Size, Efficiency, Reliability and Cost Analysis of a Multiport Traction Inverter with Downsized DC-DC Converter for a Catenary/Battery Tram

The use of a NPC-type multilevel converter as multiport inverter (MPI) has recently been considered a promising solution for the compact integration of multisource systems in various applications. Despite increasing research interest in this topic, a comprehensive study of an MPI-based power conversion system for multisource rail applications is still lacking in the literature. This paper presents a broad analysis of a quasi-single stage propulsion system (QSS) that employs an NPC-type MPI and a downsized boost dc-dc converter for an urban tram vehicle with overhead line connection and onboard batteries. The control and dynamic performance are detailed and validated experimentally. Furthermore, the efficiency, weight, volume, reliability and cost of the QSS system are evaluated and benchmarked against a conventional architecture for a case-study catenary/battery tram model. To this aim, analytical design equations, manufacturers’ data, electrothermal time-domain simulations, finite element method (FEM) simulations, and Monte Carlo-based lifetime analyses are employed. The analysis reveals that the QSS system can achieve significant savings in volume, weight, and round-trip energy efficiency, higher reliability due to intrinsic redundancy, but with increased part count, complexity, and cost.