Byoung-Kuk Lee

A symmetric carrier technique of CRPWM for voltage balance method of flying-capacitor multilevel inverter

This paper presents a simple carrier symmetric method for the voltage balance of flying capacitors in flying-capacitor multilevel inverters. The carrier-redistribution pulsewidth-modulation (CRPWM) method was reported as a solution for the voltage balance but it has a drawback at the transition of voltage level. To achieve the voltage balance of flying capacitors, the utilization of each carrier must be balanced during a half-cycle of the switching period such as phase-shifted PWM. However, the CRPWM method causes the fluctuation of flying-capacitor voltages because the balanced utilization of carriers is not achieved. Moreover, it does not consider that the load current change has an influence on flying-capacitor voltages by assuming that the current flows into the load. Therefore, the charging and discharging quantities of flying-capacitor voltages do not become zero during the switching period. To overcome the drawbacks of CRPWM, it is modified by the technique where carriers of each band are disposed of symmetrically at every fundamental period. Firstly, the CRPWM method is reviewed and the theory on voltage balance of flying capacitors is analyzed. The proposed method is introduced and is verified through simulation and experimental results.

An active clamping current-fed half-bridge converter for fuel-cell generation systems

In this paper, a new active clamping current-fed half-bridge converter has been proposed, which is suitable for fuel cell based power generation systems. The proposed converter has outstanding advantages over the conventional dc-dc converters with respect to high efficiency, high power density, and high component utilization. In special, the proposed converter has predominant high boosting output voltage and high efficiency characteristics under the inherently severe low output voltage of the fuel cell through the overall load conditions. Moreover, the developed converter has been experimentally tested with the help of a fuel cell simulator, which is developed by Sungkyunkwan Univ. and can generate the V-I characteristics of polymer electrolyte membrane fuel cell (PEMFC), so that the performance of the proposed converter could be effectively examined and the validity of the converter could be verified.

An Optimal Design Methodology of an Interleaved Boost Converter for Fuel Cell Applications

In this paper, an optimal selection methodology for the number of phases will be proposed for an interleaved boost converter (IBC). Also, the analysis of the input current ripple according to CCM and DCM is carried out. The proposed design methodology will be theoretically analyzed, and its validity verified by simulation as well as with experimental results. Moreover, a comparison of cost and efficiency based on a 600W laboratory prototype using the Ballard NEXA 1.2kW PEMFC system is demonstrated.

Optimization of Powder Core Inductors of Buck-Boost Converters for Hybrid Electric Vehicles

In this paper, the characteristics of Mega-Flux®, JNEX-Core®, amorphous and ferrite cores are compared for the inductor of buck-boost converter for Hybrid Electric Vehicles (HEVs). The core losses are analyzed at the condition of 10kHz sine wave excitations. Permeability fluctuations vs. temperature and magnetizing force will be analyzed and discussed. Under the specifications of buck-boost converter for 20kW THS-II, the power inductor will be designed with Mega-Flux®, JNEX-Core® and the informative simulation results will be provided with respect of dc bias characteristics, core and copper losses.

Dynamic analysis of toroidal winding switched reluctance motor driven by 6-switch converter

This paper presents a characteristic analysis of a wye-connected toroidal winding switched reluctance motor (TSRM) driven by 6-switch converter. The voltage equations considering both TSRM and the drive topology are introduced for steady state dynamic simulation. Inductances, which mainly affect motor characteristics, are calculated by finite element analysis and stored in a look-up table. During the dynamic analysis with the proposed voltage equations, the inductances are fitted using a spline interpolation. The dynamic analysis results are compared with those of conventional winding SRM which are already examined for verification of analysis method

A new half-bridge inverter topology with active auxiliary resonant circuit using insulated gate bipolar transistors for induction heating applications

A new IGBT half-bridge inverter topology with active auxiliary resonant circuit (A/sup 2/RC) is proposed. The A/sup 2/RC permits the large lossless turn-off snubber capacitor to be successfully used. Therefore, it makes efficient use of IGBT in the high power and high frequency induction heating system. The operation principle and the design procedures of the proposed A/sup 2/RC are described in detail and the validity is verified by testing on a 55 kHz IGBT half-bridge inverter for an induction heating cooking system rated at 1.3 kW.

