150 kVA Compact Modular Three-Level NPC Auxiliary Converter for the Railways Application

This paper introduces a compact and modular three-level Neutral Point Clamped (3L-NPC) DC-DC converter designed for auxiliary inverters used in Railways. Compared to traditional topologies employing 50 Hz transformers, the 3L-NPC dual active bridge (DAB) DC-DC converters, with integrated high-frequency transformers, offer modularity, compactness, and higher power density. The proposed design enables independent control for each converter, facilitating parallel feeding of AC loads (such as fans, blowers, and pumps), with the second converter dedicated to charging 110 V batteries. The proposed topology, along with its control system, is simulated using PLECS and validated through hardware-in-loop setups under various load conditions. Additionally, the power-density of the 3L-NPC dual active bridge DC-DC converters is demonstrated to surpass that of conventional auxiliary converters while being more adaptable to scalability for higher power applications. These findings confirm the converter's simplicity, ease of operation, and potential for future power scalability.