13 research outputs found

    Active thermal control for modular power converters in multi-phase permanent magnet synchronous motor drive system

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    Modular winding structure has been employed in the Permanent Magnet Synchronous Motors (PMSMs) to increase the reliability and reduce the torque ripple. Nevertheless, the reliability of the motor system depends on the lifetime of the power semiconductor devices. Since the thermal cycles, which can generate the mechanical stress between the different material layers in power devices, are the key factors to influence the lifetime of power devices, in this paper, an Active Thermal Control (ATC) for modular power converters in PMSM drive is proposed to extend the system lifetime. The power routing method is employed to balance the power in a quadruple modular winding PMSM system. The Rainflow Counting Algorithm is used to calculate the thermal cycles with a load mission profile, and estimate the lifetime of the power converters. The proposed method is validated by both simulation and experiments

    Modeling and stability enhancement of a permanent magnet synchronous generator based DC system for More Electric Aircraft

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    The concept of the More Electric Aircraft (MEA) is aimed at electrifying the mechanical, hydraulic, and pneumatic subsystems on aircraft. With increasing usage of power electronics, the architecture of on-board electrical power distribution systems (EPDS) becomes more complicated. Therefore, it is necessary to analyze the stability of the system. This paper firstly presents and validates an impedance model of a permanent magnet synchronous generator (PMSG) as a source and dual active bridge (DAB) converter as a load. These models are used for the stability analysis of a simple DC power system. In addition, two new control strategies are proposed to enhance the stability of the system. The stabilization effects of the new control strategies are verified with experimental results

    DC Drift Error Mitigation Method for Three-Phase Current Reconstruction With Single Hall Current Sensor

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    Growth Responses and Accumulation Characteristics of Three Ornamental Plants to Sn Contamination in Soil

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    Decorative ornamental plants have been applied as hyperaccumulators/phytoremediators to a wide spectrum of heavy metal contaminants. In this study, pot culture experiments were conducted to investigate the Sn tolerance and accumulation in Impatiens balsamina L., Mirabilis jalapa L. and Tagetes erecta L., in order to assess the possibility of these three ornamental plants to be used as phytoremediators of Sn-contaminated soil. Results show that all three plants exhibited strong tolerance to Sn contamination, and no significant visual toxicity was observed for all three plants grown under most of the Sn treatments. The amount of Sn accumulated in the three plants was positively correlated with the Sn concentration in the soil. The order of the Sn accumulative capacity was Impatiens balsamina > Mirabilis jalapa > Tagetes erecta. Impatiens balsamina and Tagetes erecta showed a low translocation ability (TF) (<1), and the roots accumulated the highest Sn concentration, but Impatiens balsamina showed a relatively high bioconcentration factor (BCF, Sn concentration in each part > 100 mg/kg after Sn treatment of 500 mg/kg). Meanwhile, the TF of Mirabilis jalapa was >1, and the fluorescence accumulated the most Sn. In combination with the adaptation to high concentrations of various heavy metals, these three ornamental plants are potential candidates for Sn mining tailings or contaminated soil

    Nutrient recovery from source-diverted blackwater: Optimization for enhanced phosphorus recovery and reduced co-precipitation

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    High residual phosphorus in anaerobically digested source-diverted blackwater allows for increased phosphorus recovery through struvite (NH4MgPO4·6H2O) precipitation. Due to the complex matrix of blackwater, recovered products inevitably contain co-precipitates of other wastewater components that have not been well characterized. The potential hazards present include pathogens, antimicrobial resistance genes (ARGs), organic and inorganic compounds. In this study, several important struvite precipitation conditions (pH, Mg2+:PO4 3− molar ratio and MgCl2 dosing rate) were tested to determine their impact on phosphorus recovery, while taking into account the co-precipitation of enteric bacteria, ARGs and micro- and macronutrients. Results demonstrate that phosphorus recovery efficiency does not correlate to the degree of metal/microbial co-precipitation. Both PO4 3− recovery and co-precipitates were affected by the operation conditions examined, and the optimal condition for nutrient recovery from blackwater was at pH 9, a 1.5:1 Mg2+:PO4 3− molar ratio, and a dosing rate of 24 mM min−1. Although previous struvite recovery studies have identified optimal conditions for phosphorus recovery, limited information is available on the process optimization to minimize the potential risks. Downstream application of recovered struvite inevitably contains co-precipitated hazards that if not assessed can result in undesirable public health outcomes. It is necessary to evaluate struvite application and public health exposure to identify key steps that reduce public health impacts. Hence examination of struvite precipitation parameters on enhanced phosphorus recovery, along with co-precipitates, is necessary when considering the public health risk associated with efficiently recovering residual nutrients.</p

    Surface reactivity of the cyanobacterium Synechocystis sp. PCC 6803 – Implications for trace metals transport to the oceans

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    Highlights ‱ The adsorption of Cd to Synechocystis sp. PCC 6803 was investigated at both marine and freshwater ionic strength. ‱ The thermodynamic binding constants of Cd to Synechocystis were calculated using a surface complexation modeling approach. ‱ Synechocystis and other planktonic cyanobacteria may be an important vector of trace metals transport to marine settings. Cyanobacteria are abundant in nearly every surface environment on Earth. Understanding their chemical reactivity and metal binding capacity with varying ionic strength (IS) is paramount to understanding trace metal cycling in natural environments. We conducted an investigation on the cell surface reactivity of the freshwater cyanobacterium Synechocystis sp. PCC 6803 at freshwater (0.01 M NaCl) and marine (0.56 M NaCl) IS. Potentiometric titration data were used to develop a multiple discrete site, non-electrostatic surface complexation model (SCM), and corresponding cell surface functional group identities were verified using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Synechocystis cells were best modeled in FITEQL 4.0 using a non-electrostatic 2-site protonation model. Cadmium (Cd) adsorption experiments paired with SCM was utilized to calculate the binding constants of Cd. Synechocystis surface functional groups demonstrated a stronger affinity for Cd across the entire pH range studied (3–9) at freshwater IS, with the greatest difference at circumneutral pH (6–8) where Cd adsorption in freshwater IS was 60% greater than at marine IS. These data combined with the ubiquitous distribution of Synechocystis in freshwater and brackish environments suggest that these organisms could play an important role in trace metal cycling in environments with large salinity gradients, such as estuaries and deltas, and could act as a transport mechanism for trace metals from terrestrial to marine settings

    The kaolinite shuttle links the Great Oxidation and Lomagundi events

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    The ~2.22–2.06 Ga Lomagundi Event was the longest positive carbon isotope excursion in Earth’s history and is commonly interpreted to reflect perturbations in continental weathering and the phosphorous cycle. Previous models have focused on mechanisms of increasing phosphorous solubilization during weathering without focusing on transport to the oceans and its dispersion in seawater. Building from new experimental results, here we report kaolinite readily absorbs phosphorous under acidic freshwater conditions, but quantitatively releases phosphorous under seawater conditions where it becomes bioavailable to phytoplankton. The strong likelihood of high weathering intensities and associated high kaolinite content in post-Great-Oxidation-Event paleosols suggests there would have been enhanced phosphorus shuttling from the continents into marine environments. A kaolinite phosphorous shuttle introduces the potential for nonlinearity in the fluxes of phosphorous to the oceans with increases in chemical weathering intensity
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