On Harmonic Injection Anti-Islanding Techniques Under the Operation of Multiple DER-Inverters

A Simple Strategy to Reduce the NDZ Caused by the Parallel Operation of DER-Inverters

“…In the current work, the anti-islanding protection technique that has been proposed in reference [2] is modified, in order to take into account the effect of parallel operation of multiple DER-inverters that are connected to the same node. This problem has been also stated in reference [9], where a solution based on an external accumulator was proposed. In this work, a different solution is proposed that prolongs the harmonic injection in order to achieve a required overlap among the injected harmonic components of inverters.…”

“…Now let us assume that N current-source inverters (of P N [n] nominal power each) that utilize the anti-islanding technique in reference [2], as well as M other DER-inverters (that may or may not utilize the anti-islanding technique) of a total nominal power P Mtot that might be potentially installed are connected to the same PCC, and that P tot = P Mtot + P Ntot . According to the analysis that is conducted in reference [9], the magnitude of the induced voltage that is caused by each inverter of the N-subgroup can be expressed by the following equation:…”

“…whereas the induced harmonic voltage that is generated by the synchronous (simultaneously) harmonic injection of l-inverters (assuming that the N-subgroup consists of inverters of the same type) is given by [9]:…”

“…In this work, a different solution is proposed that prolongs the harmonic injection in order to achieve a required overlap among the injected harmonic components of inverters. The modified technique that is proposed in this work is very simple and does not require an external accumulator, which are the main reasons not to use the technique discussed in reference [9]. On the other hand, the proposed modified technique has some limitations (particularly for a large number of inverters), because of the harmonic regulations of grid-tied inverters.…”

On the Conflict between LVRT and Line Protection in LV Distribution Systems with PVs: A Current-Limitation-Based Solution

“…To this end, several inverter-design concepts have been proposed, aiming at the compliance of LV-IIDGs with LVRT requirements [5][6][7].Since LVRT requirements keep DG-units connected to the network during faults, they contradict the requirement for a quick anti-islanding detection. Indeed, despite the fact that several efficient passive [8], active [9][10][11][12], or other hybrid methods [13] have been proposed over the last years for fast anti-islanding detection, their cooperation with LVRT operation remains a challenging issue under research, especially under high DG-penetration conditions. The authors of [14] attempted to clarify this contradiction, by allowing a PV-unit to trip without complying with LVRT, if passive anti-islanding detection asserts.…”