Research On Short Circuit-current Calculation Method Of Photovoltaic Microgrid

In order to improve the operating efficiency of the distributed power supply and eliminate the direct impact of the intermittent power supply on the power quality of the surrounding users,the photovoltaic microgrid has been actively developed and widely used as an independent autonomous power supply system.However,in the event of a short-circuit fault in the photovoltaic microgrid,the short-circuit current will have a greater impact on the microgrid,causing the equipment to overheat and damage and fail to operate normally.How to calculate the short-circuit current accurately is the key to the selection of the microgrid design and protection setting values.Therefore,this article focuses on the short-circuit current calculation method for photovoltaic microgrids and has practical and theoretical values for the design,protection and safe and stable operation of photovoltaic microgrids.This thesis analyzes the impact of faults on photovoltaic microgrids in detail.Based on the traditional short-circuit current calculation model,the physical characteristics and working principle of photovoltaic cells and lead-acid batteries are analyzed to establish mathematical models for photovoltaic cells and lead-acid batteries.Combining the specific characteristics of photovoltaic microgrids,a comprehensive microgrid model with corresponding short-circuit current calculations was established.Based on the symmetry component method,a short-circuit current calculation method for photovoltaic microgrids is proposed.Firstly,this method uses the generalized Tellegen’s theorem to conveniently concatenate the mathematical models of each component of the microgrid and derive the multiplier matrix of the modified equation.Only elements on the diagonal are refreshed during iteration,which increases the calculation speed for calculating the initial value of the fault calculation.Secondly,the photovoltaic power generation system and the energy storage system in the microgrid are built with the sequence components according to the fault type,and the asymmetry fault short-circuit current is calculated using the Newton method and the symmetrical component method.The proposed method is used to calculate the short-circuit current through Matlab/Simulink simulation platform.Based on the original model,various short-circuit faults are simulated,and the fault characteristics are analyzed according to the parameter settings and the output waveform and data.Comparing Newton’s method with the generalized Tellegen’s theorem,the results show that the proposed method is feasible and improves the computational efficiency.