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This paper describes the design and operation of a 6-kW, full-bridge, zero-voltage switching, bidirectional isolated dc-dc converter for a 2-kWh lithium-ion (Li-ion) bank that is considered attractive as an energy storage system for applications to photovoltaic generation systems ranging from 10 to 30 kW. The dc voltage at the high-voltage side of the converter is controlled from 305 to 355 V as the battery voltage at the low-voltage side varies from 50 to 59 V. The galvanic isolation using a 20kHz transformer with a turns ratio of 6:1 provides flexibility in voltage matching and safety. This paper presents experimental verifications of bidirectional power flow into (battery charging), or out of (battery discharging) the Li-ion battery bank. The maximal efficiency of the dc-dc converter is measured to be 96.1% during battery charging, and 96.9% during battery discharging.

This paper proposes a new PWM rectifier/inverter system that is capable of suppressing not only supply harmonic currents but also electromagnetic interference (EMI). The conversion system consists of a PWM rectifier and inverter, and an active common-noise canceler (ACC) which has been proposed by the authors. The ACC developed for this system is characterized by sophisticated connection of a common-mode transformer which can compensate for common-mode voltages produced by both the PWM rectifier and inverter. As a result, the size of the common-mode transformer can be reduced to 1/3, compared with the previously proposed ACC. A prototype PWM rectifier/inverter system (2.2kW) has been implemented and tested. Some experimental results show reduction characteristics of the supply harmonic current and EMI.

A modular multilevel cascade inverter based on double-star chopper-cells (MMCI-DSCC) is expected to be used as one of the next-generation medium-voltage PWM inverters suitable to motor drives for energy savings. This three-phase inverter comprises six modular arms, each of which consists of a cascaded stack of multiple bidirectional chopper-cells. It suffers from ac-voltage fluctuation in the dc-capacitor voltage of each chopper-cell at low speed. The frequency of this fluctuation is equal to the stator-current frequency. This paper attempts to suppress the fluctuation by injecting a common-mode voltage of 45Hz and circulating currents among the three legs. Experimental results obtained from a 400-V, 15-kW downscaled system verify that stable operation is achieved at an ultra-low speed of 17min-1 with a load torque of τL = 40%, as well as “three-phase” dc-current feeding operation. Moreover, the motor can start up from a standstill without producing any overvoltage or overcurrent.

This paper describes a 750-V, 100-kW, 20-kHz bidirectional isolated dc/dc converter with the "dual-active-bridge" configuration using four SiC-MOSFET/SBD two-in-one modules. It pays particular attention to conversion efficiency and power-loss breakdown. The overall maximum efficiency from the dc-input to the dc-output terminals is measured accurately to be 98.7%, excluding the gate-drive and control circuit losses from the overall power loss. A power-loss breakdown at the rated (100kW) operation is carried out to separate conduction, switching, iron, copper, and unknown losses from the overall loss. The power loss breakdown indicates that the sum of the conduction and switching losses produced in the four SiC modules is about 60% of the overall loss, and that the conduction loss is almost equal to the switching loss. Moreover, this paper provides theoretical and experimental discussions on a range of dead times for achieving zero-voltage switching (ZVS).

This paper proposes a 3.3-kV transformerless AC-to-DC power conversion system consisting of a three-phase six-pulse diode rectifier and a shunt hybrid filter. The hybrid filter is formed by a single tuned LC filter per phase and a small-rated three-phase active filter, which are directly connected in series without any matching transformer. The required rating of the active filter is much smaller than that of a conventional standalone active filter be. In addition, no additional switching-ripple filter is required for the hybrid filter because the LC filter functions not only as a harmonic filter tuned at the seventh harmonic frequency but also as a switching-ripple filter around 10 kHz. Experimental results obtained from a 200-V 5-kW laboratory system and simulation results of a 3.3-kV 300-kW system confirm the validity and effectiveness of the system.

This paper presents the performance of a three-phase bidirectional isolated DC-DC converter (3P-BIDC) in wye-wye (Yy), wye-delta (Yd), delta-wye (Dy), and delta-delta (Dd) transformer configurations, using enhanced switching strategy that combines phase-shift modulation and burst-mode switching. A simulation verification using PSCAD is carried out to study the feasibility and compare the efficiency performance of the 3P-BIDC with each transformer configuration, using intermittent switching, which combines the conventional phase-shift modulation (PSM) and burst-mode switching, in the light load condition. The model is tested with continuous switching that employs the conventional PSM from medium to high loads (greater than 0.3 p.u.) and with intermittent switching at light load (less than 0.3 p.u), in different transformer configurations. In all tests, the DC-link voltages are equal to the transformer turns ratio of 1:1. This paper also presents the power loss estimation in continuous and intermittent switching to verify the modelled losses in the 3P-BIDC in the Yy transformer configuration. The 3P-BIDC is modelled by taking into account the effects that on-state voltage drop in the insulated-gate bipolar transistor (IGBTs) and diodes, snubber capacitors, and three-phase transformer copper winding resistances will have on the conduction and switching losses, and copper losses in the 3P-BIDC. The intermitting switching improves the efficiency of the DC-DC converter with Yy, Yd, Dy, and Dd connections in light-load operation. The 3P-BIDC has the best efficiency performance using Yy and Dd transformer configurations for all power transfer conditions in continuous and intermittent switching. Moreover, the highest efficiency of 99.6% is achieved at the light power transfer of 0.29 p.u. in Yy and Dd transformer configurations. However, the theoretical current stress in the 3P-BIDC with a Dd transformer configuration is high. Operation of the converter with Dy transformer configuration is less favorable due to the efficiency achievements of lower than 95%, despite burst-mode switching being applied.

This paper presents control and performance of a pulse-density-modulated (PDM) series-resonant voltage-source inverter developed for corona discharge processes. The PDM inverter produces either a square-wave ac-voltage state or a zero- voltage state at its ac terminals to control the average output voltage under constant dc voltage and operating frequency. This results in a wide range of power control from 0.5% to 100%, even in the corona discharge load with a strong nonlinear char- acteristic. A 30-kHz 6-kW surface treatment system consisting of a voltage-source PDM inverter, a step-up transformer, and a corona discharge treater shows the establishment of a stable corona discharge in an extremely wide range of power control and, therefore, succeeds in performing both strong and weak surface treatment processes for film.

No abstract is provided for this article.

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.

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.

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>

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.

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.