Active Balancing of Li-Ion Battery Cells Using Transformer as Energy Carrier

Lee, Kyung-Min,Lee, Sang-Won,Choi, Yoon-Geol,Kang, Bongkoo Institute of Electrical and Electronics Engineers 2017 IEEE transactions on industrial electronics Vol.64 No.2

<P>A circuit for balancing Li-ion battery cells is proposed. This circuit requires one small transformer and N + 3 bilateral switches to equalize the charging states of N serially connected battery cells. The transformer works as an energy carrier, and the switches select two unbalanced cells that require an energy transfer from one to the other cell. The circuit was tested for a 12-cell Li-ion battery under static, cyclic, and dynamic charging/discharging conditions. Under static condition, the power-transfer efficiency was measured as 80.4% at a balancing power of 0.78W; two 4400-mA . h battery cells at a state of charge (SOC) = 70 and 80% were equalized after 78 min. The results of cyclic and dynamic charging/discharging conditions show that the circuit is appropriate for balancing the Li-ion battery cells for vehicles and energy storage systems.</P>

Modularized Design of Active Charge Equalizer for Li-Ion Battery Pack

Lee, Sang-Won,Lee, Kyung-Min,Choi, Yoon-Geol,Kang, Bongkoo IEEE 2018 IEEE transactions on industrial electronics Vol.65 No.11

<P>A modularized design of an active charge equalizer and a charge equalization algorithm for a Li-ion battery pack are proposed in this paper. The equalizer consists of one module-balancing circuit and <TEX>$M$</TEX> cell-balancing circuits, where <TEX>$M$</TEX> is the number of modules in the battery pack. Each balancing circuit uses an inductor that is placed in a bridge of four bidirectional switches and works as an energy carrier, and uses a cell/module access network that enables energy transfer from one cell/module to another cell or module. The charge equalization between modules can be performed simultaneously with that between cells, so the proposed circuit can significantly reduce the time required to equalize the charges of all cells in the battery pack. The proposed circuit was tested under various charging/discharging conditions for a battery pack composed of four serially connected modules, with four serially connected cells per module. Experimental results show that the proposed circuit and algorithm comprise a good solution to balance a Li-ion battery pack.</P>

Increase in Power Conversion Efficiency of Bidirectional DC–DC Converter Using 1:1 Transformer and Pulse-Frequency Modulation Control

Choi, Yoon-Geol,Lee, Sang-Won,Lee, Hyeon-Seok,Lee, Su-Chang,Kang, Bongkoo Institute of Electrical and Electronics Engineers 2018 IEEE transactions on power electronics Vol.33 No.12

<P>This paper proposes a circuit structure of bidirectional dc–dc converter. This structure uses two switches, two capacitors, a 1:1 transformer, and a control circuit for pulse-frequency modulation. The windings of the transformer are connected in a series-aiding configuration to reduce current ripples and to increase power conversion efficiency <TEX>$\eta _{e}$</TEX>. The capacitors and the leakage inductance of the transformer provide soft-switching conditions. When the proposed converter was designed to operate at a switching frequency of 110–240 kHz, input/output voltages of 100–400 V, and output power <TEX>$P_{o}$</TEX> of 30–300 W, <TEX>$\eta _{e}$</TEX> was ≥97% for <TEX>$P_{o}\,\geq \,{\text{90}}\,{\text{W}}$</TEX> and 93.5% at <TEX>$P_{o}\,= \,{\text{30}}\,{\text{W}}$</TEX>. Experimental results show that the proposed converter is suitable for use in photovoltaic power conversion systems and energy storage systems.</P>

Quasi-Resonant Passive Snubber for Improving Power Conversion Efficiency of a DC–DC Step-Down Converter

Lee, Sang-Hoon,Choe, Hyung-Jin,Kang, Bongkoo Institute of Electrical and Electronics Engineers 2018 IEEE transactions on power electronics Vol.33 No.3

<P>A quasi-resonant passive snubber for the conventional dc-dc step-down converter is proposed. The snubber uses six passive components to achieve a zero-current turn-ON and zero-voltage turn-OFF of the switch, and to suppress the reverse recovery current of diode. At input voltage of 200 V, output voltage of 100 V, output power of 300 W, and switching frequency of 190 kHz, the snubber increased the power conversion efficiency eta(e) by 2.8% and stabilized the temperature of MOSFET switch at similar to 68 degrees C. The snubber worked well for both MOSFET and insulated gate bipolar transistor (IGBT) switches without increasing the voltage stress. These experimental results show that the proposed snubber is very helpful for improving eta(e) of a dc-dc step-down converter that operates at a high frequency.</P>

