Analysis, Design, and Comparison of Isolated DC-DC Converters for Traction Application

Solid-state transformers (SSTs) have recently been proposed in the literature as a promising solution for traction application. SSTs consist of a two-stage topology that includes an ac-dc and dc-dc stage. The optimization of the different stages involved in energy conversion (rectification, isolated dc-dc conversion, and inversion) is necessary for their efficient operation. The dc-dc conversion stage is an important stage as isolated dc-dc converters enable galvanic isolation offer higher power density and efficiency, support bidirectional power flow, and provide a wide voltage range. Therefore, with the aim of having a compact and more efficient railway traction systems, study of the isolated dc-dc converters with high efficiency, power density and improved thermal management is of utmost importance for creating compact and efficient railway traction systems based on SSTs. This paper presents a detailed analysis and design of various isolated bidirectional dc-dc converters suitable for traction applications in SST-based systems. The objective is to identify topologies that offer high efficiency and power density to improve the performance of SST-based systems. A 5kW prototype is designed and developed using SiC devices with a flexibility to test each of these topologies. An analysis is conducted to evaluate the efficiency, control complexity, component stress and soft switching range.