Publications

This paper considers the transient performance and stability of a recurrent discrete Fourier transform (DFT) based control method for a series active filter integrated with a 12-pulse diode rectifier. The control method targets specific harmonics and/or the negative sequence fundamental component of the supply current, and is intended for use with nonsinusoidal/unbalanced supply voltages. The proposed control method is based on DFTs instead of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -method, and a simple approach is used to account for small frequency variations found in practical power systems.

The case of a 60-year-old man with a unilateral laryngeal mucosal lesion and complete left vocal cord paralysis is reported. The lesion localized to the left side of the larynx covered the laryngeal vestibule, arytenoid, false vocal cord and true vocal cord, but did not extend to the hypopharynx or oropharynx. Enzyme immunoassay for varicella-zoster virus (VZV) led to a diagnosis of VZV infection.

The authors present a combined system with a passive filter and a small-rated active filter, both connected in series with each other. The passive filter removes load produced harmonics just as a conventional filter does. The active filter plays a role in improving the filtering characteristics of the passive filter. This results in a great reduction of the required rating of the active filter and in eliminating all the limitations faced by using only the passive filter, leading to a practical and economical system. The active filter has a much smaller rating than a conventional active filter. Experimental results obtained from a prototype model are shown to verify the theory developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper presents a dynamic voltage restorer (DVR) that is characterized by the use of a high-frequency unidirectional isolated dc-dc converter. A traditional DVR has a large and bulky series transformer even for three-phase low-voltage up to 480-V applications because the transformer operates at the line frequency (50 or 60 Hz). The emergence of state-of-the-art semiconductor devices and magnetic cores has driven power electronic engineers to develop compact high-frequency isolated dc-dc converters. This paper discusses the control and performance of a low-voltage DVR using a high-frequency isolated dc-dc converter. The high-frequency (20-kHz) transformer in the dc-dc converter is much smaller, for example, one-hundredth, in volume than the line-frequency transformer. Moreover, connecting the shunt converter to the load side brings a significant reduction in energy-storage capacity to the DVR. Experimental results obtained from a three-phase three-wire 200-V 5-kW laboratory system confirm the viability and effectiveness of the system configuration.

No abstract is provided for this article.

With the remarkable progress of switching devices, the switching frequency of a voltage‐source PWM inverter has become higher and higher. A high‐frequency PWM inverter gives great benefits in the reduction of current ripples and acoustic noises. However, high‐frequency hard switching causes the increase of switching losses and EMI to be solved. The authors propose a zero‐current‐switching based three‐phase PWM inverter which has small resonant circuits on the ac side. The current flowing in a switching device is a sum of the resonant current and the load current. Since the switching device is turned on and off at zero current, the switching losses and electromagnetic noises are greatly reduced. This paper described the principle of the zero current switching operation, the design of the resonant circuits and the control scheme for the new soft switching inverter. Moreover, it shows interesting experimental results obtained by the zero‐current‐switching PWM inverter which drives an induction motor of 2.2 kW.

This paper discusses a distributed constant circuit model of power cables for representing high-frequency oscillatory currents, and evaluates electromagnetic interference (EMI) generated by a PWM inverter-fed induction motor drive system. While the lumped constant circuit model which has already been proposed by the authors has only one resonant frequency, the distributed model proposed here can simulate plural resonant phenomena existing in a high frequency range over the first resonant frequency. Frequency characteristics of both common-mode and normal-mode currents are analyzed by using a circuit simulator with the distributed model. As a result, it is shown experimentally and theoretically that the resonant phenomena in the high frequency range are originated from behavior of the power cables as the distributed constant circuit, and that the common-mode transformer (CMT) and the normal-mode filters (NMF's) can damp the resonances.

This paper discusses harmonic propagation and damping in a long‐distance distribution feeder having many capacitors for power factor correction, and presents harmonic damping characteristics of a shunt active filter based on voltage detection. A distributed constant‐circuit model for the feeder is derived to perform analysis with the focus on harmonic propagation and damping. As a result, it is clarified by theory and experiment that harmonic propagation throughout the feeder can be mitigated by installing the active filter, which acts as a harmonic terminator, on the end terminal of the feeder. © 2002 Scripta Technica, Electr Eng Jpn, 139(1): 73–81, 2002; DOI 10.1002/eej.1148

This paper presents a fully-digital-controlled shunt active filter for harmonic termination of a power distribution system. The main purpose of the active filter based on voltage detection is not to compensate for current harmonics but to damp out harmonic propagation caused by line inductors and shunt capacitors for power factor correction. However, time and phase delays inherent in digital controllers might lead to unsatisfactory harmonic-damping performance although digital controllers are preferable to analog controllers. This paper deals with the design and implementation of a digital controller for a shunt active filter based on voltage detection. Experimental results obtained from a laboratory system developed in this paper verify the viability and effectiveness of the fully-digital-controlled active filter.

