Case Study · Railway

HV input 3ph inverter for demanding railway HVAC systems

Rolling stock railway systems are usually fed from secured battery voltage (typically: 24V, 36V, 72V or 110V) or from the AC voltage supplied by a high-power auxiliary converter. However, when it is time to refurbish an old train, many peculiarities can arise.

The Challenge

In this case our customer faced the need to feed an HVAC system (fans and compressors) with an atypical voltage line: 500Vdc +/-2%. The challenge consisted on designing a new versatile 3-phase inverter to be used in two independent subsystems: supplying power to 3.2kVA HVAC compressors and feeding impulsion AC fans. In both cases it had to be possible to trim the output voltage and frequency and, most important, the input had to be fed with 500Vdc.

Powering The Challenge

We built a 3.2kVA railway inverter according to EN50155:2017 norm and with special design for enhanced life expectancy. The product featured a 500Vdc input and a configurable output voltage (from 200Vac to 460Vac and from 5Hz to 60Hz), remote controlling signals, alarms, soft-start ramps and RS-232 programming. Based on our experience in designing and manufacturing ruggedized 3-phase inverters, we were able to provide a custom product design meeting a tight schedule and reaching competitive NRE costs.

During the design phase and through follow-up meetings with our customer, we discovered that they wanted to use some contactors and relays between the inverter and the motor to be able to change configuration from Star to Delta so they would have two different motor speeds. We suggested to skip all these components, connect motor directly to the inverter and control the fan speed directly through the inverter output. Finally, we modified our initial design to add a control pin to indicate “high speed” or “low speed” so the converter fed the motors with the appropriate voltage and frequency (both programmable), saving costly extra components.