A novel PWM technique with switching‐loss reduction for independent drive of two 3‐phase AC motors fed by a five‐leg inverter

This paper presents a novel pulse width modulation (PWM) technique with switching‐loss reduction for a five‐leg inverter (FLI). The PWM technique, in which the available maximum voltage for two motors adds up to DC bus voltage, has been proposed as the strategy for the FLI. Therefore, the DC bus voltage is fully available as the PWM strategy. However, the conventional PWM technique requires the frequency, phase, and amplitude of the phase voltage commands of a motor to produce zero‐sequence voltages (ZSVs). The novel PWM strategy has some efficient features. These features are discussed in this paper. The validity of the novel PWM technique will be shown by experimental results. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Relationship between melt flows based on three-dimensional X-ray transmission in situ observation and spatter reduction by angle of incidence and defocussing distance in high-power laser welding of stainless steel

ABSTRACT

The objective of this research is to reveal relationship between melt flows and spatter reduction by angle of incidence and defocusing distance in partial penetration welding of an SUS304 stainless steel plate using a 6-kW power laser beam. In welding speeds from 50 to 250 mm/s, underfilled weld beads with spatters were obtained at more than 150 mm/s. According to the three-dimensional X-ray transmission in situ observation of melt flows at 150 mm/s in welding speed with tungsten carbide (WC) tracers, the melt flows achieved approximately 2.3 m/s in speed and made convex molten-pool surface behind a keyhole inlet grow higher, resulting in spattering over 0.1 mm in diameter. A 2 mm inner defocusing distance or a 20° angle of advance decreased the number of spatter over 0.1 mm in diameter by half or one-third in comparison with that at focal point and 0°. The X-ray transmission images demonstrate that the appropriate defocusing distance and angle of incidence made the speed of the melt flow decrease and the melt flow behind a keyhole inlet circulate, which led to not only suppressing the convex surface but also improving the frequency that the convex surface went back to the molten pool.     

Amino Acid Synthesis in a Supercritical Carbon Dioxide - Water System

Mars is a CO₂-abundant planet, whereas early Earth is thought to be also CO₂-abundant. In addition, water was also discovered on Mars in 2008. From the facts and theory, we assumed that soda fountains were present on both planets, and this affected amino acid synthesis. Here, using a supercritical CO₂/liquid H₂O (10:1) system which mimicked crust soda fountains, we demonstrate production of amino acids from hydroxylamine (nitrogen source) and keto acids (oxylic acid sources). In this research, several amino acids were detected with an amino acid analyzer. Moreover, alanine polymers were detected with LC-MS. Our research lights up a new pathway in the study of life’s origin.     

Lower speed range drive for sensorless vector controlled induction machines with stator voltage offset compensation method

The vector control method is widely used for induction machine drives. Recently, sensorless vector control for induction machines has been investigated and proposed. The speed range for the drives is limited to about 1:100 in industry. The main reason for this limitation is the inaccuracy of stator voltage measurement. The lower the rotor speed is, the lower the stator voltage. Therefore, it is difficult to detect the stator voltage accurately in the lower speed region, and difficult to control motor speed and motor torque precisely. This paper presents a method of improving the lower speed performance of sensorless vector controlled induction machine drives using offset compensation of stator voltage. The offset is compensated by using the fluctuation of the estimated rotor flux. The validity of the proposed method is verified by experimentation. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 79–86, 2000     

A Novel Driving and Protection Circuit for Reverse-Blocking IGBT Used in Matrix Converter

A novel drive and protection circuit for reverse-blocking insulated gate bipolar transistor (RB-IGBT) is proposed in this paper. For the drive circuit, a dynamic current source is introduced to reduce the turn-on and turn-off transients. Meanwhile, the di/dt of the collector current and the dv/dt of the collector-emitter voltage are strictly restricted, so do the respective stresses. The drive circuit consists of a conventional push-pull driver and two controllable current sources-a current generator and a current sink. These two current sources work in switching transitions. For the protection circuit, a novel collector current detecting circuit suitable for RB-IGBT is proposed. This method detects the collector current by sensing collector-emitter voltage of the device. Further study shows that this method can be used to acquire the current signs in commutation transitions of matrix converter. A series of experiments has been carried out concerning the proposed drive and protection circuit and the experimental setup; results as well as detailed analysis are presented     

Speed sensorless field-oriented control of induction motor withrotor resistance adaptation

Several field-oriented induction motor drive methods without rotational transducers have been proposed. These methods have a disadvantage that the rotor resistance variation causes an estimation error of the motor speed. Therefore, simultaneous estimation of the motor speed and the rotor resistance is required. This paper presents a method of estimating simultaneously the motor speed and the rotor resistance of an induction motor by superimposing AC components on the field current command. The validity of the proposed method is verified by simulation and experimentation     

Changes in laryngeal muscle activities during hypercapnia in the cat

This article reports two studies aimed at validating the 25-item self-report McGreal and Joseph (1993) Depression-Happiness Scale (D-H S). In the first study, principal component data are reported on the D-H S with 194 respondents. A forced 1-factor solution confirmed the unidimensionality of the scale (item loadings ranged from .38 to .77) and thus the feasibility of a statistically bipolar measure. In the second study, data on the convergent validity of the D-H S with the Beck Depression Inventory (r=-.75) and the Oxford Happiness Inventory (r=.59) with 100 respondents are reported confirming the construct validity of the scale. Implications for research in social and clinical psychology are discussed along with the possible uses of the D-H S in a clinical setting.