717 publications from this institution
This paper describes power electronics technology relevant to active filtering and energy storage for the purpose of power conditioning. The combination of active filtering and energy storage leads to a versatile system in terms of compensation under nonperiodic conditions. However, energy storage is much more difficult and costly in realization than active filtering because modern science offers only chemical action, electromagnetic or electrostatic field, and kinetic or potential energy as viable ways of energy storage. This paper is focused on the present status of active filters, and energy storage systems for power conditioning, along with a 200 MJ/20-MW flywheel energy storage system which was commercially installed on a 66 kV power system for the purpose of line-frequency regulation in 1996.
This paper presents an intensive discussion on a high-voltage direct-current (HVDC) long-distance transmission system combining two modular multilevel double-star chopper-cells (DSCC) converters with dc power cables. Hereinafter, each converter is referred to simply as a DSCC converter, or just as a DSCC for more simplicity. Such an HVDC transmission system is required to provide low-voltage-ride-through (LVRT) capability to enhance system availability. This paper proposes a practical LVRT control characterized by the use of power-line communications between the two DSCC converters. The validity and effectiveness of the LVRT control is verified not only by simulated waveforms obtained from the software package "PSCAD/EMTDC" but also by experimental waveforms from a three-phase 200-V, 400-Vdc, 10-kW, 50-Hz downscaled system with 300-m-long dc power cables.
No abstract is provided for this article.
This paper presents a zero-current-switched voltage-fed inverter equipped with resonant circuits on the AC side. The current flowing through a switching device, i.e., an IGBT is a sum of the load current and the resonant current. If the amplitude of the resonant current is larger than that of the load current, the current in a switching device becomes zero at an instant in each resonant cycle. This allows the switching device to be turned on or off at the zero current. The zero-current-switching makes a significant contribution to reduction of switching losses and electromagnetic noises. In this paper, the principle of zero-current-switching operation, and a novel control scheme are described from a theoretical and practical point of view. Experimental results obtained from a laboratory system of 5 kVA verify the practicability. Moreover, the efficiency and losses of the proposed soft-switched inverter are compared with those of a hard-switched inverter.
No abstract is provided for this article.
This paper proposes a new PWM rectifier/inverter system that is capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). The conversion system consists of a PWM rectifier and inverter, and an active common‐noise canceler (ACC) which has been proposed by the authors. The ACC developed for this system is characterized by the sophisticated connection of a common mode transformer which can compensate for common mode voltages produced by both the PWM rectifier and inverter. As a result, the size of the common mode transformer can be reduced to one‐third, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2 kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 59–68, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10062
This paper presents an equivalent circuit for high-frequency leakage currents in pulsewidth modulation (PWM) inverter-fed AC motors, which forms a series resonant circuit. The analysis based on the equivalent circuit leads to such a conclusion that the connection of a conventional common-mode choke or reactor in series between the AC terminals of a PWM inverter and those of an AC motor is not effective to reduce the rms and average values of the leakage current, but effective to reduce the peak value. Furthermore, this paper proposes a common-mode transformer which is different in damping principle from the conventional common-mode choke. It is shown theoretically and experimentally that the common-mode transformer is able to reduce the rms value of the leakage current to 25%, where the core used in the common-mode transformer is smaller than that of the conventional common-mode choke.
This paper develops a systematic and mathematically formal study of the balancing theory of series-stacked multilevel converters. It is shown that the DC bus voltages of these converters balance naturally, provided that the switching frequency is chosen high enough. Two balancing mechanisms, one associated with losses and the other with the load impedance, are identified. A 2 MVA series-sacked power quality device was constructed and the theoretical results were verified experimentally.
This paper describes the design, construction and testing of a 750-V, 100-kW, 20-kHz bidirectional isolated dual-active-bridge dc-dc converter using four 1.2-kV 400-A SiCMOSFET/SBD dual modules. The maximum conversion efficiency from the dc-input to the dc-output terminals is accurately measured to be as high as 98.7% at 42-kW operation. The overall power loss at the rated-power (100 kW) operation, excluding the gate-drive and control circuit losses, is divided into conduction and switching losses produced by the SiC modules, iron and copper losses due to magnetic devices, and an unknown loss. The power-loss breakdown concludes that the summation of the conduction and switching losses is about 60% of the overall power loss, and that the conduction loss is nearly equal to the switching loss at the 20-kHz, 100-kW operation.
