Publications

モジュラー・マルチレベル・カスケード変換器(MMCC)―V. DSBC(Double-Star Bridge-Cells) 方式の風力発電システムへの応用―

Control Schemes and Waveform Analysis of Bridge Cycloconverters

No abstract is provided for this article.

Performance evaluations of a position-sensorless IPM motor drive system based on detection of current switching ripples

This paper deals with the effect of inner current control loops on the system performance of a position-sensorless interior permanent magnet (IPM) motor drive system. The position estimation method applied to the motor drive system has been proposed by the authors. Some simulation results show that the inner current loops integrated in the control system make it possible to suppress interference between the q-axis voltage and the d-axis current, thus leading to significant improvements in the stability of position control. Furthermore, this paper discusses a simulation method using the so-called "variable-sampling-time discrete-time system" available in MATLAB/Simulink. The simulation method is intended for the position-sensorless IPM motor drive system including a digital-controlled PWM inverter.

Multilevel Converters: Recent Development of Topologies and PWM Control Methods

No abstract is provided for this article.

Pulse-density-modulated power control of a 4 kW, 450 kHz voltage-source inverter for induction melting applications

This paper presents a 4 kW, 450 kHz voltage-source inverter with a series resonant circuit for induction melting applications, which is characterized by the power control based on pulse density modulation (PDM). The pulse-density-modulated inverter makes an induction melting system simple and compact, thus leading to higher efficiency. A modulation strategy is proposed to realize the induction melting system capable of operation at the frequency and power level of interest. Some interesting experimental results are shown to verify the validity of the concept.

A Combined System of a Series Active Filter and a Double-Series Diode Rectifier with a DC Smoothing Capacitor.

This paper proposes a new rectifing system consisting of a series active filter and a double-series three-phase twelve-pulse diode rectifier. The supply current in the proposed system has a sinusoidal wave shape because the series active filter suppresses the current harmonics produced by the diode rectifier. Since almost no 5th- and 7th-harmonics are produced by the double-series twelve-pulse diode rectifier, the required peak rating of the series active filter is only 7% of the diode rectifier.In this paper, the control scheme and operating characteristics of the series active filter are theoretically and experimentally discussed. A novel conception that connection of a parallel capacitor to each diode of the rectifier makes a great contribution to reducing the required rating of the series active filter is also presented and verified by some experimental results.

A 21‐level (line‐to‐line) BTB system based on series connection of 16 converter cells. Experimental verification by a 200‐V, 20‐kW laboratory system

A 21‐level (line‐to‐line) self‐commutated BTB (Back‐To‐Back) system based on series connection of 16 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 reason as high as 3 ms. This paper presents experimental verifications of the self‐commutated BTB system intended for achieving power flow control in transmission systems. Experimental results obtained by a 200‐V, 20‐kW laboratory prototype confirm effectiveness and validity of both the system configuration and the developed control strategy. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 61– 70, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20324

Control and characteristics of a static VAr generator under single-line-to-ground faults

In recent years, static VAr generators (SVGs) have been developed for improving power factor and stabilizing transmission systems. The active/reactive power control based on the p-q theory or the d-axis/q-axis current control based on d-q transformation is applied to an SVG. This paper deals with a comparative study of the two control schemes under single-line-to-ground faults. With the focus on three-phase supply currents and the DC capacitor voltage of the SVG, the two schemes are compared by computer simulation under an unbalanced condition that a supply voltage sag is caused by a single-line-to-ground fault.

Zero-Voltage Ride-Through Capability of a Transformerless Back-To-Back System Using Modular Multilevel Cascade Converters for Power Distribution Systems

This paper focuses on the zero-voltage ride-through (ZVRT) capability of a transformerless back-to-back (BTB) system intended for installation on a power distribution system with many distributed power generators. The BTB system consists of two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) and their ac sides are connected to a common ac mains via ac-link inductors. This paper provides an experimental discussion on the DSCC-based BTB system under voltage sags by using a three-phase 200-V 10-kW downscaled system. Experimental results show that the BTB system is equipped with ZVRT capability without causing any overvoltage and/or overcurrent even under the most severe voltage sags.

Design optimization of an active resonant snubber for high power IGBT converters

The design optimization procedure for a new active resonant snubber topology, specifically suited for high power insulated gate bipolar transistor (IGBT) converters, is introduced. After the basic operation principles and certain implementation consideration are discussed, the optimization strategy, based on an analytical loss evaluation, is described. Experimental results obtained on an IGBT phase-arm fitted with an optimally designed snubber are presented.

Application of zero-voltage-switching to a DC voltage-controlled static VAr compensator using quad-series voltage-source inverters

This paper discusses the potential of applying the zero-voltage-switching technique to a DC voltage-controlled static VAr compensator. The main circuit of the static VAr compensator (SVC) consists of quad-series voltage-source six-step inverters and four three-phase transformers. The SVC is characterized by a "commutation capacitor" connected in parallel with each switching device, without any additional active or passive element. The commutation capacitor plays an essential role in achieving zero-voltage-switching. Experimental results obtained From a small-rated laboratory model of 10 kVA verify the operating principle and effectiveness of the zero-voltage-switched SVC proposed in this paper. The zero-voltage-switching enables reduction of dv/dt across each switching device, thus resulting in reduced EMI and switching losses.

