Flexible HF Distribution Transformers for Inter-connection Between MVAC and LVDC Connected to DC Microgrids: Main Challenges

Solid-state transformers or so called flexible high-frequency (HF) distribution transformers are likely to become a more efficient inter-connection between medium voltage (MV) AC grids and low voltage (LV) DC grids which can eventually be connected to DC microgrids. This paper addresses the main challenges in order to implement this technology. High-Frequency Transformers (HFTs) are one of the key elements of such converters which are the main contributor to realize the voltage adaption, isolation requirements, as well as high-power density. This paper addresses the essential design considerations taking into account the magnetic materials, leakage inductance integration as well as thermal management of such transformers. Moreover, the limitations of the currently available semiconductors are discussed and the applicability and performance of the latest generations of 10 kV SiC MOSFETs are discussed. The highlighted design considerations within both the transformer and HV SiC devices are then demonstrated using experimental results

Grounding Architectures for Enabling Ground Fault Ride-Through Capability in DC Microgrids

Distributed generation in the power grid will result in considerable efficiency improvement and increase in reliability and stability of the grid. And DC microgrids have clear benefits such as higher reliability, higher efficiency, better compatibility with DC loads, expandability and etc., over their AC equivalent systems. Although DC microgrids have clear advantages over the AC microgrids, but there is not sufficient information available on their grounding. Realizing the grounding of DC systems would accelerate employing of these systems in the power grid. Grounding is a complex topic involving many design considerations and trade-offs and it is needed to ensure the safety of personnel and equipment as well as detection of ground fault in the system. Grounding of DC power system should be designed to 1) minimize the leakage current during normal operation, 2) maximize the safety of personnel and equipment under fault conditions. This work examines the different grounding methods and system architectures and discusses the design trade-offs in terms of safety, reliability, detection, mitigation, noise, and cost. We examine impedance grounding, isolation, and bi-polar architectures and discuss their benefits with respect to these criteria

A Novel Control Method for Preventing the PV and Load Fluctuations in a DC Microgrid from Transferring to the AC Power Grid

DC microgrids are gaining popularity due to the higher efficiency, reliability, lower costs and better compatibility with DC loads compared to their AC counterparts. Large-scale deployment of distributed renewable energy resources like solar in the microgrids, has to provide utilities and grid operators the capability to safely and reliably mitigate the impact of solar and loads intermittency on the main AC power grid. In this paper, a novel control method is proposed to prevent solar and load variations inside a DC microgrid from transferring to the AC power grid while the microgrid is operating in grid-tied mode. The control method works based on having multiple slack terminals with different voltage controller response times in parallel. The response times can be adjusted such that the battery converters of the microgrid absorb solar and load fluctuations while the grid-tied inverters contribute to their voltage regulation\u27s shares smoothly according to their droop parameters. This method improves upon previously discussed methods in literature in that it does not require single slack terminal, DC bus signaling or converter mode changes

Performance and loss evaluation of a hard and soft switched 2.4 MW, 4 kV to 6 kV isolated DC-DC converter for wind energy application

In this paper, a hard switched and zero-voltage switching full bridge converter for high power applications are compared in terms of their losses. The important issue in designing these kinds of converters is to manage the converter parasitics. Moreover, evaluating the losses at the high frequency transformer with square wave input is another critical point in designing such a high power density converter. The proposed full bridge converters are designed to convert 4 kV input voltage to 6 kV with rated power of 2.4 MW. The comparison is done for three different frequencies: 500 Hz, 1 kHz and 2 kHz. Also, the simulation results and loss calculations are presented

U.S. Authority for Military Operations under Regional Organization Sponsorship

Moderator: Alex Roland, Professor and Acting Chair, Department of History, Duke University Panelists: William W. Van Alstyne, William R. Perkins and Thomas C. Perkins Professor of Law, Duke University School of Law Robert F. Turner, Associate Director, Center for National Security Law Dr. Louis Fisher, Senior Specialist, Library of Congress, Congressional Research Servic

High interleukin-6 and impulsivity : determining the role of endophenotypes in attempted suicide

The dysregulation of inflammation has been associated with depression and, more recently, with suicidal behaviors. The reports regarding the relationship between interleukin-6 (IL-6) and suicide attempts are inconsistent. Personality traits such as impulsivity and aggression are considered endophenotypes and important factors that underlie suicidal behaviors. The aim of the current study was to assess whether plasma and cerebrospinal fluid (CSF) levels of IL-6 are associated with personality traits among suicide attempters. We assessed the relationships among personality traits, IL-6 and violent suicide attempts. The plasma and CSF levels of IL-6 were measured in suicide attempters (plasma=58, CSF=39) using antibody-based immunoassay systems. Personality domains were assessed using the Karolinska Scale of Personality (KSP). IL-6 levels in plasma and CSF were used to predict personality domains via regression models. Plasma IL-6 was significantly and positively correlated with extraversion as well as the KSP subscales impulsivity and monotony avoidance. CSF IL-6 was positively correlated with monotony avoidance. Violent suicide attempts tended to be associated with high plasma IL-6 levels. Plasma and CSF levels of IL-6 were not significantly associated with each other. These results indicate that impulsivity and the choice of a violent suicide attempt method might be related to higher levels of IL-6 in individuals who attempt suicide. The neuroinflammation hypothesis of suicidal behavior on the basis of elevated IL-6 levels might be partly explained by the positive association between IL-6 and impulsivity, which is a key element of the suicidal phenotype

Microparticles expressing myeloperoxidase as potential biomarkers in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV)

To investigate presence of circulating myeloperoxidase-positive microparticles (MPO(+)MPs) in relation to disease activity in patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Forty-six patients with AAV and 23 age- and sex-matched healthy controls were included. Vasculitis disease activity was assessed using the Birmingham Vasculitis Activity Score (BVAS). MPs were analyzed in citrate plasma by flow cytometry and phenotyped based on MPO expression and co-expression of pentraxin-3 (PTX3), high mobility group box 1 protein (HMGB1), and tumor necrosis factor-like weak inducer of apoptosis (TWEAK). Serum levels of PTX3, sTWEAK, and HMGB1 were also determined. Twenty-three patients had active vasculitis (BVAS >= 1). Concentrations of MPO(+)MPs expressing PTX3, HMGB1, and TWEAK were significantly higher in patients compared to healthy controls (p< 0.001,p< 0.01,p< 0.001, respectively), while concentrations of PTX3(+)and HMGB1(+)MPO(+)MPs were significantly higher in active AAV compared to patients in remission. MPO(+)MPs expressing either PTX3 or HMGB1 were associated with BVAS (r= 0.5,p< 0.001;r= 0.3,p= 0.04, respectively). Significantly higher serum PTX3 levels were found in active- than in inactive AAV (p< 0.001), correlating strongly with BVAS (r= 0.7,p< 0.001). Serum levels of sTWEAK and HMGB1 did not differ between patients and controls. Concentration of MPO(+)MPs is increased in plasma from AAV patients compared to healthy individuals. PTX3 in serum as well as PTX3 and HMGB1 expressed on MPO(+)MPs were associated with disease activity in the investigated patients. Key messages Myeloperoxidase-positive microparticles (MPO+MPs) are increased in plasma from patients with ANCA-associated vasculitis. Concentrations of MPO+MPs expressing PTX3, HMGB1, and TWEAK were significantly higher in patients compared to healthy controls. MPO+MPs expressing PTX3 and HMGB1 are associated with disease activity in ANCA-associated vasculitis