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This paper aims at minimizing capacitor-voltage fluctuations inherent in a modular multilevel cascade inverter based on double-star chopper cell (DSCC) or a modular multilevel DSCC inverter. The inverter can drive an induction motor loaded with a quadratic-torque load. Both theoretical analysis and numerical calculation reveal that the voltage fluctuations can be minimized when the ratio of a magnetizing-current component with respect to a torque-current component in the motor current is set to unity, regardless of the motor mechanical speed. A three-phase DSCC inverter is designed and constructed to drive a 380-V, 15-kW, 50-Hz, four-pole, induction motor loaded with a quadratic torque that is proportional to a square of the motor mechanical speed. Experimental results confirm the validity of the theoretical and numerical calculations. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a new hybrid dc circuit breaker producing no conducting power loss under normal operating conditions and having the capability to interrupt a large amount of short-circuiting current within several milliseconds. It consists of two reactors for current limiting and current control, two mechanical contactors, and a multilevel converter based on the cascade connection of multiple full-bridge dc/dc converter cells. It is characterized by achieving current commutation from the main mechanical contactor to the multilevel converter with fast current control. This results in eliminating auxiliary power semiconductor switches that produce a nonnegligible conducting power loss under normal operating conditions. This paper discusses both principles of operation and control method of the new hybrid dc circuit breaker. Experimental verification is performed by a downscaled system rated at 300 V and 150 A, along with verification by computer simulation. [ABSTRACT FROM AUTHOR]

This paper provides an experimental discussion on an adjustable-speed electrical drive fed by a modular multilevel triple-star bridge-cell (TSBC) converter. The TSBC converter is suitable for medium-voltage high-power motor drives with regenerative braking. However, it suffers from capacitor-voltage fluctuation that becomes more serious as the motor frequency gets closer or equal to the supply frequency. This paper presents a practical solution of it with an acceptable increase in all the nine cluster currents. The solution is characterized by a motor-magnetizing-current controller that makes a significant contribution to theoretically eliminating the low-frequency component contained in each capacitor voltage. Experimental waveforms, which are obtained from a three-phase downscaled model rated at 400 V and 15 kW, verify exhibit satisfactory start-up performance from a standstill to the rated motor frequency that is equal to the supply frequency. [ABSTRACT FROM AUTHOR]

This paper makes an intensive comparison in operating performance between a modular multilevel double-star chopper-cells (DSCC) inverter and a modular multilevel triple-star bridge-cells (TSBC) converter. Both inverter and converter are intended to drive medium-voltage motors in industrial applications. First, it makes numerical comparisons, thus, resulting in revealing that the torque and frequency of a driven motor produce a significant effect on capacitor-voltage fluctuation and arm or cluster current in the individual DSCC inverter and TSBC converter. Next, a three-phase DSCC inverter and a three-phase TSBC converter with the same rating as 400 V and 15 kW are designed and compared to drive the following two general purposes and specially-designed induction motors; one is rated at the 380-V, 15-kW, 50-Hz four-pole motor, and the other is at the 320-V, 15-kW, 38-Hz six-pole motor. This experimental comparison based on the two downscaled drive systems confirms the validity of the numerical comparison. Finally, this paper concludes that the DSCC inverter is more suitable for driving medium-voltage high-speed motors loaded with quadratic-torque-to-speed profiles like fans, blowers, pumps, and centrifugal compressors. On the other hand, the TSBC converter is more suitable for driving medium-voltage low-speed high-torque motors like mills, kilns, conveyors, and extruders. [ABSTRACT FROM AUTHOR]

