Publications

A broad range of speed control of a permanent magnet synchronous motor driven by a modular multilevel TSBC converter

A 21-level (line-to-line) BTB system based on series connection of sixteen converter-cells for power flow control: experimental verifications by a 200-V, 10-kW laboratory system

A 21-level (line-to-line) self-commutated BTB (back-to-back) system based on series connection of sixteen converter-cells has attractive features as follows: i) Both active and reactive powers can be controlled independently even in transient states, ii) The BTB system produces almost sinusoidal voltage at the AC side without performing PWM (pulse-width-modulation) control, so that no harmonic filter is required, iii) The BTB system provides an active-power response as high as 3 ms. This work presents experimental verifications of the self-commutated BTB system for the purpose of achieving power flow control in transmission systems. Experimental results obtained by a 200-V 10-kW laboratory prototype confirm effectiveness and validity of both the proposed system configuration and control strategy developed in this paper.

Short-Circuit Protection Method Based on a Gate Charge Characteristic

This paper describes a high-speed protection circuit against a hard-switching fault (HSF) and a fault under load (FUL). The demand for high-speed protection circuits for insulated-gate bipolar transistors (IGBTs) subjected to an HSF increases with increasing power density of power semiconductor devices. The reverse transfer capacitance of an IGBT depends on the collector-emitter voltage, such that it produces a significant effect on the switching behavior under HSF conditions as well as under normal conditions. Accordingly, a significant difference appears in the gate charge characteristics between under HSF conditions and under normal turn-on conditions. Hence, an HSF can be detected by monitoring the gate-emitter voltage and the amount of gate charge. IGBTs can be rapidly protected from destruction because no blanking time is required. An FUL can be also detected by the same protection procedure because a gate charge characteristic under FUL conditions also differs from that under normal turn-on conditions. Simulated and experimental results verify the validity of the novel protection circuit based on a gate charge characteristic.

130 kHz 7.5 kW current source inverters using static induction transistors for induction heating applications

A control scheme of a high-frequency high-power current source inverters using static induction transistors is described which aims at the suppression of the surge voltage and reduction of the switching loss during the commutation of current. The inverter is operated at a leading power factor, which requires the phase angle of the output current to be adjusted to each specific load point by the controller. The stable operation is verified by the experiments under the commutation inductance 1.8 mu H, i.e., 18% reactance (130 kHz, 250 V, 30 A, base). As a result, the inverter efficiency is estimated to be 97%, excluding the loss of the drive circuit and the control circuit.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Enhancement of Power Conversion Efficiency in a Low-Power Range of a Bidirectional Isolated DC-DC Converter by Intermittent Operation

This paper describes a 750-Vdc, 100-kW, 20-kHz bidirectional isolated dual-active-bridge (DAB) dc-dc converter using SiC-MOSFET modules without free-wheeling diodes, focusing on the output voltage ripple and power conversion efficiency. Intermittent operation brings higher conversion efficiencies in a low-power range to the dc-dc converter than does continuous operation because it makes a significant contribution to reducing switching (snubber) and iron losses. Experimental results reveal that the efficiency at 10kW (10% of the rated power) is 95.1% in continuous operation, whereas it is improved to 98.2% in intermittent operation. The combination of intermittent operation with continuous operation makes the efficiencies in a power range from 3 to 100kW higher than 98%, excluding power losses produced by the control and gate-drive circuits. However, the intermittent operation may bring additional voltage ripples to the dc output terminals. Theoretical analysis confirms that the voltage ripples in a power range from 1 to 18kW are lower than 7V in peak-to-peak, which is only 0.9% of 750Vdc. Theoretical results are confirmed by comparison to simulated and experimental ones.

Development of Wavelength Converter for Arc Light Detection

Contact loss measurement based on arc light detection makes it possible to estimate the current-collecting performance from catenary lines in electric railways before commercial operation, or after the installation, of new overhead contact systems and new pantographs. This measurement system consists mainly of a photo acceptor, a photo detector and a plastic optical fiber for connecting them. However, the system performance is affected by sunlight because the system detects only visible rays. Therefore, the authors develop a conversion system that can change a broad range of wavelengths—from ultraviolet to visible rays—emitted by the arc light to a voltage signal. The developed measurement system equipped with the wavelength converter can detect ultraviolet rays indirectly. This paper describes the operating principles of the wavelength converter and presents experimental results obtained with the measurement system.

