3.3-kV SiC MOSFETs Promise a More Efficient and Quieter Train Ride

On the current PCIM Europe 2023 convention, a number of silicon carbide machine producers and college researchers launched and shared efficiency traits of SiC MOSFETs on the 3.3-kV voltage score. This voltage is more and more being seen as key to assembly a number of future functions, equivalent to medium-voltage grid energy conversion at a 1,500-V DC-link voltage, photovoltaics and wind renewable-energy converters, in addition to traction inverters for electrical rail. On this article, we are going to focus on the brand new 3.3-kV SiC MOSFET modules from Infineon Applied sciences that may make important enhancements in fashionable railway traction programs.

The railway traction system

Determine 1 illustrates a simplified block schematic of the power-conversion necessities in an electrical practice software. The SiC gadgets discover functions within the rectifiers wanted to transform incoming AC energy from overhead strains to the DC-link voltage, the inverters to transform this DC-link energy to the motors and the DC/DC converters wanted for auxiliary energy programs and, within the case of hybrid propulsion trains, on-board batteries or hydrogen gasoline cells. A few of the key necessities for this software are:

• Excessive energy density and power effectivity, which guarantee much less cooling wants and better transport capability
• Lengthy lifetime (>30 years) beneath a mission profile that requires frequent power-level modifications from the acceleration and braking phases of the practice
• Use of standardized energy modules which might be scalable for the assorted energy ranges highlighted in Determine 1
• Particularly for the SiC MOSFET used right here, quick switching with low overshoots throughout transitions, in addition to strong short-circuit safety and surge-current ruggedness to make sure that module security specs are met

The three.3-kV CoolSiC MOSFET

The three.3-kV CoolSiC MOSFET utilized in these energy modules leverages the numerous years of expertise that Infineon has within the lower-voltage class of CoolSiC MOSFETs. As proven in Determine 2a, these are trench MOSFETs that reap the benefits of the elevated channel mobility alongside the favored A-plane (11-20). This improves the precise on-state resistance (R_DS(on)) in contrast with a planar MOSFET machine. A thicker gate oxide ensures good reliability.

As proven in Determine 2b, the JFET area of the three.3-kV machine wanted to be optimized for R_DS(on) enhancements. This was completed together with the optimization of the machine capacitances and short-circuit face up to time (tsc). Simultaneous reductions within the machine saturation present (Isat) and the ratio of the Miller gate-drain to gate-source capacitances (Cgd/Cgs) was doable by way of the tuning of the deep p-implant.2 The Isat discount improves the tsc. A decrease Cgd/Cgs ratio will increase dV/dt transitions for decrease switching losses whereas additionally minimizing overshoots seen on the gate and giving a better margin for the prevention of parasitic turn-on of the machine. The interior MOSFET physique diode is used for commutation. As a result of a Schottky diode is just not utilized in parallel, the general MOSFET chip space might be optimized for the module’s present score whereas additionally having a better surge-current score.

3.3-kV CoolSiC MOSFETs in XHP2 package deal with XT know-how

The XHP2 energy module package deal addresses voltage lessons from 1.7 kV to three.3 kV for each silicon IGBTs and SiC MOSFETs. This package deal optimizes the format and design of the DC (±) terminals and bus bar for a low module stray inductance of Ls~10 nH.² In a traction inverter software, the power-cycling necessities can create stress on the interconnections and restrict module lifetime. The .XT know-how, which was first applied in Infineon’s IGBT modules,⁴ is used for the three.3-kV CoolSiC gadgets housed within the XHP2 modules. As proven in Determine 3, the .XT options copper (Cu) front-side metallization on the SiC dies, together with heavy Cu bond wires. Thermal resistance is diminished, therefore bettering energy biking.

A few of the key options of the general module are depicted in Determine 4. The FF2000UXTR33T2M1 is a 2-mΩ module rated for a nominal present of 1,000 A, whereas the FF2600XTR33T2M1 is a 2.6-mΩ module rated at 750 A. The package deal has an isolation score (V_ISOL) of 6 kV and a stray inductance of Ls~10 nH.

Switching efficiency of the three.3-kV XHP2 modules

Determine 4 reveals the switching efficiency of the module at 25°C and 150°C beneath nominal working circumstances of I_DS = 1,000 A, V_DS = 1,800 V, V_GS = 15 V/–5 V and Ls = 30 nH. Flip-on di/dt = 7 kA/µs and turn-off dV/dt = 17.5 kV/µs had been measured with the gate-resistor choice used to make sure secure switching traits.

To guage the rise in energy density, the three.3-kV CoolSiC in XHP2 was in contrast with a 3.3-kV IGBT module with the identical module footprint of 140 × 100 mm (FF450R33T3E3). The simulation outcomes proven in Determine 6(a) had been completed at a DC-link voltage of 1,800 V and an operational junction temperature of T_vj = 125°C. It reveals that at a 4-kHz switching frequency, the SiC module produced a 7.3× increased I_rms worth (Irms_2 in Determine 6), in contrast with the Irms_1 worth produced by the silicon IGBT.

Evaluating the switching losses, at 4 kHz, the IGBT produced 561 mJ of loss, although its I_rms present was a lot decrease, in contrast with the lack of 395 mJ from the SiC MOSFET. If the SiC MOSFET had been to be run on the decrease I_rms worth of the IGBT, its losses can be 9.3× decrease than that of the IGBT. Decreasing lifeless instances throughout synchronous rectification within the converter can additional cut back the reverse-recovery losses, particularly at excessive temperatures, therefore lowering turn-on losses. For instance, utilizing a 1-µs lifeless time in contrast with 5 µs can enhance the I_rms present output by as a lot as 12% at a switching frequency of 10 kHz.

Discipline trial outcomes of the three.3-kV CoolSiC XHP2 module for railway traction

A joint area trial was carried out in 2022 by Siemens Mobility and Stadtwerke München (SWM) on a streetcar in Munich that was outfitted with the three.3-kV CoolSiC XHP2 energy modules for the traction inverter. This check was completed for a interval of 1 12 months, protecting a complete of 65,000 km. The outcomes from these checks confirmed a ten% enchancment in power effectivity, as proven in Determine 7. The burden and quantity discount of the converter and traction system are between 10% and 25%.⁷ As a result of much less warmth must be dissipated with SiC, smaller warmth exchangers might be used at decrease airflow charges, serving to enhance the aerodynamic drag on the practice. One of many enhancements from a passenger consolation viewpoint is the a lot quieter journey enabled by SiC. This comes from the mix of the upper switching frequency within the traction converter and smaller heat-exchange models. Trains that function on a hybrid propulsion system (equivalent to utilizing batteries or hydrogen gasoline cells for the power supply) for some components of the monitor that do not need the AC enter energy strains (i.e., catenary-free) will profit from the SiC-based traction inverter as a result of benefits talked about above. This could translate to prolonged catenary-free mileage.

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