New voltage feedback‐based islanding detection method for grid‐connected photovoltaic systems of microgrid with zero non‐detection zone

Abstract

This study proposes a fast and precise voltage feedback-based islanding detection method (IDM) for grid-connected photovoltaic systems (GCPVSs) based microgrid. In this algorithm, a disturbance containing the absolute deviation of the output voltage is injected into the inverter's d-axis reference current which tunes the active power output. In islanded mode, the applied disturbance reduces the active power output and consequently point of common coupling voltage beyond the standard setting while its effect at the presence of the grid is negligible. The assessment of the proposed IDM has been conducted in the MATLAB/Simulink platform under extensive scenarios defined by IEEE 1547-2008 and UL 1741 standards for a case study system with two large-scale GCPVSs. The provided outputs remark accurate islanding classification in all cases within 810 ms, much lower than the maximum permissible time postulated in islanding standards. This time is short enough to restore GCPVS for autonomous operation of microgrid as well. The comparative analysis of the proposed strategy with a few existing IDMs confirmed its overall superiorities in the terms of non-detection zone, detection time, being applicable into the microgrid, simple threshold determination, and straightforward and cost-effective implementation.

Hybrid Islanding Detection Method of Photovoltaic-Based Microgrid Using Reference Current Disturbance

“…Moreover, a further condition is established in the presented IDM to discriminate short-circuit fault situation. Similar to [8,16], this state is identified whilst DG output current (I DG ) in any phase exceeds 125%, as shown in Section 3.5.…”

“…The active power output drops sharply through the injected disturbance; however, the P DG fall has an insignificant impact on PCC voltage in the normal operating mode since it is strictly governed by the utility. In contrast, the PCC voltage in the islanded operating mode can be expressed by [14][15][16]:…”

“…The injection of an intentional disturbance into the DG's controller has been adopted in active IDMs [14][15][16][17][18][19]. This disturbance does not influence the PCC frequency and voltage in the grid-tied mode.…”

“…The upper and lower margins of the positive feedback gain have been also reformulated to attain the minimum NDZ and maximum stability. It is argued in [16] that the VPF scheme fails to distinguish islanding situations with a surplus active power due to the PV input power limitation in a given meteorological condition. Consequently, negative absolute feedback has been introduced to shift the PCC voltage beyond the minimum standard limit in all scenarios.…”

Two-Level Islanding Detection Method for Grid-Connected Photovoltaic System-Based Microgrid With Small Non-Detection Zone

“…The proposed technique is designed in a way that MPP is restored after islanding classification; the GCPVS can generate its maximum possible power in the autonomous microgrid to shorten the charging/discharging energy of the backup resources. Contrary to this, most active IDMs are structured to destabilize a local variable after island formation; thus, the DG output power is zero and maximum backup energy is needed [21]- [24].  In the proposed two-level IDM, the PCC voltage and active power output are measured to quantify |ROCOV1|, ROCOV2, and ROCOP2 and a disturbance is injected into the DMPP under |ROCOV1| Th1 (Fig.…”