Resonant Tank Switch Methodologies for Narrow Switching Frequency Range in Wide Output Range LCC Converter

Wide switching frequency range is required for LCC resonant converter with wide gain and load ranges which will lead to low power density and slow dynamic responses. Resonant tank switch is an effective approach to limit the operation frequency range without sacrificing the power transistor's zerovoltage switching (ZVS) switching and system complexity too much. However, the current approach of resonant tank switch failed to provide a generalized and engineering practicability methodology. In this article, a new resonant tank design method is first proposed considering voltage and current stress for higher efficiency and improved design feasibility. Resonant tank switch methodologies are developed with a single switch parameter (C-s-Switch, L-s-Switch, and L,-Parallel) and a multi-switch parameter (full range, fixed slope, and fixed inflection point). Operation range divisions for different tanks are further proposed under gain and load covariations. A 5 kW LCC converter with gain variations of 0.3-1.2 and an output current range of 03-18 A is built to verify the tank switch approaches. The targeted frequency range is 400-500 kHz. Under constant load, the switching frequency range can be limited to 25% with one primary tank and one compensated tank, compared with 66.7% frequency variation with one resonant tank. It is also found that the L-s-Switch approach achieves desired gain range with the smallest switching frequency range, moderate voltage stress, and smallest current stress under constant load, and variable gain. With three resonant tanks, full gain, and load range can be covered under required frequency ranges. The switching frequency range is limited to 25% compared with 78.6 % variation with one resonant tank. Soft switching is also achieved under the full operation range.

Automated summary

This article proposes a new design methodology for resonant tanks in LCC converters, aiming to improve efficiency and design feasibility by considering voltage and current stress. The proposed tank switch approaches, such as C-s-Switch, L-s-Switch, and L-Parallel, effectively limit the switching frequency range. The results showed that the L-s-Switch approach achieved the desired gain range with the smallest switching frequency range, moderate voltage stress, and smallest current stress. The proposed methodologies are verified through the construction of a 5 kW LCC converter.