Publications

Power Flow Analysis and DC-Capacitor Voltage Regulation for the MMCC-DSCC

This paper discusses the power flow analysis and dc-capacitor voltage regulation for the modular multilevel cascaded converter (MMCC) based on double-star chopper cells (DSCC). This analysis reveals the relationship between the circulating current through the dc link and the mean power flowing out of or into each chopper cell. The dc component on the circulating current supplies a half of the active output power to the upper and lower strings of chopper cells, whereas the fundamental-frequency component transfers an amount of power between the upper and lower strings. Thus, the MMCC-DSCC can balance the capacitor voltages among the cells by controlling the amplitude of the fundamental-frequency component on the circulating current. A new control method based on the power flow analysis is employed, and its effectiveness is verified by circuit simulation.

Analysis and design of a DC voltage-controlled static VAr compensator using quad-series voltage-source inverters

This paper presents a DC voltage-controlled static VAr compensator (SVC) using quad-series voltage-source non-PWM inverters. The SVC consists of four three-phase voltage-source inverters having a common DC capacitor and four three-phase transformers, the primary windings of which are connected in series with each other. Although each inverter outputs a square wave voltage, the synthesized AC voltage of the SVC has a 24-step waveshape. This results not only in a great reduction of harmonic currents and DC voltage ripples but also in less switching and snubbing losses. This paper develops the analysis of the transient response and the resonance between the AC reactors and the DC capacitor, with the focus on practical use. Experimental results obtained from a 10-kVA laboratory system are shown to agree well with the analytical results, thus verifying the analysis and leading to the design of DC capacitance value.

Application of a Modular Multilevel Cascade Converter (MMCC-SDBC) to a STATCOM: —Control of Active Power and Negative-Sequence Reactive Power—@@@—有効電力・逆相無効電力制御—

No abstract is provided for this article.

Quantitative analysis of interleukin 6 (IL-6) in patients with IgA nephropathy after tonsillectomy

The biological response to tonsillectomy was studied in 21 patients suffering from chronic tonsillitis with or without IgA nephropathy (IgAN). Serum and urinary interleukin-6 (IL-6) levels were measured before and after tonsillectomy. Serum IL-6 levels in case of IgAN peaked 3 h after tonsillectomy and more rapidly than control cases. No significant differences were observed between two cases through the time. Urinary IL-6 levels were significantly higher before and at 6 and 48 h after tonsillectomy in IgAN cases. Stimulation of tonsils caused serum IL-6 elevation and changes in urinary IL-6 levels in IgAN cases. Elevation of urinary IL-6 levels after tonsillectomy in patients with IgAN may reflect an increase in the production of IL-6 in the kidneys. Measurement of urinary IL-6 levels after tonsillectomy is useful to elucidate the efficacy of tonsillectomy in IgAN patients.

Decoupled Control of a Modular Multilevel Cascade Converter Based on Triple-Star Bridge-Cells (MMCC-TSBC)

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.

An Approach to Suppressing Both Shaft Voltage and Leakage Current in an AC Motor Driven by a Voltage-Source PWM Inverter-A Passive EMI Filter Making Use of the Motor Neutral Line-

This paper proposes a practical approach to suppressing both shaft voltage and leakage current in an ac motor driven by a voltage-source PWM inverter. This approach is characterized by using a neutral line of the ac motor. A common-mode inductor is connected between the inverter and the motor. Moreover, a resistor and a capacitor are connected in series between the motor neutral point and the inverter negative dc bus. This unique circuit configuration makes the common-mode inductor effective in reducing the common-mode voltage appearing at the motor terminals. As a result, both shaft voltage and ground current are significantly suppressed with low cost. Over-voltages at the end of a cable can be suppressed by a normal-mode inductor and a resistor which are connected in parallel. The validity and effectiveness of the new approach are verified by experimental results from a 5-kVA laboratory system.

Bi-Directional Isolated DC-DC Converter for Next-Generation Power Distribution - Comparison of Converters using Si and SiC Devices

In this paper two bi-directional DC-DC converters for a 1MW next-generation BTB system of a distribution system, as it is applied in Japan, are presented and compared with respect to design, efficiency and power density. One DC-DC converter applies commercially available Si-devices and the other one high voltage SiC switch, which consists of a SiC JFET cascode (MOSFET+1 JFET) in series with five SiC JFETs. In the comparison also the high frequency, high voltage transformer, which ensures galvanic isolation and which is a core element of the DC-DC converter, is examined in detail by analytic calculations and FEM simulations. For validating the analytical considerations a 20kW SiC DC-DC converter has been designed in detail. Measurement results for the switching and conduction losses have been acquired from the SiC and also for a Si system for calculating the losses of the scaled 1MW system.

Control Strategy of Active Power Filters Using Multiple Voltage-Source PWM Converters

The control strategy of active power filters using switching devices is proposed on the basis of the instantaneous reactive power theory. This aims at excellent compensation characteristics in transient states as well as steady states. The active power filter is developed, of which the power circuit consists of quadruple voltage-source PWM converters. As the result, interesting compensation characteristics were verified experimentally which could not be obtained by the active power filter based on the conventional reactive power theory.

