Speed, valid results and test benches that are always state-of-the-art - these are the key cornerstones of drivetrain testing, i.e. testing and measuring the performance of a drivetrain in the overall system. Atesteo (formerly known as GIF - Gesellschaft für Industrieforschung), headquartered in Alsdorf, North Rhine-Westphalia, is a company that has been working in this field for 30 years and now operates around 130 drivetrain test benches worldwide.

The entire system has a modular design. All six inverter units have their own control panel. It is recessed into the control cabinet door and allows a quick status check even during operation.

© Danfoss

In order to be able to offer the right measurements and tests for every task, Atesteo uses a large pool of machines with up to 8000 rpm and 3000 Nm torque, which can be individually combined depending on the task. In this particular application, the task was to test an all-wheel drive transmission. The transfer case receives its speed and torque directly from an electric motor, which is a special design for high speeds with high torques. As this is a transfer case for an all-wheel drive vehicle, there is one output shaft for the front-wheel drive and one for the rear-wheel drive. Both output machines are torque-controlled and thus simulate the speed of the wheels and the resulting torque acting on the transfer case.

The control system, which reads the original, pre-recorded and slightly smoothed driving data from the test track to be used into the control program, then specifies the speed and the desired torque to the 'Vacon NXP' frequency inverter used in the test bench. Only the control unit is fast enough to calculate all the necessary data in good time and to regulate the torque almost every second. The frequency inverters operate in the range from 0 to 200 Hz, which places enormous demands on their performance. In addition, the speed and torque must be in line with the original vehicle, otherwise there would be a slight shift in the signals.

However, the Vacon inverters used are not only subject to enormous demands in terms of performance; the cabling between the motor and frequency inverter also had to be implemented quickly and easily. Atesteo is taking a new approach here by installing all the inverters or the individual modules of the system in an overseas container.

Frequency inverter in container

Original data from test tracks is used for testing. Only the control unit can calculate the data in good time and then specify the speed and desired torque to the frequency inverter.

© Danfoss

The advantage of this solution is that the container, which was built in Finland by a Danfoss Drives partner company specializing in such containers, arrives at the installation site fully designed, assembled and tested. The specialists there then only have to lay and connect the supply, motor and control lines as well as the cooling circuit. Last but not least, this solution also offers robust protection against cold and wet conditions.

The container accommodates the entire Vacon NXP system inverter system, which consists of an active front-end unit. On the one hand, this feeds the necessary energy into the intermediate circuit - also known as the DC bus - which serves as the power supply for the inverter units. On the other hand, it also feeds energy generated during braking back into the grid. A total of four 'small' converter units with 730 A each and two large converters with 1640 A each operate in the container.

Atesteo opted for this setup because it allows the small inverters to be connected individually (master-follower mode) or two inverters to be connected in parallel, depending on the power of the connected motor. In the test setup described here, one of the more powerful inverters drives another motor. The second 1640 A inverter is still free and can be used for another setup, for example. The connections running in a double floor of the container are very easy to establish from the container to the test stand. Overall, this system design allows extremely flexible use and simple adaptation to the task at hand - with short conversion times and therefore short reaction times.

To enable installation in the container, a compact cooling solution was also required, which is why Atesteo opted for the so-called 'Liquid Cooled Series' from Danfoss Drives. The fact that the Aachen site has its own cooling tower also spoke in favor of water cooling. Danfoss developed the modules from scratch for this type of cooling. These only give off 0.1 % to 0.15 % of their heat losses to the air (example for a liquid-cooled frequency inverter with 400 kW, 690 V(AC).

Finally, the inverters are controlled by the test stand's control system via an Ethercat connection, while the frequency inverters are also parameterized and monitored from the test stand's master computer via a dedicated CAN bus or the CANopen protocol. And Atesteo can use the five built-in expansion slots to adapt the devices to the test stands with additional I/O, fieldbus and functional safety cards if required.

Author:
Ulrich Mauel works at Vacon in Essen, a member of the Danfoss Group.