Output power leveling of wind turbine generator by pitch angle control using H∞ control

Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuels. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which causes fluctuating power of wind turbine generator (WTG). In order to reduce the fluctuating power of WTG, this paper presents an output power leveling technique of WTG by pitch angle control using H_∞ control, and the control input of WTG linear model is separated from the disturbance. The simulation results using actual detailed model for WTG show the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 17–24, 2008; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20657     

Realization of acceleration control using multirate sampling method

This paper focuses on the realization of high‐performance motion control based on acceleration control. The characteristics of acceleration control are investigated and the relationship between the performance and sampling frequency of the system is discussed. This paper then describes that a higher sampling frequency is required for acquisition of output information than for updating the input value. Based on this idea, a new multirate sampling method for an acceleration control system is proposed. A disturbance observer for the multirate system is designed by adopting a new definition of disturbance torque. A bilateral system is introduced as a preeminent example of a system that requires robust acceleration control. Both simulations and experiments are performed on the system, and the validity of the proposition is verified by the results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 72–81, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20507     

Anode-supported micro tubular SOFCs for advanced ceramic reactor system

In this study, micro tubular SOFCs under 1 mm diameter have been fabricated and investigated at 450–550 °C operating temperature with H₂ fuel. The performance of the 0.8 mm diameter tubular SOFC was 110–350 mW cm⁻² at 450–550 °C operating temperatures. To maximize the performance of the cell as well as to optimize the geometry of tubular cells, a current collecting method used in the experiment was examined. A model was proposed to estimate the loss of performance for single cell due to the current collecting method as functions of anode tube length and thickness. The results showed that the losses of performance were calculated to be 0.8, 2.0, and 4.6% at 450, 500, and 550 °C operating temperatures, respectively, for the 0.8 mm diameter tubular SOFC with the length of 1.2 cm.     

How accurately people can discriminate the differences of floor materials with various elasticities.

Tactile ground surface indicators installed on sidewalks help visually impaired people walk safely. However, these indicators sometimes cause the nonvisually impaired to stumble. Thus, these indicators also have to be made safer and less of a problem for those who do not use them. There are several facilities in Japan that have installed floor materials of different elasticity to indicate paths for the visually impaired. However, the effectiveness of this method has not been tested. Therefore, this study examined how accurately people can discriminate differences in the elasticity of flooring samples. Flooring samples of different elasticity were presented by placing two walking boards made of plywood, each surfaced with one of three different flooring samples, in an end-to-end fashion. Ten young adults whose sight was temporarily cutoff by eye masks were asked to walk on the path for 144 trials and indicate whether the flooring samples were different or not. Interestingly, the percentages of correct answers were high for most pairs of samples. Moreover, there was a strong positive correlation between the percentage of correct answers and the magnitude of difference in floor elasticity. These results indicate that people can distinguish changes of flooring samples fairly accurately, even when there are no convexities, if there is sufficient difference in elasticity between the flooring samples.     

Enhancement of electric conductivity of the rust layer by adsorption of water

The rust layers on the weathering steels exposed for 17 or 18 y at seven different sites in Japan were studied by electrochemical impedance under wet condition and measurement of amount of water vapor adsorbed. The transient of amount of adsorbed water vapor into the rust layer during humidity jump from 0% to 80% RH indicated that saturation of adsorbed water vapor took place within 1 h. From the semi-infinite model of diffusion, apparent diffusion coefficients of H₂O in the rust were calculated. It was found the apparent diffusion coefficient was higher when the amount of air-borne salt of exposure sites was higher. The impedance diagram of the rusted steels was analyzed with an equivalent circuit consisting of a series connection between an ohmic resistance and a parallel circuit of charge transfer resistance-redox capacitance. The double layer capacitance on the gold electrodes pressed onto the rust layer was further added on the circuit. The impedance showed that the rust layer behaved as a dielectric layer under dry condition, while the conductance was greatly enhanced with wet condition. The charge transfer resistance evaluated from the simulation under wet condition was largely dependent on the amount of air-borne salt in environment. It was concluded that the rust layer formed in the site with relatively large amount of air-borne salt revealed high conductivity under wet condition. For the rust formation followed by the Evans model during wet-dry cycles, the higher conductivity induced the more facilitative reduction of the rust layer under wet condition and the larger growth of the rust layer in a wet-dry cycle.     

