Il-Oun Lee

Analysis and Design of a Three-Level LLC Series Resonant Converter for High- and Wide-Input-Voltage Applications

In this paper, the analysis and design of a three-level LLC series resonant converter (TL LLC SRC) for high- and wide-input-voltage applications is presented. The TL LLC SRC discussed in this paper consists of two half-bridge LLC SRCs in series, sharing a resonant inductor and a transformer. Its main advantages are that the voltage across each switch is clamped at half of the input voltage and that voltage balance is achieved. Thus, it is suitable for high-input-voltage applications. Moreover, due to its simple driving signals, the additional circulating current of the conventional TL LLC SRCs does not appear in the converter, and a simpler driving circuitry is allowed to be designed. With this converter, the operation principles, the gain of the LLC resonant tank, and the zero-voltage-switching condition under wide input voltage variation are analyzed. Both the current and voltage stresses over different design factors of the resonant tank are discussed as well. Based on the results of these analyses, a design example is provided and its validity is confirmed by an experiment involving a prototype converter with an input of 400-600 V and an output of 48 V/20 A. In addition, a family of TL LLC SRCs with double-resonant tanks for high-input-voltage applications is introduced. While this paper deals with a TL LLC SRC, the analysis results can be applied to other TL LLC SRCs for wide-input-voltage applications.

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.

Soft-Switching DC/DC Converter With a Full ZVS Range and Reduced Output Filter for High-Voltage Applications

A new soft-switching dc/dc converter, which can solve the drawbacks of existing phase-shifted full-bridge converters such as narrow zero-voltage-switching (ZVS) range, large circulating current, large duty-cycle loss, and a large output filter in high-voltage applications, is proposed in this paper. The proposed converter is composed of two symmetric half-bridge inverters 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, two full-bridge rectifiers sharing two low-current-rating diodes are employed. This structure allows the proposed converter to have the advantages of a full ZVS range, no problems related to duty-cycle loss, no circulating current, and a significantly reduced output filter. In this paper, the circuit configuration, operation principle, and relevant analysis results of the proposed converters are presented. Experimental results on a prototype converter realized with the specification of 80-in plasma display panel sustain power module (320-385 Vdc input, 205 Vdc/5 A output) validate the theoretical analysis.

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

A novel hybrid pulse-width-modulation resonant converter is presented in this paper for electric vehicle (EV) 3.3-kW on-board battery chargers (OBCs). While the proposed converter has all the benefits of the earlier developed hybrid converters for OBCs, the proposed converter has fewer components and achieves much lower voltage stress in the rectifying diodes compared to the earlier hybrid converters. As a result, it is possible to employ superior diodes such as Schottky barrier diodes below 300 V featuring low forward-voltage drop and better reverse-recovery for EV 3.3-kW OBC applications. In addition, the proposed converter achieves much better transformer utilization compared to the earlier hybrid converters. Due to this, the proposed converter can achieve more optimal efficiency over the overall battery charging profile. The effectiveness of the proposed converter has been verified with the experimental results under an output voltage range of 250-420-V dc at 3.3 kW.

Resonant Tanks for High-Input-Voltage Applications

This paper proposes an asymmetrical half-bridge (AHB) converter with a new secondary rectifier. Due to the new rectifier stage, the proposed AHB converter has a zero dc-offset current in the transformer at any operating conditions so that the transformer core loss becomes very small compared to the conventional AHB converter. This results in higher efficiency. Besides, magnetic components can be optimally utilized because maximum flux density can be applied when designing the magnetic components. It also allows a flexible design to improve the efficiency or reduce the cost. This paper presents the operation principle and relevant analysis results of the proposed converter. A 300 W, 200-400-V input, and 50-V output laboratory prototype operating at 100 kHz is built and tested to verify the effectiveness of the proposed converter.

Hybrid PWM-Resonant Converter for Electric Vehicle On-Board Battery Chargers

In this paper, a hybrid dual full-bridge dc-dc converter for radio frequency (RF) power generator application is proposed to overcome the drawbacks of a conventional phase-shift full-bridge (PSFB) converter such as the large circulating current of the primary side and large output filter size. The proposed converter adopts a dual full-bridge hybrid structure with a small series capacitor in the primary side and a full-bridge rectifier with two additional low-voltage-rated diodes in the secondary side. With this structure, the proposed converter has advantages of reduction of circulating current, zero-voltage switching (ZVS) operation of all primary switches, size reduction of the output inductor, and low conduction loss of the rectifier stage. Furthermore, the proposed converter can regulate the output voltage very wide by changing the operational mode according to the output voltage. These advantages result in the improvement of whole load efficiency. The operational principle and analysis of the proposed converter are presented and analyzed. A 3-kW 40-200-V output laboratory prototype is designed and built to verify the feasibility and the effectiveness of the proposed converter.

A New Asymmetrical Half-Bridge Converter With Zero DC-Offset Current in Transformer

In this paper, a phase-shifted dual H-bridge converter, which can solve the drawbacks of existing phase-shifted full-bridge converters such as narrow zero-voltage-switching (ZVS) range, large circulating current, large duty-cycle loss, and serious secondary-voltage overshoot and oscillation, is analyzed and evaluated. The proposed topology is composed of two symmetric half-bridge inverters 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. Moreover, 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.

Hybrid Dual Full-Bridge DC–DC Converter With Reduced Circulating Current, Output Filter, and Conduction Loss of Rectifier Stage for RF Power Generator Application

This paper suggests a new hybrid dc-dc converter for a neighborhood electric vehicle battery charger. The proposed converter is based on the conventional phase-shift full-bridge (PSFB) converter with center-tap rectifier. By integrating an LLC series resonant converter into the conventional PSFB converter, the proposed converter has many advantages like wide soft-switching range without duty-cycle loss, zero-current-switching operation of rectifying diodes, minimized circulating current, reduced size of filter inductor, and much better transformer utilization than before presented hybrid dc-dc converters. The proposed converter can be modulated in phase-shift manner or frequency variation. The feasibility of the proposed converter has been verified with the experimental results under an output voltage range of 36-72 V dc at 1 kW.