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In this study, we propose the use of a short-distance and fixed-type wireless power transmission transformer via a half-bridge LLC resonant converter. A ceramic insulating layer was used instead of an air gap, meaning that the heat generated from the transformer core and the PCB winding was quickly transferred to the external metal case, with the ceramic insulating layer acting as a heat pipe. In order to stabilize the output voltage, we proposed the use of IR photo tunnel technology, and it was applied to two ceramic insulating layers so that the voltage error signal of the secondary output voltage could be transmitted as light to the primary side. As a result, it was possible to physically separate the primary and secondary sides of the power circuit centering on the ceramic insulating layer. The experiment was carried out with the input voltage of 400 V, the output voltage of 54 V, the maximum output power of 1 kW, and the switching frequency of 1.3 MHz or higher. As a result, the maximum operating frequency was 1.83 MHz, and the output voltage stability to the load was 0.49% or lower. The power density of the experimental circuit was 380 W / in 3 or higher, and the maximum power conversion efficiency was approximately 93% or higher. [ABSTRACT FROM AUTHOR]

In this paper, a steady-state model of an LLC resonant half-bridge converter with internal loss resistance is proposed, in order to maximize power conversion efficiency, and steady-state characteristic equations of DC voltage gain and input impedance are derived for the optimal design of the converter. First, to confirm the validity of the steady-state characteristic equation and the optimal design process, a prototype converter with a maximum output of 2 kW was designed. Through comparison of simulation, calculation, and experimental results obtained from the prototype test, it is shown that the calculation results proposed in this paper were closer to the experimental results than the calculation results obtained under the lossless condition. In addition, the relationship between the switching frequency and the load current of the prototype was compared, in order to determine the operating range of the switching frequency, which is important in the converter design stage. In this case, it was confirmed that the calculated value reflecting the internal loss showed a close result. In conclusion, we confirm the usefulness of the analysis results reflecting the internal loss resistance proposed in this paper and the optimal design process. [ABSTRACT FROM AUTHOR]