717 publications from this institution
This paper has an experimental discussion on low-voltage-ride-through (LVRT) capability of a phase-shifted-PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). The cluster-balancing control, that produces a significant effect on the LVRT capability, is modeled and analyzed with focus on either low-pass filter (LPF) or moving average filter (MAF) to attenuate the 100Hz (double the line frequency) component inherent in each dc capacitor voltage. The cluster-balancing control using the MAF is better in transient performance than that using the LPF. A three-phase downscaled system rated at 150 V and 10 kVA is designed, constructed, and tested to verify the LVRT capability of the SSBC-based STATCOM under the severest single-phase, two-phase, and three-phase voltage sags with a voltage depth of 100%. Experimental waveforms show that the STATCOM continues operating stably as if no voltage sag occurred.
No abstract is provided for this article.
This paper presents an intensive discussion on an overvoltage appearing at the motor terminals of an adjustable-speed drive that consists of a voltage-source pulsewidth-modulated inverter, an induction motor, and a three-phase symmetric long cable. It describes a design procedure for a simple passive electromagnetic-interference filter based on parallel connection of an inductor and a resistor, which is intended for mitigating the overvoltage at the motor terminals. The modeling of the cable and the motor is characterized by focusing on the natural frequency or ringing frequency inherent in the cable used, which is inversely proportional to cable length. Impedance mismatch at the inverter and motor terminals causes the overvoltage that may reach double the inverter dc-link voltage. The effectiveness and validity of the simple design procedure of the filter are confirmed on the 400-V 15-kW experimental system with either a 100- or 200-m-long cable, as well as on computer simulation based on the modeling of the cable and the motor.
Preface. 1. Introduction. 1.1. Concepts and Evolution of Electric Power Theory. 1.2. Applications of the p-q Theory to Power Electronics Equipment. 1.3. Harmonic Voltages in Power Systems. 1.4. Identified and Unidentified Harmonic-Producing Loads. 1.5. Harmonic Current and Voltage Sources. 1.6. Basic Principles of Harmonic Compensation. 1.7. Basic Principles of Power Flow Control. References. 2. Electric Power Definitions: Background. 2.1. Power Definitions Under Sinusoidal Conditions. 2.2. Voltage and Current Phasors and the Complex Impedance. 2.3. Complex Power and Power Factor. 2.4. Concepts of Power Under Non-Sinusoidal Conditions -Conventional Approaches. 2.5. Electric Power in Three-Phase Systems. 2.6. Summary. References. 3 The Instantaneous Power Theory. 3.1. Basis of the p-q Theory. 3.2. The p-q Theory in Three-Phase, Three-Wire Systems. 3.3. The p-q Theory in Three-Phase, Four-Wire Systems. 3.4. Instantaneous abc Theory. 3.5. Comparisons between the p-q Theory and the abc Theory. 3.6. Summary. References. 4 Shunt Active Filters. 4.1. General Description of Shunt Active Filters. 4.2. Three-Phase, Three-Wire Shunt Active Filters. 4.3. Three-Phase, Four-Wire Shunt Active Filters. 4.4. Shunt Selective Harmonic Compensation. 4.5. Summary. References. 5 Hybrid and Series Active Filters. 5.1. Basic Series Active Filter. 5.2. Combined Series Active Filter and Shunt Passive Filter. 5.3. Series Active Filter Integrated with a Double-Series Diode Rectifier. 5.4. Comparisons Between Hybrid and Pure Active Filters. 5.5. Conclusions. References. 6 Combined Series and Shunt Power Conditioners. 6.1. The Unified Power Flow Controller (UPFC). 6.2. The Unified Power Quality Conditioner (UPQC). 6.3. The Universal Active Power Line Conditioner (UPLC). 6.4. Summary. References. Index.
This paper presents a high-efficiency bidirectional isolated dc-dc converter for a battery energy storage system connected to the grid. It discusses the design of the converter, an optimal operating frequency range, and the optimal dead times for a 6-kW, full-bridge, bidirectional isolated dc-dc converter with focus on improving converter efficiency. This paper also provides a power-loss breakdown of the dc-dc converter at the rated power. The optimal frequency range of the dc-dc converter is defined by making its frequency-dependent loss equal to its frequency-independent loss. The optimal dead time is defined by one-fourth of the resonant period. The maximum efficiency of the dc-dc converter operating at 4 kHz 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% in a wide range of power transfer.
No abstract is provided for this article.
This paper discusses the power flow analysis and dc-capacitor voltage regulation for the modular multilevel cascaded converter (MMCC) based on double-star chopper cells (DSCC). This analysis reveals the relationship between the circulating current through the dc link and the mean power flowing out of or into each chopper cell. The dc component on the circulating current supplies a half of the active output power to the upper and lower strings of chopper cells, whereas the fundamental-frequency component transfers an amount of power between the upper and lower strings. Thus, the MMCC-DSCC can balance the capacitor voltages among the cells by controlling the amplitude of the fundamental-frequency component on the circulating current. A new control method based on the power flow analysis is employed, and its effectiveness is verified by circuit simulation.
This paper addresses a bi-directional 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 one of the dc buses 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 droops 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. A laboratory model of the energy storage system rated at 200 V and 2.6 kJ designed and constructed in this paper verifies that the dc/dc converter can charge and discharge the capacitor bank properly. Moreover, the dc/dc converter can charge the capacitor bank from zero to the rated voltage without any external precharging circuit.
