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Automatic resonant frequency tracking for DCX‑LLC based on magnetizing current cancellation
Cheng Gu,Qinsong Qian,Dalin Xu,Tianhao Tan 전력전자학회 2024 JOURNAL OF POWER ELECTRONICS Vol.24 No.1
The LLC resonant converter has been widely used as a DC-DC transformer (DCX) to provide a semi-regulated or unregulated bus voltage. However, due to circuit parameter variations, the switching frequency is usually different from the designed resonant frequency, which results in converter efficiency degradation. To achieve the highest efficiency under different scenarios, a novel primary-side regulation (PSR) scheme for LLCs based on magnetizing current cancellation is presented. The transformer magnetizing current component on the sampling resistor can be offset by the compensating current, which is generated by the auxiliary winding and the added compensating inductor. The effect of magnetizing current in the sampled primary resonant current can be effectively eliminated. Thus, the output current can be accurately estimated on the primary side of the LLC resonant converter. Finally, a prototype of a 20-60 V LLC is constructed to validate the theoretical analysis. In the experiment section, various scenarios are tested to assess the efficacy of the solution. It is shown that the LLC converter can always realize resonant frequency tracking with the highest transmission efficiency.
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Cheng Gu,Qinsong Qian,Dalin Xu,Tianhao Tan 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.9
Planar transformers have been widely used in isolated power supplies. However, with a large current density, the parallel windings usually cannot share the current evenly. This uneven current-sharing may cause additional winding losses, and damage the performance of the power converter. In this paper, a novel central-tapped planar transformer structure is proposed. Regardless of whether it is in the first half cycle or the second half cycle, the proposed twelve-layer transformer can be simplified as four three-layer transformers connected in parallel. Moreover, there is a “shielding layer” between adjacent three-layer transformers. In addition, the proposed transformer structure is optimized with a symmetrical layer arrangement, and the skin effect and proximity effect can be further reduced. Simulation and experimental tests indicate that the optimized planar transformer can stably provide 476.1 W of output power at a frequency of 1.25 MHz. The peak efficiency of the optimized transformer is up to 99.2%, and there is no obvious hot spot on the PCB board. It is noteworthy that the temperature difference in the secondary windings is less than 5 °C, which means the current-sharing in the secondary windings works well.
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Zhang, Cheng,Ju, Haoran,Zhang, Dalin,Wu, Shuijin,Xu, Yijun,Wu, Yingwei,Qiu, Suizheng,Su, G.H. Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.5
The flow characteristics of reactor fuel assembly always intrigue the designers and the experimentalists among the myriad phenomena that occur simultaneously in a nuclear core. In this work, the visual experimental method has been developed on the basis of refraction index matching (RIM) and particle image velocimetry (PIV) techniques to investigate the detailed flow characteristics in China fast reactor fuel subassembly. A 7-rod bundle of simulated fuel subassembly was fabricated for fine examination of flow characteristics in different subchannels. The experiments were performed at condition of Re=6500 (axial bulk velocity 1.6 m/s) and the fluid medium was maintained at 30℃ and 1.0 bar during operation. As for results, axial and lateral flow features were observed. It is shown that the spiral wire has an inhibitory effect on axial flow and significant intensity of lateral flow mixing effect is induced by the wire. The root mean square (RMS) of lateral velocity fluctuation was acquired after data processing, which indicates the strong turbulence characteristics in different flow subchannels.
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