A New Islanding Detection Scheme for Multiple Inverter-Based DG Systems

A new islanding detection technique is proposed for the application in multiple inverter-based distributed generation (DG) systems. In the proposed method, a harmonic current disturbance is imposed to the grid at one of the harmonic frequencies associated with the grid voltage. This is done by changing the equivalent parallel impedance of the grid-connected inverters. The output current of the grid-connected inverters at this specific harmonic frequency is used as the islanding detection signal. The harmonic resonance is imposed over a short time interval, hence the overall power quality is not significantly affected. As opposed to most of the active islanding detection methods, in the proposed method, no interference among parallel DGs is observed, which makes it well suited for the application in systems involving a large number of parallel inverter-based DGs. Comprehensive analyses are performed to investigate various technical aspects of the proposed scheme. The performance of the proposed method is verified using time-domain simulations carried out in Matlab/Simulink environment.