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

This paper addresses a 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 down-scaled model to verify the validity and effectiveness of the medium-voltage motor drive. This down-scaled 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 PWM (SPWM) 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 (THD) values of the input line current and the output motor current are 3.9% and 3.35%, respectively.

A 6.6-kV Transformerless Motor Drive Using a Five-Level Diode-Clamped PWM Inverter for Energy Savings of Pumps and Blowers

This paper describes a 6.6-kV adjustable-speed motor drive for pumps and blowers without transformer. The power conversion system consists of a front-end diode rectifier, a five-level diode-clamped pulsewidth modulation (PWM) inverter with a voltage balancing circuit, and a hybrid active filter for harmonic-current mitigation of the diode rectifier. The control of the inverter is characterized by superimposing a third-harmonic zero-sequence voltage on each of the three-phase reference voltages to achieve the so-called overmodulation and reduce the switching stress of insulated gate bipolar transistors (IGBTs). A 200-V 5.5-kW downscale model is designed, constructed, and tested with focus on the five-level PWM inverter and the voltage balancing circuit. Experimental results obtained from the 200-V downscale model verify the viability and effectiveness of the 6.6-kV adjustable-speed motor drive, showing that the four split dc capacitor voltages are well balanced in all the operating conditions and that the switching stress of the IGBTs is reduced at low modulation indexes.

A Real-Time Real-Power Emulator of a Medium-Voltage High-Speed Induction Motor Loaded With a Centrifugal Compressor

This paper provides an experimental discussion on a real-time real-power emulator that plays an important role in achieving a total test of medium-voltage, high-power, high-speed induction motor drives. The use of the emulator brings cost and time savings to the test. The test bench including the emulator is characterized by connecting two modular multilevel double-star chopper-cell (DSCC) converters connected in a front-to-front way. This paper designs, builds, and tests a 400-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> , 10-kW downscaled test bench. It mainly consists of the following two identical DSCC converters: 1) one DSCC converter is used as an inverter under test; and 2) the other as a real-time real-power high-fidelity emulator. Experimental waveforms confirm that the emulator can reproduce electrical and mechanical operating performance of the three-phase 200-V, 10-kW, four-pole, 9000-r/min induction motor loaded with a centrifugal compressor.

A Transformerless Hybrid Filter Using a Three-Level Diode-Clamped PWM Converter

This paper deals with a transformerless hybrid active filter integrated into a medium-voltage three-phase diode rectifier used as the front end of an adjustable-speed motor drive. The hybrid filter is formed by a single LC filter tuned to the 7th-harmonic frequency per phase and a small-rated active filter based on a three-phase three-level diode-clamped PWM converter. A three-phase downscaled system rated at 400V and 15kW is designed, constructed, and tested to verify the filtering performance of the hybrid filter. Experimental results show that the current THD (total harmonic distortion) gets less than 5%, and that the voltage-balancing control proposed in this paper works properly even in transient states.

A practical approach to harmonic compensation in power systems-series connection of passive and active filters

The authors present a combined system with a passive filter and a small-rated active filter, both connected in series with each other. The passive filter removes load produced harmonics just as a conventional filter does. The active filter plays a role in improving the filtering characteristics of the passive filter. This results in a great reduction of the required rating of the active filter and in eliminating all the limitations faced by using only the passive filter, leading to a practical and economical system. The active filter has a much smaller rating than a conventional active filter. Experimental results obtained from a prototype model are shown to verify the theory developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Dynamic Voltage Restorer Equipped With a High-Frequency Isolated DC–DC Converter

This paper presents a dynamic voltage restorer (DVR) that is characterized by the use of a high-frequency unidirectional isolated dc-dc converter. A traditional DVR has a large and bulky series transformer even for three-phase low-voltage up to 480-V applications because the transformer operates at the line frequency (50 or 60 Hz). The emergence of state-of-the-art semiconductor devices and magnetic cores has driven power electronic engineers to develop compact high-frequency isolated dc-dc converters. This paper discusses the control and performance of a low-voltage DVR using a high-frequency isolated dc-dc converter. The high-frequency (20-kHz) transformer in the dc-dc converter is much smaller, for example, one-hundredth, in volume than the line-frequency transformer. Moreover, connecting the shunt converter to the load side brings a significant reduction in energy-storage capacity to the DVR. Experimental results obtained from a three-phase three-wire 200-V 5-kW laboratory system confirm the viability and effectiveness of the system configuration.

Enhancement on capacitor-voltage-balancing capability of a modular multilevel cascade inverter for medium-voltage synchronous-motor drives

This paper discusses both dc-voltage balancing and ac-voltage minimizing of all the floating capacitors in a modular multilevel cascade inverter (MMCI-DSCC) intended for medium-voltage high-power synchronous-motor drives. It presents theoretical and numerical design considerations on both amplitude and phase of three-phase motor currents. A three-phase DSCC inverter with phase-shifted-carrier pulsewidth modulation (PWM) is designed and constructed to drive a 370-V, 15-kW, 75-Hz, six-pole, interior-permanent-magnet synchronous motor loaded with a hypothetical centrifugal compressor. Experimental results show satisfactory performance in dc-voltage balancing and ac-voltage minimizing of all the capacitors.