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Open AccessArticle

Flux-Balance Control for LLC Resonant Converters with Center-Tapped Transformers

Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
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Energies 2019, 12(17), 3211; https://doi.org/10.3390/en12173211
Received: 9 July 2019 / Revised: 18 August 2019 / Accepted: 19 August 2019 / Published: 21 August 2019
(This article belongs to the Special Issue Advances in High-Efficiency LLC Resonant Converters)
LLC resonant converters with center-tapped transformers are widely used. However, these converters suffer from a flux walking issue, which causes a larger output ripple and possible transformer saturation. In this paper, a flux-balance control strategy is proposed for resolving the flux walking issue. First, the DC magnetizing current generated due to the mismatched secondary-side leakage inductances, and its effects on the voltage gain are analyzed. From the analysis, the flux-balance control strategy, which is based on the original output-voltage control loop, is proposed. Since the DC magnetizing current is not easily measured, a current sensing strategy with a current estimator is proposed, which only requires one current sensor and is easy to estimate the DC magnetizing current. Finally, a simulation scheme and a hardware prototype with rated output power 200 W, input voltage 380 V, and output voltage 20 V is constructed for verification. The simulation and experimental results show that the proposed control strategy effectively reduces the DC magnetizing current and output voltage ripple at mismatched condition. View Full-Text
Keywords: LLC resonant converter; center-tapped transformer; flux walking; flux-balance control loop; magnetizing current estimation LLC resonant converter; center-tapped transformer; flux walking; flux-balance control loop; magnetizing current estimation
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MDPI and ACS Style

Lin, Y.-C.; Chen, D.-T.; Chen, C.-J. Flux-Balance Control for LLC Resonant Converters with Center-Tapped Transformers. Energies 2019, 12, 3211.

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