Posted on 02 November 2019

First Frequency Converter for Compact Drives in Railway Applications

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Introduced at InnoTrans 2012

The compact drive is certified following to the railway standard EN 50155. Railway applications require a much higher quality level and more robustness than other industrial designs, especially in terms of mechanical and temperature shock resistance. The drive with 3 kW is used to drive a fan for cooling the engines of a high-speed train.

By Rainer Ihra, Marketing Direktor of A.S.T. Group

The fans used in high-speed trains for cooling the engine have to control the temperature to avoid overheating of the engines. During the train start driving and accelerating, the engines are heating up and the fans need to blow a lot of air through the engines for cooling. This requires the fan motor to drive at full speed, because during this phase there is not enough air stream through the driving wind blowing yet.

Compact drive 3kW

This is also a special challenge for the frequency converter and its electronics since especially in summer times the temperature very often is already at critical values. When the train drives at constant speed or reaches a train station, less cooling is required and the fans can slow down which also reduces noise emission.

The company SYSTEMAIR is designing and producing fan systems for tunnel and railway applications. Their engineers have designed the new fan for cooling the engines of highspeed trains and they have selected the new frequency converter controlled compact drive. The new compact drive consists of a motor unit manufactured by VEM and the frequency converter is designed and manufactured by A.S.T. Group. This system could be successfully tested already to meet all of the railway requirements. Such a system not only must reach the higher quality standards but also pass additional high voltage, temperature and climate tests which are explained below in this article. Normally, a normal industrial drive would be tested at temperatures of 0 to 40 degrees Celsius. In railway applications, however all components have to guarantee their nominal performance during quick temperature and climate changes. In hot summer the engine of high-speed train can be heated up to 70 degrees C even during standby. In this environment while the train starts moving and accelerating, it generates extra heat by powering up the engine, the frequency converter must control the fan to cool the engine down to 50 degrees Celsius within 10 minutes. Aditional temperature shocks occur which impact the electronics when the train passes through tunnels. All components must pass several climate and temperature tests as well as mechanical tests with shocks at 5 times earth gravities following the DIN standard EN 61373.

Other railway applications for compact drives using A.S.T.s frequency converters with the same high robustness and power specified up to 8.5 kW have been seen at InnoTrans 2012.

To design a frequency converter that drives a motor at variable speeds is actually very simple in the first step. However, to make the product robust to guarantee it‘s performance in the railway industry requires a lot of experience, simulation and testing. During the design phase, A.S.T. engineers always spend most of their development time in their testing labs to get EMI approvals as well as shock and temperature stress resistance. They need to repeat all tests after any slight change or modification, even after the change on components layout.

Complete fan unit with compact drive

One of the requirements in the railway industry which refers to the mechanical stress resistance, all parts and electronic components must be available to have 5 times stronger shock resistance than the earth gravities, while several additional tests must be performed in the same surroundings. A 5 times of the earth gravities is much higher than the vibrations in a typical industrial application. Design engineers therefore must not only select all components carefully but also consider the positioning and mounting of the different parts. The question of selecting and using any glue, moulding or the mounting material must refer to the temperature and climate shock tests and so on. Mechanical stress in a high-speed train could otherwise cause components to fall from the PCB board or material cracks could cause short circuits within the insulation material.

Compact drive with 8,5 kW

Furthermore, during and after the mechanical stress tests there are a lot of temperature and humidity cycles to be carried out in order to guarantee no humidity could shorten the high voltage insulation under any circumstances. The engineers have to consider all of these impacts when selecting the components and also when deciding certain production processes and housing technologies for electronic components as well as the motor parts. When running such a system in a train application the actual vibrations and mechanical stress to the parts shall not have any effect on the nominal performance of the system.

The same is true for temperature resistance. At high temperatures of 70 degrees Celsius, the product must still be able to perform within its specified limit, especially since in trains very often the highest performance is required at the same time when the high temperature occurs and less cooling support is coming from the driving airstream. In other applications like air pressure controls, the high performance is required when the train passes a tunnel with high speed to avoid uncomfortable air pressure changes in the cabins.

In all of these designs it is important during the components selection to understand the impact of quick temperature changes and mechanical stress. For example, what will be the temperature impact to switching speeds of the IGBTs and the driving circuits. Especially, even the two parts are close together there could be sudden temperature changes and differences that impact only the driving circuit to be at -20 degrees Celsius while the IGBTs have a temperature of 70 degrees Celsius. All of these extreme situations must be simulated and tested as close to the practical use as possible.

Furthermore, the finished product has to go through actual operating tests during the time of qualification. These tests are done with the train driving through various tracks simulating several extreme situations.

Even the new compact drive being qualified for railway applications needed to go through these additional tests from the railway production companies before getting full approval and acceptance. The partners VEM and A.S.T. are the first manufacturers to meet all of these high robustness and quality requirements in this market. We are looking forward to higher quality travelling in modern highspeed trains as well as saver products where more robust drives are required.

About the Author:

Rainer Ihra is Marketing Director of A.S.T. Group. With its headquarter in Wolnzach (next to Munich) the A.S.T. Group also has facilities for research and development, production and testing in Dresden and Berlin. Before joining A.S.T. Group Rainer Ihra has been working for various high power semiconductor manufacturers. email:


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