Impedance Measurement and Detection Frequency Bandwidth, a Valid Island Detection Proposal for Voltage Controlled Inverters

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.

Integrated Microgrid Islanding Detection with Phase Angle Difference for Reduced Nondetection Zone

“…The grid code limit for ROCOF is 1 Hz/sec with detection time 100 ms. The NDZ is large with high error ratio but with less detection time and with no power quality issue [13]. Differential of frequency over power method: the method is dependent on variations in rate of change of frequency over power during islanding.…”

Review of Local Network Impedance Estimation Techniques

“…Therefore, the main techniques utilised in the literature are the P/Q variation and the nonharmonic excitation techniques [12]- [15]. The most recent literature on this subject is [112], which focuses on applying an impedance estimation to detect islanding within 100 ms.…”

A Simple Methodology to Develop Bifilar, Quadrifilar, and Octofilar Calculable Resistors

“…Since with the CRs, the frequency dependence of impedance standards with traceability to the QHR can be measured, they are used as references for high-accuracy electrical measurement systems [7][8][9]. Applications with medical and technologic impact involve high-accuracy impedance measurements, such as electrical characterization of tissue [10,11], cell detection [12], supercapacitors developments [13], impedance matching in wireless power transfer systems [14], voltage-controlled inverters for electrical grids [15], and characterization of lead-acid batteries [16,17], only to cite a few examples. To ensure the certainty of the results of environmental research, like solar cell characterization [18], toxicity measurements of nanoparticles [19], or Nitrogen fertilizer monitoring in plants [20], the traceability to fundamental constants of their impedance measurements needs to be fulfilled.…”