Publications

Recounts the career and contributions on Akira Nabae.

This paper proposes a small-sized passive EMI filter for the purpose of eliminating high-frequency shaft voltage and ground leakage current from an ac motor. The motor is driven by a general-purpose PWM inverter connected to a three-phase grounded voltage source. The passive EMI filter requires access to the ungrounded neutral point of the motor. This unique circuit configuration makes the common-mode inductor effective in reducing the high-frequency common-mode voltage generated by the PWM inverter with a carrier frequency of 15kHz. As a result, both high-frequency shaft voltage and ground leakage current can be eliminated very efficiently. However, the common-mode inductor may not play any role in reducing the low-frequency common-mode voltage generated by the diode rectifier, so that a low-frequency component still remains in the shaft voltage. Such a low-frequency shaft voltage may not produce any bad effect on motor bearings. The validity and effectiveness of the EMI filter is verified by experimental results obtained from a 200-V 5-kVA laboratory system.

This paper proposes a DC model of a series active filter integrated with a double-series diode rectifier. The model is developed with the help of the d-q coordinates transformation. It can be used to accurately and simply analyze transient characteristics of the integrated system around the fundamental frequency, instead of analyzing a complex AC-DC system taking into account the behavior of switching devices. The analysis makes the following assumptions: the system is balanced, and the three-phase supply currents are continuous; supply current harmonics in the integrated system are not so large as to affect the transient characteristics; and the DC load is resistive. The analysis using the DC model tells us that either increasing the active filter gain or decreasing the cut-off frequency of the harmonic detector results in a slow response, and causes a large and long transient of the DC voltage. Simulation results using the EMTDC software package verify the validity of the proposed DC model.

This paper presents the modular multilevel cascade converter based on triple-star bridge-cells (MMCC-TSBC) with a focus on experimental verification for motor drives. The TSBC is one of the direct ac-to-ac power converters, which is characterized by achieving bidirectional power flow, drawing and feeding three-phase sinusoidal input (supply-side) and output (motor-side) currents with any power factor at both sides. Therefore, it is suitable especially for a low-speed, high-torque application of a medium-voltage high-power motor drive requiring regenerative braking. A downscaled system rated at 400 V and 15 kW is designed, constructed, and tested to confirm the validity and effectiveness of the motor drive. Experimental results show that stable operation is verified at such a low speed as 60 min <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the rated torque. In addition, it is verified that the motor loaded the rated torque can start up from a standstill without producing any overvoltage or overcurrent.

The 32 papers in this special section cover a wide range of power electronics technology from low power to high power.

This chapter describes the "active filters for power conditioning" or simply uses the term "active filters" as long as no confusion occurs. Much research has been performed on active filters for power conditioning and their practical applications since their basic principles of compensation were proposed around 1970. In order to distinguish active filters in power processing from active filters in signal processing, the term "active power filters" often appears in many technical papers or literature. Active filters are divided into alternating current and Direct Current (DC) filters. The DC terminals of the diode rectifier and the active filter form a common DC bus equipped with an electrolytic capacitor. The active filter is controlled in such a way as to present zero impedance for the fundamental frequency and to act as a resistor with high resistance of K for harmonic frequencies. A hybrid active filter for harmonic damping has been installed at the Yamanashi test line for high-speed magnetically-levitated trains.

This paper presents the application of a modular multilevel cascade converter based on single‐delta bridge‐cells (MMCC‐SDBC) to a STATic synchronous COMpensator (STATCOM), particularly for negative‐sequence reactive‐power control. The SDBC is characterized by cascade connection of multiple single‐phase H‐bridge (or full‐bridge) converter cells per leg, which facilitates flexible circuit design, low voltage steps, and low electromagnetic interference (EMI) emissions. However, there is no published report on such a STATCOM with experimental verification or a control strategy. This paper designs, constructs, and tests a 100‐V 5‐kVA PWM STATCOM based on the SDBC with focus on the operating principle and performance. Experimental results confirm that this converter can control not only the positive‐sequence reactive power but also the negative‐sequence reactive power and low‐frequency active power intended for the flicker compensation of arc furnaces. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 33–44, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22365

This paper presents a magnetic saliency based position estimation approach for a PM motor fed by a voltage-source PWM inverter. The proposed real-time estimation algorithm detects the motor current harmonics and calculates the inductance matrix including the rotor position information. The position estimation can be performed every period of pulse-width-modulation or carrier cycle. An experimental system using an interior permanent magnet (IPM) synchronous motor has been constructed. Experimental results verify that the position estimation within 10 degrees in electrical angle is obtained at standstill and such an extremely low-speed as 1 r/min by the proposed approach.

