This paper focuses on an application of the modular multilevel cascade converter based on triple-star bridge-cells (MMCC-TSBC) to adjustable-speed motor drives. The TSBC is a direct ac-to-ac power converter capable of bidirectional power flow with three-phase sinusoidal input and output currents. Therefore, it is suitable to medium-voltage high-power motor drives requiring regenerative braking. However, the TSBC suffers from such a serious problem that capacitor-voltage fluctuation becomes larger as the motor (output) frequency is closer to the supply (input) frequency. Recent research has solved this problem by using a new control method. However, no experimental results applied this control method have been presented. The aim of this paper is to show experimental verification applying the new control method when the output frequency is close to the input frequency. A specially-designed downscaled system rated at 400 V and 15 kW is used to confirm the validity and effectiveness of the new control method.
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.
A voltage-source back-to-back system for the purpose of achieving power flow control and/or line-frequency change in transmission systems has the attractive features of reliable and continuous operation, even during power line faults. However, an overvoltage appearing across the dc link during the faults should be limited to as low a value as possible because it does affect the power device ratings. This paper proposes a dc-link voltage regulator for effectively suppressing the overvoltage during power line faults. This regulator is characterized by compensating for a time delay inherent in each current controller, and for a power flow imbalance occurring during power line faults. The validity of the proposed regulator is confirmed by theory and computer simulation.
No abstract is provided for this article.
This paper discusses the potential of a transformerless STATic synchronous COMpensator (STATCOM) intended for installation on the 6.6-kV industrial and utility distribution systems. The STATCOM consists of a five-level diode-clamped pulsewidth-modulation 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.
This paper presents a fully-digital-controlled shunt hybrid filter for damping of harmonic propagation in power distribution systems. The harmonic propagation is caused by resonance between line inductances and power capacitors installed for power factor correction. A possible solution to damping out harmonic propagation is based on installation of a shunt pure active filter at the end of a feeder This paper proposes a shunt hybrid active filter characterized by series connection of a 7th tuned LC filter per phase and a small-rated three-phase active filter. Like the pure filter, the hybrid filter is connected to the end bus of a feeder. The capacitor of the LC filter imposes a high impedance to the fundamental frequency, so that the fundamental voltage appears across the capacitor. This unique feature allows us to directly connect the hybrid filter to the 6.6 kV power line without step-down transformers. Furthermore, the capacitor used in this hybrid filter is lighter, cheaper and smaller than the transformer used in the pure filter. Theoretical analysis, along with experimental results obtained from a 200-V, 20-kW laboratory system, verifies the viability and effectiveness of the proposed hybrid filter.
This paper analyzes conducted EMI generated by a PWM inverter-fed induction motor drive system. It is shown experimentally and analytically that resonant phenomena in a high-frequency range beyond a dominant resonant frequency are originated from the behavior of power cables as a distributed-constant circuit. Spectra of common-mode and differential-mode currents are simulated by means of introducing a distributed-constant model of the power cables, which consists of a 20-step ladder circuit. As a result, it is also shown that these resonances can be damped out by a single common-mode transformer (CMT) and three differential-mode filters (DMFs), both of which have been proposed by the authors.
The integration of a series active filter with a 12-pulse diode rectifier can provide an effective means for supply current harmonic free AC/DC conversion. Controlling the series active filter as a frequency selective impedance requires low delays and is not well suited for implementation by digital control. This paper suggests two control methods intended for implementation by digital control. The suggested current-mode control method for supply current balancing and voltage regulation is verified experimentally.
No abstract is provided for this article.
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.