This paper describes a novel compact model for a SiC-MOSFET. The model is useful to achieve accurate simulation of output characteristics from a linear region to a saturation region, selecting both gate–source voltage and temperature as parameters. In order to construct the model systematically, attention is paid to a physics-based modeling procedure with channel mobility as an adjustable parameter. The model also features characterization and modeling of an internal drain–gate capacitor. The model shows fairly good agreement in the output characteristics and the dynamic behavior of both gate drive circuit and main power circuits between the experimental and simulated results. This successful validation indicates that this model offers a promising circuit-based simulation tool for designing whole power conversion systems using SiC-MOSFETs. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents an experimental discussion on modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). Hereinafter, a single MMCC-DSCC is referred to simply as a 'DSCC'. A couple of DSCCs are used to form a front-to-front (FTF) system capable of dc voltage matching and galvanic isolation between two dc grids. The FTF system can be considered as a dc-ac-dc power conversion system including an ac-link high-power transformer. The higher the ac-link frequency, the smaller and lighter are the ac-link transformer and dc capacitors. When the so-called 'phase-shifted-carrier PWM' is applied to the DSCC, theoretical analysis and computer simulation have confirmed that a ratio of the carrier frequency with respect to the ac-link frequency can be reduced to 5/2. This paper designs, constructs, and tests a 400-Vdc 10-kW downscaled FTF system with a carrier frequency of 450 Hz and an ac-link frequency of 180 Hz, where their ratio is 5/2. Experimental waveforms obtained from the downscaled system are compared with simulated ones obtained from a software package, PSCAD/EMTDC, under the same operating and circuit conditions. They agree well each other not only under steady states but also under transient states. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive discussion on voltage balancing of all the floating capacitors in a modular multilevel cascade inverter based on double-star chopper cells (DSCC) or a modular multilevel DSCC inverter. It intends to use the inverter for driving a medium-voltage synchronous motor. Theoretical and numerical design considerations on both amplitude and phase of the three-phase motor currents achieve better capacitor-voltage balancing in a low-power low-frequency range. A three-phase DSCC inverter with phase-shifted-carrier pulse width modulation is designed, constructed, and tested to drive the 370-V 15-kW 75-Hz six-pole interior-permanent-magnet synchronous motor loaded with a hypothetical centrifugal compressor. Experimental results verify the validity of the theoretical analysis, as well as the effectiveness and viability of the DSCC inverter for such a specific electrical drive. [ABSTRACT FROM PUBLISHER]

This paper provides theoretical and experimental discussions on an optimal carrier frequency for a phase-shifted pulsewidth modulation modular multilevel cascade converter for grid connections. The theoretical discussion concludes that a ratio of the optimal carrier frequency with respect to the supply (ac) frequency is 5/2. A three-phase downscaled front-to-front system is designed, constructed, and tested to confirm validity of the theoretical discussion. It consists of a pair of three-phase modular multilevel cascade converters rated at 400 Vdc and 10 kW, where the carrier frequency is set to 450 Hz and the ac frequency to 180 Hz, that is, their ratio is equal to 5/2. Moreover, simulated waveforms are compared to experimental ones under the same operating conditions. Both experimental and simulated waveforms agree well with each other not only in steady states but also in transient states. [ABSTRACT FROM AUTHOR]

This paper focuses on the zero-voltage ride-through (ZVRT) capability of a transformerless back-to-back (BTB) system intended for installation on a power distribution system with many distributed power generators. The BTB system consists of two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) and their ac sides are connected to a common ac mains via ac-link inductors. This paper provides an experimental discussion on the DSCC-based BTB system under voltage sags by using a three-phase 200-V 10-kW downscaled system. Experimental results show that the BTB system is equipped with ZVRT capability without causing any overvoltage and/or overcurrent even under the most severe voltage sags. [ABSTRACT FROM PUBLISHER]

