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Performance Improvement Strategy for Parallel-operated Virtual Synchronous Generators in Microgrids
Hui Zhang,Ruixue Zhang,Kai Sun,Wei Feng 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.2
The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG’s controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.
Performance Improvement Strategy for Parallel-operated Virtual Synchronous Generators in Microgrids
Zhang, Hui,Zhang, Ruixue,Sun, Kai,Feng, Wei The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.2
The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.
Yi Zhang,FuXiang Niu,Jian Sun,Fei Xu,RuiXue Yue 한국식품과학회 2015 Food Science and Biotechnology Vol.24 No.4
Obesity and associated diseases are world-wide problems. The preventive effect of purple sweet potato color (PSPC) on high fat diet (HFD) induced obesity was investigated along with the mechanism underlying the effect. Eight-week-old male Sprague Dawley strain rats were grouped into 7 groups and intragastrically administered PSPC once a day. Obesity was prevented and abnormal glucose, triglyceride, and total cholesterol levels induced by the HFD for 6 weeks were restored to near-normal levels. PSPC significantly (p<0.05) reduced the level of reactive oxygen species and inhibited the receptor of advanced glycation end products and thioredoxin interacting protein in the hypothalamus, compared with controls. PSPC preserved the leptin signaling capability, leading to a decrease in hypothalamic adenosine 5'-monophosphate activated protein kinase activity. The anti-obesity effects of PSPC were mediated via attenuation of oxidative stress and regulation of leptin/AMPK signaling in the hypothalamus.
Ming Yao,Jiali Zhou,Yicheng Zhu,Yinxin Zhang,Xia Lv,Ruixue Sun,Ao Shen,Haitao Ren,Liying Cui,Hongzhi Guan,Honglong Wu 대한신경과학회 2016 Journal of Clinical Neurology Vol.12 No.4
Background and Purpose Encephalitis caused by Listeria monocytogenes (L. monocyto¬genes) is rare but sometimes fatal. Early diagnosis is difficult using routine cerebrospinal flu¬id (CSF) tests, while next-generation sequencing (NGS) is increasingly being used for the detection and characterization of pathogens. Methods This study set up and applied unbiased NGS to detect L. monocytogenes in CSF collected from three cases of clinically suspected listeria meningoencephalitis. Results Three cases of patients with acute/subacute meningoencephalitis are reported. Magnetic resonance imaging and blood cultures led to a suspected diagnosis of L. monocy¬togenes, while the CSF cultures were negative. Unbiased NGS of CSF identified and se¬quenced reads corresponding to L. monocytogenes in all three cases. Conclusions This is the first report highlighting the feasibility of applying NGS of CSF as a diagnostic method for central nervous system (CNS) L. monocytogenes infection. Routine application of this technology in clinical microbiology will significantly improve diagnostic methods for CNS infectious diseases.