717 publications from this institution
This paper presents a medium-voltage motor drive with a three-phase modular multilevel PWM inverter and focuses on its control method and operating performance. This motor drive is particularly suitable for fans, blowers, pumps, and compressors, in which the load torque is proportional to the square of the rotating speed. Particular attention is paid to the dc-capacitor voltage fluctuation of each chopper-cell because it may affect the voltage rating of the power switching devices used. This paper describes the theoretical equations related to the amount of the voltage fluctuation. A downscaled model rated at 400V and 15kW is designed and built to confirm the validity and effectiveness of the nine-level (17-level in line-to-line) PWM inverter that is intended for use in medium-voltage motor drives to achieve energy savings.
Switched reluctance type bearingless motors are characterized by integration of switched reluctance motors and magnetic bearings. Therefore, these motors can control radial rotor positions with magnetic force actively. Production of suspension force for rotor shaft magnetic suspension is explained with differential stator windings. In the previous paper, accurate theoretical formulae of instantaneous torque and suspension force generated by one phase excitation were derived from an assumption of simple permeance distribution. From the derived theoretical formulae, it is found that there exist cross coupling between the instantaneous torque and the suspension force. This paper derives a possible output area of the instantaneous torque and the suspension force considering the cross coupling in order to realize a stable operation. It is shown with experimental results that the possible output area of the proposed motors is very accurate in terms of practical application.
Artificial intelligence (AI) translators have made remarkable progress in translation accuracy, resulting from the emergence of "generative AI. " Doraemon is a fictional cat-like robot from the 22nd century, who brings various unknown tools out of his pockets. One of the tools is the universal translator "Honyaku Konjac. " Current AI translators, including DeepL, Google, and ChatGPT, are available easily through the internet. It would be as if Doraemon's translator did a time-slip from the 22nd century into the modern world. A reader may use an AI translator for writing technical English papers. Before the advent of the AI translators, anyone had consulted with both English-Japanese and Japanese-English dictionaries to find unknown or unclear words, understand their meanings, and learn how to use them by referring to example sentences. Japanese is much more ambiguous than English in terms of bidirectional translation between these two languages. Haiku is one of the shortest poems in the world. It is compliant to a strict writing format, including a seasonal Japanese word. However, this form does not need to accurately convey the intentions of the writer to a reader, thus resulting in being open to multiple interpretations. In contrast, any technical paper written in any language must accurately convey the claims and/or thoughts of the author to a reader without misunderstanding. Thus, Japanese authors should write their technical Japanese papers clearly, concisely, consistently, correctly, and simple before using AI translators. They should subsequently check, proofread and revise their English-translated versions because any AI translator based on reasoning from context cannot avoid mistranslation. This article may look like, not a paper, but an essay. It describes how to make the best use of AI translators, including its hints and tips, based on the long-term experiences of the author in the field of power electronics.
The prognostic value of tonsillar provocation tests using direct irradiation with ultramicrowaves was evaluated in this study. The results of preoperative tonsillar provocation tests among 10 IgA nephropathy cases, in which tonsillectomy was considered to be effective after a 6 month follow-up period (effective-tonsillectomy cases), were compared retrospectively to results obtained from 10 healthy controls, as well as 5 IgA nephropathy cases which showed no significant improvement after tonsillectomy (ineffective-tonsillectomy cases). The average age was 34.7 years for the effective-tonsillectomy cases, 32.6 years for the healthy controls and 22.6 years for the ineffective-tonsillectomy cases, respectively.Positive provocation results were obtained in 80% of the effective-tonsillectomy cases, 60% of the healthy controls and 80% of the ineffective-tonsillectomy cases. Changes in body temperature, erythrocyte sedimentation rate, and number of white blood cells showed no statistically significant differences among these three groups. Urinary findings after the provocation test were worsened in 40% of the effective-tonsillectomy cases (2 cases of proteinuria and 2 cases of hematuria), while none of the healthy controls and 20% of the ineffective-tonsillectomy cases (one case of proteinuria and no cases of hematuria) showed positive results after the provocation test. Hematuria seemed to have the best prognostic value as a tonsillar provocation test for tonsillectomy in patients with IgA nephropathy.
A self-commutated BTB (back-to-back) system is an AC-DC-AC power flow controller between two utility grids, and PLL (phase-locked-loop) circuits are typically used for detecting their phase information. The performance of the BTB system during line faults is strongly affected by the dynamic behavior of the PLL circuit in terms of the AC-current fluctuation, the DC-voltage fluctuation, and the DC magnetic flux deviation in the converter-transformers. However, no paper or article has been discussed explicitly on their mutual relationship. The aim of this paper is to establish a design procedure of the PLL circuit which is suitable for the BTB system. This paper also deals with the DC magnetic flux deviation in the converter-transformers under double-line-to-ground (DLG) faults.
This paper addresses a bidirectional dc-dc converter suitable for an energy storage system with an additional function of galvanic isolation. An energy storage device such as an electric double layer capacitor is directly connected to a dc side of the dc-dc converter without any chopper circuit. Nevertheless, the dc-dc converter can continue operating when the voltage across the energy storage device drops along with its discharge. Theoretical calculation and experimental measurement reveal that power loss and peak current impose limitations on a permissible dc-voltage range. This information may be useful in design of the dc-dc converter. Experimental results verify proper charging and discharging operation obtained from a 200-V, 2.6-kJ laboratory model of the energy storage system. Moreover, the dc-dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.
