Bipolar DC microgrid (MG) based on two voltage levels with three wires has higher reliability and flexibility than unipolar DC MG. However, the voltages of bipolar buses are coupled and the voltage ...of the PN bus affects the voltages of the bipolar buses in bipolar DC MG. In this paper, a hierarchical control with voltage balancing and energy management based on the characteristics of bipolar DC MG is proposed. To perform distributed power sharing with coupled voltages, droop-based primary controls for three buses and the coupling relationships between three buses are analyzed. Furthermore, in secondary control, balancing and voltage restoration controls are proposed to compensate for voltage drops caused by the balanced and unbalanced loads. To design the proposed hierarchical control, the stability analysis is performed. Additionally, a tertiary control based on an artificial neural network (ANN) is proposed for state-of-charge (SoC) management of bipolar DC MG. Experimental results of the proposed hierarchical control are verified by a lab-scale bipolar DC MG and performance analysis is performed with experimental and ideal results.
The main assignment of a bipolar dc microgrid is the settlement of the bipolar voltage imbalance due to unbalanced loads and asymmetric powers. It is necessary to consider maintaining the bipolar ...systems whether in grid-connected mode or islanded mode of the microgrid. This article introduces the control strategy of the triple-active-bridge (TAB) converter for the bipolar dc microgrid by voltage balancing. The presented control strategy performs PN voltage regulation and voltage balancing based on the interrelation analysis between power and voltage in the bipolar dc microgrid. With the separately configured voltage balancing loop in the controller, the active voltage balancing through the power transfer between the bipolar buses is ensured even in the islanded mode without additional circuit components. The TAB converter operates with phase-shift modulation as conventional, and the control strategy is implemented through the digital signal processor. The validity of the proposal is verified by lab-scale experimental results.
is an emerging worldwide fungal pathogen. Over the past 20 years, 61 patient isolates of
(4 blood and 57 ear) have been obtained from 13 hospitals in Korea. Here, we reanalyzed those molecularly ...identified isolates using two matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) systems, including Biotyper and Vitek MS, followed by antifungal susceptibility testing, sequencing of the
gene, and genotyping. With a research-use-only (RUO) library, 83.6% and 93.4% of the isolates were correctly identified by Biotyper and Vitek MS, respectively. Using an
diagnostic (IVD) library of Vitek MS, 96.7% of the isolates were correctly identified. Fluconazole-resistant isolates made up 62.3% of the isolates, while echinocandin- or multidrug-resistant isolates were not found. Excellent essential (within two dilutions, 96.7%) and categorical agreements (93.4%) between the Clinical and Laboratory Standards Institute (CLSI) and Vitek 2 (AST-YS07 card) methods were observed for fluconazole. Sequencing
for all 61 isolates revealed that only 3 fluconazole-resistant isolates showed the Erg11p amino acid substitution K143R. All 61 isolates showed identical multilocus sequence typing (MLST). Pulsed-field gel electrophoresis (PFGE) analyses revealed that both blood and ear isolates had the same or similar patterns. These results show that MALDI-TOF MS and Vitek 2 antifungal susceptibility systems can be reliable diagnostic tools for testing
isolates from Korean hospitals. The Erg11p mutation was seldom found among Korean isolates of
, and multidrug resistance was not found. Both MLST and PFGE analyses suggest that these isolates are genetically similar.
Dielectric capacitors have greater power densities than batteries, and, unlike batteries, they do not utilize chemical reactions during cycling. Thus, they can become ideal, safe energy storage ...devices. However, dielectric capacitors yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Here, we present a rational approach for designing ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca2Na m–3Nb m O3m+1; m = 3–6). Individual Ca2Na m–3Nb m O3m+1 nanosheets exhibit an ultrahigh dielectric strength (638–1195 MV m–1) even in the monolayer form, which exceeds those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibit ultrahigh energy densities (174–272 J cm–3), high efficiencies (>90%), excellent reliability (>107 cycles), and temperature stability (−50–300 °C); the maximum energy density is much higher than those of conventional dielectric materials and even comparable to those of lithium-ion batteries. Enhancing the energy density may make dielectric capacitors more competitive with batteries.
This study aims to analyze the zero-voltage-switching (ZVS) region of a Triple-Active-Bridge (TAB) converter with five degrees of freedom. A TAB converter is an isolated converter derived from a ...dual-active-bridge (DAB) converter and composed of three full bridges (FBs) coupled to three winding transformers. To reduce the switching loss of the 12 active switches that compose 3 FBs, the ZVS operation is essential. However, owing to the numerous operation modes derived by five-phase shift ratios, ZVS analysis is complicated, particularly in the time domain. Therefore, this study presents the ZVS analysis model of the TAB converter based on the generalized harmonic approximation (GHA). Through the GHA of a TAB converter, the proposed model consists of unified formulas applicable to all operating ranges of the converter. Unified formulas consider all parameters, such as series inductance, port voltage, parasitic capacitance, transformer voltage, and turn ratio. In the proposed model, the ZVS area is confirmed using five-phase ratios with voltage modulation ratios as variables and verified using MATLAB and experiments.
