DC Series Arc Detection In PV Systerm

In PV(photovoltaic) system, electric shock and fire phenomenon occur frequently in recent years and many of these accidents are caused by dc arc faults. Dc arc fault is a very common phenomenon of gas discharge and loose line terminals、broken line insulation skin and many other likely reasons can easily lead to arc phenomenon. In the front of most of PV systems are a long list of PV cells containing tens of thousands of electrical contacts and electrical cables, which can easily cause dc series arc faults, so the purpose of this dissertation is to detection the series dc arc fault in PV systems.This paper studies the time domain detection method for dc series arc current. After analyzing mutation characteristics、fractal feature and statistical feature of the dc series arc current and normal dc line current, this paper designs a time-domain detection scheme by using the fittest characteristics of arc current as the detection basis successfully.This paper studies the frequency domain detection method for dc series arc current. By use of Fourier decomposition for dc series arc current and normal dc line current, this paper gets the current spectrum data. After analyzing the spectrum amplitude characteristics and spectrum profile variation characteristics within 40 k Hz to 120 k Hz, this paper designs an arc detection scheme in frequency domain by taking the fittest frequency characteristics as the detection basis.This paper studies the wavelet detection method for dc series arc current. Through wavelet decomposition for dc series arc current and normal dc line current, this paper gets the wavelet coefficients of current. After analyzing approximation wavelet coefficients characteristics and detail wavelet coefficients characteristics based on the time and frequency domain method, this paper designs a wavelet detection scheme by choosing the fittest wavelet coefficients characteristic as the detection basis.This paper tests the detection precision of these three kinds of detection scheme. By analyzing the cause of dc series arc, this paper designs an arc generator device with a knife switch. After producing dc series arc successfully, this paper collects lots of current data and uses them to test and analyze the detection schemes.