717 publications from this institution
The emergence of high-power semiconductor devices such as insulated-gate bipolar transistors (IGBTs) or injection-enhanced gate transistors (IEGTs) and gate-commutated turn-off (GCT) thyristors or integrated gate-commutated thyristors (IGCTs) enables large static converters to expand into utility and industry applications. For instance, a /spl plusmn/80 kV 50 MW HVDC transmission system based on a string of many IGBTs connected in series was commissioned in 1999. This paper describes the present status of large static converters, with focus on their applications to utility and industry. The applications discussed are: HVDC transmission system, UPFC, flywheel energy storage system, pumped hydro plant adjustable speed generator, active filters for power conditioning, and steel mill drives. The paper also describes their future prospects and directions in the 21st century, including the personal views and expectations of the author.
This paper deals with integrating a small-sized passive electromagnetic interference (EMI) filter with a voltage-source pulse-width modulated (PWM) inverter. The purpose of the filter is to eliminate both high-frequency common-mode and normal-mode voltages from the three-phase output voltages of the inverter. A laboratory 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 filter. As a result, both line-to-line and line-to-neutral output voltages look purely sinusoidal as if the inverter were an ideal three-phase variable-voltage, variable-frequency power supply when viewed from the motor terminals. This results in a complete solution to serious EMI issues related to high-frequency common-mode and normal-mode voltages produced by the PWM inverter.
A bidirectional isolated dc-dc converter manages the power flow between an energy storage device and a dc bus with functions of galvanic isolation and voltage matching. Research and development of these converters focus on improving efficiency and power density. This paper presents and compares various configurations of bidirectional isolated dc-dc converters. It also illustrates the performance of a 6-kW, full-bridge, bidirectional isolated dc-dc converter operating at 4 kHz, which is suitable for output power leveling of photovoltaic generation systems connected to homes and office buildings. The maximum efficiency of the dc-dc converter is measured at 98.1% during battery charging and at 98.2% during battery discharging. The converter maintains a high efficiency of more than 97% for a wide range of power transfer.
This paper describes a 6.6-kV adjustable-speed motor drive for use in fans, blowers, and pumps without a transformer. The power-conversion system consists of a diode rectifier, a five-level diode-clamped PWM inverter, and a voltage-balancing circuit. A 200-V 5.5-kW downscale model is developed, constructed, and tested. The five-level PWM inverter and the voltage-balancing circuit are studied in detail. Experimental results obtained from testing the 200-V downscale model confirm the viability and effectiveness of the 6.6-kV adjustable-speed motor drive, indicating that the dc mean voltages of the four split dc capacitors are well balanced under all the given operating conditions.
No abstract is provided for this article.
This paper deals with a dynamic voltage restorer (DVR), or a voltage-sag compensator, which consists of a set of series and shunt converters connected back-to-back, three series transformers, and a dc capacitor installed on the common dc link. The DVR is characterized by installing the series converter on the source side and the shunt converter on the load side. This system configuration allows the use of an extremely small dc capacitor intended for smoothing the common dc-link voltage. This paper provides a design procedure of the dc capacitor under a voltage-sag condition and proposes a control method for the series converter, which is capable of reducing the voltage ratings of both the series converter and the series transformers. Experimental results obtained from a 200-V 5-kW laboratory system are shown to confirm the validity of the design procedure and the effectiveness of the control method.
The instantaneous torque produced by an AC machine is controllable when vector control is applied. However, the published papers on vector control deal with either induction machines or synchronous machines. A generalized vector-control theory is developed, considering a generalized AC machine as a salient-pole synchronous machine having three kinds of torque, i.e., the field torque, the reluctance torque, and the induction torque. The theory can be extended to the AC machines producing a voluntarily combined torque among the three. The experimental system consisted of applying the generalized vector control theory to a nonsalient-pole synchronous machine with damper winding. It was verified experimentally that the instantaneous torque was controllable, not only in synchronous or induction-machine operation, but also in the transient state between the synchronous-machine operation and induction-machine operation, without any change of the control circuit.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper describes a control scheme of a high frequency, high power current source inverter using static induction transistors to suppress the surge voltage and to reduce 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, 1.8µH, i.e., 18% reactance (130kHz, 250V, 30A base). As a result, the switching loss is estimated to be half of the conducting loss and the efficiency of the inverter to be 95%.
