A comparative study of voltage gain tolerance in conventional and three-level LLC converters against circuit variation

This paper clarifies the relationship between voltage gain tolerance and resonant circuit components variation for mass production of LLC converters. The LLC converter is a good solution for high power application, hence many PV systems which use LLC converter have been proposed. The combination of the LLC converter and a multi-level conversion technique is also proposed to overcome a drawback of the LLC converter. It is important on mass production stage to clarify the relationship between its voltage gain tolerance and resonant circuit component variations, however it has rarely studied. Therefore, we study the voltage gain tolerance against three normalized parameters related to the resonant circuit with Monte Carlo simulation. As a result, it has found that a conventional LLC converter and a three-level LLC converter have approximately same voltage gain tolerance characteristics; small inductance ratio makes the voltage gain tolerance to be small and a quality factor has an insignificant effect on the tolerance when a normalized frequency is almost unity; small tolerance area appears on a quality factor-inductance ratio plane when the normalized frequency is lower than unity.