The possibility to monitor and evaluate power system stability in real-time is in growing demand. Whilst most stability-related studies focus on long-term voltage stability and frequency stability, very little attention is given to the issue of short-term (voltage) instability. In this paper, the most common evaluation methods present in the literature are summarized, with a focus on their applicability to modern power systems with a large amount of renewable energy integration. The paper presents a first-of-a-kind structured review of this topic. We find that all existing methods have noteworthy limitations that necessitate further improvements. Additionally, the need of having an inclusive short-term instability prediction method is demonstrated, due to strong interactions between various short-term instability mechanisms. These findings provide a good foundation for further research and advancement in the field of real-time stability monitoring.
Renewable energy sources (RES) penetrate power grids at all voltage levels. A large number of RES units are connected to medium-voltage (MV) and low-voltage (LV) levels resulting in a significant share of overall generation. Therefore, the dynamic behavior of such distribution grids should be thoroughly examined. The goal of this paper is to show how various changes in the composition of the dynamic power flows interact with Low-Voltage Ride Through (LVRT) requirements, and how they affect the very important aspect of the RES-penetrated grids-voltage stability. The analysis is performed on a selected network, which is modeled with real grid data. The concluding concepts, however, are applicable for any distribution grid topology with a large number of distributed energy resources (DER). The results show essential grid details that should be modeled more precisely. This paper also addresses the level of complexity needed to obtain accurate results. Models are generally always imperfect and therefore, having more detailed data for a specific study is of the uttermost importance.
To facilitate the increasing penetration of inverterbased resources, understanding and evaluating system strength becomes one of the central questions for the resilient operation of power systems. However, this is a very challenging and nuanced task, currently without a clear consensus in the industry and academia. This paper provides a comprehensive review of the proposed notion for system strength, followed by a consequent introduction of a novel classification. Furthermore, an exhaustive examination of present system strength evaluation methods is performed. Finally, a critical outlook on remaining and emerging challenges of system strength evaluation is presented, with several key recommendations for future research directions.
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