Research On Islanding Detection Method For Photovoltaic Grid-connected Power System

The rapid development of the global economy, energy shortages and increasingly severe environmental pollution problems made the development and utilization of new energy imperative. Solar energy had became an integral part of the current system and photovoltaic power generation was a major development trend of solar energy utilization. The relevant technologies of photovoltaic(pv) grid power generation system had became a hot spot of research. Problems arising therefrom could not be ignored, islanding operation was one of them. The research of islanding phenomenon and preventing strategy were the key problems to ensure the new power system safe and reliable operation, thus the research of islanding detection technology had great significance.The paper reviewed photovoltaic grid system islanding phenomenons and resulting hazards, expounded the phenomenon occurrence mechanisms, islanding detection standards, islanding detection models, in-depth analyzed and discussed the existing islanding detection methods, focused on the advantages, disadvantages and range of applications of passive and active detections based on inverter side. Introduced the effectiveness evaluations of detection methods in various coordinate systems.The paper focused on in-depth analysis and research of the principles for Active Frequency Offset Detection Method and Positive Feedback Active Frequency Offset Detection Method. In 0f normQ ?C load parameters coordinate system, made a quantitative description of islanding detection blind deduced the size and location of blind area for the frequency offset islanding detection methods. Described the specific blind area plan. Verified the consistency of the blind area for frequency offset class islanding detection method and formulas through the simulations. Made a deep analysis of the influences from detection parameters to text results and power qualities in this detection method.In order to take into account of the relationships between islanding detection effect and power quality inverter output, analyzed the selection of traditional active frequency offset class islanding detection algorithm parameters, came up with an improved proactive detection method named Adaptive Frequency Shift Islanding Detection Method. The method used system frequency variation adaptive tuning truncated coefficients cf and feedback gain k. The algorithm improved the islanding detection performance and reduced the harmonic distortion of grid-connected photovoltaic systems. At the same time, reduced the harmonic distortion of grid-connected photovoltaic systems. Reduced the adverse effects of harmonics on power quality. Avoided the phenomenon of the failure to detect caused by load resonant frequency shift because of different load characteristics and the offset result from the opposite direction of the disturbance signal frequency offset. The positive feedback gain k in algorithm could be adjusted accordingly with the load of different quality factors overcame the problems of difficulties for high quality factor load. This proactive approach formed a combined detection scheme combined with traditional passive over/under voltage detection method. Built a photovoltaic power generation system model on the platform of MATLAB/Simulink. The new proposed islanding detection algorithm was embedded in the simulation model. Simulated the improved methods coming up with the conclusion the method had characteristics of detected quickly, without blind spots and low distortion. In the case of different load characteristics were feasible and effective.