Energy storage systems have been widely applied in power distribution sectors as well as in renewable energy sources to ensure uninterruptible power supply. This paper proposes a modified model predictive control (MMPC) method based on the Lyapunov function to improve the performance of a bidirectional ac–dc converter, which is used in an energy storage system for bidirectional power transfer between the three-phase ac voltage supply and energy storage devices. The proposed control technique utilizes the discrete behavior of the converter, considering the unavoidable quantization errors between the controller and the control actions selected from the finite control set of the bidirectional ac–dc converter. The proposed control method reduces the execution time delay by 18% compared with the conventional model predictive control. Moreover, the nonlinear system stability of the proposed MMPC technique is ensured by the direct Lyapunov method and a nonlinear experimental system model. Detailed experimental results with a 2.5-kW downscaled hardware prototype are provided to show the efficacy of the proposed control system. [ABSTRACT FROM PUBLISHER]

This paper provides experimental verification of a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed, high-torque motor drive. The TSBC is one of direct ac-to-ac power converters capable of achieving bidirectional power flow and drawing/feeding three-phase sinusoidal input (supply-side) and output (motor-side) currents with any power factor at both sides. This paper designs, constructs, and tests a downscaled drive system combining a 400-V, 15-kW, phase-shifted-carrier PWM TSBC equipped with four bridge cells per cluster and a 320-V, 38-Hz, 6-pole, 15-kW induction motor loaded at the rated torque. Experimental waveforms obtained from the downscaled drive system verify stable operation across a broad range from a standstill to the rated speed, showing satisfactory start-up performance. [ABSTRACT FROM PUBLISHER]

Model predictive control (MPC) is a powerful and emerging control algorithm in the field of power converters and energy conversion systems. This paper proposes a model predictive algorithm to control the power flow between the high-voltage and low-voltage DC buses of a bidirectional isolated full-bridge DC–DC converter. The predictive control algorithm utilises the discrete nature of the power converters and predicts the future nature of the system, which are compared with the references to calculate the cost function. The switching state that minimises the cost function is selected for firing the converter in the next sampling time period. The proposed MPC bidirectional DC–DC converter is simulated with MATLAB/Simulink and further verified with a 2.5 kW experimental configuration. Both the simulation and experimental results confirm that the proposed MPC algorithm of the DC–DC converter reduces reactive power by avoiding the phase shift between primary and secondary sides of the high-frequency transformer and allow power transfer with unity power factor. Finally, an efficiency comparison is performed between the MPC and dual-phase-shift-based pulse-width modulation controlled DC–DC converter which ensures the effectiveness of the MPC controller. [ABSTRACT FROM PUBLISHER]

This paper presents an intensive discussion on a transformerless back-to-back (BTB) system using modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). It is expected to be applied to a power distribution system with many distributed power generators. This paper designs, constructs, and tests a three-phase 200-V, 10-kW DSCC-based BTB system installed on a 200-V, 40-kW power distribution simulator consisting of two radial feeders. Experimental results show that the BTB system can mitigate power-flow imbalance between the two feeders. Moreover, the zero-sequence current circulating between the two feeders can be suppressed to be as small as 10 mA (0.02%) in rms by connecting a common-mode choke to the common dc link of the BTB system. [ABSTRACT FROM AUTHOR]

This paper describes a high-speed protection circuit for insulated-gate bipolar transistors (IGBTs) subjected to hard-switching faults (HSFs). The reverse transfer capacitance depends on the collector–emitter voltage, and it produces a significant effect on the switching behavior not only under normal conditions but also under HSF conditions. A gate charge characteristic under HSF conditions differs from that under normal turn-on conditions. Hence, an HSF can be detected by monitoring both the gate–emitter voltage and the amount of gate charge during the turn-on transient period. IGBTs can be rapidly protected from destruction by using this method because a blanking time is unnecessary. Simulation and experiment verify the validity of the proposed high-speed protection circuit. [ABSTRACT FROM PUBLISHER]

