Publications

Improvement of Cycloconverter Power Factor by use of Unsymmetrical Triggering Method

No abstract is provided for this article.

Analysis of variation of neutral point potential in neutral-point-clamped voltage source PWM inverters

The authors present the analysis of the neutral-point potential variation of the neutral-point-clamped voltage source PWM (pulse-width-modulation) inverter (NPC-VSI) for AC motor drives and static VAr compensators (SVC). The potential variation is analyzed with the focus on the current flowing out of or into the neutral point of the DC link. The theoretical minimum capacity of the DC link capacitors is discussed for its application to both a vector-controlled induction motor system of 2.2 kW and a SVC system of 10 MVA, 6.6 kV, 60 Hz. It is shown that the proposed control scheme makes it possible to suppress the neutral-point potential variation within a few percent, so that the total capacity of the DC link capacitors in the NPC-VSI is almost the same as that in the conventional voltage source inverter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Implementation and performance of automatic gain adjustment in a shunt-active filter for harmonic damping throughout a power distribution system

This paper discusses automatic gain adjustment in a fully-digital-controlled shunt active filter. This is the first step in cooperative control of the multiple active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, the active filter should be equipped with an optimal control gain corresponding to the characteristic impedance of a distribution line. However, it is difficult to know circuit parameters of a real distribution line having various shunt capacitors and loads. Therefore, a main purpose of the gain adjustment is to make the active filter damp out harmonic propagation without considering the circuit parameters. In addition, the gain adjustment can reduce the compensating currents and losses in the active filter, and moreover it can avoid over-damping performance. Experiment results obtained from a 200-V, 20-kW laboratory system verify the effectiveness of the active filter equipped with automatic gain adjustment.

How Power Electronics Engineers Should Write and Present Technical Papers in English

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.

Control and analysis of a unified power flow controller

This paper presents a control scheme and comprehensive analysis for a unified power flow controller (UPFC) on the basis of theory, computer simulation and experiment. This developed theoretical analysis reveals that a conventional power feedback control scheme makes the UPFC induce power fluctuation in transient states. The conventional control scheme cannot attenuate the power fluctuation, and so the time constant of damping is independent of active and reactive power feedback gains integrated in its control circuit. This paper proposes an advanced control scheme which has the function of successfully damping out the power fluctuation. A UPFC rated at 10 kVA is designed and constructed, which is a combination of a series device consisting of three single-phase pulsewidth modulation (PWM) converters and a shunt device consisting of a three-phase diode rectifier. Although the dynamics of the shunt device are not included, it is possible to confirm and demonstrate the performance of the series device. Experimental results agree well with both analytical and simulated results and show viability and effectiveness of the proposed control scheme.

A national project on Optimal Control and demonstration of the Japanese smart grid for massive integration of photovoltaic systems

This paper describes one of Japanese smart grid related activities, "Demonstration Projects for Next Generation Optimum Control of Power Transmission and Distribution Network" which deals with issues associated with mass penetration of photovoltaic power generation systems. Research subjects covered by this project and some results obtained so far are presented.

Capacitor-Voltage Balancing for a Modular Multilevel DSCC Inverter Driving a Medium-Voltage Synchronous Motor

This paper provides a comprehensive discussion on voltage balancing of all the floating capacitors in a modular multilevel cascade inverter based on double-star chopper cells (DSCC) or a modular multilevel DSCC inverter. It intends to use the inverter for driving a medium-voltage synchronous motor. Theoretical and numerical design considerations on both amplitude and phase of the three-phase motor currents achieve better capacitor-voltage balancing in a low-power low-frequency range. A three-phase DSCC inverter with phase-shifted-carrier pulse width modulation is designed, constructed, and tested to drive the 370-V 15-kW 75-Hz six-pole interior-permanent-magnet synchronous motor loaded with a hypothetical centrifugal compressor. Experimental results verify the validity of the theoretical analysis, as well as the effectiveness and viability of the DSCC inverter for such a specific electrical drive.

Current controlled PWM inverter of high current response speed and low harmonic content

No abstract is provided for this article.

Method of Improvement in Displacement Factor of Series Connected Cycloconverter and its Gate Control Scheme

No abstract is provided for this article.

A Back-To-Back (BTB) System Using Modular Multilevel Cascade Converters Based on Double-Star Chopper-Cells (MMCC-DSCC): Verification of Operation by Experiment and Simulation

This paper presents a detailed discussion on the modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC). Hereinafter, it is simply referred to as the DSCC. A couple of DSCCs are used to form a three-phase 6.6-kV back-to-back (BTB) system installed between two power distribution feeders. Each DSCC, using 3.3-kV IGBTs, consists of 16 cascaded chopper-cells per leg. Low voltage steps bring about significant reductions in the harmonic voltage and current to the BTB system. A conventional power conversion system employs bulky line-frequency transformers and dc-link capacitors, whereas this system does not require either of them, thereby reducing the overall physical size and weight. Although no voltage sensor is installed on the common dc link of the BTB system, an indirect feedback loop in the control system makes it possible to regulate the mean dc-link voltage to its reference. This paper describes the design, construction, and evaluation of a three-phase 200-V, 10-kW downscaled model, with focus on operating principles and performance. Finally, experimental waveforms are compared with simulated ones obtained from a software package of PSCAD/EMTDC under the same operating conditions, including steady and transient states. The experimental and simulated waveforms agree well with each other.

