Overview of Mechanism and Mitigation Measures on Multi-frequency Oscillation Caused by Large-scale Integration of Wind Power

In recent years,the large-scale integration of re-newable energy sources represented by wind power and the widespread application of power electronic devices in power systems have led to the emergence of multi-frequency oscillation problems covering multiple frequency segments,which seriously threaten system stability and restrict the accommodation of renewable energy.The oscillation problems related to renewable energy integration have become one of the most popular topics in the field of wind power integration and power system stability research.It has received extensive attention from both academia and industries with many promising research results achieved to date.This paper first analyzes several typical multi-frequency oscillation events caused by large-scale wind power integration in domestic and foreign projects,then studies the multi-frequency oscillation problems,including wind turbine’s shafting torsional oscillation,sub/super-synchronous oscillation and high frequency resonance.The state of the art is systematically summarized from the aspects of oscillation mechanism,analysis methods and mitigation measures,and the future research directions are explored.

Anti-diabetic effects and mechanisms of action of a Chinese herbal medicine preparation JQ-R in vitro and in diabetic KKAy mice

Refined-JQ(JQ-R) is a mixture of refined extracts from Coptis chinensis(Ranunculaceae),Astragalus membranaceus(Leguminosae) and Lonicera japonica(Caprifoliaceae), the three major herbs of Jin Qi-Jiang Tang tablet, a traditional Chinese medicine(TCM) formula. The mechanisms by which JQ-R regulates glucose metabolism and improves insulin sensitivity were studied in type 2 diabetic KK^(Ay)mice and insulin-resistant L6 myotubes. To investigate the mechanisms by which JQ-R improves insulin sensitivity, a model of insulin-resistant cells induced with palmitic acid(PA) was established in L6 myotubes. Glucose uptake and expression of factors involved in insulin signaling, stress, and inflammatory pathways were detected by immunoblotting. JQ-R showed beneficial effects on glucose homeostasis and insulin resistance in a euglycemic clamp experiment and decreased fasting insulin levels in diabetic KK^(Ay)mice. JQ-R also improved the plasma lipid profiles. JQ-R directly increased the activity of superoxide dismutase(SOD) and decreased malondialdehyde(MDA) as well as inducible nitric oxide synthase(iNOS) levels in insulin-resistant L6 cells, and elevated the insulin-stimulated glucose uptake with upregulated phosphorylation of AKT. The phosphorylation levels of nuclear factor kappa B(NF-κB p65), inhibitor of NF-κB(IκBα), c-Jun N-terminal kinase(JNK1/2) and extracellular-signal-regulated kinases(ERK1/2) were also changed after JQ-R treatment compared with the control group. Together these findings suggest that JQ-R improved glucose and lipid metabolism in diabetic KK^(Ay)mice. JQ-R directly enhanced insulin-stimulated glucose uptake in insulin-resistant myotubes with improved insulin signalling and inflammatory response and oxidative stress. JQ-R could be a candidate to achieve improved glucose metabolism and insulin sensitivity in type 2 diabetes mellitus.

The application of 2-NBDG as a fluorescent tracer for assessing hepatic glucose production in mice during hyperinsulinemic euglycemic clamp

Methods of performing insulin clamps vary between laboratories.Here we present a protocol of insulin clamping in conscious mice,with the significant advantage of avoiding multiple surgical catheterizations and non-physiologic metabolism during the induction of anesthesia.Using this technique we also established a new method for measuring hepa tic glucose production(HGP)using a fuorescent D-glucose analog,2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglu-cose(2-NBDG).To prove the reliability and feasibility of this method,whole-body insulin sensitivity was compared between conscious normal ICR mice and diabetic KK^(Ay) mice using the insulin clamp.Basal and clamp HGP was compared between normal C57 mice and diabetic db/db mice by using the modified clamp with 2-NBDG as a tracer.The glucose infusion rate(GIR),an index of insulin sensitivity,was significantly lower in KKAy mice than normal ICR mice.(6.2±1.3 mg/kg/min vs.31.3±2.9 mg/kg/min,P<0.001).The db/db mice also showed higher basal hepatic glucose production(25.8±2.2 mg/kg/min vs.16.7±2.5 mg/kg/min,P<0.05),higher clamp HGP after insulin suppression(7.3±1.0 mg/kg/min vs.0 mg/kg/min,P<0.001),and lower GIR(71.6±2.8 mg/kg/min vs.15.2±1.6 mg/kg/min,P<0.001)than that obtained with normal C57 mice.In conclusion,this is the first report of the application of 2-NBDG,rather than isotopic tracers,for the determination of HGP in vivo.