Bipolar DC microgrids (BDCMGs) have several issues related to the voltage and require numerous converters to supply power to both poles. To solve these issues, a bidirectional dual-input dual-output ...(DIDO) converter is proposed for the voltage balancer in BDCMG. The DIDO converter has dual-input sources and a dual-output port connected to the grid. Additionally, the DIDO converter simultaneously performs independent bidirectional power control and voltage balancing control. Based on the input voltages, this paper proposes modulation methods for three cases. The modulation method of the second case has a wide operating range and low balancing current ripple without increasing the switching frequency. Moreover, only voltage balancer mode without active input sources is proposed, considering the intermittent source. Therefore, it can operate as a voltage balancer under all conditions. The voltage balancing performance of the three cases was analyzed. Finally, the proposed modulation and control method of the DIDO converter were verified through experimental results.
Despite the known association between non-alcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD), whether NAFLD predicts future CVD events, especially CVD mortality, remains ...uncertain. We evaluated the relationship between fatty liver index (FLI), a validated marker of NAFLD, and risk of major adverse cardiac events (MACEs) in a large population-based study.
We identified 3011,588 subjects in the Korean National Health Insurance System cohort without a history of CVD who underwent health examinations from 2009 to 2011. The primary endpoint was a composite of cardiovascular deaths, non-fatal myocardial infarction (MI), and ischemic stroke. A Cox proportional hazards regression analysis was performed to assess association between the FLI and the primary endpoint.
During the median follow-up period of 6 years, there were 46,010 cases of MACEs (7148 cases of cardiovascular death, 16,574 of non-fatal MI, and 22,288 of ischemic stroke). There was a linear association between higher FLI values and higher incidence of the primary endpoint. In the multivariable models adjusted for factors, such as body weight and cholesterol levels, the hazard ratio for the primary endpoint comparing the highest vs. lowest quartiles of the FLI was 1.99 (95% confidence interval CIs, 1.91-2.07). The corresponding hazard ratios (95% CIs) for cardiovascular death, non-fetal MI, and ischemic stroke were 1.98 (1.9-2.06), 2.16 (2.01-2.31), and 2.01 (1.90-2.13), respectively (p < 0.001). The results were similar when we performed stratified analyses by age, sex, use of dyslipidemia medication, obesity, diabetes, and hypertension.
Our findings indicate that the FLI, which is a surrogate marker of NAFLD, has prognostic value for detecting individuals at higher risk for cardiovascular events.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Diabetic retinopathy (DR) is a disease that causes visual deficiency owing to vascular leakage or abnormal angiogenesis. Pericyte apoptosis is considered one of the main causes of vascular leakage in ...diabetic retina, but there are few known therapeutic agents that prevent it.
is a safe natural product that has been used in traditional medicine and is attracting attention as a potential treatment for various diseases, but its effect on pericyte loss or vascular leakage in DR is not known at all. In the present study, we investigated on the effects of 60% edible ethanolic extract of
(U60E) and catechin 7-O-β-D-apiofuranoside (C7A), a compound of
, on pericyte survival and endothelial permeability. U60E and C7A prevented pericyte apoptosis by inhibiting the activation of p38 and JNK induced by increased glucose and tumor necrosis factor alpha (TNF-α) levels in diabetic retina. Moreover, U60E and C7A reduced endothelial permeability by preventing pericyte apoptosis in co-cultures of pericytes and endothelial cells. These results suggest that U60E and C7A could be a potential therapeutic agent for reducing vascular leakage by preventing pericyte apoptosis in DR.
A voltage balancer (VB) can be used to balance voltages under load unbalance in either a bipolar DC microgrid or LVDC (Low voltage DC) distribution system. An interleaved buck-type VB has advantages ...over other voltage balance topologies for reduction in output current ripple by an aspect of configuration of a physically symmetrical structure. Similarly, magnetic coupling such as winding two or more magnetic components into a single magnetic component can be selected to enhance the power density and dynamic response. In order to achieve these advantages in a VB, this paper proposes a VB with a coupled inductor (CI) as a substitute for inductors in a two-stage interleaved buck-type VB circuit. Based on patterns of switch poles under load variation, the variation in inductor currents under four switching patterns is induced. The proposed CI is derived from self-inductance based on the configuration structure that has a two-stage interleaved buck type and mathematical design results based on the coupling coefficient, where the coupling coefficient is a key factor in the determination of the dynamic response of the proposed VB in load variation. According to the results, a prototype scale is implemented to confirm the feasibility and effectiveness of the proposed VB.
Ensuring a protection scheme in a DC distribution system is more difficult to achieve against pole-to-ground faults than in AC distribution system because of the absence of zero crossing points and ...low line impedance. To complement the major obstacle of limiting the fault current, several compositions have been proposed related to mechanical switching and solid-state switching. Among them, solid-state circuit breakers (SSCBs) are considered to be a possible solution to limit fast fault current. However, they may cause problems in circuit complexity, reliability, and cost-related troubles because of the use of multiple power semiconductor devices and additional circuit configuration to commutate the current. This paper proposes a SSCB with a coupled inductor (SSCB-CI) that has a symmetrical configuration. The circuit is comprised of passive components like commutation capacitors, a CI, and damping resistors. Thus, the proposed SSCB-CI offers the advantages of a simple circuit configuration and fewer utilized power semiconductor devices than the other typical SSCBs in the DC microgrid. For the analysis, six operation states are described for the voltage across the main switches and fault current. The effectiveness of the SSCB-CI against the short-circuit fault is proved via simulation and experimental results in a lab-scale prototype.
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