Analytical model for LLC resonant converters in operation below resonance

Abstract

AbstractElectric cars are a great opportunity for reducing greenhouse gas emissions caused by transportation. High-power chargers are required to charge electric vehicles in a reasonable amount of time and considerably increase the driving range. As these high-power chargers currently need to be isolated with respect to the grid, the LLC converter topology emerged as a very good solution for implementing the required isolated DC/DC converter stage. The analysis and optimal design of this resonant converter stage are a challenging task, as some models are oversimplified, resulting in major errors and a high amount of processing time. This paper presents a novel analytical model for the LLC converter operating below resonance, which allows accurate modeling of the converter with minimal effort. In most cases, no iterations are required, and a comparison to numerical results taken from time domain simulations shows that the relative deviation of the proposed model stays far below 1% for a wide range of operating conditions.