H-Bridge Zero-Voltage Switch Controlled Rectifier (HB-ZVSCR) Transformerless Mid-Point-Clamped Inverter for Photovoltaic Applications

A single-phase transformerless mid-point clamped H-bridge zero-voltage switch-controlled rectifier inverter topology is proposed in this paper for photovoltaic (PV) systems to address the issue of common mode (CM) voltage and leakage currents. Apart from the full H-bridge inverter, the proposed voltage clamping circuit consists of two switches and a full-bridge diode which clamps the AC terminal to the DC midpoint (consisting of two DC-link capacitors) during the freewheeling period. As a result, the common mode voltage is held constant which makes it suitable for the grid-connected PV system. The operating principle and CM effect of the proposed topology are analysed and compared with the conventional topologies. This is followed by the thermal analysis and loss calculation, which shows that the proposed circuit is more efficient over the conventional topologies. Validation is carried out using MATLAB-Simulink using the PLECS toolbox followed by a scale down prototype of 1.5 kW. It is shown that the proposed inverter has the 98±1% efficiency over a wide range of loads with a peak efficiency of 98.96%, and the total harmonic distortion of the output current relatively low (≤1.8 %). The leakage current (icm) is measured for different values of parasitic capacitance that reaches a maximum of 16.65 mA for 330 nF capacitor under consideration which is well below the limit set by different safety standard

Impedance-Oriented Transient Instability Modeling of SiC MOSFET Intruded by Measurement Probes

Due to the breakneck switching speed, SiC mosfet is extremely sensitive to parasitics in the power device, circuit layout, and also measurement probe. It is not clear how the parasitics of measurement probes affect the transient stability of SiC mosfet, and it poses an unsolved challenge for the industrial field. This paper focuses to uncover the transient instability mechanism of SiC mosfet intruded by probes. Mathematical and circuit models of voltage and current probes are created, by considering the parasitics, input impedance, and bandwidth issues. To reveal the stability principles of SiC mosfet associated with probes, impedance-oriented and heterogeneity-synthesized models combining device with probes are proposed. Furthermore, an assessment methodology and root locus analysis are presented to demonstrate the transient stability schemes and the stable boundaries of SiC mosfet influenced by multiple factors, including probe parasitics, device parameters, gate resistances, and snubber circuits. Comparative experiments are presented to confirm the transient behaviors of SiC mosfet intruded by probe parasitics and regulated by control circuits. It is proven that, because of low bandwidth specifications, the large input capacitance of the voltage probe and coil inductance of the current probe degrade the transient stability of SiC mosfet. Due to the deteriorated stability margin of SiC mosfet intruded by the inserted parasitics of probes, instability may also be activated by using the small gate resistance. The snubber circuit is helpful to enhance the transient stability. Advanced probes with high bandwidth and high impedance are crucially needed for stable measurement of wide bandgap power devices like SiC mosfet.Ministry of Education (MOE)Nanyang Technological UniversityThis work was supported in part by the National Natural Science Foundation of China under Grant 51607016, in part by the National Key Research and Development Program of China under Grant 2017YFB0102303, in part by Singapore ACRF Tier 1 Grant RG 85/18, and in part by the NTU Startup Grant (SCOPES) for Prof Zhang Xin

Active Power Sharing and Frequency Restoration in an Autonomous Networked Microgrid

© 1969-2012 IEEE. Microgrid (MG) concept is considered as the best solution for future power systems, which are expected to receive a considerable amount of power through renewable energy resources and distributed generation units. Droop control systems are widely adopted in conventional power systems and recently in MGs for power sharing among generation units. However, droop control causes frequency fluctuations, which leads to poor power quality. This paper deals with frequency fluctuation and stability concerns of f-P droop control loop in MGs. Inspired from conventional synchronous generators, virtual damping is proposed to diminish frequency fluctuation in MGs. Then, it is demonstrated that the conventional frequency restoration method inserts an offset to the phase angle, which is in conflict with accurate power sharing. To this end, a novel control method, based on phase angle feedback, is proposed for frequency restoration in conjunction with a novel method for adaptively tuning the feedback gains to preserve precise active power sharing. Nonlinear stability analysis is conducted by drawing the phase variations of the nonlinear second-order equation of the δ-P droop loop and it is proved that the proposed method improves the stability margin of f-P control loop. Simulation results demonstrate the effectiveness of the proposed method