A doubly-fed flywheel generator-motor consists of a wound-rotor induction machine and a cycloconverter or a voltage-source PWM rectifier-inverter which is used as an ac exciter. Adjusting the rotor speed makes the generator-motor either release the kinetic energy to the power system or absorb it from the power system. Thus, the generator-motor has the capability of achieving, not only reactive power control, but also active power control based on a flywheel effect of the rotor. A 200-MJ flywheel generator-motor for the purpose of line-frequency regulation on a 132-kV bus has been installed and commissioned by the Okinawa Electric Power Company. However, little literature has been published on control strategy and dynamic performance analysis of doubly-fed flywheel generator-motors. This paper proposes a new control strategy for a doubly-fed flywheel generator-motor, which is characterized by the combination of vector control and decoupling control. The control strategy enables the flywheel generator-motor to perform active power control independent of reactive power control even in transient states. The validity of the theory developed in this paper; along with the effectiveness of the control strategy, is confirmed by computer simulations using EMTDC. In addition, this paper discusses the transient behavior of a magnetizing current of the flywheel generator-motor. The flywheel generator-motor based on leading edge power electronics and electric machine technologies shows promise as a versatile power conditioner, in particular, being capable of repetitively absorbing or releasing electric energy for a short period of time less than a minute. 18 refs., 9 figs., 1 tab.
This paper describes position-sensorless control of an interior permanent magnet synchronous motor (IPM motor), which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation argorithm proposed in this paper determines the inductance matrix including rotor position information from current harmonics produced by switching operations of an inverter driving the IPM motor, and then estimates the rotor position every period of pulse-width modulation (PWM). Position estimation without any special signal injection is achieved with a satisfactory response and accuracy even at a standstill and at low speed. An experimental system consisting of an IPM motor and a voltage-source PWM inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20rad/s and a settling time of 300ms.
A modular multilevel cascade inverter based on double-star chopper-cells (MMCI-DSCC) has been expected as one of the next-generation multilevel PWM inverters for medium-voltage high-power motor drives. This paper has theoretical and experimental discussions on a speed-sensorless startup of an induction motor driven by the MMCI-DSCC, especially when this motor drive is applied to fans, blowers, and compressors, the torque of which is proportional to a square of a motor mechanical speed. A theoretical analysis focusing on ac-voltage fluctuation of each dc capacitor indicates that the ac-voltage fluctuation can be kept within an acceptable level over a wide range of motor mechanical speeds by controlling the three-phase stator currents. Experimental steady-state waveforms obtained from a downscaled motor drive verify operating performance with a quadratic-torque load.
Thirty-two adult cases of acute exacerbation of chronic otitis media (COM) were treated by high-dose (600mg/day) oral administration of levofloxacin (LVFX). Clinically, 27COM cases (84.4%) were effectively treated, and no apparent side effects were noted during this study protocol. Among 31 clinically isolated strains whose therapeutic outcomes were bacteriologically confirmed, 28 (90%) strains were not detectable after high-dose LVFX treatment. Bacteriological therapeutic failures in the treatment were observed in three COM patients with MRSA and a patient with coagulase-negative staphylococci. High-dose administration of LVFX was effective in the treatment of acute exacerbation of COM except in cases that were caused by drug resistant staphylococci.
The moire topography video visualizes the facial movement dynamically in three dimensions. By using the digital video, we analyze facial movements in expression more precisely, because we can handle dynamic images as the series of static images with time axis. This technique reveals several special features on the facial expression.
This paper describes principles, system configurations, control strategies and implementations, and filtering characteristics of active and hybrid filters for power conditioning. Their practical applications are expanding not only into office-buildings, hospitals, water supply utilities and rolling stock but also into electric power utilities. For example, a hybrid filter consisting of a 5 MVA series active filter and a 25 MVA shunt passive filter has been installed at the Yamanashi test line for high-speed magnet-levitation trains. The series active filter makes a great contribution to damping of harmonic resonance between the supply inductor and the shunt passive filter.