This paper presents and discusses a phase-shifted-PWM distribution static synchronous compensator (D-STATCOM) using the modular multilevel cascade converter based on single-star bridge cells (MMCC-SSBC). A three-phase 140-V 10-kVA SSBC-based STATCOM with a cascade count $N=6$ is designed, constructed, and tested for verifying the performance and functionality of the medium-voltage D-STATCOM in both steady and transient states. The 13-level line-to-neutral (25-level line-to-line) voltage at the ac side yields an almost sinusoidal line current with a total harmonic distortion value of 1.7%. An analytical model for the phase-shifted PWM is proposed to design the current control gains. Two phase-shifted PWM methods, which are named as one-cell and all-cells update methods, are theoretically and experimentally compared. The all-cells update method can reduce the inherent time delay, thus resulting in a faster and more stable system response than the one-cell update method. [ABSTRACT FROM AUTHOR]

Renewable energy sources such as wind turbine and photovoltaic power generators may make the power grid unstable due to their output fluctuations. Battery energy storage systems (BESSs) are being considered as a countermeasure for this issue. A modular multilevel cascade converter (MMCC) is expected as a power conversion circuit for BESSs because each bridge cell can control the state of charge of a battery unit, independent of that of another one, and the harmonic current generated is low enough to eliminate the ac filter, normally installed on conventional two-level converters, from the MMCC. This paper describes the development of a real-scale (500 kW) single-star-bridge-cell-based MMCC for BESSs and reports successful test results obtained from a downscaled grid model and a 6.6-kV real-scale distribution line. [ABSTRACT FROM AUTHOR]

This paper presents the average power balancing (APB) control method for the modular multilevel cascaded converter based on single-star bridge cells in the static synchronous compensator applications. The proposed control method accomplishes both the reactive power compensation and the dc bus voltage balancing control even under grid voltage sags. The low-voltage ride-through capability of the proposed method will become more and more important as more distributed generation resources are integrated into the grid. Laboratory test results are provided to validate the proposed APB control method. [ABSTRACT FROM AUTHOR]

This paper provides an intensive discussion on analysis, simulation, and experiment of a back-to-back (BTB) systemunifying two modular multilevel cascade converters based on double-star chopper cells (MMCCs-DSCCs). Each of the twoDSCCs connected back-to-back consists of multiple cascaded chopper cells and a center-tapped inductor per leg. Lowvoltage steps bring significant reductions in harmonic voltage and current to the BTB system. Neither dc-link capacitornor voltage sensor is required for regulating the dc-link voltage and controlling the dc-link current. A three-phase200-V, 10-kW, 50-Hz downscaled BTB system with phase-shifted PWM is designed, constructed, and tested to verify itsoperating principles and performance. Analytical, simulated, and experimental results agree well with each other insteady and transient states. Experimental waveforms confirm the effectiveness of a self-starting/restartingprocedure. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a reverse-recovery analysis of parallel-connected pin diodes using a physics-based device model. Since the pin diode model is based on a physical equation, the excess carrier distribution in the drift layer is estimated. A precise device model enables us to understand the transient characteristics of the parallel-connected pin diodes. We investigated the reverse-recovery characteristics of parallel-connected pin diodes by using a physics-based pin diode model. A difference in the wiring inductance or device temperature between the two pin diodes causes a transient current imbalance. Complicated reverse-recovery current waveforms are observed under both conditions-a difference in the wiring inductance and a difference in the device temperature. They result from a difference in the starting time of forming each depletion layer between the two pin diodes. Simulation results are in good agreement with experimental ones within an error of 10% in terms of the reverse-recovery loss. We find that a precise physics-based pin diode model is very useful when designing a power electronics apparatus. [ABSTRACT FROM AUTHOR]

Renewable energy sources such as wind turbine generators and photovoltaics are intermittent in nature, thus resulting in fluctuating electric power. Leveling of their electric power is indispensable to realize large-scale renewable energy sources and to avoid severe power quality problems when they are interconnected into the grid. A battery energy storage system (BESS), combining batteries with a power converter and digital control, should be installed in the vicinity of an intermittent energy source. The fluctuating power is compensated by appropriately controlling active power stored in, or released from, the battery. This paper describes a 6.6-kV transformerless battery energy storage system based on a cascade multilevel PWM (pulse-width-modulation) converter, with focus on a control method for active power and SOC (state-of-charge) balancing. A down-scaled 200-V, 10-kW, 3.6-kWh (13-MJ) laboratory model using nine NiMH (Nickel Metal Hydride) battery packs was designed, constructed, and tested to verify the viability and effectiveness of the 6.6-kV system. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 43-54, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21127 [ABSTRACT FROM AUTHOR]

