No abstract

Abstract-Loss of synchronization between wind farm and power grid during severe grid faults would cause wind farm tripping. In this paper, the mechanism of grid-synchronization is uncovered, described as motion of an autonomous nonlinear differential equation with specific initial states. The revealed mechanism indicates that even though steady state working point exists, improper initial states and poor system dynamic properties could lead to synchronization instability. In order to keep wind farm synchronous with the power grid during severe grid faults, special requirements on system dynamic properties are stated. Moreover, to satisfy all the requirements, a current injecting method is proposed. By adjusting active and reactive output currents of the wind farm, the proposed method could ensure system synchronization stability during severe grid faults. Implementation of the proposed method on PMSG and DFIG based wind farm is illustrated. Simulation results validate the analysis and the control method.

No abstract

No abstract

For doubly-fed induction generator (DFIG)-based wind energy conversion systems (WECS), large electromotive force (EMF) will be induced in the rotor circuit during grid faults. Without proper protection scheme, the rotor side of DFIG will suffer from over-currents, which may even destroy the rotor side converter (RSC). To mitigate this problem, a new flux linkage tracking-based low voltage ride-through (LVRT) control strategy is proposed to suppress the short-circuit rotor current. Under the proposed control strategy, the rotor flux linkage is controlled to track a reduced fraction of the changing stator flux linkage by switching the control algorithm of RSC during grid faults. To validate the proposed control strategy, a case study of a typical 1.5 MW DFIG-based WECS is carried out by simulation using the full order model in SIMULINK/SimPowerSystems. In the case study, a comparison with a typical LVRT method based on RSC control is given, and the effect of the control parameter on the control performance is also investigated. Finally, the validity of the proposed method is further verified by means of laboratory experiments with a scaled-size DFIG system.Index Terms-Doubly-fed induction generator (DFIG), flux linkage tracking, low voltage ride-through (LVRT), rotor side converter.

An active-damping strategy is proposed for the suppression of speed and torsional oscillations in permanent-magnet synchronous generator (PMSG)-based wind-energy conversion systems (WECSs). Direct-driven configuration with PMSG is an attractive choice for WECS because of the gearbox elimination and cost reduction due to small pole-pitch design. However, speed and torsional oscillations appear when the generator is directly connected to the wind turbine without any assistant damping device. Based on small-signal analysis, a low-bandwidth design for the power or generator torque controller of PMSG can help to reduce the oscillation amplitude, but the system dynamic performance is thus sacrificed. From the power-flow's point of view, the oscillation is reflected in the dc-link current. With the help of switch function modeling based on the space-vector-modulation scheme, the average dc-link current can be estimated and applied to the compensation strategy, which provides positive damping resulting in stability improvement. The simulation and experiment results verify the theoretical analysis and the validation of the proposed strategy.Index Terms-Active damping, dc-link current estimation, permanent-magnet synchronous generator (PMSG), torsional oscillation, wind-energy conversion system (WECS).

Abstract. Low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA) shows powerful advantages for the characterization of ambient particulate matter in environmental and geological applications. By the application of the low-Z particle EPMA single particle analysis, an overall examination of 1800 coarse and fine particles (aerodynamic diameters: 2.5-10 µm and 1.0-2.5 µm, respectively) in six samples collected on 28 April-1 May 2006 in the marine boundary layer (MBL) of the Bohai Sea and Yellow Sea was conducted. Three samples (D1, D2, and D3) were collected along the Bohai Bay, Bohai Straits, and Yellow Sea near Korea during an Asian dust storm event while the other three samples (N3, N2, and N1) were collected on non-Asian dust (NAD) days. Based on X-ray spectral and secondary electron image data, 15 different types of particles were identified, in which soil-derived particles were encountered with the largest frequency, followed by (C, N, O)-rich droplets (likely the mixture of organic matter and NH 4 NO 3 ), particles of marine origin, and carbonaceous, Fe-rich, fly ash, and (C, N, O, S)-rich droplet particles. Results show that during the Asian dust storm event relative abundances of the (C, N, O)-rich droplets and the nitrate-containing secondary soil-derived particles were markedly increased (on average by a factor of 4.5 and 2, respectively in PM 2.5−10 fraction and by a factor of 1.9 and 1.5, respectively in PM 1.0−2.5 fraction) in the MBL of the Bohai Sea and Yellow Sea, implying that Asian dust aerosols in springtime are an important carrier of gaseous inorganic nitrogen species, especially NO x (or HNO 3 ) and NH 3 .

Exposure to ambient fine particulate matter (PM2.5) increases the risk of respiratory disease. Although previous mitochondrial research has provided new information about PM toxicity in the lung, the exact mechanism of PM2.5-mediated structural and functional damage of lung mitochondria remains unclear. In this study, changes in lung mitochondrial morphology, expression of mitochondrial fission/fusion markers, lipid peroxidation, and transport ATPase activity in SD rats exposed to ambient PM2.5 at different dosages were investigated. Also, the release of reactive oxygen species (ROS) via the respiratory burst in rat alveolar macrophages (AMs) exposed to PM2.5 was examined by luminol-dependent chemiluminescence (CL). The results showed that (1) PM2.5 deposited in the lung and induced pathological damage, particularly causing abnormal alterations of mitochondrial structure, including mitochondrial swelling and cristae disorder or even fragmentation in the presence of higher doses of PM2.5; (2) PM2.5 significantly affected the expression of specific mitochondrial fission/fusion markers (OPA1, Mfn1, Mfn2, Fis1, and Drp1) in rat lung; (3) PM2.5 inhibited Mn superoxide dismutase (MnSOD), Na(+)K(+)-ATPase, and Ca(2+)-ATPase activities and elevated malondialdehyde (MDA) content in rat lung mitochondria; and (4) PM2.5 induced rat AMs to produce ROS, which was inhibited by about 84.1% by diphenyleneiodonium chloride (DPI), an important ROS generation inhibitor. It is suggested that the pathological injury observed in rat lung exposed to PM2.5 is associated with mitochondrial fusion-fission dysfunction, ROS generation, mitochondrial lipid peroxidation, and cellular homeostasis imbalance. Damage to lung mitochondria may be one of the important mechanisms by which PM2.5 induces lung injury, contributing to respiratory diseases.