Study Of Islanding Detection For Grid-connected Photovoltaic Inverters

The increasingly serious energy crisis and environmental problem force thehumanity to seek alternative energy sources. Solar energy is renewable, clean and safe,which is developed actively around the world. The grid-connected PV system canimprove the utilization of solar energy and enhance the quality of power supply,which is a research focus. The grid-connected PV systems producing reverse powerflow into power system which made the islanding phenomenon become a secondaryhazard. The islanding phenomenon may damage the equipments and do harm touniformed maintenance personnel, and the islanding function an indispensable featurefor PV-systems. The increasingly applications of the grid-connected equipmentsincrease the probability of occurrence of islanding phenomenon，and the impact of theislanding phenomenon must be taken into account.This thesis described the mechanism of islanding phenomenon, the analysismodel and main research methods of anti-islanding protection. Popular islandingdetection methods are described in detail.Based on the MATLAB simulation environment, a number of issues aboutanti-islanding protection are studied. This paper has completed the following researchwork: Improved the phase shift islanding detection algorithm. Compared and analyzedthe frequency shift method and phase shift method. The impacts of inverter outputmode, multivariable disturbance on islanding detection in single invert system isanalyzed. Islanding detection assessment of multi-inverter systems based onsimulation study is developed, and the causes of islanding detection failure inmulti-inverter systems are analyzed, possible solutions are suggested at the end ofdiscussion.Completed the hardware and software design of the inverter controlling system,includes the signal acquisition and processing module, PWM wave generation module,islanding detection function module. The islanding detection functions of theprototype are tested in experiment.