Fast islanding detection of PV grid connected inverters

This paper proposes a new method for fast detection of the point of common coupling (PCC) voltage variations for a grid connected PV inverter. The main feature of this method is the rapidity of the algorithm in such a way that the detection can be carried out even when protection devices are not yet activated. The method uses only voltage sensors at the PCC and the algorithm is based on temporal redundancies obtained with previous stored measurements. The method consists in obtaining a residual, which is generated using simplifications introduced by the real-time constraints. The operation principle is as follows: in healthy mode, the residual is lower than a certain threshold. However, if there is PCC voltage variation, the residual value will increase, allowing a fast detection of this change. The theoretical analysis is performed in order to establish threshold analytic expressions in both cases, with and without PCC voltage variations, and to explain the residual waveform during faults. The proposed method is easy to implement, fast and does not require system parameters knowledge. Simulations and experimental results are presented to demonstrate the effectiveness of the proposed method.