An active islanding detection technique for current controlled inverter

This paper presents an active islanding detection technique suitable for current controlled inverters. The method is based on reducing the magnitude of the injected current periodically and monitoring the voltage at the point of common coupling (PCC). Under grid failure, the change in voltage at the PCC exceeds the allowable voltage threshold and islanding is detected. The change in the PCC voltage depends on the ratio by which current is reduced and is independent of the magnitude of current. Hence the voltage threshold remains the same irrespective of the loading conditions. A simple control circuit is incorporated into the inverter control to enable islanding detection. The perturbation caused by this method does not affect the zero crossing of the inverter current nor introduce any distortion as in case of other active anti islanding techniques. The performance of the proposed technique applied to a current controlled inverter is simulated in MATLAB/Simulink environment. The feasibility of the technique is ascertained by conducting experimental test on the prototype unit built in the laboratory. The algorithm is implemented on an ALTERA CYCLONE II FPGA board and the results are presented to show that the proposed method can effectively detect the islanding condition regardless of the load conditions.

► Islanding detection without degrading power quality.
► Voltage threshold independent of loading conditions.
► Simple control logic incorporated into inverter control.