Design And Realization Of Power Quality Monitoring Device For Low Voltage Distribution Network

In the recent past,the usage of electrical equipment for the generation,transmission,and distribution of electrical power has been rapidly introducing imbalances,voltage distortions,and harmonics in the power systems.Such types of disturbances have increased the necessity of better power quality in the area of power line conditioning.Simultaneously,power quality has a direct influence on overall efficiency of national economy.With powerful computing capabilities of DSP and powerful management features of ARM,this system features fully integrated control of all functions like multi-parameter calculation,display,as well as telecommunication of data.The scheme has the advantages of simple structure,strong portability and low power consumption,and it is convenient for later development.This thesis focuses on the following:(1)Relevant knowledge of power quality,standards of power quality,monitoring terminal's research status and development tendency at home and aboard,the development of testing techniques are introduced,finally the the necessity of better power quality in the area of power line conditioning is pointed out.(2)The definition,damange and computational type of three phase unbalance are discussed.Three-phase imbalance is calculated by using the symmetric component method.At the same time,the power system model is built with MATLAB,the interference factors are simulated and the results are compared.According to,there may be a qualitative understanding of the various problems which may lead to three-phase imbalance.(3)Firstly,this chapter discusses the general application of traditional DFT in power system.However,the existence of spectrum leakage and picket-fence will influent the accuracy of measurement.The extended DFT algorithm based on Fourier integral transformation to optimize the transformation base in the extended frequency range is introduced.The principle of the algorithm,the realization process and the application in the harmonic monitoring are presented.(4)A modern power quality monitor based on double CPU structure of TMS320F2812 and LPC1758 is designed.This method can exert the features of the two different processors and ensure a high performance of the device.DSP subsystem mainly includes signal acquisition circuit,AD conversion circuit,TMS320F2812 minimum system.We use ARM as a data management system including clock synchronization module,SIM800 wireless communication,LCD driver module.The working principle of the various modules and the hardware circuit design are introduced in detail.(5)According to the hardware structure,C/C++ language is used to design and develop the software system.In accordance with the modular programming idea,the software design flow and software development platform of DSP and ARM subsystem are described in detail.On one hand,DSP initialization,AD conversion driver,data analysis and calculation,and data transmission program are mainly included.On the other hand,clock synchronization program,GPRS send SMS and connect remote server program,HT1626 drive LCD screen program are also involved.(6)In order to ensure the stability of the device,the device sub-module debugging,each module can run independently to complete the specified function and then the overall debugging.For the purpose of improving accuracy,standard source is used as input signal by setting different values.Besides,the monitoring device of power quality is installed in the power grid,the results can be transferred wirelessly through the GPRS to the server,It becomes easily to monitor the power quality situation of low voltage distribution at any time.