Morphology of a hydrogen-bonded LC polymer prepared by photopolymerization-induced phase separation under an isotropic phase

A hydrogen-bonded LC polymer was prepared by photopolymerization of an LC blend composed of 4-(6-acryloyloxyhexyloxy)benzoic acid (A6OBA) and 4-hexyloxy-4′-cyanobiphenyl (6OCB), containing small amounts of an inhibitor and photoinitiator, at two different temperatures in an isotropic phase. To elucidate the factors determining the morphology of the obtained polymer (poly(A6OBA)), we chose two irradiation temperatures: one in the LC temperature range of the polymer, the other in the isotropic range. We investigated structures of the polymers by optical microscopy and scanning electron microscopy. SEM images showed that the film obtained at the lower temperature consisted of randomly extended fibers having a diameter of ca. 1.0 μm and some branches, whereas the film prepared at the higher temperature was composed of polymer particles with a diameter ca. 1.5 μm. By comparing these results with those of an earlier experiment in which we obtained macroscopically oriented LC fibers by photopolymerization under the LC phase of the blend, we infer the following; (i) the presence of an LC phase in the resulting polymer itself during photopolymerization is necessary for it to form fibrous morphology and (ii) the LC ordering field present prior to photopolymerization is not indispensable for the fibrous morphology but it is for the macroscopic orientation and reduction of the branches in the fibers.     

Unsteady transonic flow control around an airfoil in a channel

Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle fatigue failure and so on. Present study investigates the effectiveness of perforated cavity to control this unsteady flow field. The cavity has been incorporated on the airfoil surface. The degree of perforation of the cavity is kept constant as 30%. However, the number of openings (perforation) at the cavity upper wall has been varied. Results showed that this passive control reduces the strength of shock wave compared to that of baseline airfoil. As a result, the intensity of shock wave/boundary layer interaction and the root mean square (RMS) of pressure oscillation around the airfoil have been reduced with the control method.     

Simultaneous Measurements of an Ultrasound and a Torsional Oscillator for Pressurized 4He in a Nanoporous Glass

Recently, torsional oscillator (Yamamoto et al. in Phys. Rev. Lett. 93:075302, 2004) and ultrasound (Kobayashi et al. in AIP Conf. Proc. 128:797, 2007) measurements were carried out for pressurized ⁴He filled in a nanoporous glass (Gelsil), and the superfluid transition temperature T _C shows a different pressure dependence. Thus motivated, we have performed simultaneous measurements with a torsional oscillator and with ultrasound for pressurized ⁴He in Gelsil. T _C is in agreement between the two techniques at all pressures, and the superfluid component above 0.5 K shows most of the same temperature dependence. Furthermore, it was found that the χ-factor (the fraction of superfluid which remains locked to the substrate ) is independent of measuring frequency between the torsional oscillator (kHz-order) and the ultrasound (MHz-order) ranges.     

SiO2 film deposition on the inner wall of a narrow polymer tube by a capacitively coupled μplasma

SiO₂ thin films were deposited on the inner wall of a narrow commercial poly(propylene) tube with inner/outer diameters of 1.0 mm/3.0 mm by plasma-enhanced chemical vapor deposition using He or Ar carrier gases and tetraethoxysilane (TEOS)/O₂ feedstock gases at high pressures from 30 kPa to atmospheric pressure and at room temperature. A glow μplasma was generated inside the tube by a radio frequency (RF 13.56 MHz) capacitively coupled discharge. X-ray photoelectron spectra and infrared spectra revealed that the inner surface of the plasma-treated tube was covered by a SiO₂ film. Scanning electron microscopy images indicated that the film produced by He/TEOS/O₂ μplasma had a smooth surface whereas the surface of the film produced by Ar/TEOS/O₂ μplasma appeared granulated. Typical deposition rates of approximately 300 nm/min were obtained by He/TEOS/O₂ μplasma at atmospheric pressure and a RF power of 11 W.