This paper describes a modular multilevel cascade inverter based on double-star chopper-cells (MMCI-DSCC) for a medium-voltage motor drive with a passive front end. Unlike the traditional two-level PWM inverter, the DSCC can operate without common dc-link capacitors because the DSCC itself possesses energy-storage components. However, a certain amount of switching-ripple voltage is generated in the common dc link when a passive front end is utilized. In this paper, the attenuation of the switching-ripple voltage by using a dc passive filter consisting of a series-connected film capacitor and resistor is attempted. A 400-V, 15-kW downscaled model is utilized to confirm the suitability of the design procedure developed in this paper. Experimental results show that the switching-ripple voltage can be attenuated satisfactorily by a small-capacity film capacitor. Moreover, the loss of the filter is negligible compared to the rated power of 15kW.
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 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 algorithm detects motor current harmonics and determines the inductance matrix including rotor position information. 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 20 rad/s and a settling time of 300 ms.
A parallel connected thyristor converter with an interphase reactor has been used widely as a low voltage high current DC power supply because of high efficiency, compared with a series one. It seems to be the most suitable for superconducting magnetic energy storage systems in particular. If the parallel converter consisting of two thyristor converters is operated under different firing angles in the two due to imperfect adjustment in the control circuit or something like that, unbalance may occur in the output DC current of each converter.The purpose of this paper is to discuss the current unbalance of a parallel thyristor converter in detail. The main points are summarized as follows:(1) It is clarified theoretically that the unbalance of DC output current may occur even when the difference of firing angles is less than 1°.(2) It is verified experimentally that the proposed simple current feedback makes it possible to balance the DC output current of the parallel thyristor converter.(3) An interphase reactor without gap is able to take the place of a conventional interphase reactor with gap which is used widely. Compared with the conventional one, the volume of the interphase reactor without gap is much small.
This paper deals with the hybrid shunt active filter for harmonic compensation of a three-phase diode rectifier in a 480-V adjustable-speed motor drive system. The hybrid filter is formed by a three-phase LC filter tuned around the seventh harmonic frequency and a small-rated three-phase voltage-source PWM inverter. The LC filter and PWM inverter are directly connected in series. As a result, the DC capacitor voltage of the PWM inverter in the hybrid filter is much lower than that of a conventional pure shunt active filter. This results in higher efficiency, less switching ripple, and less EMI emission. Computer simulation is carried out to compare the hybrid filter with the pure filter in terms of circuit configuration and filtering performance. Simulation results indicate that the hybrid filter is superior in effectiveness and viability to the pure filter. In addition, theoretical analysis based on vector loci confirms the validity of the simulation results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(2): 61–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20145
This paper addresses a transformerless 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 downscaled model to verify the validity and effectiveness of the medium-voltage motor drive. This downscaled 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 pulsewidth modulation 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 values of the input line current and the output motor current are 3.9% and 3.5%, respectively.
We report 3 rare cases of Ménière's disease in children. In Case 1 and 3, vertigo, hearing loss and tinnitus recovered soon after medical therapy. In Case 2, however, vertigo recurred and the hearing level on the right side markedly deteriorated. The equal-loudness contours on three-dimensional audiogram showed that right-sided aggravated hearing loss fluctuated for 4 years at middle-and low-frequencies despite medication. Finally intratympanic injection of gentamicin sulfate was performed. The patient has had no definitive spell of vertigo after gentamicin therapy. At our department, the incidence of Ménière's disease in pediatric patients with vertigo was 2.9%.
No abstract is provided for this article.
This paper presents an experimental discussion on a 6-kW, full-bridge, zero-voltage switching bidirectional isolated dc/dc converter for a 53.2-V, 2-kWh Li-ion battery energy storage system. The combination of high-frequency switching devices, 600-V/200-A IGBTs and 100-V/500-A MOSFETs with a high-frequency transformer reduces the weight and physical size of the bidirectional isolated dc/dc converter. The dc voltage on the high-voltage side of the converter is controlled in a range of 300V to 355V as the battery voltage on the low-voltage side varies from 50V to 59V. Experimental verification of bidirectional power flow into (battery charging) or out of (battery discharging) the Li-ion battery bank is also presented. The maximal efficiency of the dc/dc converter is measured to be 98.1% during charging and 98.2% during discharging, excluding the gate drive loss and control circuit loss.
This paper presents a three-phase transformerless cascade PWM STATCOM intended for installation on industrial and utility power distribution systems. It proposes a control method that devotes itself mainly to meeting a demand of reactive power, as well as to voltage-balancing of the multiple isolated and split dc capacitors. The control method is characterized by fast and stable voltage-balancing performance and easy expansion into a higher number of levels. Experimental waveforms confirm that a 200-V, 10-kVA cascade PWM STATCOM with star-configuration has the capability of inductive to capacitive (or capacitive to inductive) operation at the rated reactive power of 10 kVA within 20 ms, keeping the nine DC mean voltages controlled and balanced, even during the transient state
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 PWM inverter, an induction motor, and a three-phase symmetric long cable. It describes a design procedure for a simple passive EMI 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 are prominent in 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-m or 200-m-long cable, as well as on computer simulation based on the modeling of the cable and the motor.
This paper presents a medium-voltage motor drive with a modular multilevel PWM inverter, and focuses on a startup method and its performance. It is formed by six modular arms, each of which consists of a cascaded stack of multiple bidirectional chopper-cells. The frequency of the dominant ac-voltage fluctuation is equal to the motor (inverter) frequency. These fluctuations occur in the dc capacitor of each chopper-cell, and the magnitude of the fluctuation is inversely proportional to the motor frequency. Because of the increased voltage fluctuation in low-frequency regions, the so-called “volt-per-hertz control” cannot be applied in motor starting. The startup method proposed in this paper is suitable for a motor drive with the modular multilevel PWM inverter. It enables the motor to produce a startup torque loaded on the motor at an initial amplitude and a fixed frequency of the inverter while taking into account constraints on the motor current and the ac-voltage fluctuation. The validity of the startup method as well as the startup performance is confirmed by experiment and simulation.
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.
The conventional theory of active and reactive power in single‐phase or three‐phase systems is based on an average value concept, thus making it impossible to define instantaneous active and reactive power in a real sense. On the basis of an instantaneous value concept, the authors have already proposed a new definition of instantaneous active and reactive power in three‐phase circuits for arbitrary voltage and current waveforms without any restriction. This is called the instantaneous reactive power theory or the p‐q theory, which is considered a basic theory of active power line conditioners such as reactive power compensators and active power filters for harmonic compensation.
This paper presents the analysis and design of a shunt hybrid active filter for harmonic damping in a 6.6-kV power distribution system. This hybrid filter has been proposed and tested experimentally with a 200-V, 20-kW laboratory system, showing good damping performance. Another possible solution for harmonic damping is to install a shunt pure active filter at the end of a feeder. However, the pure filter is too costly and bulky to be installed in a 6.6-kV system. This paper discusses the design criteria for a hybrid filter intended for installation on a 6.6-kV power distribution system. Detailed comparisons between the pure filter and the hybrid filter are also included as a foundation for the design of the hybrid filter. The performed design confirms the feasibility of installation of the hybrid filter on a 6.6-kV power distribution system.
