Design Of Power Quality Monitoring System Based On The Visual Instrument

With the power loads being more and more complex,the disturbance of power quality harms power system and the electricity users more seriously.The harm of steady-state disturbance is widespread such as harmonics,flicker,etc.Therefore sags,swells and other transient disturbances harm power quality badly,and the comprehensive online monitoring of power quality detection is becoming a necessary means in running a high-quality power network,and the realization foundation of online monitoring which is based on reasonable and efficient methods of power quality analysis.This research work focuses on the improvement.However,the traditional power quality detection device takes hardware as the core and has single function.Furthermore,it is difficult to upgrade and has high development and maintenance costs.Therefore,power quality monitoring system based on virtual instruments is designed.Firstly,the virtual instrument architecture is used in this thesis.In terms of hardware,the thesis uses the modular design concept and ideas to complete the overall design and analysis of the hardware.At the same time,the PCI-6220 data acquisition card from National Instruments is used to complete the real-time acquisition of the actual three-phase voltage signals.Then,according to the module division and composition of the power quality detection system,the design and analysis of the signal conditioning module,the functions and settings of the signal acquisition module,and the design and analysis of the second-order high-pass filtering device are completed.Besides,the functions of de-drying and amplification of the original electric signal,the function of the signal acquisition module and the storage configuration,and harmonic suppression are realized.In terms of software,under the virtual instrument development framework,the Lab VIEW development environment is used as the platform and the data flow programming mode is used to complete the design and analysis of the overall system software solution.On this basis,detailed design of each functional module was completed,including the design of the electrical signal measurement module,the design of the power quality analysis module,and the design of the remote monitoring module.The functions of data acquisition and basic parameter measurement of the original electrical signal,signal frequency deviation,three-phase imbalance measurement,voltage fluctuation calculation,voltage flicker measurement and harmonic measurement function,long-distance transmission and playback function of power quality analysis results are realized.In order to effectively analyze the amounts of harmonics of the signal,this paper uses a method of combining the Fourier transform and Harming window,which can effectively reduce the spectrum leakage caused by spectral aliasing and improve the accuracy of harmonic calculation and analysis.In addition,in order to enhance the applicability of the system,this article also uses Browser/Server mode to complete the design of remote data monitoring and data storage playback functions.Finally,this thesis has completed the testing and verification of various functions and performance indicators of the power quality monitoring system.Take the actual 220 V commercial three-phase power as the test object,and compare and analyze the test results with the MI2392 Power Q Plus handheld three-phase power quality analyzer.The test results show that the power quality detection system designed has high measurement accuracy.The maximum relative error of the basic signal measurement is 2.03% and the maximum measurement error of the frequency deviation is 0.133 Hz.The maximum relative error of the three-phase electrical imbalance measurement is 0.20%,and the maximum error of the harmonic distortion rate measurement is 0.38%.At the same time,this system can also comprehensively and comprehensively reflect the power quality problems in the power grid,and provide scientific and accurate data support for improving power quality.