In recent years, attention has been paid to the concept of FACTS (Flexible AC Transmission Systems), along with significant progress in power electronic technology. A high-speed phase shifter, which is one of the most promising devices in the FACTS concept, has the potential of power flow control and/or voltage stability in power transmission systems. In this paper, theory and experiment reveal that conventional high-speed phase shifters may cause power swings in a transient state as a result of coupling between instantaneous active and reactive power control loops. Thus, two new control schemes for a high-speed phase shifter are proposed to achieve both power flow control and power swing damping. The second proposed control scheme is based on the control scheme of an already proposed series active filter. Simulated and experimental results agree well with analytical results, not only in steady states but also in transient states. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 74–82, 1999

Attention has been paid to active filters for power conditioning which provide the following multifunctions: reactive power compensation; harmonic compensation; flicker/imbalance compensation; and voltage regulation. Active filters in a range of 50 kVA-60 MVA have been practically installed in Japan. In the near future, the term "active filters" will have a much wider meaning than it did in the 1970s. For instance, active filters intended for harmonic solutions are expanding their functions from harmonic compensation of nonlinear loads into harmonic isolation between utilities and consumers, and harmonic damping throughout power distribution systems. This paper presents the present status of active filters based on state-of-the-art power electronics technology, and their future prospects and directions toward the 21st Century, including the personal views and expectations of the author.

This paper proposes a new suppression method of magnetic-flux deviation in series transformers used in a dynamic voltage restorer. A dc flux as well as an ac flux appears in the series transformers at the beginning of voltage-sag compensation. Since an amount of dc flux depends on a phase angle of the source voltage at the beginning of compensation, the sum of an ac flux and a dc flux may reach twice the rated flux. Therefore, the cross section of a series-transformer core should be designed twice as large as that of a generally-designed transformer, in order to avoid flux saturation. The proposed method to eliminate dc flux from the series transformer makes the compensating voltage zero for a short duration. As a result, only an ac flux appears in the series transformer, thus allowing us to use a generally-designed transformer. Experimental results obtained from a 200-V, 5-kW laboratory system are shown to verify the viability of the proposed method.

It has been reported that oral administration of Lactobacillus acidophilus strain L-55 (L-55) suppressed nasal symptom and antigen-specific IgE induced by antigen challenge in mice. We investigated clinical effects of L-55-contained yogurt on symptoms and IgE production in the patients with Japanese cedar pollinosis.The study was performed as a randomized double blind placebo-controlled trial. L-55-contained yogurt (L-55 yogurt) or placebo yogurt was started to administer to each subject from 4 weeks prior to the onset of Japanese cedar pollen release for total 13 weeks.The mean value of symptom score and symptom medication score were lower in L-55 yogurt group compared with placebo yogurt group during 5th week to 9th week from the first week of Japanese cedar pollination. Especially, in medicated subjects, total symptom score and throat symptom score were significantly lower in L-55 yogurt group compared with placebo yogurt group at 5th and 4th week from the first week of Japanese cedar pollination, respectively. Moreover, in medicated subjects, change ratio of serum total IgE was significantly lower in L-55 yogurt group compared with placebo yogurt group at 1st week from the first week of Japanese cedar pollination.Intake of L-55 during Japanese cedar pollinating season may be effective in alleviating the allergic symptoms related to Japanese cedar pollinosis. From these finding, it was suggested that L-55 is a possible candidate as a complementary medicine for Japanese cedar pollinosis.

This paper describes a bidirectional isolated dc-dc converter considered as a core circuit of 3.3-kV/6.6-kV high-power-density power conversion systems in the next generation. The dc-dc converter is intended to use power switching devices based on silicon carbide (SiC) and/or gallium nitride, which will be available on the market in the near future. A 350-V, 10-kW and 20 kHz dc-dc converter is designed, constructed and tested. It consists of two single-phase full-bridge converters with the latest trench-gate insulated gate bipolar transistors 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%, excluding gate drive and control circuit losses from the whole loss. Moreover, loss analysis is carried out to estimate effectiveness in using SiC-based power switching devices. Loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc-dc converter. As a result, the overall efficiency may reach 99% or higher

This paper provides an analytical and experimental discussion on a power hardware-in-the-loop (P-HIL) test bench for a medium-voltage high-power high-speed synchronous motor drive. This test bench consists of two modular multilevel double-star chopper-cell (DSCC) converters connected front-to-front without a transformer. An experimental downscaled P-HIL test bench is designed, constructed, and tested to confirm its operating performance. The three-phase 400-Vdc 10-kW DSCC inverter with eight chopper cells per arm is used as a "real" inverter under test. The other DSCC rectifier is used as a set of a "virtual" three-phase 200-V 10-kW 300-Hz four-pole 9000-r/min synchronous motor and a "virtual" high-speed centrifugal compressor with a quadratic torque-to-speed load characteristic.

This paper proposes an “active common-mode noise canceler” that is capable of eliminating the common-mode voltage produced by a voltage source PWM (pulsewidth modulated) inverter. It generates a compensating voltage which has the same amplitude as, but the opposite phase to, the common-mode voltage produced by the PWM inverter. The compensating voltage is superimposed on the inverter output by a common-mode transformer. As a result, the common-mode voltage applied to the load is canceled completely. The design method of the active common-mode noise canceler is also presented in detail. A prototype has been constructed and tested to verify the effectiveness for an induction motor drive system of 3.7 kW using an IGBT (insulated gate bipolar transistor) inverter. Some experimental results show that the proposed active common-mode noise canceler makes a significant contribution to eliminating the common-mode current or the ground current, and it prevents an electric shock from being received by anyone handling it. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 64–72, 1998