A novel method of reducing the supply current harmonics of a 12-pulse thyristor rectifier with an interphase reactor

A novel design concept of an interphase reactor in a three-phase twelve-pulse thyristor rectifier is proposed for reducing supply current harmonics. This concept requires only an interphase reactor with a small inductance value, and requires no additional switching devices. As the inductance value is decreased, the supply current approaches a sinusoidal waveform, which is more sinusoidal than that of a 36-pulse thyristor rectifier. The basic principle of the proposed concept is discussed in detail, and confirmed by using digital computer simulation. Experimental results verify the effectiveness and practicability of the proposed design concept of the interphase reactor.

A hybrid active filter for damping of harmonic resonance in industrial power systems

This paper proposes a hybrid active filter for the damping of harmonic resonance in industrial power systems. The hybrid filter consists of a small-rated active filter and a 5th-tuned passive filter. The active filter is characterized by detecting the 5th-harmonic current flowing into the passive filter. It is controlled in such a way as to behave as a negative or positive resistor by adjusting a feedback gain from a negative to positive value, and vice versa. The negative resistor presented by the active filter cancels a positive resistor inherent in the passive filter, so that the hybrid filter acts as an ideal passive filter with infinite quality factor. This significantly improves damping the harmonic resonance, compared with the passive filter used alone. Moreover, the active filter acts as a positive resistor to prevent an excessive harmonic current from flowing into the passive filter. Experimental results obtained from a 20-kW laboratory model verify the viability and effectiveness of the hybrid active filter proposed in this paper.

Modeling and Analysis for Simulation of Common-Mode Noises Produced by an Inverter-Driven Air Conditioner

This paper presents an intensive discussion on conducted electromagnetic interference (EMI) emissions from an inverter-driven air conditioner. Common-mode voltages produced by the pulsewidth-modulated (PWM) inverter may cause a high-frequency leakage current. The use of a spectrum analyzer and a line-impedance stabilization network (LISN) makes it possible to refer the leakage current in the time domain to the conducted-EMI emission levels in the frequency domain, which are prescribed by the EMI regulations. Simulation-based estimation of the conducted-EMI emission levels in advance allows engineers to efficiently design a cost-effective EMI filter intended for meeting the regulations. This paper achieves modeling of the inverter-driven air conditioner with focus on common-mode voltages and leakage-current propagation paths. The simulation circuit developed can be used to predict conducted-EMI emission levels and to design the cost-effective EMI filter. Simulated results agree fairly with experimental ones in both cases of the EMI filter being connected and disconnected.

A Proposal of a 3.3-kV/6.6-kV Transformerless Hybrid Filter, and Experimental Verification Based on a 200-V Laboratory System

This paper proposes a transformerless shunt hybrid filter for harmonic compensation of a three-phase six-pulse diode rectifier, where the ac line-to-line voltage is 3.3kV or 6.6kV. The hybrid filter consists of a single tuned LC filter per phase and an active filter with a dc capacitor voltage as low as 300V or 600V. The two filters are directly connected in series with each other without any transformer. The passive filter absorbs harmonic currents produced by the rectifier, whereas the active filter improves the filtering characteristics of the passive filter. The required rating of the active filter is much smaller than that of a conventional shunt active filter used alone. In addition, no additional switching-ripple filter is required for the active filter, because the LC filter acts not only as a tuned LC filter around the 7th-harmonic frequency but also as a switching-ripple filter around 10kHz. A feedforward control scheme is also proposed to improve the active filter performance. 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. The hybrid filter gives satisfactory compensation performance, thus allowing us to put it into practical use.

A shunt active filter based on voltage detection for harmonic termination of a radial power distribution line

This paper focuses on a shunt active filter based on the detection of harmonic voltages at the point of installation. The objective of the active filter is to attenuate harmonic propagation resulting from series/parallel resonance between capacitors for power factor correction and line inductors in a power distribution line. The active filter acts as a low resistor to the external circuit for harmonic frequencies, and it is installed on the end bus of the power distribution line, just like a 50 /spl Omega/ terminator installed on the end terminal of a signal transmission line. Therefore, the function of the active filter is referred to as "harmonic termination" in this paper. Experimental results obtained from a laboratory system rated at 200 V and 20 kW verify that the active filter for the purpose of harmonic termination has the capability of harmonic damping throughout the power distribution line.

Expectations for the IEEJ Industry Applications Society

No abstract is provided for this article.

