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Analysis on Gain Formula and Mode Boundary Condition for LLC Resonant Converter in PO Mode
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School of Electrical Engineering and Automation, Hefei University of Technology, Hefei 230009, China

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This work is supported by National Key R&D Program of China (No. 2018YFB0904100) and State Grid Corporation of China (No. SGHB0000KXJS1800685).

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    Abstract:

    The calculation of voltage gain-frequency characteristic is vital in the design of LLC resonant converter. The LLC converter have various operation modes due to the existence of nonlinearity in the rectifier part of the converter. And the voltage gain-frequency characteristic is closely related to operation modes. The PO mode is a discontinuous conduction mode (DCM), which is beneficial to reduce switching losses of the converter. However, the voltage gain-frequency characteristic of converter in the PO mode is hard to be solved because it involves complex computations. On the basis of subinterval analysis method, this paper analyzes the operation characteristics in the PO mode of LLC resonant converter, and deduces a simplified and high-accuracy calculation formula of voltage gain. In addition, the parsing and concise expressions of power boundary conditions both in DCM mode and PO mode are provided according to the nonlinear characteristic in the rectifier part of the converter. Finally, a simulation model and an experimental prototype of LLC converter are developed. The simulation and experiment results verify the validity of the deduced voltage gain formula and power boundary condition.

    表 1 Table 1
    图1 LLC谐振变换器拓扑Fig.1 Topology of LLC resonant converter
    图2 不同模式下的电压与电流波形Fig.2 Voltage and current waveforms in different modes
    图3 LLC谐振变换器的电压增益-频率特性Fig.3 Voltage gain-frequency characteristic of LLC resonant converter
    图4 LLC谐振变换器等效电路Fig.4 Equivalent circuit of LLC resonant converter
    图5 PO模式下电压与电流波形Fig.5 Voltage and current waveforms in PO mode
    图6 不同R L值下开关频率-电压增益关系Fig.6 Relationship between switching frequency and voltage gain with different values of R L
    图7 不同L m值下开关频率-电压增益关系Fig.7 Relationship between switching frequency and voltage gain with different values of L m
    图 等效电阻模型Fig. Equivalent resistance model
    图 ω≥ω 0 时的等效电路Fig. Equivalent circuit when ω≥ω 0
    图 不同模式O状态附近仿真波形Fig. Simulation waveforms nearby O state under different modes
    图 PO模式实验波形Fig. Experimental waveforms under PO mode
    图 PN模式实验波形Fig. Experimental waveforms under PN mode
    图 P状态振荡正半周期等效电路Fig. Equivalent circuit in oscillating positive half cycle under P state
    图 P状态振荡负半周期等效电路Fig. Equivalent circuit in oscillating negative half cycle under P state
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LIU Shuo,SU Jianhui,LAI Jidong,et al.Analysis on Gain Formula and Mode Boundary Condition for LLC Resonant Converter in PO Mode[J].Automation of Electric Power Systems,2020,44(6):164-170.DOI:10.7500/AEPS20190408002

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History
  • Received:April 08,2019
  • Revised:September 16,2019
  • Adopted:
  • Online: March 21,2020
  • Published: