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Thermal camera has been applied in photovoltaic (PV) array monitoring to detect defects and hot spots. However, the infrared (IR) image is often degenerated and the temperature information displayed from the image can lead to erroneous interpretation. Hot spots will be obscured and a gradual change phenomenon will emerge when monitoring a large PV array. In this paper, the mechanism of IR image degeneration and gradual change phenomenon are studied and verified with experiments. The variations of atmospheric transmission and directional emissivity have been identified to be the cause of image degeneration. The sensitivity of atmospheric transmission and directional emissivity are defined to analyze the impact of these two factors on the temperature displayed. Based on this mechanism, a recovery method has been proposed to recover the real temperature from the degenerated IR image. Experiments have been conducted to test the effectiveness of the recovery method. In addition, the temperature sensitivity has been defined to analyze how atmospheric transmission and directional emissivity will affect the temperature difference displayed in the IR image. The proposed temperature sensitivity has been used as the criteria to assess the quality of IR image. Some rules of thumb are proposed to deploy the thermal camera in order to increase the quality of the IR image. [ABSTRACT FROM AUTHOR]

Resonant two-photon ionization spectrum of C[sub 6]H[sub 5]CH[sub 3]...N[sub 2] has been recorded, which exhibits rich information about the van der Waals vibrational modes and internal rotation of N[sub 2]. An ab initio calculation shows a C[sub s] point group for the complex, in which the mass center of N[sub 2] is ∼0.35 nm above the benzene ring and the molecular axis of N[sub 2] is in the symmetry plane but tilted slightly away from the CH[sub 3] group by ∼2°. With the help of isotopic substitution, quantum mechanics calculations, and systematic comparisons, we have tentatively assigned all the observed spectral features. The van der Waals bonding is shown to have an inhibitory effect on the internal rotation of the CH[sub 3] group. Bond dissociation energies for the complex C[sub 6]H[sub 5]CH[sub 3]...N[sub 2] in the excited electronic state and in the ground electronic state are estimated to be 494 and 474 cm-1, respectively, in good agreement with the calculated value. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on photofragmentation studies of small selenium cluster cations. Detection of the parent and daughter cluster ions using a reflectron time-of-flight mass spectrometer; Estimating the appearance potentials of all the observed cluster fragment ions; Decrease in dissociation thresholds of the odd-numbered cations with the increase in cluster size.

Studies the resonant two-photon ionization (R[sub2]PI) spectra of three van der Waals complexes through the S1 to S0 transition with mass selectivity. Analysis of structure, electronic transition, band shift and intermolecular motions of p,m,o-C[sub6]H[sub4]F[sub2]...Ar and p,m,o-C[sub6]H[sub4]F[sub2]...N[sub2]; Estimation of dissociation energies.

Examines the resonant two-photon ionization spectra of the van der Waals complexes of 1,2-difluorobenzene...argon (Ar) and 1,3-difluorobenzene...Ar. Derivation of the intermolecular vibrational energy levels; Use of quantum calculations in the study; Spectral shifts of the intramolecular bands.

In this study, the spatial structure of randomly distributed clusters of fungi An0429 spores was simulated using a cluster aggregation (CCA) model, and the single scattering parameters of fungi An0429 spores were calculated using the discrete dipole approximation (DDA) method. The transmittance of 10.6 mm infrared (IR) light in the aggregated fungi An0429 spores swarm is simulated by using the Monte Carlo method. Several parameters that affect the transmittance of 10.6 mm IR light, such as the number and radius of original fungi An0429 spores, porosity of aggregated fungi An0429 spores, and density of aggregated fungi An0429 spores of the formation aerosol area were discussed. Finally, the transmittances of microbial materials with different qualities were measured in the dynamic test platform. The simulation results showed that the parameters analyzed were closely connected with the extinction performance of fungi An0429 spores. By controlling the value of the influencing factors, the transmittance could be lower than a certain threshold to meet the requirement of attenuation in application. In addition, the experimental results showed that the Monte Carlo method could well reflect the attenuation law of IR light in fungi An0429 spore agglomerates swarms. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) in a doubly-fed induction generator-based wind turbine (DFIG-WT). The space vector pulse width modulation (SVPWM) technique is simplified and unified duty ratios are used for controlling the FSTP GSC. Steady DC-bus voltage, sinusoidal three-phase grid currents and unity power factor are obtained. In addition, the balance of capacitor voltages is accomplished based on the analysis of current flows at the midpoint of DC bus in different operational modes. Besides, external disturbances such as fluctuating wind speed and grid voltage sag are considered to test its fault-tolerant ability. Furthermore, the effects of fluctuating wind speed on the performance of DFIG-WT system are explained according to an approximate expression of the turbine torque. The performance of the proposed FSTP GSC is simulated in Matlab/Simulink 2016a based on a detailed 1.5 MW DFIG-WT Simulink model. Experiments are carried out on a 2 kW platform by using a discrete signal processor (DSP) TMS320F28335 controller to validate the reliability of DFIG-WT for the cases with step change of the stator active power and grid voltage sag, respectively. [ABSTRACT FROM AUTHOR]

