An improved method for anti-islanding by reactive power control

Recently, the study of the islanding phenomenon, which unfavorably maintains its operation even when the utility grid is removed, has led to the trend of utility interactive inverters in the photovoltaic generation system. In this paper, a novel anti-islanding method is presented. The proposed method can keep the real average power component constant by MPPT control and causes the load current frequency with only a change of the reactive power component under islanding conditions. Its periodical change of the reactive power component can decrease the NDZ (non-detective zone) so that the detection of various loads will be possible. Therefore, the proposed method enables islanding detection, in the worst case, no load-variation compared to before removal of the grid. It has been proven theoretically that the influence of the grid can be minimized in the case of an additional reactive power component and the islanding detection is also confirmed from the experimental results with an inverter for a 3 kW photovoltaic generation system, by applying the proposed anti-islanding method.