High-Efficiency Asymmetric Forward-Flyback Converter for Wide Output Power Range

Lee, Hyeon-Seok,Choe, Hyung-Jin,Ham, Seok-Hyeong,Kang, Bongkoo IEEE 2017 IEEE TRANSACTIONS ON POWER ELECTRONICS - Vol.32 No.1

<P>This paper proposes an asymmetric forward-flyback dc-dc converter that has high power-conversion efficiency eta(e) over a wide output power range. To solve the problem of ringing in the voltage of the rectifier diodes and the problem of duty loss in the conventional asymmetric half-bridge (AHB) converter, the proposed converter uses a voltage doubler structure with a forward inductor L-f in the second stage, instead of using the transformer leakage inductance, to control output current. Lf resonates with the capacitors in the voltage doubler to achieve a zero-voltage turn-on of switches and a zero-current turn-off of diodes for a wide output power range. The proposed converter could operate at a wider input voltage range than the other AHB converters. eta(e) was measured as 95.9% at output power P-O = 100 W and as 90% at P-O = 10 W, when the converter was operated at input voltage 390 V, output voltage 142 V, and switching frequency 100 kHz.</P>

A Comparative Study of Involvement and Motivation among Casino Gamblers

이충기,BongKoo Lee,Bo Jason Bernhard,이태경 대한신경정신의학회 2009 PSYCHIATRY INVESTIGATION Vol.6 No.3

Objective: The purpose of this paper is to investigate three different types of gamblers (which we label “non-problem”, “some problem”, and “probable pathological gamblers”) to determine differences in involvement and motivation, as well as differences in demographic and behavioral variables. Methods: The analysis takes advantage of a unique opportunity to sample on-site at a major casino in South Korea, and the resulting purposive sample yielded 180 completed questionnaires in each of the three groups, for a total number of 540. Factor analysis, analysis of variance (ANOVA) and Duncan tests, and Chi-square tests are employed to analyze the data collected from the survey. Results: Findings from ANOVA tests indicate that involvement factors of importance/self-expression, pleasure/interest, and centrality derived from the factor analysis were significantly different among these three types of gamblers. The “probable pathological” and “some problem” gamblers were found to have similar degrees of involvement, and higher degrees of involvement than the non-problem gamblers. The tests also reveal that motivational factors of escape, socialization, winning, and exploring scenery were significantly different among these three types of gamblers. When looking at motivations to visit the casino, “probable pathological” gamblers were more likely to seek winning, the “some problem” group appeared to be more likely to seek escape, and the “non-problem” gamblers indicate that their motivations to visit centered around explorations of scenery and culture in the surrounding casino area. Conclusion: The tools for exploring motivations and involvements of gambling provide valuable and discerning information about the entire spectrum of gamblers. Objective: The purpose of this paper is to investigate three different types of gamblers (which we label “non-problem”, “some problem”, and “probable pathological gamblers”) to determine differences in involvement and motivation, as well as differences in demographic and behavioral variables. Methods: The analysis takes advantage of a unique opportunity to sample on-site at a major casino in South Korea, and the resulting purposive sample yielded 180 completed questionnaires in each of the three groups, for a total number of 540. Factor analysis, analysis of variance (ANOVA) and Duncan tests, and Chi-square tests are employed to analyze the data collected from the survey. Results: Findings from ANOVA tests indicate that involvement factors of importance/self-expression, pleasure/interest, and centrality derived from the factor analysis were significantly different among these three types of gamblers. The “probable pathological” and “some problem” gamblers were found to have similar degrees of involvement, and higher degrees of involvement than the non-problem gamblers. The tests also reveal that motivational factors of escape, socialization, winning, and exploring scenery were significantly different among these three types of gamblers. When looking at motivations to visit the casino, “probable pathological” gamblers were more likely to seek winning, the “some problem” group appeared to be more likely to seek escape, and the “non-problem” gamblers indicate that their motivations to visit centered around explorations of scenery and culture in the surrounding casino area. Conclusion: The tools for exploring motivations and involvements of gambling provide valuable and discerning information about the entire spectrum of gamblers.