耳鼻咽喉科以外の施設に所属する医師が, 扁桃とIgA腎症との関係をどのように考えているかを知る目的で, アンケート調査を行った.対象は, IgA腎症診療指針作成合同委員会の委員の方々, および最近の日本腎臓学会学術総会においてIgA腎症に関する報告を行っている, 耳鼻咽喉科以外の施設に所属する医師とした. 154名の対象医師のうち回答を得られたのは93名 (内科医79名, 小児科医12名, 病理医2名) で, 回答率は60.4%であった.結果は, IgA腎症の予後予測に最重視しているのは腎組織障害度 (72.0%), 最も有効な治療法 (薬) は副腎皮質ステロイド薬 (73.1%), 治療効果判定に最も有用なのは尿蛋白 (37.6%) という回答が最多であった. 最も有効な治療法が口蓋扁桃摘出術 (以下, 扁摘) と回答した医師は, 1名のみであった. IgA腎症発症に扁桃の関与が考えられる症例の割合は50%未満 (51.6%), 扁桃誘発試験はほとんど施行されていないが, 施行する場合の最重視項目は尿蛋白 (51.6%), 扁摘効果がある症例の割合は50%未満 (57.0%) という回答が最多であった.IgA腎症に対する扁摘効果は, 耳鼻咽喉科以外の医師にはまだまだ知られておらず, 啓蒙の必要があると考えた.
Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. These motors are characterized by integration of switched reluctance motors and magnetic bearings. It is essential for a control system to consider magnetic saturation in real time in order to realize stable operation at a full torque load. Thus, this paper proposes a method for fast calculation of radial force and torque of a bearingless switched reluctance motor operating in a region of magnetic saturation. It is shown experimentally that the proposed method is effective in calculating the radial force and the torque under conditions of magnetic saturation.
The so‐called three‐level inverters have been widely used for industry applications because of high‐voltage output ability and low harmonic contents. These applications are mainly suitable for AC motor drives. Recent attention has been paid to larger‐capacity inverters applicable to power system control. This paper describes their applications to power systems. First, harmonic analysis of a three‐level inverter is achieved under the condition that its two DC capacitor voltage are unbalanced. Second, a control method for balancing the two DC capacitor voltages is described. Finally, applications of single‐phase three‐level inverters to STATCOM and BTB are introduced. Their control performance is confirmed by computer simulation. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(1): 54–62, 2006; Published online in Wiley InterScience ( http://www.interscience.wiley.com ). DOI 10.1002/eej.20306
This paper deals with active circuits for cancellation and compensation of common-mode voltage caused by a PWM inverter. A non-negligible amount of leakage or ground current would flow through stary capacitors between stator windings and a motor frame due to a large step change in the common-mode voltage at every switching operation of the PWM inverter. First, it is shown experimentally that the active common-noise canceler (ACC), which has been proposed by the authors, is effective in reducing not only conducted EMI but also motor shaft voltage and bearing current. Next, a new ACC characterized by an isolated power supply is developed to enlarge an applicable voltage range in which it is possible to integrate the ACC with a PWM inverter. Furthermore, the authors proposes another type of ACC, the purpose of which is, not to achieve complete cancellation, but to restrain only a slope in a change of the common-mode voltage applied to the the motor. As a result, the core size of the common mode transformer used in the active compensating circuit becomes smaller considerably. Some experimental results show good effects of the proposed active circuits on both ground current and conducted EMI.
This paper presents a modular multilevel cascade converter based on triple-star bridge-cells (MMCC-TSBC) with a focus on its decoupled control. The TSBC is one of the direct ac-to-ac power converters having the capability of bidirectional power flow with three-phase sinusoidal input (supply-side) and output (motor-side) currents. Therefore, it is suitable for a medium-voltage motor drive requiring regenerative braking. This paper has an intensive discussion on control strategy for the TSBC, which includes current control, capacitor-voltage-balancing control, and fluctuation-mitigating control for low-speed operation. This control strategy succeeds in achieving decoupling among supply (input) currents, motor (output) currents, and circulating currents, using the αβ0 coordinate transformation. The validity and effectiveness of the control strategy are confirmed by theoretical analysis and computer simulation.
A novel approach to compensating for harmonics in power systems is presented. It is a combined system of a shunt passive filter and a small rated series active filter. The compensation principle is described, and some filtering characteristics are discussed in detail. Excellent practicability and validity to compensate for harmonics in power systems are demonstrated experimentally. Although the source harmonic voltage was only 1%, the source harmonic current reached about 10% before the series active filter was started. After it was started, no harmonic current flowed into the shunt passive filter. In addition, no harmonic voltage appeared at the terminals of the shunt passive filter, because the source harmonic voltage was applied to the series active filter. The total loss of the series active filter was less than 40 W. It is concluded that the combined system is far superior in efficiency to conventional shunt active filters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
