Trapezoidal Current Modulation for Bidirectional High-Step-Ratio Modular DC–DC Converters

A modular dc-dc converter (MDCC) has been proposed for high-step-ratio interconnection in dc grid applications. To further optimize the performance of the MDCC, this article presents a trapezoidal current modulation with bidirectional power flow ability. By giving all the submodule (SM) capacitors an equal duty to withstand the stack dc voltage, their voltages are balanced without additional feedback control. Moreover, based on soft-switching performance and circulating current analysis, three-level and two-level operation modes featured with high efficiency conversion and large power transmission, respectively, are introduced. The control schemes of both modes are designed to minimize the conduction losses. Besides, the SM capacitor voltage ripples with different switching patterns are compared, and the option for ripple minimization is presented. A full-scale case study is provided to introduce the design process and device selection of the MDCC. The experimental tests based on a downscaled prototype are finally presented to validate the theoretical analysis.