System efficiency and cost effectiveness are of critical importance for photovoltaic (PV) systems. This paper addresses the two issues by developing a novel three-port dc-dc converter for stand-alone PV systems, based on an improved Flyback- Forward topology. It provides a compact single-unit solution with a combined feature of optimized maximum power point tracking (MPPT), high step-up ratio, galvanic isolation, and multiple operating modes for domestic and aerospace applications. A theoretical analysis is conducted to analyze the operating modes followed by simulation and experimental work. This paper is focused on a comprehensive modulation strategy utilizing both PWM and phase-shifted control that satisfies the requirement of PV power systems to achieve MPPT and output voltage regulation. A 250- W converter was designed and prototyped to provide experimental verification in term of system integration and high conversion efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a new thermography-based maximum power point tracking (MPPT) scheme to address photovoltaic (PV) partial shading faults. Solar power generation utilizes a large number of PV cells connected in series and in parallel in an array, and that are physically distributed across a large field. When a PV module is faulted or partial shading occurs, the PV system sees a nonuniform distribution of generated electrical power and thermal profile, and the generation of multiple maximum power points (MPPs). If left untreated, this reduces the overall power generation and severe faults may propagate, resulting in damage to the system. In this paper, a thermal camera is employed for fault detection and a new MPPT scheme is developed to alter the operating point to match an optimized MPP. Extensive data mining is conducted on the images from the thermal camera in order to locate global MPPs. Based on this, a virtual MPPT is set out to find the global MPP. This can reduce MPPT time and be used to calculate the MPP reference voltage. Finally, the proposed methodology is experimentally implemented and validated by tests on a 600-W PV array. [ABSTRACT FROM AUTHOR]

A series of Sm3+/Eu3+ singly and co-doped Ba2Ln(BO3)2Cl (Ln=Y3+, Gd3+) phosphors were prepared via the solid-state method. The XRD results indicate that the as-prepared products keep the monoclinic structure with a P21/m space group of Ba2Ln(BO3)2Cl, which belongs to the isomorphic substitution for Ln3+ sites in the Ba2Yb(BO3)2Cl host. The photoluminescence (PL) spectra demonstrate that Ba2Ln(BO3)2Cl:Sm3+,Eu3+ emits red light centered at 593 nm under the 393 nm excitation which is in good agreement with the emission wavelength from near ultraviolet light-emitting diodes (LEDs). The luminescence decays suggest that the energy transfer from Sm3+ to Eu3+ ions in Ba2Ln(BO3)2Cl:Eu3+, Sm3+ occurs. All results mean that Ba2Ln(BO3)2Cl:Eu3+, Sm3+ phosphors exhibit potential to act as a kind of red phosphor for near ultraviolet white light-emitting diodes (w-LEDs). [ABSTRACT FROM AUTHOR]

Grid-connected current control plays an important role in the renewable grid-connected system. This paper investigates the grid-connected current hysteresis control of the asymmetry three-level inverter. In order to effectively utilize asymmetry three-level inverter and conquer the disadvantages of traditional hysteresis control, the multistage hysteresis control and current predict hysteresis control are developed. In the multistage hysteresis control method, the switching times of main switches can be declined by regularly adjusting the bus voltage without altering the inductor and bandwidth. In addition, the current predict hysteresis control is developed, which adapts to proper bus voltage without dividing bus switching time. In order to overcome the invalidation issue of the bandwidth in hysteresis control, virtual sample technology is used without increasing real sample frequency. Both simulation and experimental tests have been conducted to verify the efficacy of the proposed methods. [ABSTRACT FROM AUTHOR]

