Improvement And Realization Of Island Detection Based On Active Frequency Shift

Solar energy is an indispensable part of the new energy system.Photovoltaic power generation technology is the mainstream of solar energy utilization.Therefore,the related problems have become one of the hot spots in the field of photovoltaic technology nowadays.The islanding effect is one of them.Islanding detection method is to ensure the safe and stable operation of modern intelligent power system,the core technology,so the island of detection technology is of great significance[1].In this paper,the mechanism of island phenomenon,the standard of islanding scheme and the detection model of islanding effect were discussed and discussed in depth.At the same time,the serious consequences brought by the islanding effect of photovoltaic grid-connected system were summarized.In order to evaluate the validity of different islanding schemes,four kinds of coordinate systems are introduced in this paper,and the relationship between the horizontal and vertical coordinates of the four coordinate systems is deduced.The advantages and disadvantages of various coordinate systems are pointed out.The actual design needs to determine the evaluation of the coordinate system used in this article.Secondly,the thesis focuses on the active frequency shift detection scheme and the active frequency shift improvement scheme with positive feedback.In the coordinate system[2],the size of the non-detection area of the two schemes is quantitatively described and depicted The non-detection area is located in the specific position of the coordinate system,and the consistency between the non-detection area and the formula is verified through the simulation modeling.The influence of the detection parameters on the power quality and the detection result is deeply analyzed.Again in order to take into account the relationship between islanding detection and inverter output power quality,as well as to reduce the non-resistive load to bring the extension of time,the article made some improvements on the basis of the traditional active frequency shift algorithm,that is truncated Coefficients can be adaptively changed,or cyclically uninterrupted on the inverter to apply positive and negative direction of the disturbance signal[3].The method avoids the phenomenon that the load resonance frequency is opposite to the frequency shift direction of the disturbance signal in the different load characteristics so that the detection errors caused by the offset cancel each other and the detection time is reduced and the injection time of the photovoltaic grid-connected system into the grid Harmonic distortion rate,improve the detection of the effectiveness.The method is combined with the passive over/under voltage detection method to form a combined detection scheme..Through the MATLAB/Simulink simulation software,the photovoltaic system is modeled and the improved method is simulated.The results show that the proposed scheme has the advantages of detection speed Faster,lower dead zone and in different load characteristics can be effective and so on.Finally,according to the design,this paper adopts TI's DSP28335 as the master chip,hardware design around the island detection technology,gives the corresponding flow chart and the specific experimental waveform.