This paper describes techniques that Japanese power electronics engineers can use to improve the quality of their technical papers written in English and the accompanying technical presentations. These techniques are based on the experience that the author has gained by participating in international conferences. Such techniques are important to discuss because the significant differences exist in writing and presentation styles between Japanese and American engineers. The author believes that such style differences are caused by differences between the Japanese and American cultures. The objective of this paper is to help Japanese engineers understand these cultural differences and improve their technical communication skills in English. The paper also includes some practical tips on writing and presentation techniques for improving the quality of their technical communications in English.
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This paper discusses a transformerless hybrid active filter integrated into the 6.6-kV, 1-MW adjustable-speed motor drive having a three-phase diode rectifier at the front end. The hybrid filter consists of an active filter using a three-level diode-clamped PWM converter rated at 60 kVA, and a 250-kVA passive filter tuned to the 7th-harmonic frequency. They are directly connected in series without transformer. This circuit configuration enables to use 1.2-kV IGBTs because the dc voltage of the three-level converter is 1.32 kV (20% of 6.6 kV). Voltage-balancing control characterized by superimposing a 6th-harmonic zero-sequence voltage on the active-filter voltage reference in each phase is introduced to the three-level converter with triangle-carrier modulation. Experimental waveforms obtained from a 400-V 15-kW down-scaled system verify the viability and effectiveness of the proposed hybrid filter, keeping the two dc-capacitor voltages balanced well.
This paper proposes an active common-noise canceler (ACC) that is capable of eliminating the common-mode voltage produced by a pulsewidth modulation (PWM) inverter. An emitter follower using complementary transistors and a common-mode transformer are incorporated into the ACC, the design method of which is also presented in detail. Experiments using a prototype ACC, whose design and construction are discussed in this paper, verify its viability and effectiveness in eliminating common-mode voltage in a 3.7 kW induction motor drive using an insulated gate bipolar transistor (IGBT) inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted electromagnetic interference (EMI). In addition, the ACC can prevent an electric shock on a nongrounded motor frame and can suppress motor shaft voltage.
Although accessory parotid glands are found in 20-70% of normal persons, tumors arising from accessory parotid glands are reportedly rare. We demonstrated a case of pleomorphic adenoma arising from the accessory parotid gland. A 43-year-old female was brought to our hospital with a left cheek mass. Imaging demonstrated an oval-shaped tumor on the masseter muscle located in the mid-portion of her cheek, without any evidence of relationship with the parotid gland. Surgically the tumor was completely removed through a transparotid approach and pathologically diagnosed as pleomorphic adenoma.Reports of the incidence of accessory parotid glands in humans are inconsistent, so we investigated the various reported values. We concluded that over 55% of normal people have accessory parotid glands in their left or right cheeks.
A large-capacity low-speed flywheel energy storage system based on a doubly-fed induction machine basically consists of a wound-rotor induction machine, and a cycloconverter or a voltage-source pulse width modulation (PWM) rectifier-inverter which is used as an AC exciter. Adjusting the rotor speed makes the machine either release the kinetic energy to the power system or absorb it from the utility grid. Thus, the machine has the capability of achieving not only reactive-power control, but also active-power control based on the flywheel effect of the rotating parts. This paper proposes a new control strategy for a doubly-fed induction machine intended as a flywheel energy storage system, which is characterized by the combination of vector control and decoupling control. The control strategy enables the induction machine to perform active-power control independent of reactive-power control even in transient states. The validity of the theory developed in this paper, along with the effectiveness and viability of the control strategy, is confirmed by computer simulation. In addition, this paper discusses a transient behavior of a magnetizing current in the induction machine.
This paper describes a holistic approach to the theory of instantaneous power in three-phase four-wire systems, focusing on the original theory created in 1983 and a modified theory presented in 1994. The two theories are perfectly identical if no zero-sequence voltage is included in a three-phase three-wire system. However, they are different in the instantaneous active and reactive power in each phase if a zero-sequence voltage and current are included in a three-phase four-wire system. Theory and computer simulations in this paper lead to the following conclusions: an active filter without energy storage components can fully compensate for the neutral current even in a three-phase four-wire system including a zero-sequence voltage and current, when a proposed control strategy based on the original theory is applied. However, the active filter cannot compensate for the neutral current fully, when an already-proposed control strategy based on the modified theory is applied.
This paper deals with transient analysis of a series active filter integrated with a double-series diode rectifier. A DC model is developed with the help of the p-q coordinates transformation. It can be used to accurately and simply analyze transient characteristics around the fundamental frequency of the integrated system. The analysis using the DC model tells us that either increasing the active filter gain or decreasing the cut-off frequency of low-pass filters used in the harmonic detector results in a slow response, and causes a large and long transient of the DC voltage. Simulation results using a software package "EMTDC" and experimental results verify the validity of the proposed DC model.
