A Comparison of Different Types of Resonant Tanks for OBC Applications by Using a Universal and Automatic Design Methodology

CLLLC class resonant converters are widely applied in bidirectional isolated DC-DC power conversion for the advantages of high efficiency and high power density. With the increasing scenarios of wide voltage gain range, the time domain model is widely used in the design process of resonant converters since it has much higher accuracy. Additionally, the asymmetrical resonant tank parameter design can further utilize the design freedom and reach a better performance. However, the design process of the asymmetrical CLLLC (ACLLLC) resonant tanks has excessive computational burden and complicated steps, especially when the optimal design of the power devices and magnetic core are included, which introduces many engineering restrictions such as the magnetic core saturation, current density, window coefficient, etc. Furthermore, by removing one resonant inductor, CLLC resonant converter is also widely used resonant tanks for bidirectional power conversion. The comparison of these two types of resonant tanks is lacking, which increases the burden of topology selection. This paper proposes a universal and automatic design methodology for CLLLC class resonant converter, which includes the parameter design and magnetic core design. The engineering restrictions are also included, which ensures that the design results can be applied directly. By using the parameter equivalence principle and the proposed design procedure, the comparison of CLLC and ACLLLC can be conducted for all common applications, which shows that CLLC and ACLLLC have identical electrical characteristics, but CLLC has smaller magnetic related loss and better power density characteristics. The design process and comparison results are verified by a 1 kW prototype with peak efficiency of 98.44%, which shows that the CLLC resonant tank has better power density and efficiency performance.