Low-Loss Chokes for Inverters in Rail Vehicles

SMP Sintermetalle Prometheus GmbH & Co KG (SMP) has developed a range of chokes for use in railway technology. The inductive components are installed in the inverters for three-phase asynchronous motors and on-board units. They are low-loss, resistant to temperature and impact, and quiet.

The task of the chokes is to limit not only the input current on the primary side, but also the output current on the secondary side in the inverters for three-phase asynchronous motors and on-board units. In order to minimise losses in the inductive components, SMP uses core material of powder composites developed specifically for these applications. Besides their low loss characteristics, the components for use in rail vehicles must fulfill a number of other demanding requirements: they must be resistant to vibration and impacts as well as to high temperatures, they must fit into small spaces, they must be completely impenetrable by dust, dirt and water, and those that are used in the passenger cars must also be very quiet.

Inductive components from SMP are able to sustain voltage rise rates of up to 10 kV/µs. After installation in the inverters, they undergo rigorous shake tests to ensure that they are resistant to impacts and vibration in all directions. In order to withstand the high temperatures that prevail in railway applications, all chokes from SMP are constructed in compliance with the UL-listed Class H insulation system, which provides thermal protection up to 180°C. A protective paint coating according to IP66 protects them from dust and water and enables them to be fitted outside the inverters. The advantage of this kind of installation is that the heat generated by the choke is discharged outside the inverter, so fans are not needed to dissipate the heat. Another advantage is that the inverter can then be designed with considerably smaller dimensions. The choke can also be adapted to the substantially lower ambient temperatures in underfloor-mounted electronics. To simplify mounting outside the inverters, SMP also provides the chokes with special mounting fixtures. SMP chokes for use in passenger coaches are made from a magnetostriction-free material developed specially for this purpose, which makes them very quiet.

Besides railway engineering, SMP’s inductive components are used in inverters for industrial applications, in wind turbines, in photovoltaic inverters, in medical engineering and many other drive and power electronics applications. SMP’s inductive components can be produced for frequencies of up to 200 kHz and currents of up to 1000 amperes. Their sizes range from 36 mm to 300 mm diameter and their weight from 50 g to 130 kg. Depending on the application, degrees of protection from IP00 to IP66 are available. All components are RoHS- and REACH-compliant and the materials used are UL-listed.