This paper discusses a shunt active filter intended for installation on a power distribution system, with focus on voltage regulation capability. The active filter has capability of regulate the distribution-line voltage by means of adjusting its reactive power. Theoretical analysis investigates the dynamic performance of harmonic damping and voltage regulation as well as computer simulation does. As a result, it is clarified that a harmonic detection error may increase the voltage fluctuations in transient states. A new compensation method is proposed to reduce the voltage fluctuations in transient states. Experimental results show that the proposed method makes it possible to reduce the voltage fluctuation in transient states

This paper presents a modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC), which is intended for grid connection to medium-voltage power systems without the use of line-frequency transformers. The converter is characterized by a modular arm structure consisting of cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. It is necessary to achieve voltage-balancing control of all the dc capacitors. However, the voltage control achieved by averaging control and individual-balancing control imposes certain limitations on the operating conditions. This paper proposes arm-balancing control to achieve voltage balancing under all the operating conditions. The validity of the arm-balancing control as well as the theory developed in this paper is shown by performing a computer simulation and experiment.

This paper discusses harmonic propagation and damping in a long-distance distribution feeder having many capacitors for power factor correction, and presents harmonic damping characteristics of a shunt active filter based on voltage detection. A distributed-constant-circuit model for the feeder is derived to perform analysis with the focus on harmonic propagation and damping. As a result, it is clarified by theory and experiment that harmonic propagation throughout the feeder can be mitigated by installing the active filter, which acts as a harmonic terminator, on the end terminal of the feeder.

The authors have already proposed a passive EMI filter that does require access to the motor-neutral point. The EMI filter has been applied to an induction motor driven by a voltage-source PWM inverter with a three-phase diode rectifier used as the front end. Experimental results have shown that the EMI filter can mitigate leakage currents flowing out of the motor and the heat sink, as well as bearing currents circulating inside the motor. This paper deals with a passive EMI filter for preventing high-frequency leakage currents from flowing through the heat sink of a voltage-source PWM inverter together with a voltage-source PWM rectifier used as the front end. Both rectifier and inverter have the same carrier frequency as 14kHz. The tested motor equipped with the motor-neutral line is an interior permanent magnet synchronous motor (IPM-SM) rated at 190V, 5.5kW, 6 poles and 1,800rpm. This paper designs, constructs and tests two types of EMI filters. These filters consist mainly of two 10-mH identical common-mode inductors that are installed on the ac sides of the rectifier and the inverter, respectively. However, the two filters are slightly different in that one accesses to the dc-link mid-point, and the other does not access to it. Experimental waveforms verify that the former is superior to the latter in eliminating the high-frequency leakage currents from both the heat sink and the motor.

Several internal auditory canal (IAC) anomalies have been reported. To our knowledge, only one case with an abnormal direction of the IAC has been reported in an infant with Pierre Robin syndrome. In this paper, we present the first report of two non-syndromic cases with abnormal IAC direction.

This paper presents an intensive discussion on modeling an adjustable-speed motor drive system consisting of a voltage-source PWM inverter and an induction motor that are connected by a three-phase symmetric, long cable with a grounding wire lead. Then, it describes a design procedure for a parallel-connected R-L filter in each phase that can mitigate the overvoltage appearing at the motor terminals. The model developed in this paper focuses on the inherent “ringing frequency” of the cable, where the ringing frequency is inversely proportional to cable length. When no filter is used, the so-called “impedance mismatch” causes the reflection of a voltage-traveling wave at both the inverter and the motor terminals. As a result, the impedance mismatch generates an overvoltage that may reach twice the inverter dc-link voltage at the motor terminals. The overvoltage may damage the motor-winding insulation, and may cause it to breakdown. Although an R-L filter installed on the ac side of the inverter can reduce the overvoltage, it would be difficult to design the filter effectively for long cables of different lengths. The effectiveness and validity of the simple design procedure described in this paper are confirmed on a 400-V, 15-kW experimental system with either a 100-m or 200-m-long cable.