Abstract
Anti-islanding detection methods have been part of a secure operation for distributed energy resource inverters, avoiding the creation of non-intentional energization when the mains are lost. These detection mechanisms were conceived historically for current-controlled inverters. New control possibilities have broken ground, and current- or voltage-controlled inverters are a reality; however, special attention must be paid to detection strategies when applied to the latter ones. This paper addresses two topics: it exposes the lack of effectiveness of those detection algorithms based on the voltage/frequency displacement concept under voltage-controlled inverters and evaluates the applicability limits of the others based on the impedance measurement (IM). The IM is presented as a valid mechanism to achieve the islanding detection, but the exploration of its limits drives the concept of detection frequency bandwidth (DFBW), introduced in this paper. The DFBW is suggested as a practical approach to select the proper injection frequency to measure. Therefore, an improved strategy based on the IM and DFBW is proposed to allow achieving the detection towards (non-)resonant loads considering low computational burden. The results were experimentally validated in a 90-kVA four-wire voltage-controlled inverter, offering detection times of less than 100 ms in any case.
Highlights
Utility deregulation has sped up the possibilities for distributed energy resources (DER)
Note that even in the case of using an active methods (AM)-impedance measurement (IM) as AI detection methods (AIDM), it is not always valid and is highly dependent on the type of grid, the resonant load quality factor, and mainly, on the frequency used for the detection
The total time for the high frequency calculations represented less than 4% of the available 125 μs, and for the low frequency case, less than 0.5% of the available 1 ms
Summary
Utility deregulation has sped up the possibilities for distributed energy resources (DER). Most DER inverters were conceived of in the past to behave as CC-VSI (current-controlled voltage source inverters), this situation is evolving. The use of information technologies, and the progress of power electronics have boosted alternative options for either grid-connected or grid-disconnected operation. Other behaviors like voltage-controlled (VC)-VSI inverters enhance grid flexibility services such as power sharing or non-zero voltage crossing between operation modes [2,3,4]. It is possible to distinguish between three main types of grid integration inverters [5]: Grid supply inverters (GSI) are unidirectional CC-VSI when grid-connected, and their aim is to deliver the maximum power to the mains by means of maximum power point tracking
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