Sustainable Rail Transportation With High Power SiC Modules: Part 2

In the first part of this blog, we had a look at how energy-efficient high-power modules contribute to the decarbonization of railway transportation. This part will focus on the future of traction: high-power silicon carbide modules, their key features, and the multiple system benefits they enable.

Silicon carbide power modules and hybrid-propulsion trains: It’s a match!

As we inch towards a future of net-zero emissions, diesel trains are being replaced by hybrid-propulsion trains. These can operate with the support of electricity from overhead lines or – where electrification of railway track is not feasible – from on-board batteries or hydrogen fuel cells. For such hybrid-propulsion trains, energy efficiency and weight optimization are of crucial importance. Both can be delivered by Infineon’s new high power silicon carbide modules.

From key features to system benefits

Compared to silicon power semiconductors, silicon carbide semiconductors have significantly lower power losses and therefore enable energy-efficient traction converters. In a field test organized by Siemens Mobility and the Munich public transportation company SWM, Infineon’s XHP 2 CoolSiC power modules demonstrated a 10% increase in energy efficiency compared to silicon modules.

Fig. 1: Field test in Munich tram: Infineon’s XHP 2 CoolSiC MOSFET with .XT enabled 10% energy savings.

Infineon’s new silicon carbide power modules pack a lot of power in a small footprint and therefore enable more compact traction converters.  Specifically, when comparing the performance of the 2-level, 3-phase motor inverter based on the 3.3 kV IGBT IHV solution to the performance of the 2-level, 3-phase motor inverter based on the new 3.3 kV SiC XHP 2 modules, the silicon carbide-based solution (with 50% smaller footprint!) results in 50% lower losses compared to the IGBT solution, resulting in 50% more output current at the same switching frequency (1.5 kHz), or the same output current at a four times higher switching frequency (6 kHz instead of 1.5 kHz).

Fig. 2: Key features of XHP 2 CoolSiC MOSFET 3.3kV with .XT technology.

Moreover, by enabling traction converters to operate at high switching frequencies, silicon carbide power modules enable a reduction in the size and weight of various bulky magnetic components in the system.

Energy efficiency and weight optimization are of crucial importance for hybrid propulsion trains. Both aspects help extend the range that these trains can cover when powered by batteries or fuel cells. In the case in which there is no need for extending the catenary-free mileage of the train, improved energy efficiency and weight reduction can be used to decrease the size of the battery, which will result in corresponding cost-down. This is important because batteries are still the main cost drivers of such trains.

Last but not least, silicon carbide power semiconductors contribute to quieter train systems. On one hand, low-loss, energy-efficient silicon carbide semiconductors require less cooling, which allows for simplified cooling systems (for example, passive air cooling instead of forced air cooling), meaning the fans can be eliminated and cooling made quieter. On the other hand, operating traction converters at higher switching frequencies makes it possible to reduce the audible noise emanating from the train motor.

Fig. 3: Key features of XHP2 CoolSiC MOSFET with .XT enable multiple system benefits.

Enhancing the lifetime in the application

In addition to power density, energy efficiency, and weight optimization, certain applications like railway transportation also require high cycling capability from the power modules. To understand this, let’s consider an example of a regional train. During its service lifetime of about 30 years, such a train will make approximately 900,000 start and stop events. Each of these events comes with a temperature and power cycle that causes thermomechanical stress on the interconnection layers in the power module, for example on the chip’s bond wires or on the die-attach layer just underneath the chip. This thermomechanical stress causes aging and reduces the lifetime of the power modules in the application.

Fig. 4: .XT technology enhances the lifetime of silicon carbide power modules in applications with demanding mission profiles, like railway traction.

Infineon’s XHP 2 CoolSiC MOSFET solution combines high-power silicon carbide with advanced .XT interconnection technology. The .XT technology is targeting exactly the layers under the most stress in such cycling events, making them more robust and reliable. This boosts the power cycling capability and extends the lifetime of the product in the application.

To illustrate the power of .XT, a lifetime simulation based on the exemplary mission profile of a line-converter in a regional hybrid-propulsion train was performed. We compared SiC with standard joining technology (Al bond-wires, Al front-side metallization of the chip, soldered chip on a substrate, system solder) and SiC with .XT (Cu bond-wires, Cu front-side metallization of the chip, sintered chip on a substrate, hi-rel system solder).

Fig. 5: Results of a lifetime simulation of SiC with standard joining technology (left) and SiC with .XT (right) in a line converter of a hybrid propulsion train.

The simulation results showed that .XT extended the lifetime of the product by an order of magnitude — from approximately 4 years in the case of SiC with standard joining technology to approx. 40 years in the case of SiC with .XT.  This demonstrates that .XT is crucial for enabling the full utilization of silicon carbide at higher junction temperatures, in applications with demanding mission profiles, like railway traction.

On the (train) track to a sustainable future

The future of railway transportation is electric. High power technologies like Infineon’s XHP 2 CoolSiC MOSFET with .XT interconnection technology are paving the way toward this reality. By enabling energy-efficient, compact, quiet systems with enhanced lifetimes, these technologies are accelerating rail transport’s decarbonization. As we progress along this electrification journey we may not be at the final destination yet, but with technologies like these, we are certainly on the right track.

To find out more about these power modules and how they contribute to the decarbonization of transportation, check out part 1 of this blog and watch our Mobility Tech Talk.