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A novel five-level (5L) full-scale converter is proposed for large direct-drive wind turbines. In this scheme, a 5L-Vienna rectifier is used as a robust generator-side converter and a 5L neutral-point-clamped inverter as a grid-side converter, a flying-capacitor auxiliary bridge leg is proposed to maintain the voltage balance of the dc capacitors. This study first discusses the neutral-point balancing method based on the flying-capacitor auxiliary bridge leg and modulation. Furthermore, it presents the control strategies for the proposed 5L converter. Finally, simulation and small-scale experiments are carried out to verify the analysis.

To investigate the interaction between hydrogen sulfide (H2S)/cystathionine gamma-lyase (CSE) system and nitric oxide (NO)/nitric oxide synthase (NOS) system on cardiac protection in metabolic syndrome (MS) rats.Forty one male Sprague-Dawley rats were randomly divided into 6 groups: control group, MS group, H2S donor group, CSE inhibitor group, NOS inhibitor group, and NO donor group. The MS rat model was established by a high-fat diet of 16 weeks. Rats in control and MS groups were subjected to normal saline and the other four groups were respectively subjected to sodium hydrosulfide (NaHS, 56 μmol/kg), D,L-propargylglycine (PPG, 37.5 mg/kg), Nψ-nitro-L-arginine methyl ester (L-NAME, 18 mg/kg), L-Arginine (500 mg/kg) every day. Four weeks later, the obesity indices, blood sugar of oral glucose tolerance test in each time point (0,30,60, and 120 minutes) and blood lipids (cholesterol, triglyceride, high density lipoprotein, low density lipoprotein) were measured. The computer-based electrophysiological recorder system was used to measure the changes of the left ventricular systolic pressure (LVSP), the left ventricular end diastolic pressure (LVEDP), the maximal rate of pressure increase in the contraction phase (+dP/dtmax), and the maximal rate of pressure decrease in the diastole phase (-dP/dtmax). H2S and NO concentration in plasma and myocardium, as well as CSE, constitutive NOS (cNOS), and inducible NOS (iNOS) activities in myocardium were measured with colorimetric method. Reverse transcription-polymerase chain reaction was used to assess the gene expression of CSE and endothelial NOS (eNOS) mRNAs.Compared with control group, the obesity indices, blood sugar at each time point, and blood lipids significantly increased in MS group (P0.05). H2S and NO concentration in plasma and myocardium, CSE and cNOS activities in myocardium, the expressions of CSE mRNA and eNOS mRNA, and the myocardial function significantly decreased in MS group (P0.05). Compared with MS group, NO concentration in plasma and myocardium, cNOS and iNOS activities in myocardium, and the expression of eNOS mRNA significantly increased in CSE inhibitor group (P0.05). However, activities of cNOS and iNOS in myocardium and the expression of eNOS mRNA were significantly decreased in H2S donor group (P0.01), while the myocardial function significantly increased (P0.05). H2S concentration in plasma and myocardium, and the expression of CSE mRNA significantly increased in NOS inhibitor group (P0.05). However, in NO donor group, the CSE activity in myocardium and the expression of CSE mRNA significantly decreased (P0.05). And the myocardial function was improved significantly (P0.05).Both the H2S/CSE and NO/NOS systems appear to have a mutual down-regulation effect on myocardium in MS rats. Meanwhile, exogenous H2S and NO supplement is cardioprotective in rat model of MS.

Considering wind farms real operation characteristics, a novel method using sensitivity analysis and Tabu algorithm for reactive power compensation allocations is proposed. In this paper, the sensitivity coefficient is defined as partial derivative of voltage/reactive power. The nodes that have higher sensitivity coefficient are selected for install capacitors or SVC to reduce the voltage to the largest extent. The stochastic primary solution of the problem is obtained by Tabu algorithm, and then an optimized solution is achieved by iterative solving algorithm. At last the proposed method tested in an actual wind farms in Inner Mongolia, computational results show that the proposed method is feasible and effective.

Considering the dynamic characteristic of wind farms, especially the wind turbines' output fluctuate with wind speed, the optimal reactive power compensation problem for wind farms is formulated and solved by genetic/tabu search hybrid algorithm (GATS). A mathematical model of reactive power compensation, focused on voltage stability and power losses of wind farms, is developed, and the reactive power optimization scheme using GATS is also presented. Further, the optimization method is tested in a MATLAB based simulation model for an actual wind farm in Inner Mongolia. Test result indicated that the GATS has more powerful global searching ability and can converge more quickly than the genetic algorithm or tabu search respectively. With the computed result, the voltage of wind farms can be restricted within regular range, the power losses is also reduced greatly.