Synchronverter-based control for wind power

More and more attention has been paid to the energy crisis due to the increasing energy demand from industrial and commercial applications. The utilisation of wind power, which is considered as one of the most promising renewable energy sources, has grown rapidly in the last three decades. In recent years, many power converter techniques have been developed to integrate wind power with the electrical grid. The use of power electronic converters allows for variable speed operation of wind turbines, and enhanced power extraction. This work, which is supported by EPSRC and Nheolis under the DHPA scheme, focuses on the design and analysis of control systems for wind power. In this work, two of the most popular AC-DC-AC topologies with permanent magnet synchronous generators (PMSG) have been developed. One consists of an uncontrollable rectifier, a boost converter and an inverter and a current control scheme is proposed to achieve the maximum power point tracking (MPPT). In the control strategy, the output current of the uncontrollable rectifier is controlled by a boost converter according to the current reference, which is determined by a climbing algorithm, to achieve MPPT. The synchronverter technology has been applied to control the inverter for the grid-connection. An experimental setup based on DSP has been designed to implement all the above mentioned experiments. In addition, a synchronverter-based parallel control strategy, which consists of a frequency droop loop and a voltage droop loop to achieve accurate sharing of real power and reactive power respectively, has been further studied. Moreover, a control strategy based on the synchronverter has been presented to force the inverter to have capacitive output impedance, so that the quality of the output voltage is improved. Abstract The other topology consists of a full-scale back-to-back converter, of which the rectifier is controllable. Two control strategies have been proposed to operate a three-phase rectifier to mimic a synchronous motor, following the idea of synchronverters to operate inverters to mimic synchronous generators. In the proposed schemes, the real power extracted from the source and the output voltage are the control variables, respectively, hence they can be employed in different applications. Furthermore, improved control strategies are proposed to self-synchronise with the grid. This does not only improve the performance of the system but also considerably reduces the complexity of the overall controller. All experiments have been implemented on a test rig based on dSPACE to demonstrate the excellent performance of the proposed control strategies with unity power factor, sinusoidal currents and good dynamics. Finally, an original control strategy based on the synchronverter technology has been proposed for back-to-back converters in wind power applications to make the whole system behave as a generator-motor-generator system

Pharmacological inhibition of GSK-3β rescues the impaired myogenic differentiation caused by dexamethasone.

<p>C2C12 myoblasts were treated with DEX (10⁻⁵ M) or a combination of DEX and various concentrations of LiCl (2.5, 5, 7.5 mM) after switching to DM. (A and B) Western blot analysis of MyHC protein expression when induced for 4 d (A) and 6 d (B). (C and D) Western blot analysis of MyoD and myogenin expression at the early stage of myogenic differentiation, <i>i.e.</i>, induced for 24 h (C) and 48 h (D). (E) C2C12 myoblasts were treated with DEX (10⁻⁵ M) or a combination of DEX and LiCl (5 mM) and induced to differentiate for 4 d. Immunofluorescence detection of MyHC (red) and DAPI counterstaining of nuclei (blue) were used to label myotubes. The scale bar is 50 µm. (F) Quantitative analysis of the fusion index from (E). (G) C2C12 myoblasts were induced to differentiate for 3 d in the presence of DEX (10⁻⁵ M) or a combination of DEX and LiCl (5 mM), and MCK mRNA levels were measured by real-time RT-PCR and compared to control myoblasts (without DEX or LiCl in DM). The data are shown as the means ± SEM of three independent experiments. *<i>P</i><0.05 versus the control group (without DEX or LiCl in DM).</p

GSK-3β inhibition attenuates dexamethasone-mediated repression of myogenic differentiation of primary satellite cells.

<p>(A) Immunofluorescence analysis of PAX-7 (green) and DAPI (blue) expression in primary satellite cells. (B) Differentiating primary satellite cells were treated with 10⁻⁵ M DEX and harvested for cytotoxicity assays using a CCK-8 kit at 12 h, 24 h, and 48 h. (C) Myogenic differentiation assay to determine the GR specificity of DEX using RU-486. Immunofluorescence detection of MyHC (red) and DAPI (blue) was used to detect myotubes (left panel). The fusion index is shown in right panel. The scale bar is 50 µm. (*<i>P</i><0.05 versus RU-486(−)/CON; ^&<i>P</i><0.05 versus RU-486(−)/DEX. n = 3 independent experiments). (D) Differentiating primary satellite cells were incubated with DEX and RU-486 (10 µM), alone or in combination, or control DM (CON). Phosphorylation of GSK-3β at serine 9 at the indicated time points was determined using Western blot analysis. (E and F) Primary satellite cells were treated with DEX (10⁻⁵ M) or a combination of DEX and 5 mM LiCl after switching to DM. Western blot analysis of MyoD and myogenin at 24 h and 48 h (E) and MyHC at 4 d and 6 d (F). (G) The GSK-3β abundance was assessed by Western blot analysis to detect the silencing efficiency after shRNA transfection for 24 h. (H) shNC and shGSK-3β satellite cells were differentiated in the absence (CON) or presence of DEX (DEX) for 4 d. Immunofluorescence detection of MyHC (red) and DAPI (blue) were used to detect myotubes (left panel). The fusion index is shown in right panel. The scale bar is 50 µm. The data are shown as the means ± SEM of three independent experiments. *<i>P</i><0.05; ^&<i>P</i><0.05 versus shNC/CON; ^#<i>P</i><0.05 versus shNC/DEX.</p

Real-time PCR primer sequences used in this study.

