Highly modular and scalable power module platform for railway traction converter applications

Abstract

Electrical railway vehicles are widely used for public and good transportation with the advantages of zero carbon emission, great efficiency, and low operating costs. They can be categorized as light rail vehicles (LRVs), electrical multiple units (EMUs) and locomotives considering vehicle speed, power and vehicle configuration. In terms of traction converter power requirement, railway vehicles can be roughly divided into three segments: low-, mid- and high-power segments. LRVs traction converters power levels are up to 400 kW which is in the low-power segment. The mid-power segment consists of metros and low-speed EMUs with >400 kW and <1000 kW power rating. The high-power segment with >1000 kW power rating comprises locomotives and high-speed EMUs. IGBT modules are one of the most critical components of traction converters which are critical systems for electric railway vehicles since they control and convert electrical power for traction to traction motors. In high-power traction converters, single IGBT modules with a footprint of 140x190 mm or 140x130 mm are used due to the need for high current. For low- and mid-power applications, IGBT modules with a footprint of 100x140 mm are widely utilized due to features like low commutation inductance, high power density, and terminal design that simplifies DC busbar design despite that 140x130 mm footprint IGBT modules are also applicible in low- and mid-power levels. These packages have a wide range of applications with voltage levels of 1.7 kV, 3.3 kV, 4.5 kV, and 6.5 kV and current levels ranging from 225 A to 1200 A. Traction converters can be generally classified into 2-level, 3-level and multi-level converters. 2-level and 3-level converters are mostly used in railway traction converters. 2-level converters offer advantages such as simple control, simpler DC bus structure, and fewer circuit components, making them preferred in converters using up to 1.8 kV DC bus voltage. 3-level converters are known for lower power loss, lower current and voltage total harmonic distortion, and lower voltage levels for circuit components along with low common-mode currents and voltages. On the other hand, 2-level converter employing SiC semiconductors can be preferable since it allows higher switching frequencies with lower power losses. Some of the advantages of the 3-level converter can also be achieved in the 2-level converter, indicating that the 2-level converter will likely continue to be used for railway traction converters. In this thesis, a power module platform is proposed as a subassembly for traction converters including IGBT modules, gate drivers, DC-link capacitors, heatsink, DC busbar, AC busbars, current sensor and temperature sensor. 100x140 mm footprint 3.3 kV IGBT modules with the current ratings of 450 A, 600 A and 800 A are applicable to the platform. Using these IGBT modules by no-paralleling, two-in-parallel and four-in-parallel, the power module platform can be utilized to build the rectifier and inverter circuits of the traction converters by only changing IGBT module type, gate driver configuration and AC busbar. Using appropriate power module configurations, 400 kW, 800 kW and 1250 kW traction converters that correspond low, mid- and high-power traction converters can be built up. The 800 kW and 1250 kW traction converter electrical and thermal simulation models are created using PLECS. The power modules are used in traction converter models to obtain power module electrical and thermal performances. Power losses and chip junction temperatures for rectifier and inverter modules are determined at the nominal operating points of the traction converters. According to the results, PM452 and PM454 (power modules with two-in and four-in-parallel 450 A IGBT modules) are found to be the most suitable for 800 kW traction converters while PM802 and PM804 (power modules with two-in and four-in-parallel 800 A IGBT modules) are found to be the most suitable for 1250 kW in terms of junction temperatures. A test setup is introduced to execute double-pulse tests (DPT) and continuous operation tests (COT). DPT results are evaluated considering commutation inductances, current sharing deviations, switching losses, voltage overshoots during turn-off and rate of change of current (di/dt) during turn-on. COT results are evaluated in terms of power losses and thermal performance. By means of the experimental results, it has been shown that this power module platform is applicable to mid- and high power traction converters considering the limits of semiconductor junction temperatures, current sharing deviations, power losses and commutation inductances.