No abstract is provided for this article.
This paper presents theoretical and experimental discussions on a practical speed-sensorless start-up method for an induction motor driven by a modular multilevel cascade inverter based on double-star chopper cells (MMCI-DSCC) from standstill to middle speed. This motor drive is suitable, particularly for a large-capacity fan- or blower-like load. The load torque is proportional to a square of the motor mechanical speed. The start-up method is characterized by combining capacitor-voltage control with motor-speed control. The motor-speed control with the minimal stator current plays a crucial role in eliminating a speed sensor from the drive system and in reducing an ac-voltage fluctuation occurring across each dc capacitor. Experimental results obtained from the 400-V 15-kW downscaled system with no speed sensor verify that the motor-speed control proposed for the DSCC-based drive system can enhance the start-up torque by a factor of three under the same ac-voltage fluctuation. Several start-up waveforms show stable performance from standstill to middle speed with different load torques.
This paper presents a practical approach to eliminating both bearing current and ground leakage current from an inverter-driven motor rated at 400 V and 3.7 kW. When the shaft voltage with respect to the motor frame exceeds the dielectric breakdown voltage of thin lubricating grease films in two metal bearings at the drive and non-drive ends, an electrical discharge machining (EDM) current flows through the bearings. A passive electromagnetic interference (EMI) filter can keep the shaft voltage in check, as a result of having eliminated high-frequency common-mode voltage from the motor terminals. Hence, no dielectric breakdown occurs in the grease films, so that no EDM current flows in the bearings. Experimental results verify the viability and effectiveness of the passive EMI filter designed in this paper
No abstract is provided for this article.
The main purpose of a load/source simulator is to imitate an actual load/source in terms of power or current. This paper proposes a novel load/source simulator based on the unified power flow controller that is one of FACTS devices. This system takes the following prominent advantage: The converter volt-ampere rating required for the proposed system is much smaller than that for a conventional system based on a BTB (Back-To-Back) converter. Experimental results obtained from a 200-V, 10-kW laboratory system confirm the viability and effectiveness of the system. This paper also discusses the control method theoretically, and analyzes a voltage fluctuation of the dc link, thus leading to system design.
A high-performance current-controlled inverter must have a quick current response in transient state and low harmonic current content in steady state. However, in general, these requirements contradict each other. A novel control scheme is proposed which is based on the current deviation vector and satisfies both requirements. Experimental results showed good agreement with the anticipated performance.
This paper presents circuit topology, control, and application of the next-generation high-power converters that are characterized by combing the latest power semiconductor device/circuit technologies with the latest high-speed, highperformance digital control/sensor technologies. In particular, attention is paid to experimental results obtained from different downscaled systems designed, constructed, and tested in the author's laboratory with focus on control and experiment.
The basal lamina of high endothelial venules (HEVs) in human palatine tonsils was intensely stained with cationic colloidal iron at pH 1.5 and with aldehyde fuchsin. This basal lamina exhibited a thick and double- or triple-layered structure forming small compartments, in which many lymphocytes were aligned. Digestion with hyaluronidase or collagenase eliminated both the colloidal iron and aldehyde fuchsin stainings of the basal lamina of HEVs. Treatment with chondroitinase ABC reduced colloidal iron staining, but did not interfere with the aldehyde fuchsin staining. Digestion with neuraminidase, keratanase, or heparitinase did not eliminate either the cationic colloidal or the aldehyde fuchsin staining. Digestion with neuraminidase reduced the colloidal iron staining on the luminal surface coat of the HEV. Electron microscopy of ultrathin sections revealed that cationic colloidal iron particles were deposited on the basal lamina of the HEV. The basal laminae of ordinary blood vessels were thin and single-layered, and stained only weakly with cationic colloidal iron. The present study suggests that negatively charged sites in the basal lamina of HEV derive mainly from a proteoglycan complex containing hyaluronic acid and chondroitin sulfate, which firmly binds collagen. This topochemical feature is suggested to be involved in the fascilitating migration of lymphocytes after passage through the endothelial layer.
With significant development of power electronics technology, the proliferation of non-linear loads such as static power converters in a range of 50W to 300MW has deteriorated power quality in transmission/distribution systems. Notably, voltage distortion or voltage harmonics may approach or exceed its allowable level in power distribution systems. Individual electric power consumers and end-users are responsible for reducing current harmonics, while electric power companies or utilities are responsible for reducing voltage harmonics at the point of common coupling in distribution systems. Dispersive installation of shunt active filters on power distribution systems is a viable and effective way of solving “harmonic pollution.” The main objective of this paper is to develop a model for the shunt active filters, and to show how well the shunt active filters are effective in damping of harmonic propagation, much attention being paid to site selection. The system analysis concludes that a shunt active filter based on voltage detection has the capability of harmonic damping throughout a feeder, and that a shunt active filter based on supply current detection with differential compensation is suitable, not for harmonic damping, but for harmonic compensation of one or more non-linear loads. This paper discusses two shunt active filters based on voltage detection, which are dispersively installed on both end terminals of two feeders in a distribution system. Computer simulation verifies the validity of the modeling and harmonic damping effect of the shunt active filters for dispersive installation on power distribution systems.