The biological response to tonsillectomy was studied in 21 patients suffering from chronic tonsillitis with or without IgA nephropathy (IgAN). Serum and urinary interleukin-6 (IL-6) levels were measured before and after tonsillectomy. Serum IL-6 levels in case of IgAN peaked 3 h after tonsillectomy and more rapidly than control cases. No significant differences were observed between two cases through the time. Urinary IL-6 levels were significantly higher before and at 6 and 48 h after tonsillectomy in IgAN cases. Stimulation of tonsils caused serum IL-6 elevation and changes in urinary IL-6 levels in IgAN cases. Elevation of urinary IL-6 levels after tonsillectomy in patients with IgAN may reflect an increase in the production of IL-6 in the kidneys. Measurement of urinary IL-6 levels after tonsillectomy is useful to elucidate the efficacy of tonsillectomy in IgAN patients.
This paper is focused on a voltage-detection-based shunt active filter for installation on a power distribution system. A main objective of the active filter is to achieve damping of harmonic propagation coming from series/parallel resonance between capacitors for power factor correction and line inductors in the distribution system. The active filter installed at the end terminal of a distribution feeder is controlled in such a way as to present infinite impedance to the external circuit for the fundamental frequency, and to exhibit low resistance for harmonic frequencies. As a result, the active filter acts as a damping resistor for the harmonic propagation, like a 50-Ω terminator installed at the end of a signal transmission line. It is verified by experiment that the active filter intended for harmonic termination has the capability of harmonic damping throughout the distribution feeder. © 2000 Scripta Technica, Electr Eng Jpn, 133(2): 1–10, 2000
This paper describes position estimation based on magnetic saliency of an interior permanent magnet synchronous motor (IPM motor) for the purpose of achieving a wide-speed range. The position estimation, which has been proposed by the authors, is characterized by the real-time algorithm estimating the rotor position at every PWM period. Selection of PWM patterns proposed in this paper expands the speed range capable of estimating the rotor position to a higher-speed range. The PWM patterns are switched over, depending on an amplitude and phase of the average output voltage vector. Experimental results obtained from an IPM motor drive system of 100 W demonstrate that the selection of the PWM patterns makes it possible to estimate the rotor position in a wide-speed range from zero to the rated speed.
The integration of a series active filter with a 12-pulse diode rectifier can provide a cost-effective and efficient means of supply current harmonic-free AC/DC conversion. Controlling the series active filter as a frequency-selective impedance requires low delays and is not well suited for digital control. This paper suggests a current-mode control strategy to allow full digital control of the active filter. The suggested current-mode control method for supply current balancing and voltage regulation is verified experimentally.
This paper provides an intensive discussion on the low-voltage-ride-through (LVRT) capability and performance of a phase-shifted PWM STATCOM using the modular multilevel cascade converter based on single-star bridge-cells (MMCC-SSBC). It follows the previous paper having focused on current control performance. This paper describes modeling, analysis, and design of the STATCOM, paying attention to the cluster-balancing control of the dc capacitor voltages. Experimental verification with a three-phase 150-V, 10-kVA downscaled model confirms that the STATCOM provides satisfactory LVRT capability against single-, double- and triple-phase voltage sags, and even against the most severe voltage sags with a voltage depth of 100%.
This paper presents a modular push-pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium-voltage or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms consisting of a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, focusing on voltage balancing of all the floating capacitors. Moreover, a comparison is made between the MPC and a modular multilevel cascade converter (MMCC-DSCC), both of which are used as the same battery energy storage system. The validity of the operating performance and control method is confirmed by both computer simulation using the “PSCAD/EMTDC” software package and experiment using a three-phase, 200-V, and 5-kW downscaled model.
A case of rotary nystagmus evoked by lateral eye position is reported. Rotary nystagmus is often observed in patients with BPPV (benign paroxysmal positional vertigo). In most cases of peripheral vestibular disorders, the rotary nystagmus is evoked by a change in head position, is diminished by the repetition of head position and has a latent onset time. The character of rotary nystagmus in this case differs from that caused by peripheral vestibular disorders. Nystagmus was observed in the right lateral eye position, was not associated with the change in head position and had no latent onset time. Although caloric nystagmus was well developed, caloric nystagmus with gazing increased on visual suppression test.In case of central disorders, a rotary nystagmus was reported. The medulla lesion, Wallenberg syndrome, syringobulbia, may cause a rotary nystagmus in frontal eye position. Sakata reported rotary nystagmus in the lateral eye position caused by a disorder in the nucleus of the trochlear nerve and cerebellum. Büttner reported rotary nystagmus in lateral gazing. He thought that confusion of equilibrium information caused by a cerebellar lesion and rotary nystagmus had developed. The skew deviation arose from a pons disorder. We thought that the imbalanced equilibrium was not strong enough to cause skew deviation, thereby causing rotary nystagmus in the lateral eye position.In this case, we can assume several hypotheses to explain mechanism for the nystagmus. The most likely explanation is functional disorder of the pons.
In evaluating the giga‐cycle fatigue strength of some high strength steels, information on the size distribution of nonmetallic inclusions contained in the material is indispensable. To save time and effort of obtaining such data concerning the inclusions, a convenient dissolution method to evaluate the maximum inclusion size is proposed, in place of a conventional method of measuring the inclusion sizes on many cross‐sectional areas. Meanwhile, to save time‐consuming work of obtaining giga‐cycle fatigue properties of some metallic materials, an intermittent ultrasonic fatigue testing method has also been developed. In the present paper, these two newly developed methods were successfully combined to assess the long life fatigue properties of maraging steels as a function of inclusion size.
A flywheel energy storage system based on a doubly-fed induction generator-motor basically 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 utility grid. Thus, the generator-motor has the capability of achieving not only reactive power control, but also active power control based on the flywheel effect of the rotating parts. This paper proposes a new control strategy for a doubly-fed induction generator-motor, which is characterized by the combination of vector control and decoupling control. The control strategy enables the induction 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 and viability of the control strategy, is confirmed by computer simulation. In addition, this paper discusses a transient behavior of a magnetizing current in the induction machine.
