717 publications from this institution
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.
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.
Direct connection of the synchrotron magnet power supply to the utilities causes the effect of pulsed reactive and active power in the AC line. Conventionally, Static Var Control system compensates the reactive power generated by the thyristor converter to reduce the flicker in the power line. However, it is necessary to control not only a reactive power but also an active power for the future large scale synchrotron magnet power supply in order to reduce the dissipation power and to realize the stabilization in the AC line. An adjustable-speed rotary condenser is capable of not only reactive power control but also active power control since it utilize a flywheel effect of the rotor. Research and development on these problems are now under going using a model system of 7.5 kW rotary condenser with flywheel (GD/sup 2/=3kg-m/sup 2/). Control and characteristic of an adjustable-speed rotary condenser and the experiment results will be presented.
Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. The bearingless switched reluctance motors are characterized by integration of switched reluctance motors and magnetic bearings. These motors have two kinds of stator windings composed of motor main windings and suspension windings in the same stator in order to produce suspension force that can realize rotor shaft suspension without mechanical contacts or lubrication. For successful stable operation, accurate theoretical formulas of instantaneous torque and suspension force are necessary to a rotational speed controller and a rotor radial position controller. This paper derives the theoretical formulas of the instantaneous torque and the suspension force from an assumption of simple permeance distribution. This derivation process makes an assumption that fringing fluxes are distributed on elliptical lines. It is shown with experimental results that the derived theoretical formulas are very accurate in terms of practical application. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 72–82, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20157
This paper proposed the rotating p-q-r reference frames where one instantaneous active power p, and two instantaneous reactive powers q/sub q/, q/sub r/ were defined in 3-phase 4-wire systems. The three power components are linearly independent, so that compensating for the two instantaneous reactive powers leads to control the two components of the current space vector independently. With the theory, this paper shows that the neutral current of a 3-phase 4-wire system can be eliminated by only compensating for the instantaneous reactive power using no energy storage element. Simulation results verify the theory very well.
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.
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.
This paper proposes a new rectifying system consisting of a series active filter and a double-series three-phase 12-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 12-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. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(1): 85–94, 1997
This paper presents theoretical and experimental discussions on low-voltage-ride-through operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags.
This paper deals with an inverter system integrating a small‐rated passive EMI filter with a three‐phase voltage‐source PWM inverter. The purpose of the EMI filter is to eliminate both common‐mode and normal‐mode voltages from the output voltage of the inverter. The motivation of this research is based on the well‐known fact that the higher the carrier or switching frequency, the smaller and the more effective the EMI filter. An experimental system consisting of a 5‐kVA inverter, a 3.7‐kW induction motor, and a specially designed passive EMI filter was constructed to verify the viability and effectiveness of the EMI filter. As a result, it is shown experimentally that both three‐phase line‐to‐line and line‐to‐neutral output voltages look purely sinusoidal as if the inverter system were an ideal variable‐voltage, variable‐frequency power supply when viewed from the motor terminals. This results in complete solution of serious issues related to common‐mode and normal‐mode voltages produced by the inverter. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(4): 88–96, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10206
The transient compensation characteristics and stability of a combined system of shunt passive and small rated series active filters are discussed and analyzed theoretically and experimentally. The stable and unstable regions of the combined system and the problems faced when an attempt at improving transient compensation characteristics is made are revealed. A control method that allows the application of the combined system to compensation for cycloconverters is proposed. Some results obtained from the experimental model using the control method are presented to demonstrate its validity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
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">></ETX>
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.
This paper deals with active circuits for cancellation and compensation of common‐mode voltage caused by a PWM inverter. A nonnegligible amount of leakage or ground current flows through stray capacitors between stator windings and the motor frame due to a large step change in the common‐mode voltage at every switching operation of the PWM inverter. First, it is shown experimentally that the active common‐noise canceler (ACC), which has been proposed by the authors, is effective in reducing not only conducted EMI but also motor shaft voltage and bearing current. Next, a new ACC characterized by an isolated power supply is developed to enlarge the applicable voltage range in which it is possible to integrate the ACC with a PWM inverter. Furthermore, the authors propose another type of ACC, the purpose of which is not to achieve complete cancellation but to restrain only a slope in a change of the common‐mode voltage applied to the motor. As a result, the core size of the common‐mode transformer used in the active compensating circuit becomes considerably smaller. Some experimental results show good effects of the proposed active circuits on both ground current and conducted EMI. © 2001 Scripta Technica, Electr Eng Jpn, 137(1): 57–65, 2001
This paper describes a brushless DC motor system without position or speed sensor. The brushless DC motor consists of a permanent magnet synchronous motor and a voltage-source inverter which is capable of controlling the amplitude and frequency of voltage. The rectangular-shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage, just like chopper control of DC motors.In this paper, two sensorless position detecting methods, “indirect method” suited at lower speed range and “direct method” suited at higher speed range, are proposed. The combination of the two makes it possible to detect the rotor position over a wide speed range. Furthermore, a speedsensorless PLL control is proposed, applying the principle of the direct method. Experimental results obtained from a prototype brushless DC motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor is also discussed because it is impossible to detect the rotor position at a standstill.
No abstract is provided for this article.
This paper deals with a 6.6‐kV transformerless STATCOM cascading multiple single‐phase H‐bridge PWM converters in each phase. The AC voltage of the STATCOM is almost sinusoidal, so that it requires no harmonic filter. Each converter is equipped with a capacitor and a voltage sensor on the DC side, which are electrically isolated from each other. The STATCOM has the capability of self‐starting and voltage‐balancing without any external power supply or equipment. Experiments using a three‐phase 200‐V, 10‐kVA laboratory system, along with computer simulations, are carried out to confirm the viability and effectiveness of the STATCOM. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 55–64, 2010; Published online in Wiley InterScience ( www.interscience.wiley. com ). DOI 10.1002/eej.20822
