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A measured contact-loss ratio is used to estimate current-collection performance. There are two types of methods used to estimate the contact-loss ratio. One is to measure all the contact losses, including small ones; the other is to measure only contact losses that are greater than 5 ms in duration. The extent of wear of a contact strip caused by arc discharges varies as a function of the amount of electric charge. This fact makes it possible to manage the wear on a contact strip. This paper shows a calculation method for the amount of electric charge based on the output of a contact-loss measurement as well as the expected lifetime of the contact strip and the creation of a maintenance threshold level for of the contact strip.

The generator voltage of a cutting-edge wind turbine generation system (WTGS) is expected to increase from the conventional low-voltage level of 690 V to a medium-voltage level of 6.6 kV with a power level up to 10 MW without the application of a parallel connection of multiple power units. On the other hand, it is difficult to use a conventional two-level or three-level converter in a WTGS with a dc-link voltage of 10–13 kV owing to the limitations on the voltage ratings of power devices. This paper presents a 10-MW WTGS consisting of a three-phase open-winding synchronous generator equipped with six lead terminals and a modular multilevel cascade converter (MMCC) formed by three identical subconverters. The MMCC carries out direct ac/ac power conversion from three single-phase voltages with a time-varying frequency (from the generator) to a three-phase voltage with a line frequency of 50 Hz. This paper discusses the operating principles and control methods for the WTGS, followed by simulations using the software package PSCAD/EMTDC. The experimental result obtained from a 200 V 6-kW downscaled system confirms the reliability of simulation results of the complete three-phase system.

Recounts the career and contributions on Akira Nabae.

This paper describes the next-generation mediumvoltage power conversion systems based on transformerless cascade PWM converters and bidirectional isolated dc-dc converters. A 350-V, 10-kW and 20-kHz dc-dc converter is designed, constructed and tested as a core circuit for medium-voltage power conversion systems. It consists of two single-phase full-bridge converters using eight IGBTs and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%. Loss analysis clarifies that the overall efficiency may reach 99% or higher when SiC-based power devices are used. In addition, this paper presents the 6.6-kV transformerless STATCOM(STATic synchronous COMpensator) intended for achieving reactive-power control in industrial and distribution power systems. It is characterized by direct connection to the 6.6-kV grids, thus bringing significant reductions in cost, weight and size to the 6.6-kV STATCOM.

Several internal auditory canal (IAC) anomalies have been reported. To our knowledge, only one case with an abnormal direction of the IAC has been reported in an infant with Pierre Robin syndrome. In this paper, we present the first report of two non-syndromic cases with abnormal IAC direction.

Liposarcoma is an exceedingly rare tumor in the oral cavity. We report a case of a 70-year-old man with liposarcoma that presented as a lump on the tongue. The excised tumor was diagnosed as a well-differentiated lipoma-like liposarcoma. The majority of cases of well-differentiated liposarcoma follow a relatively benign course, but the disease has a high recurrence rate. It appears that accurate clinical and histopathologic diagnosis of this lesion is difficult. The prognosis seems to depend on the histologic type, size, and location of the lesion. Wide surgical excision is important for successful management of these liposarcomas.

Upper respiratory tract infection including chronic tonsillitis is considered to be involved in the onset and/or the progression of IgA nephropathy. It is well known that deterioration of urinary findings occurs after episodes of upper respiratory tract infection in patients with IgA nephropathy. We previously showed that the expression of macrophage-colony-stimulating factor (M-CSF) is increased in the glomeruli of patients with IgA nephropathy and correlated with glomerular mesangial proliferation, suggesting that M-CSF plays an important role in the progression of IgA nephropathy. In the present study, we measured the serum and urinary concentrations of M-CSF in patients with IgA nephropathy associated with chronic tonsillitis. Furthermore, we evaluated the effects of the local provocation test of tonsils (mechanical tonsil stimulation) on the serum and urinary concentrations of M-CSF in the following three groups: (1) IgA nephropathy with severe mesangial proliferation, (2) IgA nephropathy with mild mesangial proliferation, and (3) patients with chronic tonsillitis without renal disease. The serum and urinary levels of M-CSF in the groups with severe and mild IgA nephropathy were significantly higher than those in the chronic tonsillitis group. The urinary M-CSF level but not the serum M-CSF level was positively correlated with the degrees of mesangial proliferation and glomerular M-CSF expression in the renal biopsy specimens. The urinary M-CSF concentration was significantly increased after tonsillitis stimulation in both mild and severe IgA nephropathy groups. Enhanced urinary excretion of M-CSF prolonged for 7 days after tonsil stimulation in the severe IgA nephropathy group; in contrast, the urinay M-CSF level was increased for only 2 days after tonsil stimulation in the mild IgA nephropathy group. The urinary M-CSF level was not changed in the chronic tonsillitis group after tonsil stimulation. The serum concentrations of M-CSF were not changed after tonsil stimulation in these three groups. Our present results suggest that tonsil stimulation contributes to the progression of IgA nephropathy via enhancement of glomerular production of M-CSF. The urinary excretion of M-CSF may be a useful predictor to evaluate the relevance of chronic tonsillitis to the disease and the indication of tonsillectomy in patients with IgA nephropathy.

The conventional reactive power in single-phase or three- phase circuits has been defined on the basis of the average value concept for sinusoidal voltage and current waveforms in steady states. The instantaneous reactive power in three-phase circuits is defined on the basis of the instantaneous value concept for arbitrary voltage and current waveforms, including transient states. A new instantaneous reactive power compensator comprising switching devices is proposed which requires practically no energy storage components.

A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system.

The control strategy of active power filters using switching devices is proposed on the basis of the instantaneous reactive power theory. This aims at excellent compensation characteristics in transient states as well as steady states. The active power filter is developed, of which the power circuit consists of quadruple voltage-source PWM converters. As the result, interesting compensation characteristics were verified experimentally which could not be obtained by the active power filter based on the conventional reactive power theory.

A high-performance current-controlled inverter must have a quick current response in transient state and low harmonic current content in steady state. However, in general, these requirements contradict each other. A novel control scheme is proposed which is based on the current deviation vector and satisfies both requirements. Experimental results showed good agreement with the anticipated performance.

A control scheme is presented for compensating the torque transfer function of a self-controlled synchronous motor without damper windings. In effect, the armature current phase and amplitude are altered during transients to compensate for the slow response of the field current. The system also is arranged to come to unity power factor in the steady state which requires that the field current be adjusted to each specific load point by the controller. The validity of the control scheme is verified by the experiments.

The similarity between a six-pulse three-phase cycloconverter operating in the circulating current-free mode and a six-pulse three-phase bridge converter is discussed analytically with regard to the rms value and the harmonics of the respective output voltages. A method is presented for calculating the rms voltage of a family of sideband frequencies which are generated in the output voltage of the cycloconverter. The results obtained from the analysis help to predict the amplitudes of subharmonics and beat frequencies with the cycloconverter and are essential for the design of the output filters. Analytical results are verified by comparison with those of experiment and digital computer simulation.

We report an unusual case of necrosis of the tongue after transient ischemic attack in a 67-year-old man. Angiography revealed occlusion of the right external carotid artery at the bifurcation of the common carotid artery. Debridement of the wound and removal of the necrotic tissue resulted in good healing. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:316-8)