• Journal of the Korea Convergence Society
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• 제8권11호
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• pp.313-319
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• 2017

In this paper, we present a design technique that miniaturises the DC-DC converter, a key component in the electric vehicle system, using the advanced material (Ga-N HEMT) in the LLC resonant converter and freely changes the resonant frequency. This design is also proposed to improve the efficiency and temperature characteristics by adding SR Topology in the secondary side output during the operation of power supply. In this experiment, as a consequence of the constructed circuit with the operation of high switching frequency of 200 kHz, the size of LLC and PFC was able to be minimised by 40[%]. Thus, the characteristics of operating temperature demonstrated $60-65^{\circ}C$ without a heat sink, when the temperature was measured at 250W (12V/20A). The features were all due to the advantages of the change of switching frequency, switching circuits implementation, and the maximisation of switching frequency. Based on these design results, we would like to implement more than 1 [kW].

• Journal of the Semiconductor & Display Technology
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• 제21권3호
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• pp.80-86
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• 2022

In this paper, the optimal design and circuit simulation verification results of an LLC resonant half-bridge dc-dc converter using a steady-state model with internal loss resistance are reported. Above all, the input/output voltage gain and frequency characteristic equations in the steady-state were derived by reflecting the internal loss resistance in the equivalent circuit. Based on the results, an LLC resonant half-bridge dc-dc converter with an input voltage of 360-420V, an output voltage of 54V, and a maximum power of 3kW was designed, and to verify the design, the PSIM circuit simulation was executed to compare and analyze the result. In particular, the operating range of the converter could be drawn from the frequency characteristic graph of the voltage gain, and when the converter was operated under light and maximum load conditions, it was confirmed that similar results were obtained by comparing simulation results and calculation results in the switching frequency characteristic graph. In addition, the change of the switching frequency with respect to the load current at each input voltage was compared with the calculated value and the simulation result. As a result, it was possible to confirm the usefulness of the analysis result reflecting the internal loss resistance proposed in this paper and the process of the optimal design.

• The Transactions of the Korean Institute of Power Electronics
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• 제24권6호
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• pp.438-444
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• 2019

In this paper, bidirectional LLC resonant DC/DC converters with the primary auxiliary windings in transformers of resonant circuits are proposed. Although the resonant capacitors are used on both the primary and secondary sides, regardless of the direction of power flow, the main feature of the proposed converters exhibits high gain characteristics without any mutual coupling between the resonant capacitors. For one of the proposed converters, an investigation of the operating characteristics in each mode has been carried out. A prototype of a 3.3 kW bidirectional LLC resonant converter for interfacing 750 V DC buses has been built and tested to verify the validity and applicability of the proposed converter.

• The Transactions of the Korean Institute of Power Electronics
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• 제21권6호
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• pp.506-513
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• 2016

In general, LLC converters show great promise in applications that require high efficiency, especially under light load conditions. In particular, LLC converters feature wide gain capability with pulse-frequency modulation and zero voltage switching over entire load conditions. However, output voltage increases in light load conditions. In this study, Bode plot and impedance asymptotes analyses were conducted to obtain insights into the regulation characteristics of LLC converters under light load conditions. To improve the regulation characteristic of LLC converters, a new resonant tank with an additional capacitor is proposed. The design guideline for the proposed LLC converter is determined by the Bode plot and impedance asymptotes analyses. Therefore, the proposed LLC converter achieves the light load regulation while maintaining the advantages of typical LLC converters.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제65권12호
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• pp.1992-1999
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• 2016

The plasma process is applied to various industrial fields such as high-tech IT industry, textiles and medical. Therefore, there is increasing interest in the plasma power supply, and demand for power devices of high efficiency and high power density is increased. Plasma power supply for process must solve the arc problem, when the plasma is unstable. The output capacitor is closely related to the arc problem. If the output capacitor is smaller, the damage from the arc problem is reduced. However, the small value of the output capacitor affects the operating characteristics of the power supply. In this paper, a LLC resonant converter is adopted, because it can achieve high efficiency and power density in the plasma DC power supply. However, due to the small value of the output capacitor, the converter is operated as a LLCC resonant converter. Therefore, a gain characteristic of LLCC resonant converter is analyzed by using the FHA (First Harmonic Approximation) in plasma power supply. Simulation and experimental results are presented to verify the characteristic analysis of LLCC Resonant Converter.

