrified railway power quality parameter monitoring system based on virtual instrument must also have the three functional modules of the traditional monitoring system, namely the 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 traditional acquisition hardware. The difference is that the data analysis and processing module is completely realized by computer software. This part of functions are not limited by hardware, and modules can be added and modified at any time according to the needs of users. This advantage is unmatched by traditional instruments. The power quality parameter monitoring system studied in this paper, The software part 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 rest of the 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 this system is composed 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 the effective value of voltage and current, voltage deviation, electric frequency, frequency deviation, three-phase imbalance, harmonic content and flicker. Therefore, this design adopts the modular method, each function 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 you need to add system functions, you only need to add corresponding software function modules

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, that is, volt ampere measurement module, and its system functions are shown in Figure 2

the whole system of power quality monitoring can be divided into five modules: acquisition and real-time display, volt ampere measurement, power measurement, flicker measurement and harmonic measurement, which can be displayed on five pages in the front panel of the main program interface. At the same time, it can also be wiped with a general clean gauze and called different small function modules

3 power parameter measurement procedure and test results

for electrified railway, the power quality evaluation indicators of Pingmei Guoneng 10gwh high specific energy lithium ion battery project with a total investment of 5billion yuan mainly include power factor, three-phase voltage imbalance, each harmonic voltage and harmonic current, total harmonic distortion rate of voltage, voltage fluctuation and flicker, etc. The power parameters monitored by this system include current, voltage, frequency, harmonic, power factor, power (right power, reactive power, apparent power and total power), three-phase voltage unbalance, three-phase current unbalance and flicker, etc

due to spectral leakage, in order to reduce leakage error and avoid signal aliasing during harmonic analysis, the signal should be windowed first, and then the harmonic analysis should be completed through FFT transformation

the power quality parameter monitoring system of electrified railway based on virtual instrument must also have the wonderful place of the traditional monitoring system pressure experimental machine. Here are the three functional modules of the system, namely, data acquisition module, data analysis and processing module and result display module. 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

the harmonic measurement module generally needs to measure the frequency, amplitude and thd of each harmonic. There are many methods of harmonic analysis. The fast Fourier transform (FFT) analysis method is relatively mature in theory and implementation. LabVIEW provides a harmonic analysis software package for direct fast spectrum analysis

according to Article 3 of Appendix D supplement in gb/t: for harmonic sources with rapid load change (such as steel-making electric arc furnace, electric locomotive, etc.), the time interval of measurement is not more than 2 min, and the number of harmonic measurements is generally not less than 30 times. According to iec:1991, in Section 7 of Part IV of electromagnetic compatibility (EMC), the harmonic measurement range takes the fundamental wave and the 2nd to 40th harmonics. In this system, the total harmonic number is taken as 40 times

when harmonic analysis is required for the collected data, the index array can be used to take the data of each line from the data file "acquisition database, dat" and load it on the input signal pin of the function function "Hamming" in turn, Then set the harmonic number through harmonics (the harmonic number can be set to 40 times 1, so that the amplitude and frequency of each harmonic will be expressed in the form of an array. Since the amplitude and frequency of the harmonic contain the fundamental frequency component, you can use "delete from" Remove the fundamental signal, and then visually display the amplitude of each harmonic except the fundamental wave through the harmonic amplitude diagram

4 conclusion

from the simulation results, the system runs well and has stable performance. The calculation results and design ideas are consistent with the actual situation, and can meet the requirements of power quality parameter monitoring. (end)