Journal
IEEE TRANSACTIONS ON POWER ELECTRONICS
Volume 37, Issue 4, Pages 4358-4373Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TPEL.2021.3122588
Keywords
Inductors; Zero voltage switching; Power system measurements; Density measurement; Modulation; Magnetic resonance; Magnetic flux; Harmonics; high efficiency; high power density; integrated converter; LLC; phase shift; transformer air gap
Categories
Funding
- National Natural Science Foundation of China [52077094]
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This article proposes a bipolar symmetric phase shift modulation strategy to reduce the resonant inductance and correct resonant current with high power density and high efficiency in an integrated two-stage buck-boost-LLC isolated dc-dc converter. Additionally, the LLC stage is improved by decreasing the RMS current of primary switches using the choke inductor current. The experimental results show that the proposed modulation strategy effectively corrects resonant current, improving efficiency and power density.
The integrated two-stage buck-boost-LLC isolated dc-dc converter is suitable for wide-voltage regulation range, highfrequency and high-efficiency application. However, the choke inductor current of buck-boost stage injecting into LLC stage will cause nonsinusoidal resonant current and asymmetric secondary current under the conventional modulation strategy. This will result in synchronous rectification problems. Traditionally, a large resonant inductor is utilized to improve the situation, but it sacrifices power density and efficiency. Therefore, this article proposes a bipolar symmetric phase shift modulation strategy to reduce the resonant inductance and correct resonant current with high power density and high efficiency. Moreover, LLC stage is improved. The RMS current of primary switches is decreased by the entrance of the choke inductor current. Zero-voltage-switching is achieved by choke inductor current instead of magnetizing current, so that the transformer can be designed without air gap and has lower winding loss caused by leakage flux. With minimum magnetizing current, the resonant current is minimized. The conduction loss of primary switches and winding loss of transformer shows 75% and 26% reduction, respectively. Finally, a 500 kHz 400-W prototype with 97.6% peak efficiency and 142W/in3 power density is built up. The experimental results verify that the proposed modulation strategy corrects resonant current effectively and improves efficiency and power density.
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