Photoreactions in the gas-phase complexes Mg•+(1,4-dioxane) (1) and Mg•+(1,3-dioxane) (1M) have been examined in the wavelength region of 230−440 nm. Photoproduct assignments are facilitated with the help of deuterium substitution experiments. The main energy relaxation channel for both photoexcited complexes is the evaporation of Mg•+. Also observed from 1 are rich photoproducts with m/z 28, 41, 54−58, 67, 69, and 88; the most abundant one at m/z 54 is designated to Mg•+(O=CH2). In marked contrast, the photolysis of 1M yields only Mg•+(O=CH2) other than Mg•+. Density functional calculations are performed to obtain optimized geometries and potential energy surfaces of 1 and 1M. Although Mg•+(chair-1,4-C4H8O2) (1a) and Mg•+(boat-1,4-C4H8O2) (1b) are comparable in energy, the much better agreement of the experimental action spectrum of Mg•+(1,4-C4H8O2) with the calculated absorption spectrum of 1a than with that of 1b indicates the predominance of 1a in the source due to the stability of the chair-1,4-dioxane. For photoreactions, the C−O bond is found to be much more prone to rupture than the C−C bond due to the coordination of O to Mg+ in the parent complexes. Photoreaction mechanisms are discussed in terms of two key insertion complexes, which rationalize all of the observed photoproducts. [ABSTRACT FROM AUTHOR]

At present, research into optical properties of bio-smoke materials mostly concentrates on single band or single germplasm. Herein, we measured the spectral reflectance of three eukaryotic bio-smoke materials and three prokaryotic bio-smoke materials in the waveband from 0.25 μm to 14 μm. Based on the Kramers–Kroning algorithm, the complex refractive index m(λ) was calculated and the Fourier-transform infrared (FTIR) spectra of materials were analyzed. The results show that n(λ) of bio-smoke materials varies between 1.1–2, and n(λ) values in the visible light to near-infrared wavebands are significantly larger than those in other wavebands. The k(λ) of bio-smoke materials varies between 0–0.4. At 6–6.5 μm, k(λ) of prokaryotic materials is 3 times that of eukaryotic materials, which is caused by C=O stretching vibration of amide I and C–N stretching vibration of amide II in proteins. At 2.5–3 μm and 9.75 μm, k(λ) values of eukaryotic bio-smoke materials are nearly 2 times that of prokaryotic ones. The absorption peak at 2.5–3 μm is mainly triggered by C–H stretching vibration in lipid and O–H stretching vibration in bound water. The absorption peak at 9.75 μm is mainly caused by symmetric stretching vibration of in nucleic acids. [ABSTRACT FROM AUTHOR]

This paper proposes three-phase 120° phase belt toroidal windings (120°-TW) and are applied in a double-sided permanent magnet linear synchronous motor (DSPMLSM), in which the incoming ends of all coils are on the same side and have the same incoming direction. First, the structure of the proposed motor is introduced and its operation principle is analyzed by describing the variation in the armature magnet field versus time. Second, based on the similar volume, magnetic load and electrical load, the initial parameters of the DSPMLSM with different winding arrangements are presented. Then, the finite-element models (FEMs) of the DSPMLSM with 120°-TW (120°-TWDSPMLSM) and traditional toroidal windings (TTW) are established to analyze the distribution of magnetic field, back electromotive force (back-EMF), detent force, thrust, efficiency and so on. Besides, the primary optimization of the detent force is designed. Finally, the results show that the thrust density and efficiency of the 120°-TWDSPMLSM is higher than that of DSPMLSM with TTW (TTWDSPMLSM). [ABSTRACT FROM AUTHOR]

