A low‐loss snubber for reducing motor terminal surge voltage

The development of an advanced Insulated Gate Bipolar Transistor (IGBT) has enabled high‐frequency switching operation and has improved the performance of PWM inverters for motor drive. However, the IGBT's high rate of dv/dt has adverse effects on motor insulation stress. In many motor drive applications, the inverter and motor are separated, requiring long motor feeds. The long cable contributes high‐frequency ringing at the motor terminal and results in high surge voltage which stresses the motor insulation. The inverter output filter and RDC snubber are the conventional method for reducing the surge voltage. In this paper, we propose a new low‐loss snubber to reduce the motor terminal surge voltage. The snubber consists of the series connection of chraging/discharging capacitor and the voltage‐clamped capacitor. At IGBT turn‐off, the snubber starts to operate when the IGBT voltage reaches the voltage‐clamped level. Since dv/dt is decreased by snubber operating, the peak level of the surge voltage can be reduced. Also the snubber operates at the IGBT voltage above the voltage‐clamped level, and the snubber loss is largely reduced compared with the RDC snubber. The proposed snubber enables reduction of the motor terminal surge voltage with low loss. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 64–72, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10378     

Design support system for coloring illustrations by using the colors preferred by a user as determined from the hue patterns of illustrations prepared by that user

We propose a new design support system that can color illustrations according to a person's color preferences that are determined on the basis of the color patterns used by the same person in his previous work. Recently, many design tools for promoting free design have been developed. However, preferences for various colors differ depending on individual taste. Therefore, a system that can automatically color various designs on the basis of human preference is required. In this study, we propose an automatic modeling system that can be used to model illustrations. To verify the effectiveness of the proposed system, we simulate a coloring design experiment to determine the color patterns preferred by test subjects by using various design data. By using the design data, we determine each subject's preferred color pattern, and send feedback on these individual color patterns in the proposed system. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(1): 19–27, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21283     

Detection of radical species produced by catalytic decomposition of H2, O2 and their mixtures on heated Ir surfaces

Efficient production of H atoms, O atoms and OH radicals was confirmed by laser spectroscopic measurements in the catalytic decomposition of H₂, O₂ and their mixtures on a heated Ir filament. No change in electric resistivity was observed when the filament was kept at 2350 K in the presence of 1.0 Pa of pure O₂, showing that oxidation is minor. Arrhenius-type temperature dependences were observed for the densities of H (O) atoms in pure H₂ (O₂) systems. In the H₂/O₂ mixed system, the H-atom density was almost independent of the O₂ partial pressure, although the O-atom and OH-radical densities increased with the O₂ pressure. These O₂ pressure dependences are completely different from those observed for W. Ir is less poisoned by O₂ compared to W. In addition, direct production of H₂O molecules on Ir surfaces must take place besides the production of radical species.     

Control of secondary flow in a low solidity circular cascade diffuser

According to the previous experimental works on the low solidity circular cascade diffuser (LSD), a pressure recovery of a centrifugal blower was improved by the LSD significantly in a wide range of flow rate, and the pres-sure recovery was improved further by the LSD with a tandem cascade in comparison with the LSD with a sin-gle-row cascade. In the present study, the flow behavior in the LSD with the tandem cascade has been analyzed numerically by using the commercial CFD code of ANSYS-CFX12. It was shown clearly that the higher pressure recovery was achieved by applying the LSD with the tandem cascade, and the high pressure recovery is based on the high pressure rise in the vaneless space upstream of the LSD and the high blade loading of the front blade of the LSD. The high pressure recovery in the LSD could be achieved by controlling the flow separation on the suc-tion surface of the front blade and also on that of the rear blade due to formation of the favorable secondary flow and due to increase in mass flow passing through the slit section between the front and rear blades.     

Minimizing the Effects of Reflections by Using a Virtual Pulse Method, for Free-Field Reciprocity Calibration

The National Metrology Institute of Japan has developed a free-field reciprocity calibration system for type WS3 microphones as acoustic standards in the airborne ultrasonic range between 20 and 100 kHz, because numerous instruments radiate airborne ultrasound. Precise calibration of these microphones requires minimizing the influence of sound reflected from the objects such as absorbing wedges and supporting rods within the acoustic chamber. To minimize this influence, we applied the virtual pulse method, which is a signal processing technique used in the audible frequency to airborne ultrasonic range. Experimental and analytical results validated this method. Use of this method in the calibration of type WS3 microphones will decrease the calibration uncertainty in the free-field sensitivity level.     

Propagation characteristics in an underground shopping area for 5‐GHz‐band wireless access systems

5‐GHz‐band wireless access systems, such as the RLAN (Radio Local Area Network) system of IEEE 802.11a, HiperLAN/2, HiSWANa, and AWA, are deployed for indoor use at transmission rates over 20 Mbps. These 5‐GHz access systems are expected to extend service areas from the office to the so‐called “hot spots” in public areas. Underground shopping malls are one type of service area where the application of such nomadic wireless access service can be expected. In order to design radio zone configurations, it is necessary to know broadband propagation characteristics of an underground mall environment even if results obtained by previous measurements in the narrow band are available. This paper presents results of an experimental study on the propagation characteristics for broadband wireless access systems in an underground mall environment. First, broadband propagation path losses are measured and formulated considering the shadowing by human body. A ray trace simulation is used to clarify the basic propagation mechanism in such a closed environment. Next, it was determined that values of the delay spread at different distances during rush hour periods did not exceed 65 ns, which is lower than the permitted maximum value of the present 5‐GHz systems. The final conclusion is that the above propagation characteristics corroborate results of transmission tests carried out by using the AWA equipment. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(3): 55–64, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20059