Sensorless vector controlled converter for variable speed wind generation system using an induction generator

This paper proposed two types of speed sensorless converters that can control rotational speed and electric power. One is based on a slip frequency control system. The other is based on a vector control system. The rotational speed of the wind turbine is estimated with the phase voltage and phase current of the induction generator by the adaptive rotor flux observer. The estimated wind turbine rotational speed ω_r^est is used as the feedback of the speed control loop in the converter control system. Also, the estimated rotor flux ?_2d^est is used for the vector control. The simulation results confirm that both of them perform satisfactorily under the speed sensorless operation. The method based on the vector control system generates more electrical energy than does the method based on the slip frequency control system. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 62–75, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20323     

Structure Analysis of Molten Ba–Ge Alloys Using Electrostatic Levitation Technique Combined With High-Energy X-Ray Diffraction

High-energy synchrotron X-ray diffraction experiments were performed for clathrate-forming barium–germanium (Ba–Ge) alloys in the liquid state near the eutectic composition. The accurate structure information of highly reactive melts has been obtained by applying electrostatic levitation technique as a containerless method. The structure information obtained from the reverse Monte Carlo simulation suggests that the short-range ordering between the Ge atoms occurs with the addition of Ba atoms in the liquid Ba–Ge alloys. This can be associated with the formation of the cage-like structure composed of the Ge atoms in the liquid alloys near the eutectic composition.     

Potentiality of a new minimum‐order back‐EMF state observer taking acceleration into account for sensorless vector control of permanent‐magnet synchronous motors

This paper proposes new sensorless vector control methods for permanent‐magnet synchronous motors (PMSMs), which are based on a new minimum‐order back‐EMF state observer taking acceleration into account, and examines potentiality of the improved back‐EMF observer through experiments. Conventional sensorless vector control methods for PMSMs using an estimate of back‐EMF are established under the assumption of constant speed or zero acceleration, and consequently cannot operate properly at modes requiring rapid speed change especially in low speed region. On the other hand, the proposed back‐EMF observer has the following features: (1) it is a new back‐EMF state observer taking acceleration into account and requiring no additional approximation to motor mathematical model; (2) it is a minimum‐order state observer; (3) it utilizes motor parameters in the simplest manner; (4) it can be applied to both salient‐pole and non‐salient‐pole PMSMs; (5) it can be realized in both rotor and stator reference frames. Detailed designs and analyses for the improved state observer and the sensorless vector control systems in both rotor and stator reference frames are given. In relation to the sensorless vector control systems, this paper newly proposes a double‐integral‐type PLL method and an integral‐feedback‐type acceleration/speed estimation method. Their potentialities are examined through experiments. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 78–92, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20630     

A New Nonmetallic Inclusion Rating Method by Positive Use of Hydrogen Embrittlement Phenomenon

A new inclusions rating method using hydrogen embrittlement of a tensile test specimen is proposed. This method is essentially based on the statistics of extremes for inclusion rating where the maximum inclusion size is determined by simple tensile testing of a hydrogen-precharged (H-precharged) specimen. Tensile tests were conducted using two bearing steels (SAE52100 HV 346, HV 447, HV 559, HV 611, HV 678 and ASTM-A485-1 HV 706, HV 715) and one spring steel (SAE5160, HV 651). Fatigue tests were conducted using SAE52100 bearing steel (HV 682). All H-precharged tensile specimens (SAE52100, ASTM-A485-1 and SAE5160) were fractured from internal inclusions except the SAE52100 tensile specimens with a Vickers hardness of HV 346. It was confirmed that the distribution of extreme values of inclusion sizes obtained by SAE52100 tensile testing with H-precharged specimens coincided with those obtained by SAE52100 fatigue testing. From these results, it is presumed that the inclusion rating method by fatigue testing can be replaced by simple tensile testing with H-precharged specimens. The proposed method is more convenient and reliable than other existing inclusion rating methods, i.e., fatigue testing and optical microscopy. The proposed method can be applied to specimens with a Vickers hardness of higher than HV 447.     

To develop a quantitative method for predicting shrinkage porosity in squeeze casting

In order to secure high strength and high elongation of suspension parts, it is critical to predict shrinkage porosity quantitatively. A new simulation method for quantitative predic'don of shrinkage porosity when replenishing molten metal has been proposed for squeeze casting process. To examine the accuracy of the calculation model, the proposed method was applied to a plate model.     

Quantum-Mechanical Properties of Protons in Solid Molecular Hydrogen at Megabar Pressures

Quantum distributions of protons in three high-pressure phases of solid molecular hydrogen are investigated by the first-principles path integral molecular dynamics (FP-PIMD) method, in which interatomic forces are calculated precisely based on the density functional theory. The distributions have entirely different symmetries from those predicted by conventional simulation with classical treatment of protons. Especially in phase II, we found that molecular rotation is hindered by quantum fluctuation of protons, having a strong resemblance to a quantum distribution of impurity muonium in crystalline silicon. The mechanism of this “quantum localization” is clarified by a detailed study of the potential energy surface for the molecular rotation.     

Fabrication of 0.95Sn−0.05Au solder micro-bumps for flip-chip bonding

This letter describes the successful fabrication of a 0.95Sn−0.05Au solder microbump on a compound semiconductor wafer by reflowing of multi-layer metal film. Since the inherent interdiffusion in Au−Sn phases results in the alloying of multi-layer films, the composition of micro-bump is well controlled by the thickness of constituent metal films. The micro-bumps melt at about 220 C, which is close to the lowest eutectic temperature in a Au−Sn system. Solder bonding using 0.95Sn−0.05Au micro-bump is a very useful technique for the flipchip bonding of compound semiconductor devices.     

Study on dominant mechanism of high-cycle fatigue life in 6061-T6 aluminum alloy through microanalyses of microstructurally small cracks

The mechanism controlling the fatigue life of a precipitation-hardened Al–Mg–Si alloy (6061-T6) at a high-cycle fatigue (HCF) regime of over 10⁷ cycles was investigated in detail. It was found that over 90% of the total fatigue life was occupied by the growth process of a microstructurally small crack at relatively low stress amplitude. The small crack was often found to be arrested and halted for a long period (more than 10⁶ cycles) before it began to grow again, which resulted in a significantly slow growth process. The small crack was then analyzed not only by the conventional fractography but also by the cross-sectional observation of the crack tip region using a focused ion beam and transmission electron microscopy. These observations, supplemented also by a grain orientation analysis using electron backscattered diffraction, explicitly revealed the following points: (i) the small crack growth observed on the specimen surface is primarily related to facet-type cracking that occurs exclusively at the specimen surface; (ii) the growth direction of the small crack has strong anisotropy (i.e. surface-induced growth); (iii) the facet-type cracking is related to the formation of persistent fine slip bands that accompany no structural change of the matrix. On the basis of these results, the micromechanism of small crack growth and its relation to the concept of fatigue limit at the HCF regime is discussed in detail.     

Development of a new sensorless vector‐controlled and transmissionless electric vehicle using a permanent‐magnet synchronous motor

One of the most important technologies for electric vehicles (EVs) will be drive control technology for the main motor. It is desired that the drive control technology have the following characteristics. (1) It does not require a position/speed sensor for controlling motor drive, which has been mounted on the rotor shaft. (2) It has vector controls that can produce torque quickly, efficiently, and/or precisely. (3) It has wide driving‐range and allows developing EVs with no variable transmission. This paper proposes new drive control technologies for such EVs using a permanent‐magnet synchronous motor as a main motor, and verifies its usefulness through development of an actual EV that can drive on public roads. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 83–94, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20459