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M K Ju,
K H Huh,
K T Park,
S J Kim, B H Cho,
C D Kim,
B J So,
C M Kang,
S Lee,
D J Joo, Y S Kim
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ABSTRACT: The present study compared the efficacy and safety of mizoribine (MZR) with mycophenolate mofetil (MMF) in kidney transplantation. This multicenter, randomized clinical trial. Employed doses of study drug tailored to the immunosuppressive need. The primary efficacy outcome was the incidence of biopsy-proven acute rejection episodes (BPAR). The safety of the study drug was assessed using the incidences of adverse events, drug discontinuations, and abnormal laboratory results. The 7 (6.4%) BPARs above grade II were observed in the MZR group noninferior to the 2 (1.8%) in the MMF group (95% confidence interval, -0.007-0.097 > noninferiority limit [-0.2]). BPAR was significantly decreased in the MZR group after the dose change (17/41 [41.4%] vs 8/69 [11.6%]; P < .0001) and the incidence of BPAR was similar between the MZR and MMF groups after the dose change (P = .592). The uric acid level was significantly elevated in the MZR group (P = .002). In conclusion, the efficacy and safety of MZR were similar and statistically noninferior to MMF in combination therapy with tacrolimus.
Transplantation Proceedings 05/2013; 45(4):1481-1486. · 1.00 Impact Factor
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ABSTRACT: As global warming due to burning fossil fuels and natural resource depletion issues have emerged, the development of renewable energy sources such as photovoltaics (PV) has been brought to recent interest. Amongst the vast efforts to harvest and convert solar energy into electricity, module integrated converters (MIC) have become a worthy topic of research for small sized grid connected photovoltaic systems. Due to the required high boosting qualities, only a restricted amount of DC/DC converter topologies can be applied to MICs. This paper investigates the possibility of a tapped-inductor boost converter as a candidate for PV MICs. A novel tapped inductor boost converter with zero current switching (ZCS) is proposed. By deploying an auxiliary switch and an additional capacitor, the inductor current can be resonantly shaped to achieve ZCS. This results in reduced switching losses and enhanced overall efficiency. Also, the zero crossing point of the inductor current can easily be detected, which can help digitalize the converter controller. The operation and performance of the proposed converter is verified by a 200 W prototype converter.
Power Electronics and ECCE Asia (ICPE & ECCE), 2011 IEEE 8th International Conference on; 07/2011
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ABSTRACT: Half bridge magnetizing inductor (L<sub>m</sub>C) resonant dc/dc converter reduces the high current ripple of the output capacitor in LLC resonant converter maintaining narrow switching frequency and soft switching. This paper presents analysis and design of the half bridge L<sub>m</sub>C resonant converter. Using the extended describing function (EDF), the steady state analysis is carried out. Based on the results, the design considerations are suggested. The hardware prototype with 24-V/10-A is built and tested to verify the analysis results.
Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE; 03/2010
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ABSTRACT: A new energy-recovery circuit (ERC) for the plasma display panel (PDP) using a switched transformer is proposed. The proposed ERC is very cost effective due to the reduction of device count and circuit complexity such as highside gate drivers and diodes in the resonant path. Also, the leakage inductances of the transformers are used as resonant inductors for soft-switching operation of the main switches. The operation and performance of the proposed energy recovery circuit were validated through waveform and power efficiency measurement tests with prototype hardware in 200 kHz switching frequency.
IEEE Transactions on Consumer Electronics 12/2009; · 0.94 Impact Factor
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ABSTRACT: This paper presents the modeling and control of the single-phase photovoltaic grid-connected five-level cascaded H-bridge multilevel inverter. For the unity power factor, the proportional and integral current controller with the duty ratio feed-forward compensation method is used. And in order to track the maximum power point and to reduce the partial shading due to stacked photovoltaic modules, each DC voltage is stably controlled to their maximum power points by dedicated voltage controllers of each H-bridge module. The modeling approach and the control loop design method are provided in this paper. The proposed control schemes are validated from experimental results of the 2-kW prototype hardware.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: In this paper, a new zero current transition (ZCT) boost converter employing split inductors is proposed. Not only the main switch but also the auxiliary one achieves zero current turn-offs. Since the output diode does not suffer from excessive voltage stress, the proposed converter can be practically implemented as well. Additionally, the proposed converter does not have any auxiliary diode in resonant path. Mode analysis of steady-state operation is provided in detail. To confirm the validity of the proposed converter, its operation and performance are verified with 400 W prototype hardware.
Power Electronics and Motion Control Conference, 2009. IPEMC '09. IEEE 6th International; 06/2009
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ABSTRACT: Ever increasing demands for the development of compact, lightweight power supplies with more power density, higher efficiency and fast dynamics, often require power conversion through parallel connected converter. In order to realize the parallel module DC-DC converters, a current mode control scheme is essential for current sharing control among the modules. The general analog current mode control schemes, such as peak current mode control (PCM), charge current mode control (CC) and average current mode control (ACM), are reviewed and compared of their characteristics, in this paper. With recvent advances in digital systems, digital control has becmoe increeasingly visible even for high-frequency, low-to-medium power switching converters. However, digital current mode control for the parallel module converter is not easy because the switch or inductor current is a fast-changing waveform and the switching frequency is high. This paper introduces one of possible solutions for a digital current mode control employing nonlinear resistive current mode control as well.