This paper provides an experimental discussion on a real-time real-power emulator that play as 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 identical modular multilevel double-star chopper-cell (DSCC) converters in front-to-front (FTF). 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 in which one DSCC converter is used as an inverter under test, and the other as a real-time real-power high-fidelity emulator of an induction motor coupled with load. Experimental waveforms obtained from the downscaled test bench confirm that the emulator can reproduce the electrical and mechanical operating performance of a three-phase 200-V, 10-kW, four-pole, 9000-r/min induction motor loaded with a centrifugal compressor.
This paper presents a medium-voltage high-power dc-dc converter using two modular multilevel cascade converters based on double-star chopper-cells (MMCC-DSCC) for power collection. The system configuration is applicable to multi-terminal dc power networks such as off-shore wind farms. The system can be extended to use several MMCC-DSCCs at the power-collecting side (lower dc voltage side) which connected together at the ac side of the converters via a galvanic isolation. Furthermore, the system can handle dc faults inherently and existing ac circuit breakers can be used instead of dc circuit breakers for fault protection. The circuit configuration and the control method are described along with simulated results that verify the proposed front-to-front system.
This paper describes a hybrid active filter for harmonic-current compensation of a three-phase 12-pulse diode rectifier used as the front end of a medium-voltage motor drive system. This hybrid filter is characterized by the direct series connection of a simple LC filter and a small-rated active filter. This circuit configuration brings low cost, small size, and light weight to the hybrid filter. The authors design, construct, and test a three-phase experimental system rated at 400V and 15kW, which is a downscaled model of the medium-voltage motor drive system. In this experiment, the LC filter is tuned to the 11th harmonic frequency, and the active filter is based on a three-level diode-clamped PWM converter with a dc capacitor voltage as low as 28V. This hybrid filter is connected on either the first or fourth winding of a line-frequency transformer with a first Δ-winding voltage of 400V in the primary, and a second Δ-winding voltage of 220V, a third Y-winding voltage of 220V, and a fourth Δ-winding voltage of 400V in the secondary. Experimental results show that the hybrid filter performs satisfactory filtering in a range from the no-load to full-load conditions.
Characteristics of the instantaneous active/reactive powers and zero-sequence current/voltages are analyzed in three-phase four-wire systems. Control strategy for an active filter without energy storage components is proposed on the basis of mapping matrices. It can compensate for the zero-sequence current, irrespectively of whether or not a zero-sequence voltage exists in three-phase four-wire systems.
This paper presents a new method of harmonic power detection based on the instantaneous active power in three-phase circuits, and its applications to search for dominant harmonic sources in power systems. The proposed method requires only band elimination filters and a three-phase active power meter to detect the harmonic active power, and it is able to deal with harmonic power flow more easily and precisely than a conventional meter which is based on Fourier series of single-phase circuits. In addition, measurement errors of the harmonic power are discussed theoretically. The validity of the proposed method is demonstrated by digital simulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper provides a theoretical and experimental discussion on ac-inductors design for a modular multilevel triple-star bridge-cells (TSBC) converter, or shortly a TSBC converter. This converter requires multiple ac inductors for controlling nine cluster currents. This paper proposes three three-legged, six-winding, "interzigzag" inductors for the TSBC converter. Since each leg of the individual inductor has two windings, the three inductors have 18 windings in total. The wire leads are zigzagged among the three inductors. This unique structure of the "interzigzag" windings leads to the following feature: Both three-phase supply and motor currents produce no magnetic flux in each of the nine legs. This feature makes each inductor smaller in size and lighter in weight. A specially-designed downscaled motor-drive system rated at 400 V and 15 kW is constructed and tested to confirm the validity of a design of the proposed inductors, as well as to verify transient motor-drive performance during four-quadrant operation.
Ménière's disease in children comprises only a small percentage of all patients of Ménière's disease, and is known to be quite rare. A juvenile patient who has been followed for more than 8 years is reported in this paper.This 18-year-old female patient was brought to our department when she was 9 years old with a chief complaint of right-side hearing loss. She had a history of paroxysmal rotatory vertigo with accompanying headache twice per year since she was 5 years old. Right-side hearing loss and tinnitus had been noted since she was 9 years old. The hearing loss and the tinnitus were aggravated during the attacks of vertigo. Physical examinations revealed low-tone perceptive hearing loss of about 43 dB on the right ear. Caloric test revealed right canal paresis. Glycerol test results were positive. Since the vertigo attacks were episodic, and the equal-loudness contours on three-dimensional audiogram showed that aggravated hearing loss fluctuated despite medication, the patient received right-side intratympanic gentamicin injection when she was 16 years old. To date, vertigo has subsided for more than 2 years since the intratympanic injection.