A highly reliable three-dimensional network structure joint was fabricated based on Cu/Ni/Sn powder with double-layer coatings and transient liquid phase bonding (TLPB) technology for high temperature application. The Cu/Ni/Sn joint is characterized by Cu metal particles embedded in the matrix of (Cu,Ni)6Sn5/Ni3Sn4 intermetallic compounds (IMCs), with a low void ratio, and can be reflowed at low temperatures (<260°C), but it can reliably work at a high temperature up to 415°C. Cu/Ni/Sn double-layer powders with different Sn layer and Ni layer thickness were was fabricated and compressed as preform used for TLPB joint bonding. The microstructure and phase composition evolution for Cu/Sn and Cu/Ni/Sn systems during reflow and aging were comparatively studied. Two kinds of interfacial structure designs were made, and corresponding interfacialmicroscopic morphology was analyzed and compared under once and twice reflow soldering processes. The results indicated that the Sn-coating layer was completely consumed to form (Cu,Ni)6Sn5/Ni3Sn4 IMCs, and the Cu/Ni/Sn joint had a lower void ratio and a higher shear strength than those of Cu/Sn. The mechanism of the Nicoating layer inhibiting phase transformation was studied. The high reliable three-dimensional network structure joint based on Cu/Ni/Sn double-layer powder was fabricated for high temperature application. [ABSTRACT FROM AUTHOR]

This study presents a new portable eight-output light emitting diode (LED) driver. The eight output-channels are divided into two equal groups, and their output powers can be controlled individually by three active switches. In addition, a simple capacitor-based passive current balancing circuit (CBC) is employed in each port to guarantee that the currents of the four LEDs are the same. When compared with the conventionally used separate two-output isolated converters, the proposed one uses one less active switch. Moreover, zero-voltage-switching (ZVS) is achieved, which improves the power efficiency of the driver. Finally, a highly compact prototype is built, which can reach an efficiency of 94.6%. [ABSTRACT FROM AUTHOR]

A hybrid fault scenario in a late-stage offshore doubly-fed induction generator (DFIG)-based wind turbine (DFIG-WT) with converter open-circuit fault and position sensor failure is investigated in this paper. An extended Kalman filter (EKF)-based sensorless control strategy is utilized to eliminate the encoder. Based on the detailed analysis of the seventh-order dynamic state space model of DFIG, along with the input voltage signals and measured current signals, the EKF algorithm for DFIG is designed to estimate the rotor speed and position. In addition, the bridge arm open circuit in the back-to-back (BTB) power converter of DFIG is taken as a commonly-encountered fault due to the fragility of semiconductor switches. Four-switch three-phase (FSTP) topology-based fault-tolerant converters are employed for post-fault operation by considering the minimization of switching losses and reducing the circuit complexity. Moreover, a simplified space vector pulse width modulation (SVPWM) technique is proposed to reduce the computational burden, and a voltage balancing scheme is put forward to increase the DC-bus voltage utilization rate. Simulation studies are carried out in MATLAB/Simulink2017a (MathWorks, Natick, MA, USA) to demonstrate the validity of the proposed hybrid fault-tolerant strategy for DFIG-WT, with the wind speed fluctuation, measurement noises and grid voltage sag taken into consideration. [ABSTRACT FROM AUTHOR]

With the high penetration of various sustainable energy sources, the control and protection of Microgrids has become a challenging problem considering the inherent current limitation feature of inverter-based Distributed Generators (DGs) and the bidirectional power flow in Microgrids. In this paper, a hybrid control and protection scheme is proposed, which combines the traditional inverse-time overcurrent protection with the biased differential protection for different feeders with different kinds of loads. It naturally accommodates various control strategies such as P-Q control and V-f control. The parameter settings of the protection scheme are analyzed and calculated through a fast Fourier transform algorithm, and the stability of the control strategy is discussed by building a small signal model in MATLAB. Different operation modes such as the grid-connected mode, the islanding mode, and the transitions between these two modes are ensured. A Microgrid model is established in PSCAD and the analysis results show that a Microgrid system can be effectively protected against different faults such as the single phase to ground and the three phase faults in both the grid-connected and islanded operation modes. [ABSTRACT FROM AUTHOR]

