Islanding refers to a condition where distributed generators (DGs) inject power to the local load after electrical separation from the grid. Several islanding detection methods (IDMs) categorized into remote, active, passive and hybrid groups have been presented to detect this undesirable state. In active techniques, a disturbance is inserted into the output power of inverter-based DGs to drift the voltage or frequency out of permissible range. Although this disturbance leads to more effective detections, even in low active or reactive power imbalances, it raises the total harmonic distortion (THD) of the output current during the normal operating conditions. This paper analyzes the power quality aspect of the modified sliding mode controller as a new active IDM for grid-connected photovoltaic system (GCPVS) with a string inverter. Its performance is compared with the voltage positive feedback (VPF) method, a well-known active IDM. This evaluation is carried out for a 1 kWp GCPVS in MATLAB/Simulink environment, measuring the output current THD and efficiency for various levels of relative active power and disturbance under grid connection states. The output results demonstrate that while the proposed disturbance will only change the amplitude of the output current, it does not generate harmonics, and therefore, it has a negligible adverse effect on the power quality.

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