NPC assessment in insulated DC/DC converter topologies using SiC MOSFETs for Power Electronic Traction Transformer

Abstract

Power electronic traction transformers (PETT) are multilevel AC/DC on-board converters, studied for railway applications to replace traditional solution with low frequency transformers. This paper focuses on the insulated DC/DC converter in a PETT. Three variants of resonant single active bridges (R-SAB) with 3-level NPC primaries are optimised to maximise the efficiency, under mass and dimension constraints. They are sized and compared for a 2 MW PETT on a 15 kV/16.7 Hz railway infrastructure, using 3.3 kV SiC MOSFETs and nanocrystalline C-core transformers with cast resin insulation and forced air cooling. The highest efficiency at nominal power, 99.17 %, is reached for a configuration with a 3-level full bridge NPC primary, a 2-level full bridge secondary, and a 32.1 L/49.1 kg transformer operating at 6 kHz.

Review and Outlook on GaN and SiC Power Devices: Industrial State-of-the-Art, Applications, and Perspectives

“…SiC transistors are also considered in high-power, transformer-free designs in the MW range: for example, they are employed in train traction systems to adapt the low-frequency ac catenary voltage to the higher frequency ac voltage required to drive the motors. This is achieved by properly cascading ac-dc, dc-dc, and dc-ac converters, using for example resonant LLC conversion topologies for the dc-dc part, like the 2 MW one described in [20].…”

Analysis of light and no‐load operation of a 300 kW resonant single active bridge based on 3.3 kV SiC‐devices

“…In the literature, it can be found also as: series-resonant converter (SRC) [5]; resonant LLC converter [6]; and resonant single active bridge (R-SAB) [7]. It consists of a transformer and a resonant capacitor placed between an active inverter bridge and a diode rectifier bridge, as shown in Figure 1.…”

“…The first DC/DC converter to integrate a transformer and a series‐resonant capacitor was introduced in 1970 [1] and, since then, it has been extensively used in many applications [2–4]. In the literature, it can be found also as: series‐resonant converter (SRC) [5]; resonant LLC converter [6]; and resonant single active bridge (R‐SAB) [7]. It consists of a transformer and a resonant capacitor placed between an active inverter bridge and a diode rectifier bridge, as shown in Figure 1.…”