Comparison analysis of the duty control and phase-shift control methods of LLC resonant converter under low-voltage and light-load conditions

Modern fast chargers should manage output voltages that range from 200 V to 800 V and up to 1000 V to support various vehicle types and battery configurations. The input voltage of an LLC resonant converter, i.e., the DC-link voltage, can be controlled to expand the output range; however, it is limited by the need to maintain an appropriate grid voltage. This situation enables control of output voltage up to 1000 V, but an LLC resonant converter is difficult to control under low-voltage and light-load conditions due to the slight change in voltage gain despite increasing switching frequency. Under these conditions, the input voltage of a resonant network must be reduced to control the low output voltage of an LLC resonant converter. Two methods are available for achieving this control: the duty control and phase-shift control methods. In this study, a mathematical analysis was proposed to analyze and compare the steady-state operation principles of the two control methods. In addition, the proposed algorithm was implemented on a prototype of a 30 kW LLC resonant converter to validate the performance of the control method under low-voltage and light-load conditions. Given the higher peak resonant current (up to 7 A) in the duty control method, the phase-shift control method exhibited 5.63% higher efficiency at 200 V.

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Cite this article

[IEEE Style]

M. Lee, H. Yang, J. H. Kim, C. Hong, M. Lee, W. Sim, D. Joo, "Comparison analysis of the duty control and phase-shift control methods of LLC resonant converter under low-voltage and light-load conditions," Journal of Power Electronics, vol. 26, no. 4, pp. 896-906, 2026. DOI: 10.1007/s43236-026-01313-4.

[ACM Style]

MinJi Lee, Hyoung-Kyu Yang, Jin Hong Kim, ChangPyo Hong, MyungChul Lee, WooGwon Sim, and DongMyoung Joo. 2026. Comparison analysis of the duty control and phase-shift control methods of LLC resonant converter under low-voltage and light-load conditions. Journal of Power Electronics, 26, 4, (2026), 896-906. DOI: 10.1007/s43236-026-01313-4.