Implementation and position control performance of a position-sensorless IPM motor drive system based on magnetic saliency

This paper describes position-sensorless control of an interior permanent magnet synchronous motor (IPM motor), which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm detects motor current harmonics and determines the inductance matrix including rotor position information. An experimental system consisting of an IPM motor and a voltage-source PWM inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms.

Five-Level Diode-Clamped PWM Converters Connected Back-to-Back for Motor Drives

This paper addresses a transformerless medium-voltage adjustable-speed motor drive consisting of two five-level diode-clamped PWM converters connected back-to-back. It is followed by designing, constructing, and testing a 200-V downscaled model to verify the validity and effectiveness of the medium-voltage motor drive. This downscaled model has four split DC capacitors equipped with a voltage-balancing circuit using two bidirectional buck-boost choppers. The two five-level converters are based on sinusoidal pulsewidth modulation with a carrier frequency of 3 kHz. The motor tested in this paper is a three-phase four-pole induction motor rated at 200 V, 5.5 kW, and 60 Hz. Experimental waveforms show that the four split dc-capacitor voltages are well balanced in any operating conditions and that the total harmonic distortion values of the input line current and the output motor current are 3.9% and 3.5%, respectively.

Discussions on Switching-Ripple Voltages on the Common DC Link of the Modular Multilevel Cascade Inverter (MMCI-DSCC)

This paper describes a modular multilevel cascade inverter based on double-star chopper-cells (MMCI-DSCC) for a medium-voltage motor drive with a passive front end. Unlike the traditional two-level PWM inverter, the DSCC can operate without common dc-link capacitors because the DSCC itself possesses energy-storage components. However, a certain amount of switching-ripple voltage is generated in the common dc link when a passive front end is utilized. In this paper, the attenuation of the switching-ripple voltage by using a dc passive filter consisting of a series-connected film capacitor and resistor is attempted. A 400-V, 15-kW downscaled model is utilized to confirm the suitability of the design procedure developed in this paper. Experimental results show that the switching-ripple voltage can be attenuated satisfactorily by a small-capacity film capacitor. Moreover, the loss of the filter is negligible compared to the rated power of 15kW.

Active filters and energy storage systems for power conditioning in Japan

This paper describes advanced 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 power conditioning. 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. The author cannot survey the whole spectrum of active filtering and energy storage. Therefore, this paper is focused on the present status of active filters for power conditioning, along with a 200-MJ/20-MW flywheel energy storage system which has been commercially installed on a 66-kV power system for the purpose of line-frequency regulation in Japan.

Ménière's disease in childhood

We report 3 rare cases of Ménière's disease in children. In Case 1 and 3, vertigo, hearing loss and tinnitus recovered soon after medical therapy. In Case 2, however, vertigo recurred and the hearing level on the right side markedly deteriorated. The equal-loudness contours on three-dimensional audiogram showed that right-sided aggravated hearing loss fluctuated for 4 years at middle-and low-frequencies despite medication. Finally intratympanic injection of gentamicin sulfate was performed. The patient has had no definitive spell of vertigo after gentamicin therapy. At our department, the incidence of Ménière's disease in pediatric patients with vertigo was 2.9%.

Comparisons between a hybrid shunt active filter and a pure shunt active filter

This paper deals with the hybrid shunt active filter for harmonic compensation of a three-phase diode rectifier in a 480-V adjustable-speed motor drive system. The hybrid filter is formed by a three-phase LC filter tuned around the seventh harmonic frequency and a small-rated three-phase voltage-source PWM inverter. The LC filter and PWM inverter are directly connected in series. As a result, the DC capacitor voltage of the PWM inverter in the hybrid filter is much lower than that of a conventional pure shunt active filter. This results in higher efficiency, less switching ripple, and less EMI emission. Computer simulation is carried out to compare the hybrid filter with the pure filter in terms of circuit configuration and filtering performance. Simulation results indicate that the hybrid filter is superior in effectiveness and viability to the pure filter. In addition, theoretical analysis based on vector loci confirms the validity of the simulation results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(2): 61–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20145

Influence of Arc Discharge on the Surface of a Contact Wire

New trends in active filters for improving power quality

Since their basic compensation principles were proposed around 1970, active filters have been studied by many researchers and engineers aiming to put them into practical applications. Shunt active filters for harmonic compensation with or without reactive power compensation, flicker compensation or voltage regulation have been put on a commercial base in Japan, and their rating or capacity has ranged from 50 kVA to 60 MVA at present. In near future, the term of active filters will cover a much wider sense than that of active filters in the 1970s did. The function of active filters will be expanded from voltage flicker compensation or voltage regulation into power quality improvement for power distribution systems as the capacity of active filters becomes larger. This paper describes present states of the active filters based on state-of-the-art power electronics technology, and their future prospects toward the 21st century, including the personal view and expectation of the author.