• The Transactions of The Korean Institute of Electrical Engineers
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• 제61권12호
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• pp.1848-1856
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• 2012

This paper proposes a new grid-tied power conditioning system for battery energy storage, which is composed of a 2-stage DC-DC converter and a PWM inverter. The 2-stage DC-DC converter is composed of an LLC resonant converter connected in cascade with a 2-quadrant hybrid-switching chopper. The LLC resonant converter operates in constant duty ratio, while the 2-quadrant hybrid-switching chopper operates in variable duty ratio for voltage regulation. The operation of proposed system was verified through theoretical analysis and computer simulations. Based on computer simulations, a hardware prototype was built and tested to confirm the technical feasibility of proposed system. The proposed system could have relatively higher efficiency and smaller size than the existing system.

• Journal of IKEEE
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• 제22권4호
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• pp.985-991
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• 2018

In this paper, an equivalent circuit reflecting the internal loss of the LLC resonant half bridge converter was proposed and a steady state characteristic equation including the loss factors was derived. Using the results, the frequency characteristics of I/O voltage gain and input impedance were compared with the lossless model In order to verify the proposed model and the derived equation, the main components of the 1kW class LLC resonant half bridge converter were selected under the same conditions and the steady state characteristics such as voltage gain and input impedance were compared. In particular, to compare more closely the steady state error of the two models, we observed the change in switching frequency with respect to the load current, which is considered to be the most important in the actual circuit design stage. As a result, it is confirmed that the error of the operating frequency is significantly improved from the proposed model and the analysis result.

• The Transactions of the Korean Institute of Power Electronics
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• 제15권4호
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• pp.319-326
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• 2010

The power supply devices for reducing the size of the LCD TV are increasingly required for high efficiency and highe power density. Recently, the LED backlight of the LCD TV comes into the spotlight for LCD TV, because the conventional CCFL backlight has difficult to use constantly according to the mercury restrictions. And In this paper, the LLC resonant converter using the planar transformer for slim-type LED backlight of LCD TV is presented and verified through an experimental prototype for 47 inch LCD TVs with LED backlight system.

• The Transactions of the Korean Institute of Power Electronics
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• 제22권6호
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• pp.517-526
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• 2017

In this paper, we propose an LLC resonant converter that operates over a wide controllable output voltage ($50V_{DC}$ to $800V_{DC}$) and shows high efficiency characteristics under all load conditions and output voltages. Two 3.3kW prototypes are designed for an experimental comparison between the variable frequency control (control scheme 1) and the variable input voltage($V_{IN}$) control (control scheme 2) mechanisms. The experimental results show that the variable input control mechanism demonstrates high efficiency under all loads and output voltages.

• The Transactions of the Korean Institute of Power Electronics
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• 제22권2호
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• pp.126-133
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• 2017

The conventional battery charger requires two separate voltage and current compensators to achieve constant current and constant-current-charging profile. This compensator configuration leads to an inevitable transient response during the mode change between the constant current and the constant voltage operation. Futhermore, a tedious and complicated design process is required to consider a widely changing battery voltage and the nonlinear electrical properties of Li-ion battery. This study proposes a single integrated voltage-current compensator of the LLC resonant converter for Li-ion battery charger applications to overcome the aforementioned drawbacks. The proposed compensator is designed to provide a smooth and reliable performance during the entire charging process while providing the reduced design efforts and seamless mode transient response. Several experimental results based on a 300 W prototype converter and its theoretical analysis are provided to verify the effectiveness of the proposed compensator.