In this study, seven microbial materials (entomogenous fungi Bb3088 mycelia, entomogenous fungi Bb3088 spores, entomogenous fungi Ma2677 mycelia, entomogenous fungi Ma2677 spores, Bacillus subtilis 8204, Staphylococcus aureus 6725, and Saccharomyces cerevisiae 1025) were used to measure electromagnetic (EM) signal extinction. They were subjected to light absorption and reflection measurements in the range of 4000-400 cm−1 (2.5-25 µm) using Fourier transform infrared spectroscopy. The specular reflection spectrum method was used to calculate the real (n) and imaginary (k) parts of the complex refractive index. The complex refractive index with real part n and imaginary part k in the infrared band satisfies the following conditions n ≥ 1 and k ≥ 0. The mass extinction coefficient was calculated based on Mie theory. Entomogenous fungi Ma2677 spores and entomogenous fungi Bb3088 spores were selected as EM signal extinction materials in the smoke box test. The transmittances of entomogenous fungi Bb3088 spores and entomogenous fungi Ma2677 spores were 11.63% and 5.42%, and the mass extinction coefficients were 1.8337 m²/g and 1.227 m²/g. These results showed that entomogenous fungi Bb3088 spores and entomogenous fungi Ma2677 spores have higher extinction characteristics than other microbial materials. [ABSTRACT FROM AUTHOR]

Insulated-gate bipolar transistor (IGBT) power modules find widespread use in numerous power conversion applications where their reliability is of significant concern. Standard IGBT modules are fabricated for general-purpose applications while little has been designed for bespoke applications. However, conventional design of IGBTs can be improved by the multiobjective optimization technique. This paper proposes a novel design method to consider die-attachment solder failures induced by short power cycling and baseplate solder fatigue induced by the thermal cycling which are among major failure mechanisms of IGBTs. Thermal resistance is calculated analytically and the plastic work design is obtained with a high-fidelity finite-element model, which has been validated experimentally. The objective of minimizing the plastic work and constrain functions is formulated by the surrogate model. The nondominated sorting genetic algorithm-II is used to search for the Pareto-optimal solutions and the best design. The result of this combination generates an effective approach to optimize the physical structure of power electronic modules, taking account of historical environmental and operational conditions in the field. [ABSTRACT FROM AUTHOR]

This paper proposes an in situ diagnostic and prognostic (D&P) technology to monitor the health condition of insulated gate bipolar transistors (IGBTs) used in EVs with a focus on the IGBTs' solder layer fatigue. IGBTs' thermal impedance and the junction temperature can be used as health indicators for through-life condition monitoring (CM) where the terminal characteristics are measured and the devices' internal temperature-sensitive parameters are employed as temperature sensors to estimate the junction temperature. An auxiliary power supply unit, which can be converted from the battery's 12-V dc supply, provides power to the in situ test circuits and CM data can be stored in the on-board data-logger for further offline analysis. The proposed method is experimentally validated on the developed test circuitry and also compared with finite-element thermoelectrical simulation. The test results from thermal cycling are also compared with acoustic microscope and thermal images. The developed circuitry is proved to be effective to detect solder fatigue while each IGBT in the converter can be examined sequentially during red-light stopping or services. The D&P circuitry can utilize existing on-board hardware and be embedded in the IGBT's gate drive unit. [ABSTRACT FROM AUTHOR]

In this paper, the built-in transformer voltage multiplier cell is inserted into each phase of the conventional interleaved boost converter to provide additional control freedom for the voltage gain extension without extreme duty cycle. The voltage multiplier cell is only composed of the built-in transformer windings, diodes and small capacitors. And additional active switches are not required to simplify the circuit configuration. Furthermore, the switch voltage stress and the diode peak current are also minimized due to the built-in transformer voltage multiplier cells to improve the conversion efficiency. Moreover, there is no reverse-recovery problem for the clamp diodes and the reverse-recovery current for the regenerative and output diodes are controlled by the leakage inductance of the built-in transformer to reduce the relative losses. In addition, the switch turn-off voltage spikes are suppressed effectively by the ingenious and inherent passive clamp scheme and zero current switch (ZCS) turn-on is realized for the switches, which can enhance the power device reliability. Finally, a 40 V-input 380 V-output 1 kW prototype is built to demonstrate the clear advantages of the proposed converter. [ABSTRACT FROM AUTHOR]