Research On Islanding Detection Method Of Photovoltaic Grid-connected Inverter

Recently people’s demand on energy is increasing day by day. Because of power shortages andenvironment pollution, traditional way of generating power faces the reform, distributed power generationarises at the moment. Photovoltaic generation is one of the concerned distributed power generationtechnology, which has zero pollution, renewable, universality of resources, flexible and other advantages.In the global range, photovoltaic generation research is deepened and accesses to a wide range ofapplications. However, grid-connected photovoltaic generation systems could produce the islanding effectwhich has great harm to the power grid, equipments and persons. Nowadays islanding detecting andprotection is a very popular project.According to the background of the subject, based on traditional passive islanding detectionmethods and active current amplitude offset method, this paper puts forward a new combined islandingdetection method. And the main ideas of the scheme are as follows: On one hand, real-time detecting thechange on frequency and phase of the public point voltage；On the other hand, every N cycles the systemchanges initiatively invert output current amplitude signal, and detecting the occurrence of the islandingthrough the real-time detection of the change of the public point voltage amplitude. The new islandingdetection scheme not only can avoid the insufficient of the single traditional islanding detection scheme,quickly detect islanding, but also can realize no non-detection zone, no harmonic pollution on the powerquality.Second, in order to reduce the influence on photovoltaic generation system output power anddetect the islanding fast, this paper proposes a new plan about the active current amplitude offset. This planwhich chooses appropriately photovoltaic generation systems output current amplitude in the offset circlesand the frequency of photovoltaic generation systems output current offset, reduces relatively the effect onphotovoltaic generation system output power, shortens the islanding detection time and improves theperformance of the system.Finally, simulation models are built and simulations of the new method are carried out byMATLAB/SIMULINK. In order to verify the reliability of the new method, the actual structure systems based on DSP TMS320C32are built. Experiments of the new method are carried out. By analyzing of thesimulation and experimental results, we can see that the newly proposed islanding detection method caneffectively detect the islanding phenomenon.