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

Abstract

This paper proposes a fast and reliable two-level islanding detection method (IDM) for grid-connected photovoltaic systems (GCPVSs) based microgrid. In the first level of the proposed IDM, the magnitude of rate of change of output voltage (ROCOV) is computed. If this variable exceeds a predefined threshold, a disturbance is injected into the duty cycle of DC/DC converter after a given time delay to deviate the system operating point away of its maximum power point (MPP) condition. This leads to a substantial active power output and voltage reduction in islanded mode. Therefore, the ROCOV and the rate of change of active power output (ROCOP) indices, measured in the second stage, pose great negative sets at the same time in islanding states. However, the variation of at least one of these variables is nearzero in non-islanding switching events. The assessment of the presented algorithm has been conducted under extensive islanding and non-islanding scenarios for a case study system with two PV power plants using hardware-in-the-loop (HiL) simulation tests. The provided results remark precise islanding classification with eminently small non-detection zone (NDZ) within 510 ms. The presented IDM has the advantages of self-standing thresholds determination, no improper effect on the output power quality, and simple and inexpensive structure. Moreover, the fast MPP restoration of the proposed scheme after islanding identification boosts the chance of seamless reconnection and DG autonomous operation in microgrid. Index Terms-Grid-connected photovoltaic system (GCPVS), Islanding detection method (IDM), Maximum power point (MPP), Microgrid, Non-detection zone (NDZ), Rate of change of active power output (ROCOP), Rate of change of output voltage (ROCOV).

A Survey of Islanding Detection Methods for Microgrids and Assessment of Non-Detection Zones in Comparison with Grid Codes

“…RoCoV and RoCoF consist of constantly measuring the variation rate of the voltage and the frequency at the PCC, respectively. Threshold values have to be chosen to avoid false positives, i.e., to recognize islanding as common disturbances of the grid that are comprised into the admissible range according to the grid codes [26,27].…”

Review on islanding detection methods for grid‐connected photovoltaic systems, existing limitations and future insights

“…Impedance switching [60,61] S m a l l MPPT disturbance injection [62] S m a l l DC/DC converter's duty cycle disturbance injection [63] Small Therefore, the GCPVS would be destabilised after islanding detection, and its restoration would be infeasible. The transition between grid-connected and autonomous mode would also be time-consuming for a few hybrid IDMs as they attempt to drive a local variable outside the standard range in suspicious islanding events.…”

“…Therefore, the interaction between these features and islanding detection should draw more attention in future studies. • Several hybrid methodologies employed a voltage-based criterion to identify the suspicious islanding events [58,[62][63][64].…”

Islanding Detection Methods for Microgrids: A Comprehensive Review

“…However, if the microgrid is in islanding operation, the extra active power will increase the voltage amplitude at the PCC. Therefore, islanding can be detected by monitoring the PCC voltage with a detection time of less than 0.5 s. Using reactive power instead of active power for the second step was proposed in [85][86][87].…”