Abstract: Aberrant O-glycosylation of serum and tonsillar IgA1 is one of the main pathogeneses of IgA nephropathy (IgAN). However, the synthesis of underglycosylated IgA1 in tonsils has not yet been characterized. This study examined tonsillar B lymphocytes of IgAN (n =34) using tonsils derived from patients with chronic tonsillitis (n =24) and sleep apnea syndrome (n =14) as a control. Gene expression of β1,3-galactosyltransferase (β3GalT), and the core 1 β3GalT-specific molecular chaperone, Cosmc, UDP-N-acetyl-α-D-galactosamine: polypeptide N-acetylgalactosaminyl-transferase 2, were significantly decreased in tonsillar CD19-positive B lymphocytes from IgAN patients compared to control tonsillar tissues as determined by real-time RT-PCR. Tonsillar B cell β3GalT gene expression significantly correlated with estimated GFR and negatively correlated with proteinuria and histological injury score. Western blotting showed the protein expression of β3GalT in the tonsils to significantly decrease in IgAN in comparison to the controls. These data suggest the downregulation of β3GalT in tonsillar B lymphocytes to be closely associated with the clinical characteristics of IgAN. [ABSTRACT FROM AUTHOR]

This paper deals with the dynamic behavior of a 21-level (line-to-line) back-to-back (BTB) system based on series connection of 16 converter cells under a single-line-to-ground (SLG) fault condition. The BTB system is an ac-dc-ac power conversion system intended for achieving asynchronous power-flow control between transmission networks. When the SLG fault happens, an imbalance in the supply voltage brings an amount of negative-sequence current to the BTB system. The negative-sequence current should be mitigated because it would result in an increased supply current and a dc-capacitor voltage fluctuation. This paper intends for reducing both the negative-sequence current and the dc-voltage fluctuation to acceptable levels. A laboratory system rated at 200 V and 20 kW confirms the validity of the reduction scheme. In addition, this paper addresses the issue of magnetic saturation in the 16 three-phase converter-transformers. [ABSTRACT FROM AUTHOR]

This paper addresses a transformerless shunt hybrid filter integrated into a three-phase diode rectifier. The hybrid filter consists of a three-phase passive filter tuned to the seventh-harmonic frequency, and a small-rated active filter based on a three-phase voltage-source pulsewidth modulation converter. The validity of the system design is confirmed by experimental results obtained from a 400-V, 15-kW laboratory system. The experimental results show that the active filter plays an essential role in reducing supply harmonic currents. The total harmonic distortion of the supply current gets less than 5%. Moreover, the hybrid filter provides satisfactory transient performance asa result of having achieved an optimal design of circuit and control parameters including the dc capacitor voltage and feedback gains of the active filter, along with the cutoff frequency of high-pass filters for harmonic extraction. [ABSTRACT FROM AUTHOR]

A 21-level (line-to-line) self-commutated BTB (Back-To-Back) system based on series connection of 16 converter cells has attractive features as follows: (i) Both active and reactive powers can be controlled independently even in transient states. (ii) The BTB system produces almost sinusoidal voltage at the AC side without performing PWM (Pulse-Width-Modulation) control, so that no harmonic filter is required. (iii) The BTB system provides an active power reason as high as 3 ms. This paper presents experimental verifications of the self-commutated BTB system intended for achieving power flow control in transmission systems. Experimental results obtained by a 200-V, 20-kW laboratory prototype confirm effectiveness and validity of both the system configuration and the developed control strategy. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 61– 70, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20324 [ABSTRACT FROM AUTHOR]

