Modeling and simulation of a grid-connected PV generation system for electromagnetic transient analysis

This paper addresses modeling and simulation of a grid-connected photovoltaic system (GCPS) to analyze its grid interface behavior and control performance in the system design. A simple circuit model of the solar array is used to easily simulate its inherent characteristics with the basic specification data. Detailed power and protection control of the GCPS as well as its electrical circuits have been represented by user-defined and built-in components to take into account transients in normal and fault conditions, which are dominated by its power electronic controller. The model has been described with the reference to and implemented in PSCAD/EMTDC, a power system transient software package. Extensive simulation results are presented and analyzed to validate that the proposed simulation model is effective for control and protection performance evaluation of the GCPS in terms of electromagnetic transient analysis.     

Experimental study on the performance of a simultaneous heating and cooling multi-heat pump with the variation of operation mode

The cooling load in the winter season becomes significant in commercial buildings and hotels because of the wide usage of office equipment and improved wall insulation. In this study, a simultaneous heating and cooling multi-heat pump having four indoor units and an outdoor unit was designed and tested in five operation modes: cooling-only, heating-only, cooling-main, heating-main, and entire heat recovery. The performance of the system with R410a was optimized by adjusting the system's control parameters. In the cooling-main mode, the rate of the bypass flow to the heating-operated indoor unit was optimized by controlling the EEV opening of the outdoor unit. In the heating-main mode, the mass flow rate to the cooling-operated indoor unit was optimized by adjusting the EEV opening in the outdoor unit. In the entire heat recovery mode, the compressor speed was controlled to improve the system COP with appropriate heating and cooling capacities.     

Performance optimization of a hybrid cooler combining vapor compression and natural circulation cycles

A hybrid cooler combining vapor compression and natural circulation cycles was developed for the cooling of telecommunication equipment in the cabinet-type base station of mobile communication. This hybrid cooler normally operates in the vapor compression mode at high ambient temperatures, but works in the natural circulation mode at low ambient temperatures by the thermosiphon principle. The performance of the hybrid cooler was measured according to the refrigerant charge, outdoor temperature, heat exchanger geometry, and the vertical distance between the condenser and the evaporator. The optimum design conditions for these variables are discussed with respect to the performance of the hybrid cooler in both operating modes. The difference in the optimum refrigerant charge between the two operating modes was solved by installing a liquid receiver. The temperature difference between the indoor and ambient air was introduced as a control parameter for use when changing the operating mode.     

A study on restoration of iris images with motion‐and‐optical blur on mobile iris recognition devices

Iris recognition is a form of biometric technology that authenticates individuals by using the unique iris patterns between the pupil and the sclera. To solve security problems in mobile environments, mobile iris recognition devices have been commercialized recently. A motion‐and‐optical blurred image can be sometimes captured because users capture the iris images of a testee by holding the recognition devices. Motion‐and‐optical blurred images reduce iris recognition accuracy. Previous researches of restoring iris image only dealt with optical or motion blurred image. To overcome these problems, we propose a new method of restoring motion‐and‐optical blurred iris images at the same time. This article presents three contributions over previous research. (1) A new focus assessment method is proposed to measure accurate focus scores regardless of motion blurring. (2) Previous research restored coexisting motion‐and‐optical blurred images in terms of visibility, but in this article, we restored them in terms of recognition. (3) We used a modified CLS (Constrained Least Square) filter to prevent the zero‐crossing of the PSF (Point Spread Function) of motion blurring with a uniform shape. So, the iris recognition accuracy was better than when using a conventional CLS filter. Experimental results showed that the EER was 0.796% when using the proposed method and it was 1.431% when not using the proposed method. Consequently, the EER was reduced as much as 0.635% (1.431–0.796%) when using the proposed method. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 323–331, 2009     

Wetting of Low-carbon,Interstitial-free Steel Surfaces with Nanostructured Oxides by Liquid Zinc

In this study, the dynamic reactive wetting of low-carbon, interstitial-free (IF) steel by liquid zinc was investigated. In situ contact angle measurements of a liquid zinc droplet on three steel plates that contained a fixed Mn content (0.4 wt pct) and different Si concentrations (0.1, 0.3, and 0.7 wt pct) were carried out with two charge-coupled device cameras that operated at different recording rates, 3000 frames/second and 6 frames/second. The observed contact angles for the three steel plates started at almost the same value but gradually decreased at different rates with increasing time. The steel plate of medium Si content (0.3 wt pct) showed the best wetting behavior among the tested samples. The wetting characteristics were examined by analyzing the surface coverage, the morphology, and the thickness of the nanostructured oxides that formed on the steel plates during the annealing process.     

