This paper deals with a series active filter for harmonic‐current compensation of a large‐capacity diode rectifier with a capacitive load. Flux saturation may occur in a series matching transformer for connecting the series active filter to the ac side of the diode rectifier. This paper develops an analog controller of a dc magnetizing current flowing in the matching transformer, along with a model for the controller, to avoid the flux saturation. Operating characteristics of the controller are theoretically and experimentally discussed, taking into account both an offset voltage in the controller and an error in a current sensor. Finally, this paper discusses a relation between magnetizing characteristics of the matching transformer and the amplitude of the magnetizing current. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 63–72, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10188
The similarity between a six-pulse three-phase cycloconverter operating in the circulating current-free mode and a six-pulse three-phase bridge converter is discussed analytically with regard to the rms value and the harmonics of the respective output voltages. A method is presented for calculating the rms voltage of a family of sideband frequencies which are generated in the output voltage of the cycloconverter. The results obtained from the analysis help to predict the amplitudes of subharmonics and beat frequencies with the cycloconverter and are essential for the design of the output filters. Analytical results are verified by comparison with those of experiment and digital computer simulation.
This paper deals with the shaft end-to-end voltage resulting from asymmetric stray capacitances in an inverter-driven motor. The origin of the voltage can be any of the following: a ground leakage current, dielectric breakdown in bearings, and asymmetric stray capacitances on stator windings. The third origin seems to be related to the differential-mode current, but the details of the relationship have not been clarified. In this study, differential-mode tests are carried out on an ungrounded motor rated at 400V and 15kW, and the shaft end-to-end voltage generation by the asymmetric stray capacitances is theoretically discussed. Finaly, a winding model is presented for the purpose of understanding the mechanism responsible for the shaft end-to-end voltage.
This paper presents two high-voltage direct-current circuit breakers that have the capability of interrupting a short-circuit current within several milliseconds. They consist of a current-limit inductor, a current-control inductor, one or two mechanical switches, and a multilevel converter with phase-shifted-carrier pulsewidth modulation. The two breakers can commutate an almost zero current from the main branch to the auxiliary branch. This paper proposes an original breaker with low-voltage and high-voltage mechanical switches connected in series, followed by a simplified breaker with a single high-voltage mechanical switch. Finally, this paper includes experimental verification by two slightly different downscaled breakers rated at 300 Vdc and 150 Adc, as well as confirmation of an actual original breaker by circuit simulation using the "PSCAD/EMTDC" software package.
It has been reported that oral administration of Lactobacillus acidophilus strain L-55 (L-55) suppressed nasal symptom and antigen-specific IgE induced by antigen challenge in mice. We investigated clinical effects of L-55-contained yogurt on symptoms and IgE production in the patients with Japanese cedar pollinosis.The study was performed as a randomized double blind placebo-controlled trial. L-55-contained yogurt (L-55 yogurt) or placebo yogurt was started to administer to each subject from 4 weeks prior to the onset of Japanese cedar pollen release for total 13 weeks.The mean value of symptom score and symptom medication score were lower in L-55 yogurt group compared with placebo yogurt group during 5th week to 9th week from the first week of Japanese cedar pollination. Especially, in medicated subjects, total symptom score and throat symptom score were significantly lower in L-55 yogurt group compared with placebo yogurt group at 5th and 4th week from the first week of Japanese cedar pollination, respectively. Moreover, in medicated subjects, change ratio of serum total IgE was significantly lower in L-55 yogurt group compared with placebo yogurt group at 1st week from the first week of Japanese cedar pollination.Intake of L-55 during Japanese cedar pollinating season may be effective in alleviating the allergic symptoms related to Japanese cedar pollinosis. From these finding, it was suggested that L-55 is a possible candidate as a complementary medicine for Japanese cedar pollinosis.
No abstract is provided for this article.
Parotid gland tumors are usually unilateral, and bilateral parotid gland tumors are rare, Warthin's tumor (adenolymphoma) being the most common. We present a case of bilateral multiple parotid gland tumors in a patient with Sjögren's syndrome. A 62-year-old female came to our department because of a slowly growing mass in the right parotid region. CT-scan and MRI showed multiple cystic lesions in both parotid glands. The masses on the right side were removed surgically, with preservation of the facial nerve. The histological diagnosis was benign lymphoepithelial cyst (branchial cyst). Benign lymphoepithelial cysts are usually unilateral and single. The findings in this patient are very unusual.
This paper presents a transformerless hybrid active filter integrated into a medium-voltage motor drive for energy savings. This hybrid filter is intended for line harmonic-current mitigation of the three-phase diode rectifier used as the front end of the motor drive. It is based on direct connection of a passive filter tuned to the seventh-harmonic frequency in series with an active filter using a three-level pulsewidth modulated (PWM) converter. This paper provides a theoretical discussion on voltage-balancing control of two split dc capacitors of the active filter. The 400-V 15-kW motor drive system is designed, constructed, and tested, which can be considered as a downscaled model from a medium-voltage motor drive without regenerative braking. Experimental results verify that the hybrid filter has the capability of satisfactory harmonic filtering and stable voltage balancing in all the load conditions.
