Shin-Young Cho

Interleaved Buck Converter Having Low Switching Losses and Improved Step-Down Conversion Ratio

This paper proposes a new interleaved buck converter (IBC) having low switching losses and improved step-down conversion ratio, which is suitable for the applications where the input voltage is high and the operating duty is below 50%. It is similar to the conventional IBC, but two active switches are connected in series and a coupling capacitor is employed in the power path, such as Cuk, Sepic, and Zeta converters. The proposed IBC shows that since the voltage stress across all the active switches is half of the input voltage before turn-on or after turn-off when the operating duty is below 50%, the capacitive discharging and switching losses can be reduced considerably. This allows the proposed IBC to have higher efficiency and operate with higher switching frequency. In addition, the proposed IBC has a higher step-down conversion ratio and a smaller output current ripple compared with a conventional IBC. The features, operation principles, and relevant analysis results of the proposed IBC are presented in this paper. The validity of this study is confirmed by the experimental results of prototype converters with 150-200 V input, 24 V/10 A output.

A New Standby Structure Based on a Forward Converter Integrated With a Phase-Shift Full-Bridge Converter for Server Power Supplies

This paper presents a new standby structure where a forward converter is integrated with a dc-dc phase-shift full-bridge (PSFB) converter for server power supplies. While a typical standby structure consists of an independent flyback converter, the proposed standby structure is integrated with one leg of the dc-dc PSFB converter. Its main advantages are that the voltage across a standby switch is clamped at the link voltage across the link capacitor and that the standby switch achieves zero-voltage switching over entire load range. The validity of the proposed standby structure is confirmed by the experimental results from 12 V/58 A for the dc-dc output prototype and 11.5 V/1.5 A for the standby output prototype.

Three-Level Resonant Converter With Double

A new resonant converter having low voltage stress and nearly constant efficiency against line variation for high- and wide-input-voltage applications is presented in this paper. It is similar to a three-level zero-voltage-switching pulsewidth modulation converter (TL ZVS PWMC) with two flying capacitors. In the proposed converter, however, two flying capacitors are used as the resonant capacitors, and the output voltage regulation is achieved by frequency modulation. The main advantages of the proposed converter are that, since the sum of the voltages of two resonant capacitors is constant and is equal to half of the input voltage, the voltage across each switch clamps to half of the input voltage and keeps the balance. Moreover, all main switches and rectifier diodes are softly switched under full-line and full-load conditions, and high efficiency can be constantly achieved over a wide input voltage range. These advantages solve the drawbacks on TL ZVS PWMCs. The features, operation principles, and relevant analysis results over a wide input voltage range of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results of a prototype converter with 400-600-V input, 48-V/10-A output, and 200-kHz resonant frequency. The experimental results show that the maximum efficiency of the proposed converter is 95.08% under a full-load and a 600-V input and slightly varies across the 400-600-V input voltage range.

LLC

In the lithium-ion batteries for electric vehicle applications, the charge equalizer is required to enhance life time and guarantee safety. For efficient charge equalization, a cell voltage sensing module should be used. However, the cost of the sensing module is relatively high. Thus, to achieve higher equalization performance without the cell voltage sensing module, a new automatic charge equalizer based on regulated voltage source is proposed. A fast regulated voltage source with average voltage of the batteries is implemented by a bidirectional dc-dc converter. The charge equalization can be automatically achieved by periodic connections between battery cells and regulated voltage source without the sensing module. The high equalization performance can be obtained by proposed reference voltage modulation and advanced skip mode. The operational principles and design considerations of the proposed equalizer are presented and equalization performance is verified by the prototype with 7Ah lithium-ion batteries.

Resonant Tanks for High-Input-Voltage Applications

In rechargeable batteries such as lithium-ion, the charge equalization circuit is necessary to enhance life time and guarantee safety. For fast charge equalization, the equalization current is increased as increase of battery capacity, and thus the burden of power semiconductors is increased. Therefore this paper proposes new selective charge equalization circuit with small number of power semiconductors. In the proposed charge equalizer, power diode of transformer secondary side is eliminated and power MOSFET of transformer secondary side is controlled by an auxiliary transformer. By using current unbalance caused by effective voltage mismatching, the charge equalization can be achieved without current blocking switches. In this paper, the operational principle of the proposed equalizer is presented and principle of current unbalance is analyzed. To confirm the validity of the proposed scheme, a prototype of 8 lithium-ion batteries is implemented and experimental results are presented.

