Analytic solutions for LLCC parallel resonant converter simplify use of two- and three-element converters

A practical method for steady-state design of parallel resonant dc/dc converters is presented. The method uses a set of prederived equations from a two-inductor two-capacitor series-parallel resonant converter (LLCC-SPRC). Although four-tank elements are present in an LLCC-SPRC, only two ratios of the tank elements are needed during design. The values of the four-tank elements can be found from the design results. In addition to designing an LLCC-SPRC, the prederived equations can also be used to design and analyze the conventional one-inductor two-capacitor (LCC)-type SPRC's (LCC-SPRC's), two-inductor one-capacitor (LLC)-type PRC's (LLC-PRC's), and inductor-capacitor (LC)-type PRC's (LC-PRC's). In other words, the four converters can be designed by the same equations. A design procedure along with design examples is given. Experimental circuits are implemented and measured based on the design results to verify the validity of the derived equations and the design procedure.