Abstract
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.
Highlights
The LLC resonant converter is widely used in many different applications such as onboard chargers, server power systems, laptops, desktops, photovoltaic regeneration systems
The simulation and experimental results show that the proposed control strategy effectively reduces the DC magnetizing current and output voltage ripple at mismatched condition
A flux-balance control strategy, which is based on the original output-voltage control loop, is proposed in this paper
Summary
The LLC resonant converter is widely used in many different applications such as onboard chargers, server power systems, laptops, desktops, photovoltaic regeneration systems. The flux-balance control is added to Figure shows the key waveforms of the LLC resonant converter operating the resonant improve the 2b magnetizing current imbalance problem caused by the secondary sidebelow mismatches. (iLr the DC not component was obtained using a low-pass filter This solution, the mismatched condition considers the leakage inductances of the secondary side windings of the transformer and the parasitic inductances of the printed-circuit-board (PCB) traces on the secondary side. To improve the flux walking issue in the LLC resonant converter, improved winding structures for the secondary side were proposed [12,13,14]. The flux distribution of the non-symmetrical structure of the secondary side windings were analyzed in [14] They cannot consider the mismatch problems caused by the PCB circuit traces.
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