Four-level step-down soft-switching dc-dc converter for electric locomotives

This paper proposed a four-level step-down soft-switching dc-dc converter that can be applied in electric locomotive auxiliary system. All dc link capacitors of the converter are voltage self-balanced under open loop control. All switches and diodes of the converter can achieve soft-switching condition without sacrificing the reliability. This helps not only to reduce the switching losses, but also to reduce the overall system volume and weight by operating much higher frequency. Modular structure is employed for commercial manufacture and expansion. The operation principles and the voltage balancing mechanism of the dc link capacitors are introduced in detail. The feasibility and validity of the proposed converter are verified by both the simulation and experimental results.