Effect of off-State Stress and Drain Relaxation Voltage on Degradation of a Nanoscale nMOSFET at High Temperature

Nam-Hyun Lee,Dohyun Baek,Bongkoo Kang IEEE 2011 IEEE electron device letters Vol.32 No.7

<P>This paper investigates the degradation mechanism of a nanoscale n-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) that is subjected to off-state stress at high temperature and the impact of stress-induced defects on threshold voltage <I>V</I><SUB>th</SUB> during drain relaxation. Experimental results indicate that acceptor-like interface traps <I>N</I><SUB>it</SUB>, positive oxide charges <I>Q</I><SUB>ox</SUB>, and neutral electron traps were generated by the off-state stress. Although the <I>N</I><SUB>it</SUB> generated by the off-state stress caused an increase in <I>V</I><SUB>th</SUB>, it did not influence <I>V</I><SUB>th</SUB> during drain relaxation at a positive gate voltage. Drain relaxation filled the neutral electron traps and neutralized positive <I>Q</I><SUB>ox</SUB>'s, which increased <I>V</I><SUB>th</SUB> and decreased the off-current significantly. This new observation suggests that the off -state stress-induced defects in a nanoscaled nMOSFET should be seriously taken in evaluating the reliability of inverter circuits.</P>

Active Cell Balancing of Li-Ion Batteries Using <tex> $LC$</tex> Series Resonant Circuit

Kyung-Min Lee,Yoo-Chae Chung,Chang-Hyeon Sung,Bongkoo Kang Institute of Electrical and Electronics Engineers 2015 IEEE transactions on industrial electronics Vol. No.

<P>This paper proposes a new active cellbalancing method for Li-ion batteries. It uses an LC series resonant circuit as an energy carrier, which transfers the balancing energy directly from the highest charged cell to the lowest charged cell. The method requires N + 5 bilateral switches and one LC resonant circuit, where N is the number of cells in the string of batteries. The balancing speed is improved by allowing energy transfer between any two cells in the battery string, and power consumption for balancing is reduced by operating all switches in the circuit at a zero-current switching condition. An experimental cellbalancing circuit for a 12-cell Li-ion battery string shows that fast and transformerless balancing is possible using the proposed method. Measured power transfer efficiencies were 93.2% and 78.9% at balancing powers of 0.56 and 1.94 W, respectively.</P>

Experimental Method to Extract Effective Channel Length of Nanoscale n-MOSFETs

Nam-Hyun Lee,Hwan-Wook Choi,Heesung Kang,Bongkoo Kang IEEE 2009 IEEE electron device letters Vol.30 No.11

<P>An experimental method of extracting the effective channel length L<SUB>eff</SUB> from measured gate tunneling current (I<SUB>g</SUB>) of nanoscale n-MOSFETs is proposed. The tunneling current from gate to the source and drain (I<SUB>gsd</SUB>) was measured while applying a reverse bias to the substrate, and it was corrected for the depletion effect of the source/drain junctions. The gate tunneling current to the substrate (I<SUB>gc</SUB>) was obtained by subtracting I<SUB>gsd</SUB> from I<SUB>g</SUB>. L<SUB>eff</SUB> was calculated using a linear extrapolation of the I<SUB>gc</SUB> versus gate length plot. The proposed method is a very simple and quite accurate method of extracting L<SUB>eff</SUB> which does not require any additional assumptions and parameter extraction.</P>

Off-Time Control of <i>LLC</i> Resonant Half-Bridge Converter to Prevent Audible Noise Generation Under a Light-Load Condition

Yoon, Ho-Young,Lee, Hyeon-Seok,Ham, Seok-Hyeong,Choe, Hyung-Jin,Kang, Bongkoo Institute of Electrical and Electronics Engineers 2018 IEEE transactions on power electronics Vol.33 No.10

<P>This paper presents a control method that can prevent audible noise generation in an <I>LLC</I> resonant half-bridge dc–dc converter under a light-load condition, while achieving the same input voltage range and power-conversion efficiency <I>η<SUB>e</SUB></I> as the burst-control method that generates an audible noise. The proposed method reduces switching and conduction losses at light load by skipping several pairs of switch-control pulses, while varying the switching frequency less than the normal-control method does. This skip-control method enables the <I>LLC</I> resonant converter to have a large magnetizing inductance, and to have high <I>η<SUB>e</SUB></I> over a wide range of load variation. At an input voltage of 385 V, an output voltage of 24 V, and a resonant frequency of 180 kHz, the proposed method achieved <I>η <SUB>e</SUB></I> ≥ 85.46% for an output power range of 7.2–360 W; the highest <I>η<SUB>e </SUB></I> was 96.08% at <TEX>$P_o$</TEX> = 336 W.</P>