This paper proposes a transformerless shunt hybrid filter for harmonic compensation of a three‐phase six‐pulse diode rectifier, where the AC line‐to‐line voltage is 3.3 or 6.6 kV. The hybrid filter consists of a single tuned LC filter per phase and an active filter with a DC capacitor voltage as low as 300 or 600 V. The two filters are directly connected in series with each other without a transformer. The passive filter absorbs harmonic currents produced by the rectifier, whereas the active filter improves the filtering characteristics of the passive filter. The required rating of the active filter is much smaller than that of a conventional shunt active filter used alone. Another advantage is that no additional switching‐ripple filter is required for the active filter because the LC filter acts not only as a tuned LC filter around the seventh‐harmonic frequency but also as a switching‐ripple filter around 10 kHz. A feedforward control scheme is also proposed to improve the active filter performance. Experimental results obtained from a 200‐V, 5‐kW laboratory system and simulation results of a 3.3‐kV, 300‐kW system confirm the validity and effectiveness of the system. The hybrid filter gives satisfactory compensation performance, thus allowing us to put it into practical use. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 54–65, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10236
This paper presents a zero-current-switched voltage-fed inverter equipped with resonant circuits on the ac side. The current flowing through a switching device, i.e., an IGBT is a sum of the load current and the resonant current. When the amplitude of the resonant current is larger than that of the load current, the current in the switching device becomes zero at an instant in each resonant cycle. This allows the switching device to be turned on or off at the zero current. The zero-current-switching makes a significant contribution to reduction of switching losses and electromagnetic noises.In this paper, the principle of zero-current-switching operation, along with a novel control scheme, is described from a theoretical and practical point of view. Experimental results obtained from a laboratory system of 5kVA verify the practicability. Moreover, the switching and conduction losses of the proposed soft-switched inverter are compared with those of a conventional hard-switched inverter.
This paper presents theoretical and experimental relationships between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source pulsewidth modulation (PWM) inverter. A method of reducing both currents is proposed, based on an equivalent model, taking into account parasitic stray capacitors inside an induction motor. Electromagnetic interference (EMI) radiated by a 3.7-kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3 m]. Experimental results verify that the combination of the already proposed common-mode transformer (CMT) and the normal-mode filters (NMFs) being proposed in this paper is a practically viable and effective way to reduce EMI resulting from both common-mode and normal-mode currents.
No abstract is provided for this article.
This paper describes a simple and clear approach to analyze harmonic instability of phase controlled thyristor converters with input passive filters. It is shown by analysis and experiment that harmonic instability may occur at the parallel resonant frequency between the passive filter and the ac source even if the ac source impedance is low.A combined system of series active and shunt passive filters has already been proposed as a new approach to harmonic compensation in power systems by the authors. It is confirmed analytically and experimentally that the series active filter used has the capability to suppress the harmonic instability at the parallel resonant frequency. However, it is also shown that the series active filter may cause harmonic instability adversely at lower frequencies. However, harmonic instability at a frequency except for the parallel resonant frequency does not cause any practical problem. The obtained analytical results are confirmed by experiment in detail.
This paper discusses automatic gain adjustment in a fully‐digital‐controlled shunt active filter intended for installation on power distribution systems. This is the first step in cooperative control of multiple shunt active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, an optimal control gain is equal to the characteristic impedance of a distribution line. However, it is difficult to know the circuit parameters of a real distribution line, which depend strongly on feeder connections, shunt capacitors, and loads. Therefore, the main purpose of the gain adjustment is to help the active filter to damp out harmonic propagation without considering the circuit parameters. Moreover, the gain adjustment can reduce the compensating current and losses in the active filter. The active filter having the function of automatic gain adjustment is experimentally compared to that with a constant gain. Experiment results verify the effectiveness of the active filter having the function of automatic gain adjustment. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 56–65, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10094
No abstract is provided for this article.
This paper provides a theoretical and experimental discussion on a unidirectional isolated dc-dc converter equipped with a high-frequency transformer. It focuses on an application of the dc-dc converter to an auxiliary power supply for electric commuter trains. This specific dc-dc converter is required to tolerate sudden and frequent changes in the catenary voltage with a nominal value of 1.5kVdc, and has to maintain a constant output voltage. This auxiliary power supply is characterized by an input-series, output-parallel circuit configuration of two identical unidirectional isolated dc-dc converters. This configuration allows the dc-dc converter to eliminate a boost converter at the front end and a switchover circuit between series and parallel connections. The 600-Vdc, 6-kW, 16-kHz downscaled experimental system using SiC-MOSFET/SBD modules is designed, constructed and tested to verify the validity of the specially-constructed control system for regulating the dc output voltage to a reference of 150Vdc. Experimental waveforms show that the dc output voltage is well regulated even when a sudden input voltage change from 600 to 350V occurs, and a sudden load change from 3 to 6kW occurs.
No abstract is provided for this article.
Unlike traditional passive filters, active filters for power conditioning have multiple functions such as harmonic filtering/damping/isolation/termination, load balancing, reactive-power control for power factor correction and voltage regulation, voltage-flicker reduction, or their combinations. Significant cost reductions in both power semiconductor devices and signal-processing devices have inspired many manufactures in Japan, Europe and the United States to put active filters on the market. This paper deals with active filters for power conditioning, and specifically hybrid active filters for harmonic filtering of three-phase diode rectifiers
Parotid gland tumors are usually unilateral, and bilateral parotid gland tumors are rare, Warthin's tumor (adenolymphoma) being the most common. Warthin's tumor is the most common tumor of parotid gland except pleomorphic adenoma. Warthin's tumors in both parotid glands are found in 5 to 10% of all patients with Warthin's tumors in the parotid glands. We present a case with a total of 9 Warthin's tumors in both parotid glands. A 66-year-old male came to our department because of throat discomfort, and bilateral parotid tumors were subsequently revealed. CT-scan and MRI showed 8 solitary lesions in both parotid glands. The masses were removed surgically, with preservation of the facial nerves. There were a total of 3 tumors in the right parotid gland, and 6 in the left parotid gland. The histological diagnosis was Warthin's tumors in both parotid glands. Nine Warthin's tumors in a case are the most numerous ever reported in Japan.