Power Electronics and Motion Control Conference, 2009. IPEMC '09. IEEE 6th International; 06/2009
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ABSTRACT: The steady states and dynamics of a fuel cell system are influenced by both operating conditions and the frequency characteristics of electrochemical reactions in a cell. A dynamic model of a practical fuel cell system, based on an analytical theory and empirical data, is proposed. The model consists of three parts, such as an open circuit voltage model including fuel flow and reaction in channels, an equivalent circuit model caused by voltage losses of electrochemical reactions in a cell, and an air compressor model (a fuel supply model among auxiliary systems in a fuel cell system). It will be useful to design the power system and control strategy and to analyze the system dynamics in a fuel cell power system. The model is verified by experiments of 1kW PEM FC system. The dynamics of its OCV(open circuit voltage) by fuel flow effect, and the frequency characteristics of reaction dynamics in a cell are verified by experiments.
Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE; 03/2009
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ABSTRACT: This paper proposes a new recovery circuit for the capacitive load. Connecting the one side of windings to the load together, the resonant current is shared in both windings, hence the conduction loss is reduced. Simple circuit structure with transformer achieves the reduced the number of devices. Furthermore, the current-balance transformer enables ZVS operation of the switching device. To confirm the validity of the proposed circuit, prototype hardware with 12-inch mercury-free flat fluorescent lamp is experimented. The results are compared with a conventional energy-recovery circuit in perspective of luminance performances.
Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE; 03/2009
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ABSTRACT: This paper introduces an integrated AC-DC converter based on the parallel-series structure. The parallel structure is composed of two converters operate in continuous conduction mode. The parallel structure enhances the conversion efficiency and extends the power processing capability. The series connection of the output capacitors makes the output dc voltage to be regulated tightly. The operation principle and the control method with the small signal model are described. The operation of the proposed converter is experimentally verified by a 400 W prototype hardware.
Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE; 03/2009
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ABSTRACT: In this paper, a current controller design method for a DC-AC inverter in a grid-connected photovoltaic or fuel cell power conditioning system (PCS) is proposed. A state feedback current controller using a sine reference function tracking algorithm and I-P(Integral-Proportional) outer DC-link voltage controller using a 120 Hz notch filter are proposed to control the output current to be in-phase with the grid voltage and to regulate the input DC-link voltage. Since the analysis and design are performed in the time domain using the state equations, the current loop controller can be systematically designed for the required system specification using the pole placement technique. Also, the 120 Hz notch filter for DC-link voltage regulation can enhance the dynamic performance by increasing the voltage loop bandwidth. The design guideline of each controller is provided using the stability analysis. For a design example, the prototype two-stage PCS hardware with a TMS320F2812 DSP and a real 200 W solar array has been experimented to validate the proposed digital control scheme.
Applied Power Electronics Conference and Exposition, 2009. APEC 2009. Twenty-Fourth Annual IEEE; 03/2009
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ABSTRACT: The heartbeat class detection of the electrocardiogram is important in cardiac disease diagnosis. For detecting morphological QRS complex, conventional detection algorithm have been designed to detect P, QRS, T wave. However, the detection of the P and T wave is difficult because their amplitudes are relatively low, and occasionally they are included in noise. We applied two morphological feature extraction methods: higher-order statistics and Hermite basis functions. Moreover, we assumed that the QRS complexes of class N and S may have a morphological similarity, and those of class V and F may also have their own similarity. Therefore, we employed a hierarchical classification method using support vector machines, considering those similarities in the architecture. The results showed that our hierarchical classification method gives better performance than the conventional multiclass classification method. In addition, the Hermite basis functions gave more accurate results compared to the higher order statistics.
Computers in Cardiology, 2008; 10/2008
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ABSTRACT: Various power system structures are simulated and analyzed in order to improve the power and energy performance of the Fuel Cell Hybrid Electric Vehicle (FCHEV) using a supercapacitor. In this paper, an optimization of the existing Type E structure, hereafter called buck-boost Type E, and its control strategy are proposed to control the power system of the FCHEV and to operate the fuel cell in the efficient range. The performances of the buck-boost Type E are compared with those of the conventional system structures by simulating acceleration, the Japan 10-15 driving cycle, and the FTP 75 driving cycle tests. The results are verified through scaled down experimental equipment.
Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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ABSTRACT: Accurate information regarding the maximum available pulse current can help to determine the power capability of the battery and allow the battery to be operated within the safe operating voltage range. However, although estimation methods of the maximum available pulse current have been developed, they have the drawback of variation in the resistance inside the batteries. In this paper, the state of charge (SOC) and resistance of the battery are estimated from the dual extended Kalman filter (dual EKF). Furthermore, the lumped resistance, which represents the impedance inside the battery during the predefined time, is calculated using an easy numerical calculation based on the estimated values.
Applied Power Electronics Conference and Exposition, 2008. APEC 2008. Twenty-Third Annual IEEE; 03/2008
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ABSTRACT: In this paper, a simple digital control scheme for the parallel module converter is proposed using a digital state feedback control method. In this approach, the large signal average converter model is used to derive the robust tracking control algorithm of the state feedback controller instead of using the small signal modeling approach. The proposed control system can precisely achieve the interleaved current sharing and the output voltage regulation, and can achieve the systematical controller design for digital implementation using the pole placement technique. Also, a dynamic gain feed-forward control method using the operation point of the converter is proposed to improve the audio susceptibility. For a design example, a parallel module bus regulator system in the low-earth-orbit (LEO) satellite power system application, which has an input voltage step change, is implemented using a TMS320F2812 DSP.
Applied Power Electronics Conference and Exposition, 2008. APEC 2008. Twenty-Third Annual IEEE; 03/2008
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ABSTRACT: In power processing applications, switching power converter research have focused on the potential feasibility of piezoelectric transformers (PTs) for cost competitiveness, size effect and good EMI characteristics. However, the PT has a voltage conversion limit because of its physical dimensions and manufacturing procedures. The fact can be a restriction to a circuit engineer facing new application design with PT because of its in adaptivity to extreme conversion ratios of emerging applications. In order to overcome this problem, tapped inductor is introduced. The tapped inductor can transform the input voltage into the adequate level by its own turn-ratio. Consequently, this tapped inductor scheme with piezoelectric transformer makes it possible to obtain both PT's advantages and conversion gain adjustment without part-count increase. For the proposed converter evaluation, this paper provides the operation analysis and design procedures of the converter, and presents the experimental verification with a 20-W hardware prototype DC/DC converter as well. Finally, topology extension is also presented by combining tapped-inductor with other conventional resonant converters with piezoelectric transformer.
Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007
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ABSTRACT: The open circuit voltage (OCV) is widely used to estimate the state of charge (SOC) in many SOC estimation algorithms. But the relationship between the OCV and SOC can not be exactly same for all batteries. Because the conventional OCV-SOC differs between batteries, there is a problem in that the OCV-SOC data should be measured to accurately estimate the SOC in different batteries. Therefore, the conventional OCV- SOC should be modified. In this paper, a new OCV-SOC that is independent of the battery conditions is proposed. Thus, problems resulting from the defects of the EKF can be avoided by preventing the OCV-SOC data from varying. In this paper, the SOC and battery capacity are estimated using the dual EKF with the proposed OCV-SOC.
Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007
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ABSTRACT: In this paper, a digital control approach for the parallel interleaved solar array regulator (SAR) is proposed. The proposed control scheme achieves stable operation in the entire region of the solar array (SA). Additionally, by making the effective load characteristic of the SAR seen by the SA as a resistive load sink, the current sharing among the converter modules is possible. Also, this method can be applied to conventional parallel buck and boost converters. The small signal analysis with the digital sampling effect is performed. A SAR system that consists of two 100 W parallel module buck converters with a TMS320F2812 DSP has been experimented using a real 200 W solar array to validate the proposed digital control scheme
Power Electronics Specialists Conference, 2006. PESC '06. 37th IEEE; 07/2006
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ABSTRACT: In general, the current mode controller is used to share the current in the parallel operation of a power stage. However, the parallel operation of the solar array regulator system (SAR) should be carefully designed because of the nonlinear characteristic solar array (SA), such as a negative dynamic resistance (rs) and a SA V-I curve. In the post works, the detailed analysis of stability and dynamics of the SAR system employing current mode control has been not carried out. For these works, the SAR system employing current mode control was analyzed and compared using both large and small signal approaches. From the results of analysis, the stability problems and design issues of the SAR using current mode control for parallel operation were investigated. Finally, the considered problems and issues were tested for the verification through experiments
Power Electronics Specialists Conference, 2006. PESC '06. 37th IEEE; 07/2006
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ABSTRACT: An adaptive frequency control method for AC/DC adapters using a piezoelectric transformer (PT) is proposed. It combined the conventional frequency method and frequency tracking for the PT such that the main frequency control loop to regulate the output voltage is compensated by the phase loop in order to adaptively change the operating frequency range. This method provides PT gain peak tracking to tackle the resonant frequency drift problems common in the PT according to the temperature changes and sample variations, and consequently makes more efficient and stable driving of the PT possible, thus improving the overall productivity. The validity of the proposed algorithm is verified by a constructed 40W AC/DC adapter hardware using a PT
Applied Power Electronics Conference and Exposition, 2006. APEC '06. Twenty-First Annual IEEE; 04/2006
