Subjects: Dynamic and Electric Engineering >> Electrical Engineering submitted time 2022-10-11
Abstract： The temporary overvoltage (TOV) during fault recovery process of renewable energy system seriously restricts the development of renewable energy. However, the existing research lacks quantitative indicators of the TOV. Therefore, based on the mechanism of TOV, this paper proposes a method to quantify the TOV risk of multiple renewable energy station system (MRESS) considering the reactive power saturation characteristic. Firstly, based on the TOV mechanism of MRESS, the analysis model under different factors during fault recovery is established, and then the rationality of TOV assessment based on phasor model is demonstrated. After fully considering the saturation characteristics of converters after fault and the interaction between renewable energy generators, an evaluation method for TOV of MRESS is derived. Through analyzing the relationship between TOV of the system and short-circuit ratio, the temporary overvoltage short-circuit ratio (TOVSCR) of MRESS and its application method are proposed. Simulation results show that the proposed method can effectively evaluate the TOV risk and safety margin of the MRESS.
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Subjects: Biology >> Botany >> Applied botany submitted time 2022-07-05 Cooperative journals: 《广西植物》
Abstract： In order to analyze the variation characteristics and the effect of microhabitat on leaf functional traits of woody plants in Tiankeng. Shenmu Tiankeng is a typical karst Tiankeng in Dashiwei Tiankeng Group in Guangxi, and there is a well-preserved underground forest that is easily accessible. Ten leaf functional traits (leaf thickness, leaf tissue density, leaf area, etc.) were selected to study woody plants in different microhabitats (bottom, waist, and edge) of Shenmu Tiankeng. Single-factor analysis of variance and correlation analysis were conducted to investigate the relationship between leaf functional traits in different microhabitats. The results were as follows: (1) The variable coefficient for leaf area (113.9%) was highest, while leaf carbon content was relatively stable (10.5%). (2) Ten leaf functional traits were almost no significant difference (P>0.05) for woody lianas in three different microhabitats. The leaf tissue density for trees was significantly higher at the edge and waist compared to the bottom, while the leaf potassium content for trees and shrubs, that the bottom was higher than the edge. (3) Leaf thickness was extremely significantly positively correlated with leaf area (P<0.01) at the edge of Tiankeng. The results of principal component analysis suggested that leaf tissue density (-0.833), leaf potassium content (0.782), and leaf dry matter content (-0.647) were the critical indicators for leaf functional traits of woody plants in different microhabitats of Shenmu Tiankeng. This study demonstrate that different growth types of woody plants can adapt to the three microhabitats of Tiankeng via the trade-off of leaf functional traits. This study is expected to provide theoretical guidance for the protection of Tiankeng vegetation.
Subjects: Biology >> Botany >> Applied botany submitted time 2022-06-07 Cooperative journals: 《广西植物》
Abstract： The distribution characteristics and internal links of soil enzyme activities, nutrient content and woody plant diversity in negative topographic habitats of Tiankeng were studied, which provided a theoretical basis for the protection and reconstruction of plant resources in karst areas. The Tiankeng forests of the Dashiwei Tiankeng group in Guangxi were selected as the object. Based on the community diversity survey and soil habitat survey from the inner and top area to the outer area of Tiankeng, the relationship between species diversity and soil factors of woody plants was explored by correlation analysis and redundancy analysis methods. The results were as follows: (1) There were 21 species, 31 genera and 20 families of woody plants in the inside area of Tiankeng, 91 species, 58 genera and 58 families of woody plants in the top area of Tiankeng, and 47 species, 30 genera and 30 families of woody plants in the outside area of Tiankeng. The Margalef index and Patrick index in the inside area of Tiankeng were significantly lower than those in the top and outside area of Tiankeng, indicating that the individuals of species increased, but the species distribution was steady; (2) The total soil nitrogen content in the outside area of Tiankeng was significantly higher than those in the top and outside area of Tiankeng. The soil total magnesium content, soil phosphorus content and soil available phosphorus content in the inside area of Tiankeng were significantly higher than those in the top and outside area of Tiankeng. The soil alkaline phosphatase content and soil urease activities in the outside area of Tiankeng were significantly higher than those in the top and inside area of Tiankeng. The soil phosphorus content in the Tiankeng was higher, but the soil enzyme activities were lower; (3) The results of Pearson correlation analysis and redundancy analysis showed that species diversity was strongly correlated with soil nutrients and soil enzyme activities. In conclusion, it can be seen that the habitats of the Tiankeng have a great influence on the species diversity, soil enzyme activity and soil nutrient content distribution characteristics. And the soil available phosphorus content, soil alkaline phosphatase activity, soil moisture content, soil urease activity, soil full magnesium content and soil total phosphorus content are the key factors affecting the species diversity of woody plants in the Tiankeng forest.
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