Preface to a Special Issue on “Semiconductor Power Conversion Technology and its Applications”

No abstract is provided for this article.

A Case of Recurrent Ameloblastoma 24 Years after Hemimandibulectomy.

Ameloblastoma originates from the dental tissue and is generally regarded as a benign tumor although it often recurs and sometimes becomes malignant. The choice of treatment is very impor-tant in this disease. The incidence of relapse in patients treated surgically has been reported to be fewer than that in patients treated by conservative methods. Even when this tumor had been removed radically however, the possibility of recurrence remains.In this paper, a 56-year-old male with recurrent ameloblastoma is reported. The patient under-went hemimandibulectomy and an ameloblastoma was resected in 1971. The postoperative course was good.In 1995, however, he complained of swelling in the left gingiva and was referred to our hospital. On physical examination, a hard, reddish tumor located on the lateral side of the left gingiva was revealed. CT and MRI showed that the tumor was located in the left inf ratemporal f ossa, and that it grew from the bone remaining after the previous surgery. The tumor was regarded as a recurrent ameloblastoma and was removed surgically by means of Weber's incision. Histological examination confirmed a diagnosis of ameloblastoma of the follicular type. There has been no sign of recurrence 10 months after surgery.

The Theory of Instantaneous Power in Three-Phase Four-Wire Systems and its Applications

This paper discusses "the p-q theory" and "the cross-vector theory" in three-phase four-wire systems, with the focus on similarity and difference between the two theories. They are perfectly identical if no zero-sequence voltage is included in a three-phase three-wire system. However, they are different in definition of the instantaneous active power and instantaneous reactive power in each phase if a zero-sequence voltage or current is included in a three-phase four-wire system. Based on both theory and computer simulation, this paper leads to the following conclusions: An instantaneous reactive-power compensator without energy storage components can fully compensate for the neutral current even in a three-phase four-wire system including a zero-sequence voltage or current, when a proposed control strategy based on the p-q theory is applied: However, the compensator cannot compensate for the neutral current fully, when a conventional control strategy based on the cross-vector theory is applied.

An approach to position sensorless drive for brushless DC motors

A brushless DC motor without a position sensor is described. Variable speed is achieved by adjusting the average motor voltage, just like chopper control of DC motors. The position-sensorless drive proposed is based on detection of the conducting interval of free wheeling diodes connected in antiparallel with power transistors. This approach makes it possible to detect the rotor position over a wide speed range, especially at a lower speed. Experimental results obtained from a prototype brushless DC motor with a rating of 300 W are shown to confirm the validity of the sensorless drive from 45 to 2300 r/min. The starting procedure of the motor is also discussed because it is impossible to detect the rotor position at a standstill.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transient Analysis of an Advanced Static Var Compensator Using Quad-Series Voltage-Source PAM Inverters.

This paper deals with an advanced static var compensator (ASVC) using quad-series voltage-source PAM inverters. The ASVC consists of four three-phase voltage-source inverters with a common dc capacitor and four three-phase transformers, each primary winding of which is connected in series each other. Each inverter outputs a square wave voltage, while the synthesized output voltage of the ASVC has a 24-step wave shape. This results not only in a great reduction of harmonic currents and de voltage ripples but also in less switching and snubbing losses.In this paper, transient analysis is performed with the focus on the response of reactive power and the resonance between the dc capacitor and ac reactors. Experimental results obtained from a small-rated laboratory model of 10kVA are also shown to verify analytical results based on the p-q transformation. The analytical results help us to design system parameters such as the capacity of the dc capacitor and feedback gains.

Individual Battery-Power Control for a Battery Energy Storage System Using a Modular Multilevel Cascade Converter

This paper focuses on a battery energy storage system that can be installed in a 6.6-kV power distribution system. This system comprises a combination of a modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC) and multiple battery modules. Each battery module is connected to the dc side of each bridge-cell, where the battery modules are galvanically isolated from each other. Three-phase multilevel line-to-line voltages with extremely low voltage steps on the ac side of the converter help in solving problems related to line harmonic currents and electromagnetic interference (EMI) issues. This paper proposes a control method that allows each bridge-cell to independently adjust the battery power flowing into or out of each battery module. A three-phase energy storage system using nine nickel-metal-hydride (NiMH) battery modules, each rated at 72V and 5.5Ah, is designed, constructed, and tested to verify the viability and effectiveness of the proposed control method.