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In order to recover and fully charge batteries in Electric Vehicles, smart battery chargers should not only work under different loading conditions and output voltage regulations (close to zero to 1.5 times the nominal output voltage), but also provide a ripple-free charging current for battery packs and a noise-free environment for the Battery Management System (BMS). In this paper, an advanced LLC design procedure is investigated to provide advantageous extreme regulation and eliminate detrimental burst mode operation. A modified, special LLC tank driven by both Variable Frequency (VF) and Phase Shift (PS) proves to be a successful solution to achieve all the regulation requirements for battery charging (from recovery, bulk, equalization, to finish). The proposed solution can eliminate the negative impact of burst mode noises on the Battery Management System, provide a free-ripple charging current for batteries in different States of Charge, reduce the switching frequency variation, and facilitate the EMI filter and magnetic components designs procedure. In order to fully consider the characteristics of the full bridge LLC resonant converter, especially the output voltage regulation range and soft transitions of the MOSFETs in the Fixed Frequency Phase Shift mode, a new set of analytical equations is obtained for the LLC resonant converter with consideration of separated primary and secondary leakage inductances of the high frequency transformer. Based on the proposed strategy and analytical equations, multivariate statistical design methodology is employed to design and optimize a 120VDC, 3kW battery charger. The experimental results exhibit the excellent performance of the resulting converter, which has a peak efficiency of 96.5% with extreme regulation capability.Index Terms -Full bridge LLC resonant converter, hybrid modulation strategy, battery charger applications, recovering dead battery, wide output voltage regulation, full soft switching conditions. NOMENCLATURE CjDiode junction capacitance (F ).

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Power transformer is one of the most complex parts of power converters. The complicated behavior of the transformer is usually neglected in the power converter analysis and a simple model is mostly used to analyze the converter. This paper presents a precise analysis of a fifth-order resonant converter which has incorporated the resonant circuit into the transformer. The derived model, which is based on the accurate model of the power transformer, can fully predict the behavior of the fifth-order resonant converter. The proposed fifth-order resonant converter is able to effectively reduce the range of phase-shift angle from no load to full load for a fixed-frequency phase-shift control approach. Therefore, the converter is able to operate under zero voltage switching during entire load range with a fixed-frequency control method. Also, the proposed converter offers a high gain which leads to a lower transformer turns ratio. A 10-kVDC, 1.1-kW prototype has been prepared to evaluate the performance of the proposed converter. The experimental results exhibit the excellent accuracy of the proposed model and the superiority of the performance compared to the lower order resonant converters, especially for high-voltage applications.Index Terms-Fifth-order resonant converter, high-voltage dc power supply, phase-shift fixed-frequency control approach, steady state analysis, zero voltage switching (ZVS) operation.