Soft-start procedure for a three-stage smart transformer based on dual-active bridge and cascaded H-bridge converters

Power electronics based three-stage smart transformers (STs) can be seriously damaged by inrush currents and overvoltages during the start-up phase if the control of the stages is not correctly coordinated. Hence, it is crucial to design properly the start-up procedure, especially in case of modular architectures with distributed dc-links. The design of the start-up procedure depends on the ST power stages topologies, their control systems, and the operation modes. This article proposes a soft-shift start modulation technique that allows to limit the inrush current in the dc/dc isolation stage during the dc-link capacitors precharging. A fast voltage-balancing control, performed by the dc/dc isolation stage, is introduced to avoid overvoltages and unbalanced voltage conditions among the different power cells. Under the proposed method, fast control dynamics is guaranteed thanks to the high frequency bandwidth of the dc/dc isolation stage converters. Theoretical analysis, based on a detailed small signal model of the ST, and simulations are used to demonstrate the principle of the operation. Experimental results, carried out in an ST prototype, confirm the performances of proposed solution in realizing a smooth start-up without voltage/current overshoots

DC Multibus based on a Single-Star Bridge Cells Modular Multilevel Cascade Converter for DC smart grids

In the last years a growing interest towards DC Smart Grids has been registered due to high penetration of distributed generation systems with embedded storage. Trying to foresee the possible future scenarios of the power systems, it can be noticed that DC Smart Grids can be even preferable to AC Smart Grids in terms of flexibility and redundancy since they are compatible with the achievement of a DC Multibus working at different voltage levels. In this paper the Single-Star Bridge Cells Modular Multilevel Cascade Converter is used to create a DC Multibus. The performances of the system are analyzed considering different load configurations and coexistence of different voltage levels of the buses forming the DC Multibus. Results confirms the validity of the proposed solution and the robustness of the control system in case of load variations

Reactive Power Flow Control for PV Inverters Voltage Support in LV Distribution Networks

This paper proposes a reactive power flow control pursuing the active integration of photovoltaic systems in LV distribution networks. An alternative power flow analysis is performed according to the specific characteristics of LV networks, such as high resistance/reactance ratio and radial topologies. The proposed solution gives high performances,in terms of rms- voltage regulation, by estimating the reactive power reference on each node considering the influence of the rest of the nodes in terms of active and reactive power demanded/generated by them. The local control of each photovoltaic system is based on the power converter control,interfacing these units with the grid and the loads respectively. The local control is designed on the basis of locally measured feedback variables. Photovoltaic units thus guarantee universal operation,being able to change between islanding-mode and grid-connected mode without disrupting critical loads connected to them, and allowing smooth transitions. Exhaustive results are also included and discussed in this paper

Elevated levels of IL-6 in IgA nephropathy patients are induced by an epigenetically driven mechanism modulated by viral and bacterial RNA

Background: Immunoglobulin A nephropathy (IgAN) is the most frequent primary glomerulonephritis and the role of IL-6 in pathogenesis is becoming increasingly important. A recent whole genome DNA methylation screening in IgAN patients identified a hypermethylated region comprising the non-coding RNA Vault RNA 2-1 (VTRNA2-1) that could explain the high IL-6 levels. Methods: The pathway leading to IL-6 secretion controlled by VTRNA2-1, PKR, and CREB was analyzed in peripheral blood mononuclear cells (PBMCs) isolated from healthy subjects (HS), IgAN patients, transplanted patients with or without IgAN. The role of double and single-strand RNA in controlling the pathway was investigated. Results: VTRNA2-1 was downregulated in IgAN compared to HS and in transplanted IgAN patients (TP-IgAN) compared to non-IgAN transplanted (TP). The loss of the VTRNA2-1 natural restrain in IgAN patients caused PKR hyperphosphorylation, and consequently the activation of CREB by PKR, which, in turn, led to high IL-6 production, both in IgAN and in TP-IgAN patients. IL-6 levels could be decreased by the PKR inhibitor imoxin. In addition, PKR is normally activated by bacterial and viral RNA, and we found that both the RNA poly(I:C), and the COVID-19 RNA-vaccine stimulation significantly increased the IL-6 levels in PBMCs from HS but had an opposite effect in those from IgAN patients. Conclusion: The discovery of the upregulated VTRNA2-1/PKR/CREB/IL-6 pathway in IgAN patients may provide a novel approach to treating the disease and may be useful for the development of precision nephrology and personalized therapy by checking the VTRNA2-1 methylation level in IgAN patients