Development Of Power Quality Online Monitoring Device For High Voltage Switchgear

With the development of power electronic technology, there are more and morenon-linear load power equipment, which led to the deterioration of power quality.Therefore people pay more and more attention to power quality problem. The detection ofgrid signal has become a major focus of the work of power system studies, in order tosurpport for system analysis and control of power quality, the power quality on-linemonitoring devices appear at the historic moment.As an equipment that play the role of on-off control or protection in generation,transmission, distribution, energy conversion and consumption of the power system. Thefunction of the switch also enhanced gradually. In order to monitor the fluence of thespecial power users to the entire power grid, this paper designs a kind of power qualityon-line monitoring device based on TMS320F2812of TI company. The main research is asfollows:1.According to the current development of domestic and international power qualitymonitoring devices in home and aboard, this paper put forward the overall program of anonline power quality monitoring device used in high voltage switchgear, mainly includingdesign of hardware circuit, design of software program, design of PC communication andinterface.2.Choose the appropriate current voltage transformer circuit according to the input andoutput characteristics of the voltage and current,and recuperate the grid signal withconditioning circuit,finally feeding into the DSP for processing after AD conversion. At thesame time design the phase-locked multiplier circuit in order to keep the synchronicity ofthe sampling and inhibit spectrum leakage. In terms of software, using FFT and a series ofelectric parameter operation methods, the grid signals which have been converted to digitalsignals will be in real-time fast computing to get the value of voltage and current, powerand harmonic.3.By connecting the LCD circuit, power system parameters which be calculated by theprogramming process can be displayed by LCD. Realize the communication function withPC by using the serial port communication in RS485communication way, and displayreal-time grid parameters in PC interface writed by VB.After the test and debug, Theexperimental system can realize the rapidity of acquisition, the accuracy of the operationand real-time of display. 4.Research the advantages of the short time Fourier transform (STFT) on the analysisof grid signal with harmonics wave, as well as the Wigner-Ville distribution using incalculating grid harmonics and interharmonics in the grid. Simulation results show thatSTFT has better performance of time-frequency characteristics in the analysis of the signalwith the interharmonics, Using the energy gathered sex and the frequency edgecharacteristics, Wigner-Ville distribution can measure the amplitude of fundamental waveand the harmonic component more precisely, and it has good denoising power in detectingthe signal with noisy harmonics and inter-harmonics.