Reliable and optimal design of variable inductor integrated LLC converter

Abstract The variable inductor integrated LLC (VI‐LLC) converter is able to operate at constant switching frequency and avoid wide variable frequency range and thus emerged in recent years. However, VI‐LLC converter suffers two reliability problems. First, coupling between the main winding and the control winding of variable inductor (VI) causes negative effects on the converter, which are few considered in the literature. Second, parameter fluctuation (PF) of resonant elements has negative effects on operation and gain reliability of VI‐LLC converter, causing unreliable operation and voltage gain deviation. To solve the above problems, in this paper, a reliable and optimal design methodology of VI‐LLC converter is proposed. First, the coupling effects of VI are introduced and analyzed, with a coupling index proposed to quantify and reduce the coupling effects. Then, negative effects on VI‐LLC converter caused by PF are visualized and eliminated with the filtered parameter space and the redetermined variation range of VI. Based on the above consideration, a reliable final parameter space considering PF effects and the coupling problem is established. Finally, the efficiency space referring to the final parameter space is established based on the loss model of VI‐LLC converter to determine the optimal design candidate. Experimentation has shown a good agreement with theory and proven validity of the proposed design methodology.