Abstract: Objective: Adenocarcinoma ex pleomorphic adenoma is a rare tumor, and thus the management of the tumor has not been established. Methods: The retrospective review of the clinical records at Okayama University was performed. Results: We present five cases of adenocarcinoma ex pleomorphic adenoma of the head and neck, including a rare case with nasopharyngeal adenocarcinoma ex pleomorphic adenoma. There was no response to chemotherapy with nedaplatin and 5-FU, but the nasopharyngeal adenocarcinoma ex pleomorphic adenoma showed a remarkable regression after the administration of docetaxel. Conclusion: The combination therapy that includes docetaxel may be a promising treatment for adenocarcinoma ex pleomorphic adenoma of the head and neck. [Copyright &y& Elsevier]

Primary malignant fibrous histiocytoma (MFH) arising in a major salivary gland is rare. We encountered a case of MFH affecting the parotid gland. The patient was a 54-year-old man diagnosed as having pleomorphic type of MFH after extended total parotidectomy. Examination of the resected specimen revealed the tumor had not been completely removed. Accordingly treatment consisted in the resection of MFH and radiotherapy in combination with chemotherapy using carboplatin (CBDCA). This postoperative therapy was effective in controlling the growth of the remaining tumor tissue. As the patient showed no signs of local recurrence and distant metastasis for 5 years, plastic surgery was performed to improve the serious deformation of the face with a free anterolateral thigh flap. Our literature review yielded 17 cases of parotid MFH and the 2-year survival rate was 33%. [Copyright &y& Elsevier]

Background: 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., Method: 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., Result: 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., Conclusion: 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.

Objective: The objective of this study was to assess the expression of regulatory cytokines and T helper cell (Th)1/Th2 cytokines in paranasal sinus mucoceles., Materials and Methods: Fluid samples of 12 paranasal sinus mucoceles were assessed by enzyme-linked immunosorbent assay for concentrations of regulatory cytokines (interleukin [IL]-10 and IL-12), Th1 cytokines (IL-2 and interferon gamma), and Th2 cytokines (IL-4 and IL-5)., Results: IL-12 was detected in all samples, whereas IL-10 was detected in only one case. The concentration of IL-12 tended to correlate with that of interferon gamma and was significantly and positively correlated with that of IL-2., Conclusions: Th1 cytokines and the Th1 regulatory cytokine IL-12, but not IL-10, potentially play a key role in the pathogenesis of paranasal sinus mucoceles. Together with our recent report showing that lipopolysaccharide is highly detected in mucocele fluid, the data from this study suggest that the Th1 response induced by lipopolysaccharide may affect the immunological inflammation in the epithelium of paranasal sinus mucoceles.

IgA nephropathy (IgAN) is the most common form of chronic glomerulonephritis with IgA deposits present mainly in the mesangial areas. We performed a 10-year retrospective case-control study of 71 patients with IgAN to evaluate the long-term effects and prognostic factors associated with tonsillectomy. Forty-one patients (19 males and 22 females) underwent tonsillectomy (Group A) and 30 patients (13 males and 17 females) did not (Group B). These patients were followed for more than 10 years after renal biopsy. The average age at initial renal biopsy was 29.78 years in Group A and 33.0 years in Group B. The average follow-up period was 13 years and 3 months in Group A, and 12 years and 7 months in Group B. Glomerular damage demonstrated on renal biopsy was more extensive in Group A than in Group B. Prognosis after 10 years of follow-up was compared between the two groups. The clinical remission rate was 24.4% in Group A and 13.3% in Group B, the stable renal function rate was 82.9% in Group A and 70.0% in Group B, and the renal survival rate was 95.1% in Group A and 73.3% in Group B. The renal survival rate in Group A was significantly higher than that in Group B (p <0.05). Although evaluation of renal pathology based on renal biopsy was useful in predicting the long-term effects of tonsillectomy in IgAN patients, the results of tonsillar provocation tests were not.