This paper deals with a transformerless hybrid active filter integrated into a medium-voltage three-phase diode rectifier used as the front end of an adjustable-speed motor drive. The hybrid filter is formed by a single LC filter tuned to the 7th-harmonic frequency per phase and a small-rated active filter based on a three-phase three-level diode-clamped PWM converter. A three-phase downscaled system rated at 400V and 15kW is designed, constructed, and tested to verify the filtering performance of the hybrid filter. Experimental results show that the current THD (total harmonic distortion) gets less than 5%, and that the voltage-balancing control proposed in this paper works properly even in transient states.
This paper provides an experimental discussion on a real-time real-power emulator that plays an important role in achieving a total test of medium-voltage, high-power, high-speed induction motor drives. The use of the emulator brings cost and time savings to the test. The test bench including the emulator is characterized by connecting two modular multilevel double-star chopper-cell (DSCC) converters connected in a front-to-front way. This paper designs, builds, and tests a 400-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> , 10-kW downscaled test bench. It mainly consists of the following two identical DSCC converters: 1) one DSCC converter is used as an inverter under test; and 2) the other as a real-time real-power high-fidelity emulator. Experimental waveforms confirm that the emulator can reproduce electrical and mechanical operating performance of the three-phase 200-V, 10-kW, four-pole, 9000-r/min induction motor loaded with a centrifugal compressor.
This paper describes the 750-V, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converter using the latest 1.2-kV, 400-A SiC-MOSFET 4-in-1 modules integrated with SBDs. It focuses on power conversion efficiency and transient characteristics. This dc-dc converter is characterized by being capable of an appropriate switchover between continuous operation and intermittent operation for the purpose of efficiency improvement. The intermittent operation achieves more efficient power conversion for partial loads than does the continuous operation. However, the intermittent operation may cause different upper and lower peak currents in the converter, thus resulting in an increase in the amount of switching loss. This paper introduces an advanced control method for the intermittent operation, which improves the efficiency. Experimental results reveal that the advanced method improves the efficiency from 98.4% in the previous method to 98.6% at 22kW. The efficiency in continuous operation at 100kW is 98.3% in the case of using the previous four 2-in-1 modules without SBD, while it is improved to 98.9% in the case of using the two 4-in-1 modules. Experimental transient characteristics show that no dc magnetic-flux bias occurs even during switchover between continuous and intermittent operation when power reversal from -100kW to 100kW occurs within a time interval of 1ms. Finally, it is verified that the dc-dc converter is capable of providing fast power-reversing performance from -100kW to 100kW within a time interval as short as 25µs.
Granulocytic sarcoma was first described by Burns in 1811 and it is known to be an extramedullary tumor composed of immature precursor cells. It sometimes occurs with acute myeloid leukemia or myeloproliferative disorders, but there have been reports of cases occurring without such hematological disorders. A 40-year-old female with a chief complaint of neck swelling was examined in our department in 1997. CT scan showed bilateral neck lymph nodes swelling. Histological examination of open biopsy confirmed myeloblastic-type tumor cells, but peripheral blood and bone marrow examination showed no evidence of leukemia. The final diagnosis of this case was granulocytic sarcoma without hematological disorder.
No abstract is provided for this article.
This paper discusses a potential of a transformerless STATCOM (static synchronous compensator) intended for installation on the 6.6-kV industrial and utility distribution systems. The STATCOM consists of a five-level diode-clamped PWM converter rated at 1 MVA, and a voltage-balancing circuit rated at 6 kVA. Moreover, this paper designs, constructs, and tests a 200-V 10-kVA STATCOM based on a five-level converter with a carrier frequency of 3 kHz and a voltage-balancing circuit with a switching frequency of 3 kHz. The STATCOM and its experimental waveforms verify the viability and effectiveness of the 6.6-kV transformerless STATCOM.
A retrospective case-control study of 71 patients with IgA nephropathy was performed to evaluate the long-term prognostic effect of tonsillectomy. Forty-one patients (19 males and 22 females) underwent tonsillectomy (Group A) and 30 patients (13 males and 17 females) did not (Group B). These patients were followed for more than 10 years after renal biopsy. The average age at the initial renal biopsy was 29.78 years in Group A and 33.0 years in Group B. The average follow-up period was 13 years and 3 months in Group A, and 12 years and 7 months in Group B. Glomerular damage demonstrated on renal biopsy was more extensive in Group A than in Group B. Renal prognosis after 10 years of follow-up was compared between these two groups. The clinical remission rate was 24.4% in Group A and 13.3% in Group B; the stable renal function rate was 82.9% in Group A and 70.0% in Group B; and the renal survival rate was 95.1% in Group A and 73.3% in Group B. The renal survival rate in Group A was significantly higher than that in Group B (p<0.05).