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.

Control Strategy and Site Selection of a Shunt Active Filter for Installation on a Power Distribution System : Analysis of Harmonic Propagation on the basis of a Distributed Constant Circuit

No abstract is provided for this article.

A new power line conditioner for harmonic compensation in power systems

This paper proposes a new power line conditioner consisting of two small rating series active filters and a shunt passive filter. The power line conditioner aims at a general filtering system which will be installed at the point of common coupling in a power system feeding harmonic-sensitive loads and unidentified harmonic-producing loads. One of the two active filters is connected in series with the supply, while another is in series with the shunt passive filter. The purpose of the power line conditioner is to reduce voltage distortion at the connection point, and is to eliminate harmonic currents escaping into the system upstream of the connection point. A control scheme of the two series active filters which play an important role is described in this paper. Its filtering characteristics are discussed with the focus on voltage and current distortion. A prototype model of 20 kVA is constructed to verify the functionality and performance of the power line conditioner.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of IGBTs with focus on voltage dependency of terminal capacitances

This paper presents a modeling of IGBTs with a focus on voltage dependency of capacitances between terminals of the IGBT. The proposed model is based on a physics-based IGBT model for circuit simulators to get accurate switching waveforms by taking account of the variable capacitances depending on the voltage between the terminals of the IGBT model. The basic feature is that the simulation accuracy of switching waveforms can be improved by applying the measured capacitances to the capacitors between the terminals. The simulated results by using the proposed IGBT model are in good agreement with experimental results.

Low-voltage-ride-through (LVRT) capability of a phase-shifted-PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC)

This paper has an experimental discussion on low-voltage-ride-through (LVRT) capability of a phase-shifted-PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). The cluster-balancing control, that produces a significant effect on the LVRT capability, is modeled and analyzed with focus on either low-pass filter (LPF) or moving average filter (MAF) to attenuate the 100Hz (double the line frequency) component inherent in each dc capacitor voltage. The cluster-balancing control using the MAF is better in transient performance than that using the LPF. A three-phase downscaled system rated at 150 V and 10 kVA is designed, constructed, and tested to verify the LVRT capability of the SSBC-based STATCOM under the severest single-phase, two-phase, and three-phase voltage sags with a voltage depth of 100%. Experimental waveforms show that the STATCOM continues operating stably as if no voltage sag occurred.

Post-traumatic guitar-shaped deformity of the tympanic membrane

We report a unique case of post-traumatic guitar-shaped deformity of the tympanic membrane in an 8-year-old boy. After a traffic accident, he exhibited bleeding from the ear, incomplete facial palsy and a conductive hearing loss on the left side. Although his symptoms gradually improved, the deformity of the tympanic membrane and external auditory canal persisted. The tympanic membrane appeared to be duplicated. Careful examination using an otoscope was required for accurate diagnosis. Without knowledge of the deformity, the physician could easily misinterpret the appearance of the tympanic membrane. Formation of cholesteatoma was not observed and the normal migration of the epithelium in the external auditory canal seemed to be maintained. However, we were concerned that tubal dysfunction could eventually induce the retraction and atrophy of the tympanic membrane to ultimately form a cholesteatoma. We therefore recommend patients such as this to be evaluated periodically because of the risk of tubal dysfunction and cholesteatoma.

Modern active filters and traditional passive filters

Active filters for suppressing harmonics using multiple voltage-source PWM converters.

No abstract is provided for this article.

more power to you (review of Instantaneous Power Theory and Applications to Power Conditioning by Akagi, H. et al.; 2007) [book review]

This review examines a book that deals with the instantaneous active and reactive power theory in a complete for, for the first time. As it presents such an in-depth look at the subject, the book may be destined to be a classic.

A voltage‐source PWM rectifier‐inverter with feedforward control of instantaneous power

In general, diode rectifiers with electrolytic capacitors on the dc side have been used as dc power supplies for voltage‐source inverters. Rectifiers of this type, however, cause many problems such as poor power factor and harmonics. Recently, voltage‐source PWM rectifier‐inverters have been studied to provide the following advantages: (1) harmonic‐free on both ac sides; (2) unity power factor on the input ac side; (3) power flow of either direction or power regeneration; (4) reduction of the dc capacitor. However, it is difficult for a conventional voltage‐source PWM rectifier‐inverter to regulate the capacitor voltage on transient states because it has only a voltage feedback loop. This paper describes a voltage‐source PWM rectifier‐inverter with feedforward control of instantaneous power. Based on the pq theory, the instantaneous power which is calculated in the control circuit of the inverter is fed forward to the control circuit of the rectifier. The feedforward control of instantaneous power contributes greatly to sufficiently suppress voltage fluctuation of the dc capacitor on transient states. Transient characteristics are discussed, and some interesting experimental results of a laboratory model are shown.