An improved full-bridge zero-voltage-transition PWM DC/DC converter with zero-voltage/zero-current switching of the auxiliary switches

In this paper, a novel full-bridge (FB) zero-voltage-transition (ZVT) pulsewidth modulation (PWM) DC/DC converter topology is proposed. The proposed FB-ZVT PWM DC/DC converter has zero-voltage switching (ZVS) of main switches for the entire line and load range and an advantage of achieving ZVS and zero-current switching of the auxiliary switches using the auxiliary network. The auxiliary network is simply composed of a saturable inductor, auxiliary capacitors, and auxiliary diodes. With the help of the proposed auxiliary network, the improved FB-ZVT PWM DC/DC converter has such characteristics as higher overall system efficiency and better utilization of the auxiliary switches compared with the conventional FB-ZVT PWM DC/DC converter. The operation principles are explained in detail and the several interesting simulation and experimental results verify the validity of the proposed circuit with an 83 kHz 1 kW prototype converter using insulated gate bipolar transistors.

Analysis of single-phase line-start permanent-magnet motor considering iron loss and parameter variation with load angle

This paper presents analysis and design methodology of single-phase line-start permanent-magnet synchronous (LSPM) motors. The d-q-axes inductances of LSPM motors have a nonlinear variation according to the current and the load angle. The variation of d-q-axes inductances due to load angle is calculated by finite-element method in steady state. Iron loss is analyzed considering the harmonics of the flux density waveforms using iron loss curves. The validity of the presented analysis method considering the variation of the d-q-axes inductances is verified by comparison with experimental results.

Prediction of torque characteristic on barrier-type SRM using stochastic response surface methodology combined with moving least square

This paper describes a design of switched reluctance motors having barriers in the rotor. The shape and dimensional tolerance of the rotor barrier directly affect the electrical performances of the motor, such as torque characteristics. Therefore, a manufacturing design guide for the barrier is desirable and it can be accomplished by the prediction of torque characteristics of the motor. In this paper, stochastic response surface methodology and moving least square method are combined together in order to much more precisely predict the torque characteristics.

Does osteoporosis have a negative effect on the functional outcome of an osteoporotic distal radial fracture treated with a volar locking plate

We performed a retrospective study to determine the effect of osteoporosis on the functional outcome of osteoporotic distal radial fractures treated with a volar locking plate. Between 2009 and 2012 a total of 90 postmenopausal women with an unstable fracture of the distal radius treated with a volar locking plate were studied. Changes in the radiological parameters of 51 patients with osteoporosis (group 1, mean age 66.9, mean T-score -3.16 (sd 0.56)) were not significantly different from those in 39 patients without osteoporosis (group 2, mean age 61.1, mean T-score -1.72 (sd 0.57)). The mean Disabilities of the Arm, Shoulder and Hand (DASH) score at final follow-up was 11.5 (sd 12.2) in group 1 and 10.5 (sd 13.25) in group 2. The mean modified Mayo wrist score at final follow-up was 79.0 (sd 14.04) in group 1 and 82.6 (sd 13.1) in group 2. However, this difference was not statistically significant (p = 0.35 for DASH score, p = 0.2 for modified Mayo wrist score). Univariable and multivariable logistic regression analysis showed that only the step-off of the radiocarpal joint was related to both a poor DASH and modified Mayo wrist score. Pearsons correlation coefficient showed a weak negative relationship only between the T-score and the change in volar tilt (intraclass coefficient -0.26, p = 0.02). We found that osteoporosis does not have a negative effect on the functional outcome and additional analysis did not show a correlation between T-score and outcome.