<p>Real-time PCR primer sequences used in this study.</p

GSK-3β knockdown stimulates myogenic differentiation and confers resistance to DEX-induced inhibition of myogenic markers of differentiation.

<p>shGSK-3β and shNC myoblasts cells were induced to differentiate in the absence of DEX (CON), and Western blot analysis was used to assess the expression of MyoD and myogenin after induction for 24 h or 48 h (A) and the expression of MyHC after differentiation for 4 d or 6 d (B). shGSK-3β and shNC myoblast cells were induced to differentiate in the presence of DEX. Western blot analysis showing the expression of MyoD and myogenin after induction for 24 h or 48 h (C) and the expression of MyHC after induction for 4 d or 6 d (D). (E) MCK mRNA levels were measured in shGSK-3β and shNC myoblast cells after differentiation induction for 3 d in the absence (CON) or presence of DEX. The relative mRNA levels were assessed by real-time RT-PCR and compared with shNC myoblasts induced in control DM (without DEX). The data are shown as the means ± SEM of three independent experiments. *<i>P</i><0.05; ^&<i>P</i><0.05 versus shNC/CON; ^#<i>P</i><0.05 versus shNC/DEX.</p

GSK-3β knockdown attenuates DEX-induced impairment of myotube formation.

<p>(A) shRNA interference of GSK-3β was performed in C2C12 myoblasts, and GSK-3β abundance was assessed by Western blot analysis to detect the silencing efficiency after transfection for 24 h. (B) shNC myoblast cells and shGSK-3β myoblast cells were differentiated in the absence (CON, panel a, b) or presence of DEX (DEX, panel c, d) for 4 d. Immunofluorescence detection of MyHC (red) and DAPI (blue) were used to detect myotubes. The scale bar is 50 µm. (C) Quantitative analysis of the fusion index using data from (B). The data are shown as the means ± SEM of three independent experiments. *<i>P</i><0.05; ^&<i>P</i><0.05 versus shNC/CON; ^#<i>P</i><0.05 versus shNC/DEX.</p

Inhibition of Glycogen Synthase Kinase-3β Attenuates Glucocorticoid-Induced Suppression of Myogenic Differentiation <i>In Vitro</i>

<div><p>Glucocorticoids are the only therapy that has been demonstrated to alter the progress of Duchenne muscular dystrophy (DMD), the most common muscular dystrophy in children. However, glucocorticoids disturb skeletal muscle metabolism and hamper myogenesis and muscle regeneration. The mechanisms involved in the glucocorticoid-mediated suppression of myogenic differentiation are not fully understood. Glycogen synthase kinase-3β (GSK-3β) is considered to play a central role as a negative regulator in myogenic differentiation. Here, we showed that glucocorticoid treatment during the first 48 h in differentiation medium decreased the level of phosphorylated Ser9-GSK-3β, an inactive form of GSK-3β, suggesting that glucocorticoids affect GSK-3β activity. We then investigated whether GSK-3β inhibition could regulate glucocorticoid-mediated suppression of myogenic differentiation <i>in vitro</i>. Two methods were employed to inhibit GSK-3β: pharmacological inhibition with LiCl and GSK-3β gene knockdown. We found that both methods resulted in enhanced myotube formation and increased levels of muscle regulatory factors and muscle-specific protein expression. Importantly, GSK-3β inhibition attenuated glucocorticoid-induced suppression of myogenic differentiation. Collectively, these data suggest the involvement of GSK-3β in the glucocorticoid-mediated impairment of myogenic differentiation. Therefore, the inhibition of GSK-3β may be a strategy for preventing glucocorticoid-induced muscle degeneration.</p></div

Effects of DEX on GSK-3β activity during myogenic differentiation.

<p>(A) C2C12 myoblasts were induced to differentiate in the absence (CON) or presence of 10⁻⁵ M DEX. Phosphorylation of GSK-3β at serine 9 at the indicated time points was determined using Western blot analysis. (B) Differentiating C2C12 myoblasts were incubated with DEX and RU-486 (10 µM), alone or in combination, or control DM (CON). Phosphorylation of GSK-3β at serine 9 at the indicated time points was determined using Western blot analysis. The data are shown as the means ± SEM of three independent experiments. *<i>P</i><0.05 compared to control group (without DEX or RU-486 in DM).</p

Effect of butyrate on inflammatory cytokines production.

<p>Rats were subjected to total warm liver I/R injury or sham operation and pretreated with butyrate or vehicle. Liver TNF-α (A) and IL-6 (B) mRNA expression was measured by RT-PCR after reperfusion. Serum TNF-α (C) and IL-6 (D) levels was measured by Elisa after reperfusion. Data represent means ± SD, N = 3–5 rats per group. *P<0.05 vs. the sham group, ^#P<0.05 vs. the vehicle group.</p

Histopathologic analyses of livers after reperfusion.

<p>Rats were subjected to total warm liver I/R injury or sham operation and pretreated with butyrate or vehicle. HE-stained liver sections from the sham (A, D), vehicle (B, E), and butyrate (C, F) groups at 6 h (B, C) and 24 h (E, F) after reperfusion (×200).</p