Fault Analysis Method Considering Dual-Sequence Current Control of VSCs under Unbalanced Faults

Voltage source converters (VSCs) are able to provide both positive- and negative-sequence short circuit currents under unbalanced faults. Their short circuit responses can be significantly different from those of conventional synchronous generators. This paper developed a static fault analysis method by considering dual-sequence current control of VSCs under unbalanced faults where VSCs are treated as voltage-dependent current sources in both positive- and negative-sequence networks. Since the control strategy of VSCs varies, flexible parameters are included in the model to reflect their diverse short circuit behaviours. The proposed method is verified through a modified IEEE 9-bus system and a simplified western Danish power system with real time simulations. This analytical method can be used to help understand and evaluate the impact of dual-sequence current control of VSCs on future converter-dominated power systems

Association between healthy eating index-2015 and abdominal aortic calcification among US Adults

AimsTo evaluate the relationship of the healthy eating index-2015 (HEI-2015) with abdominal aortic calcification (AAC) in US adults.MethodsWe conducted a cross-sectional study with data extracted from the National Health and Nutrition Examination Survey (NHANES). AAC score was measured using the scoring system of Kauppila (AAC-24) and Schousboe (AAC-8). HEI-2015, which was used for evaluating compliance with Dietary Guidelines for Americans (DGA), was calculated through two rounds of 24-h recall interviews. HEI-2015 was categorized as inadequate (<50), average (50~70), and optimal (≥70) groups for analysis, while the AAC-24 score was grouped by whether the score was >0. Weighted multiple regression analyses were conducted to estimate the association of HEI-2015 with AAC score and the presence of AAC. Moreover, smooth curve fittings, based on a generalized additive model (GAM), were applied to evaluate a possible non-linear relationship. Sensitivity analysis and subgroup analysis were performed to provide more supporting information.ResultsA total of 2,704 participants were included in the study (mean age, 57.61 ± 11.40 years; 51.78% were women). The mean score of HEI-2015 was 56.09 ± 13.40 (41.33 ± 6.28, 59.44 ± 5.54, and 76.90 ± 5.37 for inadequate, average, and optimal groups, respectively). After adjusting for covariates, higher HEI-2015 was associated with decreased AAC score (AAC-24: β = −0.121, 95% CI: −0.214, −0.028, P = 0.010; AAC-8: β= −0.054, 95% CI: −0.088, −0.019, P = 0.003) and lower risk of AAC (OR = 0.921, 95% CI: 0.855, 0.993, P = 0.031). Among the components of HEI-2015, a higher intake of fruits, greens, and beans was associated with a lower AAC score. Subgroup analysis showed that an inverse association of HEI-2015 with AAC score existed among different groups.ConclusionThe study presented that higher HEI-2015 was related to a lower AAC score and decreased risk of having AAC, indicating that greater compliance with 2015–2020 DGA, assessed by HEI-2015, might be beneficial for preventing vascular calcification and CVD among US adults

Mapping and Analysis of the Reactive Power Balance in the Danish Transmission Network

This paper investigates the reactive power balance of the Zealand side of the Danish transmission system (DK2) by using QV-curves. The study is performed in cooperation with Energinet, who is the Danish transmission system operator (TSO). Firstly, this paper aims to map the reactive power balance with the current challenges in the system, which appears due to a decision of changing overhead lines in the scenic area to cables. Secondly, a method is derived for obtaining a comprehensive overview of the impacts that future projects might have on the system. By dividing the transmission system into smaller areas, it is possible to analyze how the reactive power will affect the voltage; moreover, it is favorable to analyze and handle the challenges in the reactive power balance locally. This helps the TSO to quickly determine the lack of reactive power devices and issues that might occur in future expansions of the system. For this paper, a full-scale model of DK2 and SCADA-data has been utilized. It covers the period from 01-01-2016 to 20-08-2017 between the TSO and the Distribution System Operator (DSO). The studies have shown how the location of the wind production will create issues in the reactive power balance