A Modular Reconfigurable Single-Stage DC-DC Converter Suitable for Wide Gain Range and its Magnetic Design

In recent years, with the development of new energy storage systems, communication base stations, server power supplies, and electric vehicle charging, the corresponding systems have put forward higher requirements for DC-DC converters. It often requires a high step-down ratio DC-DC converter with wide input and wide output capability. Resonant converters represented by LLC have become a research hotspot in the field of high-frequency, high-efficiency, and high-density power supplies due to their advantages of easy soft-switching, fewer topological components, and low electromagnetic interference. However, when the voltage gain range is relatively large, the magnetizing inductance of the LLC converter will be relatively small, resulting in relatively high primary side circulating current and switch conduction losses. Therefore, a single LLC converter cannot simultaneously meet the requirements of wide gain range and high efficiency and high power density in the above scenarios. In this paper, a reconfigurable single-stage topology combining multi-module switched capacitor units and resonant network units is proposed, which is suitable for a new high step-down ratio DC-DC converter topology for data center DC power supply systems. The topology combines switched capacitors with characteristics of easy to combine, small size, soft switching of resonant circuit, and high transmission efficiency, it is a reconfigurable single-stage transmission structure. For high input voltage, a series reconfiguration unit can be added, and for large output current, a parallel resonant unit can be added. The switched capacitor unit can be selected from a switched capacitor circuit (SC) or a switched tank converter (STC), and the resonant network unit can be selected from common resonant circuits such as LLC and CLLC. This paper takes switched capacitor and LLC resonant converter as examples to analyze the specific working principle and characteristics of the constructed topology. In this design, the switching of the order of the SC network is adopted, which further reduces the voltage input range of the LLC network. When the input voltage is 300～400V, the fourth-order SC network is fully working. When the input voltage is 200～300V, the fourth-order SC network switches to third order. In order to facilitate the current sharing on the secondary side, a matrix transformer is used in this solution to divide the synchronous rectification output network into three subunits, thereby reducing the current stress of each rectifier tube. At the same time, a new integrated design is made for the matrix transformer, which greatly reduces the installation space of the magnetic core and the length of the primary side winding, and reduces the total loss of the transformer. Based on the advantages of switched capacitor structure and resonant network stage, a modular reconfigurable single-stage DC-DC converter suitable for wide gain range is proposed. The number of series modules can be selected according to the input voltage range to achieve the equivalent compression of the input voltage range to the resonant tank. In addition, in order to reduce the uneven flow and local overheating caused by device parallel connection, a new magnetic integrated structure is designed to replace the traditional planar matrix transformer with separated magnetic cores. The advantages of the proposed magnetic integrated structure in transformer loss and power density are compared. And the transformer loss calculation model and its optimal design method are given at the same time. Finally, a prototype with input voltage of 200～400V and rated power of 500W is designed, which verifies the validity and correctness of the topology and its magnetic integration structure. © 2023 Chinese Machine Press. All rights reserved.