A Holistic Design Optimization Method for LLC Converters in Light Electric Vehicle Chargers

The passive components of LLC resonance converters are traditionally designed based on a resonance frequency and switching frequency range considering the required voltage conversion rate while ensuring zero-voltage switching (ZVS) of the primary-side power devices. Afterward, the subelements such as the transformer, power stage, and heat-sink are locally designed. However, this may only lead to locally optimized designs. In this article, a systematic design framework is proposed that attempts to determine the resonance frequency by considering the nonlinear battery load profile, power loss, volume, and cost of all main components. To achieve smaller-sized transformers, a series-connected primary and parallel-connected secondary windings with a multicore configuration is also considered. The proposed algorithm aids designers to optimally size the LLC and provides a step-by-step design methodology. An LLC stage of a light electric vehicle (LEV) battery charger converting 370-430 V to an output voltage range of 36-54 V rated at 3700 W with a peak efficiency of 98.2% has been designed validating the proposed design procedure.