Automatic charge equalization circuit based on regulated voltage source for series connected lithium-ion batteries

New phase-shift pulse width modulation (PWM) converters with a wide zero voltage switching (ZVS) range for the slim sustain power module of over 63-in plasma display panel (PDP) are proposed in this paper. Each proposed converter is composed of two symmetric half-bridge converters (TSHBCs) that are placed in parallel on the primary side and are driven in a phase shifting manner. Two power transformers are connected in series on the secondary side. All the switches in the proposed converters can be turned on with ZVS under all load conditions, while the conduction loss caused by the assistant current source extending the ZVS range can be minimized. Moreover, because the turns ratio of the transformers can be designed to be better than that of the counterparts, the voltage stress across the secondary rectifier diode and the primary conduction loss can be reduced. A low-profile design is also achieved due to the use of the two small-sized transformers, which results in a slim power supply. In this paper, the circuit configurations, operation principle, relevant analysis results, and design example of the proposed converters are presented. Experimental results demonstrate that the proposed converters can achieve a significant improvement in the efficiency for a prototype converter realized with the specification of 80-in PDP sustain power module (320-385 Vdc input, 205 Vdc/5 A output).

A cell selective charge equalizer using multi-output converter with auxiliary transformer

Sinusoidal ripple-current (SRC) charging is a new charging technique that the sinusoidal current superposed with the direct current (dc) charges the battery at the frequency where the battery-alternating current (ac)-impedance reaches a minimum. However, in analyzing the effect on the SRC charging, the dc component of the SRC has not been considered until now. This paper presents a battery impedance analysis when the dc component is considered in the SRC charging. The real battery impedance is analyzed by using an electrical second-order RC battery model and overpotential voltage waveforms. The result shows that the real battery impedance is not minimized at the minimum-ac-impedance frequency. Due to this, in comparison with the constant current (CC)-constant voltage (CV) charging, the charging time, charging amount, and charging efficiency of the SRC-CV charging are not significantly different from those of the CC-CV charging. Rather, due to the ac component, the SRC-CV charging deteriorates the RMS current and maximum rising temperature by 22.5% and 18%, respectively. Also, this paper presents that the CC-CV charging using a slightly larger dc is more suitable for practical applications, since its current stress, charging time, and maximum rising temperature are improved by 2%, 9.7%, and 8.5%, respectively, in comparison with the SRC-CV charging.

Improved Phase-Shift PWM Converter for Larger Sized PDP Slim Sustain Power Module

In this paper, a phase-shifted dual H-Bridge converter is analyzed and evaluated. The proposed topology is composed of two symmetric half-bridge inverters (TSHBIs) that are placed in parallel on the primary side and are driven in a phase-shifting manner to regulate the output voltage. At the rectifier stage, a center-tap-type rectifier with two additional low-current-rated diodes is employed. This structure allows the proposed converter to have the advantages of a wide ZVS range, no problems related to duty-cycle loss, no circulating current, and the reduction of secondary-voltage oscillation and overshoot. Besides, the output filters size becomes smaller compared to the conventional phase-shift full-bridge converters. This paper describes the operation principle of the proposed converter and the analysis and design consideration in depth. A 1-kW 320-385-V input 50-V output laboratory prototype operating at a 100-kHz switching frequency is designed, built, and tested to verify the effectiveness of the presented converter.

Battery Impedance Analysis Considering DC Component in Sinusoidal Ripple-Current Charging

The charging characteristics of non-radiative wireless power link (NWPL) have been well unknown. This paper shows that series-series (SS) compensated NWPL system behaves as a constant current power supply when the inverter operates at the resonant frequency of self-inductance and resonant capacitors.

Phase-shifted dual H-Bridge converter with a wide ZVS range and reduced output filter

A new interleaved buck converter (IBC) having low switching losses and improved step-down conversion ratio is proposed in this paper. It is similar to a conventional IBC, but two active switches are connected in series, and a coupling capacitor is employed in the power path, like Cuk, Sepic, and Zeta converters. The proposed IBC shows that since the voltage stress across all active switches is half of the input voltage before turn-on or after turn-off, the capacitive discharging and switching losses can be reduced considerably. This allows the proposed IBC to have higher efficiency and be operated at higher switching frequency. In addition, the proposed IBC has higher step-down conversion ratio and smaller output current ripple than a conventional IBC. The features, operation principles, and relevant analysis results of the proposed IBC are presented in this paper. The validity of this study is confirmed by the experimental results of prototype converters with 150–200V input, 24V/10A output.