Renewable energy is a key solution to address the challenges of energy shortages and climate change. Consequently, high-renewable-energy-penetrated power systems (HREPPS) have become a popular trend. This has led to the increasing use of voltage-source converters (VSCs) as renewable-energy interfaces. Meanwhile, other VSC-based applications such as flexible alternating current transmission systems (FACTS) are used for supporting the energy conversion of renewable energy. With the large integration of VSC-interfaced devices, there is a rising concern regarding their impact on the harmonic resonance of power systems. In this study, a new harmonically coupled impedance model is proposed to inspect the harmonic resonance caused by VSC-interfaced devices in HREPPS. The model is derived based on the penetration of a multifrequency harmonic, enabling it to fully reveal the frequency coupling effect in the system. Research has shown that frequency coupling plays an important role in harmonic resonance analysis. The correctness of the proposed harmonic impedance model and its effectiveness on harmonic resonance analysis were verified using time-domain simulations of a real-life photovoltaic integrated system.

Abstract. How to store masses of small files is a generally acknowledged problem in industry and academia. Small file merging is the most successful strategy to solve this problem, which has been supported by many distributed filesystems, such as FastDFS. However, in FastDFS, our experiments indicate that excessively wide striping causes performance degradation, and pre-allocated space causes data loss or error. Therefore, this paper presents a client-based small file merging scheme based on the characteristics of online web application. This scheme makes full use of the resources of the web server and optimizes the small file merging with the annealing algorithm to improve the throughput. Experimental results show that the write performance are improved by 52.03% and query performance by 27.69% compared with the original FastDFS small file merging scheme.

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