Group i metabotropic glutamate receptors: A potential target for regulation of proliferation and differentiation of an immortalized human neural stem cell line

© 2014 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society). Human neural stem cells (NSCs) from the developing embryo or the subventricular zone of the adult brain can potentially elicit brain repair after injury or disease, either via endogenous cell proliferation or by cell transplantation. Profound knowledge of the diverse signals affecting these cells is, however, needed to realize their therapeutic potential. Glutamate and group I metabotropic glutamate receptors (mGluRs) affect proliferation and survival of rodent NSCs both during embryonic and post-natal development. To investigate the role of group I mGluRs (mGluR1 and mGluR5) on human NSCs, we differentiated an immortalized, forebrain-derived stem cell line in the presence or absence of glutamate and with addition of either the group I mGluR agonist DHPG or the selective antagonists, MPEP (mGluR5) and LY367385 (mGluR1). Characterization of differentiated cells revealed that both mGluR1 and mGluR5 were present on the cells. Addition of glutamate to the growth medium significantly increased cell proliferation and reduced cell death, resulting in increased cell numbers. In the presence of glutamate, selective activation of group I mGluRs reduced gliogenesis, whereas selective inhibition of group I mGluRs reduced neurogenesis. Our results substantiate the importance of glutamate signalling in the regulation of human NSCs and may as such be applied to promote proliferation and neuronal differentiation.This research was supported by the Danish Parkinson Association, IMK Almene Fond, Hørslev-Fonden, Kirsten og Freddy Johansens Fond, Grosserer Brogaard og Hustrus Mindefond and Fonden for Lægevidenskabens Fremme.Peer Reviewe

A Classification of Single-Phase Transformerless Inverter Topologies for Photovoltaic Applications

© 2018 IEEE. In Photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations. However, a transformer based inverter is bulky and has high conduction losses, therefore lead to a reduction in the inverter efficiency. To overcome this issue, the transformerless inverter topologies are addressed widely, but the main challenge of a transformerless inverter is common mode issue. Numerous topological modifications with their control and modulation techniques makes them difficult to follow, generalize and highlight the advantages and disadvantages. To address the issue, this paper gives an overview on transformerless inverter and classify them into subsection to discuss the merit and demerit of some of the major topologies. Five subsections based on common mode behavior, voltage clamping and decoupling techniques have been demonstrated (i.e., common ground, mid-point clamping, AC-decoupling, DC-decoupling and AC+DC decoupling). To verify the finding and for general consensus, major transformerless topologies are simulated using PLECS. A general summary is presented at the end to stimulate readers to acknowledge the problems and identify solutions

Type I interferon-activated microglia are critical for neuromyelitis optica pathology

Neuromyelitis optica (NMO) is an inflammatory disease of the central nervous system (CNS) most frequently mediated by serum autoantibodies against the water channel aquaporin 4, expressed on CNS astrocytes, resulting in primary astrocytopathy. There is no cure for NMO, and treatment with Type I interferon (IFNI)-IFN beta is ineffective or even detrimental. We have previously shown that both NMO lesions and associated microglial activation were reduced in mice lacking the receptor for IFN beta. However, the role of microglia in NMO is not well understood. In this study, we clarify the pathomechanism for IFNI dependence of and the role of microglia in experimental NMO. Transcriptome analysis showed a strong IFNI footprint in affected CNS tissue as well as in microglial subpopulations. Treatment with IFN beta led to exacerbated pathology and further microglial activation as evidenced by expansion of a CD11c(+) subset of microglia. Importantly, depletion of microglia led to suppression of pathology and decrease of IFNI signature genes. Our data show a pro-pathologic role for IFNI-activated microglia in NMO and open new perspectives for microglia-targeted therapies