The Research On DC Weak Arc Fault Detection In Photovoltaic System

As an important part of renewable energy,photovoltaic is a component of the national energy security system.Due to the high voltage and the aging or damage of the cable caused by the external environment or other factors,arc faults may happen incidentally and much economic losses and casualties will be caused if no proper measures have been taken.This dissertation mainly focuses on arc faults in photovoltaic system,and the main studies as follow:(1)The time-frequency characteristics of DC fault arc with load or grid connected in photovoltaic system are studied.The detection methods of variance,current rate,fast Fourier transform,wavelet transform and collective empirical mode decomposition are selected to study from time domain,frequency domain and time-frequency domain.Through experiments,the applicable methods of various types of arcs and the influence of the type and location of the arc on the detection method are studied.At the same time,the accuracy,immunity and applicable occasions of these methods are determined through experiments.Consider comprehensively and the detection method that is more suitable for DC fault arc of photovoltaic system is obtained.(2)Aiming at the problem that the arc fault is not easy to detect when the feature is weak,a method of wavelet-singular value decomposition is proposed to detect weak arc signals.The noise of inverters in photovoltaic system is removed by using the characteristics of singular value de-noising,which enlarges the arc noise in current and makes the fault characteristics more obvious.The feasibility of the method is verified by experiments.In addition,this paper studies the anti-interference ability of the detection algorithm of photovoltaic system under different working conditions and external environment.(3)Based on the foreign arc hazard calculation related standards andcombining with the complex structure of photovoltaic system,the hazard analysis of DC fault arc of photovoltaic system is carried out.The distinguishing method of series and parallel arc and different protection strategies are also given in this paper.