A novel llc resonant dc-dc converter with integrated transformer

DC-DC converters in electric vehicle (EVs) and hybrid electric vehicles (HEVs) have required higher power density and high efficiency. This paper proposes a novel LLC resonant DC-DC converter with integrated transformer. This circuit is composed of three LLC converter cells which are connected in series on the primary side and in parallel on the secondary side with interleaved control scheme. The Series Input Parallel Output (SIPO) structure enables the converter cells to share the input voltage and output current. The interleaved operation diminishes the ripple current of the output capacitor, and can reduce the size of the output capacitor. Also a reduction effect of the transformers is obtained by using the integrated transformer which independent transformers are combined into a single core. All these features make the proposed converter suitable for especially high input voltage and high output current applications to realize higher power and higher efficiency. The steady state operating principle of the converter was demonstrated. The theoretical analysis, the equivalent model and voltage gain of the converter are presented based on fundamental harmonic analysis of the converter. A prototype with 330V input and 500W output was built-up to validate the theoretical analysis.