A robust current control method with disturbance observer for matrix converter under abnormal input voltage

This paper presents a robust current control method with a disturbance observer for a matrix converter (MC) under an abnormal input voltage. The MC can directly convert power from an input alternating current (AC) source to a load without any direct current (DC) link. Since the MC has no reactive elements, the imbalance and distortion of the input voltage immediately influence the load. Therefore, a high‐performance current control of the load is impossible in this condition. In this letter, we propose a robust current control method for the MC under an abnormal input voltage. Adapting the disturbance observer to a load current control, current control is possible without the influence of the imbalance and distortion of the input voltage and of a fluctuation of a load paramerter, a resistance, an inductance and so on. This current control is robust under these conditions. The proposed method is effective for the application of a high‐performance AC motor drive employing vector control because it is necessary for the proposed method to coordinate with a reference frame. The validity of the proposed method is confirmed by simulation results. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

High/low temperature operation of electric double layer capacitor utilizing acidic cellulose-chitin hybrid gel electrolyte

An acidic cellulose-chitin hybrid gel electrolyte consisting of cellulose, chitin, 1-butyl-3-methylimidazolium, 1-allyl-3-methylimidazolium bromide, and an aqueous H₂SO₄ solution is investigated for electric double layer capacitors (EDLCs) with activated carbon fiber cloth electrodes. The acidic cellulose-chitin hybrid gel electrolyte shows a high ionic conductivity comparable to that for an aqueous 2 mol dm⁻³ H₂SO₄ solution at 0-80 °C. This system's temperature dependence in EDLC performance is investigated by galvanostatic charge-discharge measurement. An EDLC cell with the acidic hybrid gel electrolyte has higher capacitance than that with the aqueous H₂SO₄ solution in the range of operation temperatures (−10 to 60 °C). Moreover, the capacitance retention of the EDLC cell with the acidic hybrid gel electrolyte is better than that of a cell with the H₂SO₄ solution at 60 °C over 10,000 cycles. This suggests that the proposed acidic gel electrolyte has excellent stability in the presence of a strong acid, even at a high temperature of 60 °C.     

Machine tool component error extraction and error compensation by incorporating statistical analysis

The extraction of component errors of a machine tool’s axes is a critical step for the synthesis of 3D volumetric error mapping, which is a prerequisite to improve the machine tool accuracy by numerical error compensation. This paper presents a method for the extraction of machine tool component errors from a statistical point of view. First, the B-Spline mathematical model is established to represent the component error function, and the least-squares fitting method to measured data points is presented. Then, statistical analysis is used to select the B-Spline model with proper flexibility, so as to separate repeatable errors from random errors in the measured data. Finally, based on the component error extraction method, numerical error compensation experiments were conducted on the XY-plane of a high precision machine tool by using a cross-grid scale system. According to the statistical analysis of the experimental data, all repeatable errors except the dynamic errors caused by machine tool control system were compensated for.     

Thermal plasma CVD of PSZ and double layered TiN/PSZ coatings by injection of alkoxides solutions with H2O

Coatings of partially Y₂O₃-stabilized ZrO₂ (PSZ) (Y > 2 at.%) and double layered TiN/PSZ films were deposited on Si wafers at 700 °C from zirconium tetra-buthoxide (ZTBO), yttrium tri-buthoxide (YTBO) and/or titanium tetra-ethoxide by chemical vapor deposition with H₂O in a thermal Ar/N₂/H₂ plasma. A small amount of H₂O was fed into the plasma to oxidize the ZTBO and YTBO to produce the PSZ coatings. Double layered TiN/PSZ film coatings were deposited without severe oxidation of under-layered TiN by controlling the feeding rate of H₂O. The product phases were identified by grazing incidence X-ray-diffractometry. The surfaces and cross-sections of the PSZ and double layered TiN/PSZ coatings were observed by scanning electron microscopy. An in-depth semi-quantitative analysis of the double layered TiN/PSZ films was performed by X-ray photoelectron spectroscopy, revealing the changes in the concentrations of Zr, Y, Ti, O, and N with depth. The effect of the Y content in mixed solutions of ZTBO and YTBO on the evolution of ZrO₂ is examined. It is proposed that the controlled feed rate of H₂O is effective in producing coatings of PSZ on TiN films without severe oxidation.     

