218 research outputs found
Symbolically Aided Model Development for an induction Machine in Virtual Test Bed
A new phase-domain induction machine model for use in power system dynamic simulation is developed with the aid of a symbolic tool. The symbolic tool can automatically construct a time-domain power system component model in the resistive companion form (RCF) that is widely used in time-domain simulators. The automatic differentiation technique (aDT) is utilized within the context of a symbolic modeling language, and the tool has been implemented for the virtual test bed (VTB) simulation environment. The new induction machine model was used to study start-up transients of an induction motor. The new model was verified by comparing the simulation results to those obtained from a standard d-q model. This paper also demonstrates that a symbolically assisted technique can provide an efficient and rapid path for developing complex nonlinear device models for power system simulations
The Impact of Transformer Winding Connections of a Grid-Connected PV on Voltage Quality Improvement
In this paper, a high-power PV power plant is connected to the weak grid by means of a three-phase power transformer. The selection of transformer winding connection is critical especially when the PV inverter has a reactive power controller. In general, transformer winding connection can be arranged in star-star (with neutrals grounded) or star-delta. The reactive power controller supports voltage regulation of the power system particularly under transient faults. Its control strategy is based on utilizing the grid currents to produce a three-phase unbalanced reactive current with a small gain. The gain is determined by the system impedance. Simulation results exhibit that the control strategy works very well particularly under disturbance conditions when the transformer winding connection is star-star with both neutrals grounded. The power quality in terms of the voltage quality is improve
Power quality improvement utilizing photovoltaic generation connected to a weak grid
Microgrid research and development in the past
decades have been one of the most popular topics. Similarly, the
photovoltaic generation has been surging among renewable
generation in the past few years, thanks to the availability,
affordability, technology maturity of the PV panels and the PV
inverter in the general market. Unfortunately, quite often, the PV
installations are connected to weak grids and may have been
considered as the culprit of poor power quality affecting other
loads in particular sensitive loads connected to the same point of
common coupling (PCC). This paper is intended to demystify the
renewable generation, and turns the negative perception into
positive revelation of the superiority of PV generation to the power
quality improvement in a microgrid system. The main objective of
this work is to develop a control method for the PV inverter so that
the power quality at the PCC will be improved under various
disturbances. The method is to control the reactive current based
on utilizing the grid current to counteract the negative impact of
the disturbances. The proposed control method is verified in PSIM
platform. Promising results have been obtaine
Characterization of garlic oil/β-cyclodextrin inclusion complexes and application
Garlic oil is a liquid extracted from garlic that has various natural antibacterial and anti-inflammatory properties and is believed to be used to prevent and treat many diseases. However, the main functional components of garlic oil are unstable. Therefore, in this study, encapsulating garlic oil with cyclodextrin using the saturated co-precipitation method can effectively improve its chemical stability and water solubility and reduce its characteristic odor and taste. After preparation, the microcapsules of garlic oil cyclodextrin were characterized, which proved that the encapsulation was successful. Finally, the results showed that the encapsulated garlic oil still had antioxidant ability and slow-release properties. The final addition to plant-based meat gives them a delicious flavor and adds texture and mouthfeel. Provided a new reference for the flavor application of garlic cyclodextrin micro-capsules in plant-based meat patties
Evaluation of genipin-crosslinked chitosan hydrogels as a potential carrier for silver sulfadiazine nanocrystals
In the present study genipin crosslinked chitosan (CHI) hydrogels, which had been
constructed and reported in our previous studies (Lei Gao, et al. Colloids Surf. B
Biointerfaces. 2014, 117: 398), were further evaluated for their advantage as a carrier
for silver sulfadiazine (AgSD) nanocrystal systems. Firstly, AgSD nanocrystals with a
mean particle size of 289 nm were prepared by wet milling method and encapsulated
into genipin crosslinked CHI hydrogels. AgSD nanocrystals displayed a uniform
distribution and very good physical stability in the hydrogel network.
Swelling-dependent release pattern was found for AgSD nanocrystals from hydrogels
and the release profile could be well fitted with Peppas equation. When AgSD
nanocrystals were encapsulated in hydrogels their fibroblast cytotoxicity decreased
markedly, and their antibacterial effects against Staphylococcus aureus, Escherichia
coli and Pseudomonas aeruginosa were still comparable to unencapsulated AgSD
nanocrystals. In vivo evaluation in excision and burn cutaneous wound models in
mice showed that AgSD nanocrystal hydrogels markedly decreased the expression of
inflammatory cytokine IL-6, but increased the levels of growth factors VEGF-A and
TGF-β1. Histopathologically, the wounds treated by hydrogels containing AgSD
nanocrystals showed the best healing state compared with commercial AgSD cream,
hydrogels containing AgSD bulk powders and blank hydrogels. The wounds treated
by AgSD nanocrystal hydrogels were dominated by marked fibroblast proliferation,
new blood vessels and thick regenerated epithelial layer. Sirius Red staining assay
indicated that AgSD nanocrystal hydrogels resulted in more collagen deposition
characterized by a large proportion of type I fibers. Our study suggested that
genipin-crosslinked CHI hydrogel was a potential carrier for local antibacterial
nanomedicines
Development of a human-size magnetic particle imaging device for sentinel lymph node biopsy of breast cancer
In this study, a novel human-size handheld magnetic particle imaging (MPI) system was developed for the high-precision detection of sentinel lymph nodes for breast cancer. The system consisted of a highly sensitive home-made MPI detection probe, a set of concentric coils pair for spatialization, a solenoid coil for uniform excitation at 8 [email protected] mT, and a full mirrored coil set positioned far away from the scanning area. The mirrored coils formed an extremely effective differential pickup structure which suppressed the system noise as high as 100 dB. The different combination of the inner and outer gradient current made the field free point (FFP) move in the Z direction with a uniform intensity of 0.54T/m, while the scanning in the XY direction was implemented mechanically. The third-harmonic signal of the Superparamagnetic Iron Oxide Nanoparticles (SPIONs) at the FFP was detected and then reconstructed synchronously with the current changes. Experiment results showed that the tomographic detection limit was 30 mm in the Z direction, and the sensitivity was about 10 μg Fe SPIONs at 40 mm distance with a spatial resolution of about 5 mm. In the rat experiment, 54 μg intramuscular injected SPIONs were detected successfully in the sentinel lymph node, in which the tracer content was about 1.2% total injected Fe. Additionally, the effective detection time window was confirmed from 4 to 6 min after injection. Relevant clinical ethics are already in the application process. Large mammalian SLNB MPI experiments and 3D preoperative SLNB imaging will be performed in the future
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