Scalable power solutions for railway applications

Author: P-DUKE Technical Department

Translation: OLFER Electronics Marketing Department

Although the external design of trains has barely changed over the years, their interiors are constantly evolving. Electrification and the incorporation of new technologies are progressing rapidly to improve safety, reliability, and operability. Increasingly, mechanical components are being replaced by more economical and less faulty electronic devices; monitoring systems allow for the supervision of all train functions, and communication with the control center is continually expanding.

This transformation is especially visible in the driver's cabs, where monitors have replaced analog gauges or warning lights, and fewer switches and levers are used. Even in less visible areas, a large number of computers, GPS systems, GSM communication units, and bus systems are employed to process the numerous control signals distributed throughout the train.

One of the biggest challenges in increasing electrification is available space. The mechanical design of a train cannot be easily modified, and devices with more features and higher power requirements must fit within the space defined by the existing system. For power supplies and DC/DC converters, this means the need for significantly higher power density and efficiency.

That's why manufacturers are looking for uniform solutions that reduce development costs and minimize the number of power variants. The key is to have modules that can be easily adapted to the different voltage and power requirements of each application, without redesigning all the electronics.

P-DUKE's new QBE family of DC/DC converters, in standard quarter-brick format (57,9 x 36,8 mm or 2,28 x 1,45 inches), allows customers to design more compact and powerful solutions that can be adapted and scaled to different applications simply by replacing the module and modifying some external components.

In one specific case, a client wanted to redesign a train's central door control unit to incorporate new safety features, including ASDO (Automatic Selective Door Opening), an automatic selective door opening system that uses GPS information. As a result of these new features, the power requirements doubled, from 12V/35W to 12V/70W. Furthermore, the client wanted to reduce development costs by using the same power supply design for a door opening circuit that required 24V/95W.

The previous system used a 40W converter, with a 2 x 1 inch format and an efficiency of 86% at 35W of output power.

The losses in the converter are:

The generated heat was dissipated into the system through the surface of the module and an additional heat sink.

The new P-DUKE QBE75W module, designed to work under the demanding environmental conditions of railway applications, uses advanced power conversion technologies and achieves an efficiency of 91% with a load of 70W, generating losses of only 6,9W.

Although the power doubled, the losses only increased by 20% (1,2W).

Thanks to the improved thermal design of this module, most of the heat can be transferred through the motherboard to the metal chassis of the device, thus reducing thermal stress on the rest of the electronic components.

The QBE family is available with different input voltage ranges:

• 24V (9-36V)
• 48V (18-75V)
• 110V (40-160V)

These ranges allow coverage of the main voltages used in railway applications, including brownouts and transients.

Why not use a single module capable of covering the entire voltage range?

A design with an input ratio of 8:1 or 12:1 makes it difficult to maintain optimal efficiency across the entire operating range, as all components must withstand both the high currents present with low input voltages and the higher operating voltages when the input voltage is high.

The input current is calculated using the following formula:

This graph shows the different input currents for different operating voltages, with an efficiency of 91% and an output power of 70W.

It is clear that a "one size fits all" design is not ideal when seeking maximum power density and efficiency, since most railway systems are designed and configured for a specific train application, where the supply voltage never changes. This allows for the optimization of external components such as EMI filters, fuses and connectors specifically for each train. In this way, it is only necessary to design the PCB to support the maximum expected currents and the different component variants.

As is the case with virtually all current CPU boards, the one used in the door opening control system incorporates a VRM (voltage regulator module) that generates the low voltages required for the microprocessor from the 12V bus, while the remaining voltages needed for memory and interfaces are generated by lower-power DC/DC converters. Due to the high isolation requirements of the interfaces, a P-DUKE module with 3000V DC isolation was selected.

For the electric door opening system that requires 24V/95W, the customer can replace the previously used half brick module with the new QBE100W, which has a quarter brick format, is 40% more compact and has a 4% increase in efficiency, thus reducing losses by 33%.

The QBE family offers output voltages from 3,3V to 54V, with identical electrical behavior, EMI, and PCB design in both the 75W and 100W versions. This allowed the 100W solution to be designed in a matter of hours, rather than weeks or months, without the need for extensive additional testing or costly certification processes.

What if an application requires a different output voltage? Simply replace the module with another model from the same family and adjust a few external components.

Blocks diagram

Products

Central Door Control

Door opening