An Input-Series-Output-Parallel Converter System Exhibiting Natural Input-Voltage Sharing and Output-Current Sharing

Input-series-output-parallel (ISOP) converter system is suitable for high-input voltage applications owing to the reduced voltage stress of power switches. This article proposes an ISOP converter system with two-stage dc-dc converter as the basic module, which is composed by a non-isolated dc-dc converter and an isolated dc-dc converter. The isolated dc-dc converter functions as a dc transformer (DCX), and the non-isolated dc-dc converter serves as the pre- or post-regulator to regulate the output voltage. With this arrangement, a common duty ratio is applied to all the pre-or postregulators, and natural input-voltage sharing (IVS) and output-current sharing (OCS) can be achieved. The LLC resonant converter is adopted as the DCX, and the design considerations are given for achieving a nearly constant voltage gain even if there is parameters drift. Meanwhile, the non-isolated converter has simple topology and the parameters are easy to be identical. Thus, the proposed ISOP converter system realizes excellent IVS and OCS even the constituent modules are not well matched. Furthermore, the improved ISOP converter system employing boost+LLC resonant converter is proposed. Two 12-kW ISOP converter systems have been fabricated and tested in the lab, and the experimental results are provided to verify the natural voltage sharing of the proposed ISOP converter system.