An improved method of voltage utility factor for PWM control of a five‐leg inverter in two induction motor drives

This paper presents an improved method of voltage utility factor (VUF) from 50 to 86.6% for a five‐leg inverter when two induction motors are driven in vector control and in a condition where the frequencies of the two motors are not very different, and the improved method of voltage utility is theoretically shown. Many modulation methods for the five‐leg inverter have been proposed, but the voltage utility factor is 50% in these methods. The voltage utility factor of the five‐leg inverter is lower than that of the three‐leg inverter as maximum voltage utility factor of the three‐leg inverter is 100%. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

X-ray diffraction measurements in high magnetic fields and at high temperatures

A system was developed measuring x-ray powder diffraction in high magnetic fields up to 5 T and at temperatures from 283 to 473 K. The stability of the temperature is within 1 K over 6 h. In order to examine the ability of the system, the high-field x-ray diffraction measurements were carried out for Si and a Ni-based ferromagnetic shape-memory alloy. The results show that the x-ray powder diffraction measurements in high magnetic fields and at high temperatures are useful for materials research.     

Effects of the geometrical configuration of a ventilation system on leaking hydrogen dispersion and accumulation

Hydrogen dispersion and accumulation in a partially open space with natural and forced ventilation are computationally investigated in this paper. After validating the present numerical method and assessing grid width against experimental data of a hallway, the present method is applied to a garage with dimensions of 2.6 m × 2.6 m × 2.6 m and leak flow rates of 0.5–4 standard cubic feet per minute (SCFM). In the simulations, different combinations of roof vents and door vents are considered by changing their sizes and positions. Based on the results, differences in concentration increase, the processes of hydrogen dispersion and accumulation, unsteadiness and vortical structures accompanying ventilation, are shown for natural and forced ventilation.     

A natural-gas fuel processor for a residential fuel cell system

A system model was used to develop an autothermal reforming fuel processor to meet the targets of 80% efficiency (higher heating value) and start-up energy consumption of less than 500 kJ when operated as part of a 1-kWe natural-gas fueled fuel cell system for cogeneration of heat and power. The key catalytic reactors of the fuel processor – namely the autothermal reformer, a two-stage water gas shift reactor and a preferential oxidation reactor – were configured and tested in a breadboard apparatus. Experimental results demonstrated a reformate containing ∼48% hydrogen (on a dry basis and with pure methane as fuel) and less than 5 ppm CO. The effects of steam-to-carbon and part load operations were explored.     

Thermal conductivity of neptunium dioxide

The thermal diffusivity of neptunium dioxide was measured in the temperature range from 473 to 1473 K by using a laser flash method. The thermal diffusivity slightly decreased with increasing temperature in the temperature range investigated. The heat capacity of NpO₂ was measured in the temperature range from 334 to 1071 K by using a drop calorimetry method. The heat capacity of NpO₂ determined in this study was slightly larger than that of UO₂ and about 7% smaller than that of PuO₂. The thermal conductivity of NpO₂ was determined from the thermal diffusivity, the heat capacity and the bulk density. It was found that the thermal conductivity of NpO₂ from 873 to 1473 K lay between those of UO₂ and PuO₂.     

Development of a tube-type solar still equipped with heat accumulation for irrigation

A tube-type solar still is found to be suitable for use in desert irrigation. The effectiveness of a heat accumulator with regard to distillate productivity is experimentally and numerically verified. The heat accumulator consists of tube bundles immersed in wax in order to utilize the latent heat of wax. The dynamic response to stepwise variation of irradiative intensity verified the contribution of wax to an increase of productivity only when the phase change of wax occurred. The effective distillate productivity was found to be 294.3 g/m² during the cyclic stepwise change of irradiative intensity, from 200 to 600 W/m² and back. Velocity vectors driven by natural convection and temperature contours estimated by numerical simulation verified the effectiveness of the heat accumulator especially after peak solar intensity. The latent heat of wax effectively contributed to a 15% increase in total distillate productivity per day. The still can feasibly meet irrigation water supply demands above an irrigative threshold of 17 MJ/m² d.