Fabrication of CuInSe2 films and solar cells by the sequential evaporation of In2Se3 and Cu2Se binary compounds

Cu₂Se/In_xSe(x≈1) double layers were prepared by sequentially evaporating In₂Se₃ and Cu₂Se binary compounds at room temperature on glass or Mo-coated glass substrates and CuInSe₂ films were formed by annealing them in a Se atmosphere at 550°C in the same vacuum chamber. The In_xSe thickness was fixed at 1 μm and the Cu₂Se thickness was varied from 0.2 to 0.5 μm. The CuInSe₂ films were single phase and the compositions were Cu-rich when the Cu₂Se thickness was above 0.35 μm. And then, a thin CuIn₃Se₅ layer was formed on the top of the CuInSe₂ film by co-evaporating In₂Se₃ and Se at 550°C. When the thickness of CuIn₃Se₅ layer was about 150 nm, the CuInSe₂ cell showed the active area efficiency of 5.4% with V_oc=286 mV, J_sc=36 mA/cm² and FF=0.52. As the CuIn₃Se₅ thickness increased further, the efficiency decreased.     

A 500-Mb/s quadruple data rate SDRAM interface using a skewcancellation technique

A quadruple data rate (QDR) synchronous DRAM (SDRAM) interface processing data at 500 Mb/s/pin with a 125-MHz external clock signal is presented. Since the QDR interface has a narrower data timing window, a precise skew control on data signals is required. A salient skew cancellation technique with a shared skew estimator is proposed. The skew cancellation circuit not only reduces the data signal skews on a printed circuit board down to 250 ps, but also aligns the data signals with an external clock signal. The entire interface, fabricated in a 0.35-μm CMOS technology, includes a high-speed data pattern generator and consumes 570 mW of power at 3.0-V supply. The active die area of the chip with the on-chip data pattern generator is 2.4 mm²     

Influence of Cure Conditions on the Adhesion of Rubber Compound to Brass-plated Steel Cord. Part II. Cure Time

The effect of the cure time of a rubber compound on the adhesion with brass-plated steel cord was investigated. The formation, growth and degradation of the adhesion interphase formed between the rubber compound and brass-plated steel cord was also observed as well as the formation of a weak boundary layer in the rubber near the adhesion interphase. With increase in the cure time from a fourth to four times of t₉₀, the pull-out force after vulcanization increased significantly up to one-half of t₉₀ followed by a slight increase to t₉₀, and then decreased slowly with further increase in cure time. This decrease in pull-out force upon prolonged vulcanization may be explained by the severe degradation of rubber compound attached to the adhesion interphase. Also, upon prolonged vulcanization, the adhesion interphase with a rich ZnS layer may act as a barrier to copper diffusion which is required to form the adhesion interphase of copper sulfide. After thermal aging of the adhesion samples, the pull-out force decreased in comparison with that of the unaged. The decrease of pull-out force after thermal aging stemmed mainly from the decline of tensile properties after thermal aging. The adhesion after humidity aging was different from that after thermal aging. Upon increasing the cure time to one-half of t₉₀, the pull-out force increased. But a further increase in the cure time caused a decline in pull-out force. This phenomenon can be explained by the degradation of the adhesion interphase. At longer cure time, a severe growth of copper sulfide and a large amount of dezincification were observed in the adhesion interphase. At shorter cure time, a significant growth of copper sulfide in the adhesion interphase does not occur, whereas the formation a of a ZnS layer appeared after humidity aging. With increasing cure time, the formation of a weak boundary layer in the rubber near the adhesion interphase increased, resulting in the cohesive failure of the rubber layer. The proper formation of the adhesion interphase and the good physical properties of the rubber compound at optimum cure time can lead to the high retention of adhesion.     

Storage modulus of polybutadiene core in acrylonitrile–butadiene–styrene polymers with different degrees of grafting

The linear viscoelastic behavior of acrylonitrile‐butadiene‐styrene (ABS) polymers in the molten state, with different degrees of grafting, was investigated within the framework of Palierne's emulsion model. The main aim of the present study is to quantitatively analyze the effect of grafting degree on the storage modulus G′ of the polybutadiene (PB) rubber core dispersed in ABS polymers. According to our model calculations, the degree of grafting significantly affects the G′ values of the PB core and, hence, the viscoelastic properties of ABS polymers. Our calculations showed that the Palierne model is very useful to calculate the storage modulus of the rubber particles dispersed in rubber‐modified polymeric materials, at least in the high‐frequency region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 924–930, 2001     

Enhancement of the dielectric properties of Pb(La,Ti)O3 thin films fabricated by pulsed laser deposition

PLT thin films with a thickness of 600 nm were grown by pulsed laser deposition (PLD) using different laser wavelengths of 355, 532 and 1064 nm, respectively. We have systematically investigated the variation of grain sizes depending on the process condition. A two-step process to grow (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) films was adopted and verified to be useful to enlarge the grain size of the film and to enhance leakage current characteristics. Structural and electrical properties including dielectric constant, ferroelectric characteristics, and leakage current of PLT thin films were shown to be strongly influenced by grain size.