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Islanding Detection Techniques: How to Ensure Power Grid Reliability

Islanding Detection Techniques: How to Ensure Power Grid Reliability


Solar micro grid

In this blog post, I will introduce a fast and accurate islanding detection technique for microgrid connected to photovoltaic system. Islanding detection is the process of identifying whether a distributed generation (DG) unit, such as a photovoltaic (PV) system, is isolated from the main grid and operating as an autonomous microgrid. This is important for the safety and reliability of both the DG unit and the grid, as well as for the power quality and stability of the microgrid.


There are different methods for islanding detection, such as passive, active, hybrid, and communication-based methods. Passive methods rely on monitoring the local parameters of the DG unit, such as voltage, frequency, or harmonic distortion, and detecting any deviation from the normal range. Active methods inject a disturbance into the DG unit or the grid, such as a change in the output power or current and observe the resulting change in the local parameters. Hybrid methods combine both passive and active methods to improve the performance and reduce the drawbacks of each method. Communication-based methods use external signals or information from other devices or locations to detect islanding.


The proposed technique is a hybrid method that uses both passive and active elements. The passive element is based on measuring the rate of change of output voltage (ROCOV) of the PV system. The active element is based on injecting a disturbance into the duty cycle of the DC/DC converter of the PV system. The technique works as follows:

- First, the ROCOV is computed and compared with a predefined threshold. If it exceeds the threshold, it indicates a possible islanding event.

- Second, after a given time delay, a disturbance is injected into the duty cycle of the DC/DC converter to deviate the operating point of the PV system away from its maximum power point (MPP). This leads to a significant reduction in the active power output and voltage of the PV system in an islanded mode.

- Third, the ROCOV and the rate of change of active power output (ROCOP) are measured again and used as islanding detection criteria. If both ROCOV and ROCOP are negative and large, it confirms an islanding condition. If at least one of them is near zero, it indicates a non-islanding event.


The advantages of this technique are:

- It is fast and accurate, with a small non-detection zone (NDZ) within 510 ms.

- It has self-standing thresholds determination, which means it does not need any prior knowledge or information about the grid or load parameters.

- It has no adverse effect on the output power quality, as the disturbance is small and short-lived.

- It has a simple and inexpensive structure, as it only requires a few measurements and calculations.

- It has a fast MPP restoration after islanding detection, which enhances the chance of seamless reconnection and autonomous operation of the microgrid.

The technique has been tested and validated using hardware-in-the-loop (HiL) simulation tests for various islanding and non-islanding scenarios. The results show that it can successfully detect islanding with different load types and sizes, different grid impedances, different PV system sizes and locations, and different weather conditions. The technique can also avoid false tripping during non-islanding events such as grid faults, load switching, or PV system switching.


The proposed technique is based on the work of Reza Bakhshi-Jafarabadi and Marjan Popov, who published their paper in IEEE Transactions on Smart Grid in 2021. For more details and references, please refer to their paper.

: Reza Bakhshi-Jafarabadi and Marjan Popov, "Two-Level Islanding Detection Method for Grid-Connected Photovoltaic System-Based Microgrid with Small Non-Detection Zone," IEEE Transactions on Smart Grid, vol. 12, no. 2, pp. 1063-1072, March 2021.


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