Abstract
Three-phase grid-connected inverters are widely applied in the fields of new energy power generation, electric vehicles and so on. Islanding detection is necessary to ensure the stability and safety of such systems. In this paper, feature recognition technology is applied and a novel islanding detection method is proposed. It can identify the features of inverter systems. The theoretical values of these features are defined as codebooks. The difference between the actual value of a feature and the codebook is defined as the quantizing distortion. When islanding happens, the sum of the quantizing distortions exceeds the threshold value. Thus, islanding can be detected. The non-detection zone can be avoided by choosing reasonable features. To accelerate the speed of detection and to avoid miscalculation, an active islanding detection method based on feature recognition technology is given. Compared to the active frequency or phase drift methods, the proposed active method can reduce the distortion of grid-current when the inverter works normally. The principles of the islanding detection method based on the feature recognition technology and the improved active method are both analyzed in detail. An 18 kVA DSP-based three-phase inverter with the SVPWM control strategy has been established and tested. Simulation and experimental results verify the theoretical analysis.
Highlights
Three-phase grid-connected inverters are an important part of distributed generation systems
The principles of the islanding detection method based on the feature recognition technology and the improved active method are both analyzed in detail
In the Vector Quantization (VQ)-based feature recognition, the decision is made by measuring the similarities between a testing pattern and every codeword achieved during training [22]-[27]
Summary
Three-phase grid-connected inverters are an important part of distributed generation systems. If the inverter is disconnected from the grid, some of the parameters may change and can be detected. A codebook is a collection of codewords which can reflect a certain feature It can be seen as a feature vector and can be obtained by a theoretical analysis of the inverter’s operation condition instead of the training of signals. To exacerbate the changes of the features and accelerate the speed of detection, an active islanding detection method is applied.
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