Investigation of unintentional island operation during large amounts of inverter based power production
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Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Electric power engineering (MPEPO), MSc
Publicerad
2024
Författare
Stenvall, Emma
Brännman, Martin
Modellbyggare
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Sammanfattning
Abstract
With increasing efforts to utilize more renewable energy sources, it is becoming more and more popular to install solar panels on buildings and in residential areas. This trend is predicted to continue to grow within the foreseeable future, which brings up questions of how an increased amount of local inverter based power production would affect the contemporary grid and its behavior. There has been concern that an increase of local energy sources, such as solar power, could potentially pose a greater risk of unintentionally transition into island operation if the connection to the utility grid is lost. The aim of this report was therefore to investigate different scenarios in the simulation software Powerfactory and discern the behavior and possible risk of unintentional island operation in different grid models with varying amounts of photovoltaic (PV) modules. All PV modules connected to the Swedish electrical power grid must comply with standards and regulations and their inverters must contain the proper unintentional island protections. The inverter protections come in forms of passive, basic monitoring, protections and active ones, which actively tries to perturb the grid in order to detect islanding events. This thesis work was conducted by building four different grid models in Powerfactory. The grid models consisted of low voltage grids with varying amounts of PV modules, loads and cables, connected to an external grid which would be disconnected in order to simulate an islanding event. Each model was tested for different potential islanding events on the low voltage side while monitoring voltage, current and frequency values. The protection activation time to detect the potential island was also monitored in seconds, where protection triggers above five seconds were regarded as insufficient detection. For one of the models, a non-detection zone was established in order to visualize the detection limits. From the different grid model behaviors, it was concluded that detection capabilities of the inverter protection was highly dependant on the load imbalance. The reactive power mismatch had a much lower threshold compared to the active power, resulting in a very narrow nondetection zone in regard of reactive power compared to the much higher threshold values of active power in said non-detection zone. It was also concluded that there is not much readily available information about the active inverter protection schemes and further investigation about how they interact with the passive protections are needed.
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Keywords: Photovoltaic inverters, Anti-islanding protection, Inverter protection, Inverter functions, Island operation, Island protection, Unintentional island operation, Unintentional islanding.