SOMA implements test line for automotive power electronics in record time

Zollner Elektronik AG, provider of electronics services, has been selected as the full-service partner by a leading German automotive manufacturer and has thus been awarded the contract for the large-scale production of the central power electronics for two new electric vehicles.

Zollner has already been involved in product and process engineering and has also played an essential role within the qualification. At their Zandt site, located in the Bavarian Forest, Zollner established specially a clean-room production line.

SOMA: pioneering testing technology for automotive power electronics

Looking for a suitable provider of electrical testing systems within production Zollner found the right partner in Schalksmuehle in SOMA GmbH. As an independent member of the globally oriented KOSTAL group with its headquarters in Luedenscheid in North Rhine-Westphalia SOMA creates complete test systems for mechanical, mechatronic and electronic products for now more than 40 years. The product range and support facilities range from endurance and specification test systems used in the course of development, through to fully automatic functional test systems employed in full production. A highly qualified workforce of more than 50 employees is working in interdisciplinary groups in order to realise solutions for test and technical automation requirements.Bild SOMA erstellt Prüflinie klein

Unit under test: the integrated power electronics

The power electronics combines all components required for the vehicle’s energy management in just one single compact housing. This includes as well the inverter for the three-phase unit (drive motor), charging circuits for high and low voltage batteries, communication interfaces as the central control unit to control all function groups. In the vehicle the power electronics is directly mounted on the electric powertrain. Various pluggable connections allow a connection to the chassis’ high voltage battery, to the range-extender (this is an optional available conventional petrol engine with an attached generator to increase the range), to the charging socket and to different further loads inside the vehicle. The power electronics is being cooled with water during operation and testing.

From the first idea through to realisation

Many elements of the testing process and its realisation came only up during the project, which SOMA was awarded with by Zollner in May 2012. One of the main challenges was implementing the test procedure, which comprised several thousand steps, into an automated test system. Accordingly important was it from the beginning to offer the possibility to react appropriately flexible to product and test procedure changes or to further changes without overruns in time and cost budgets. This was done by modular construction and smart solutions. During the planning phase a multi-step concept was developed for a test system, which met the requirements.

One crucial element of the success of the project and realising the serial testing was the very close co-operation between SOMA and Zollner’s project engineers and the end customer. SOMA could prove itself once more as a competent and flexible partner.

Key Facts

• Modular system concept with independent EOL-test system, Run-In-test cell, flash-cell, security test cell (HV test, short circuit test, ground bond test)
• Integrated E-motor emulator with a nominal load of 160kW, built by SET/SPS Smart Power Systems
• Workpiece conveyor system with a carrier total weight of approx. 120kgs each
• Expendable regarding increasing quantities and future vehicle versions
• Logistical link and data-technical connection to upstream located assembly line and the downstream located packaging process
• Clean room production

System concept

The experiences SOMA had already gathered with the construction of several test systems for power electronics, e.g. in the field of photovoltaic inverters, were a benefit for Zollner in particular during development of the concept – when choosing a workpiece carrier system in order to link the single test systems for instance.

The actual testing is carried out in so-called test cells. Two test cells are currently integrated in the system. If required, the system can be extended by two further test cells in order to increase the system’s capacity or to decrease the average testing time by parallel testing. Together with the related workpiece carrier system the unit under test are forwarded into the test cell. Here the required electrical and hydraulic connections to the workpiece are established automatically. In view of the power to be transmitted and the requirements for interference immunity the SOMA engineers faced a particular challenge with the automated electrical contacting and the installation of the test system.

The units under are programmed with their specific data after successful testing. The test software is removed and the application software is activated. In order to avoid a delay in production a separated cell has been integrated for this flash process.

The SOMA test system is coupled via a portal handling system to the Zollner assembly system.

Test contents

Included in the complete testing of the power electronics are functional tests of all integrated modules. These are communication tests, tests of the different charging processes, stress tests at different operating points, safety function tests, tests of the internal measuring sensors and many more.

As many tests need high electrical power SOMA installed high performance power sources and loads. A special highlight is the electrical simulation of the vehicle’s electric motor with a so-called E-motor emulator, which is used for the run-in-test. In this test a heating system which is part of the test system heats the power electronics to a temperature of 70°C (158°F), and it operates at its limits. The emulator is able to simulate very dynamic driving profiles; even such profiles which cannot be realised with a real electric motor. The E-motor emulator which has been built for SOMA by company SET located in Wangen (Allgaeu in Bavaria), includes as well an electrical simulation of the vehicle’s high voltage battery.

In order to minimise the energy consumption of the test system, SOMA only used components which are able to feed back into the electrical grid. In simulated drive mode the test unit leads energy to the E-motor emulator which leads it to the battery simulator. In braking mode the E-motor emulator returns energy back to the test unit. The test unit leads it to the battery simulator which would correspond to recharging the HV battery in a real vehicle (recuperation).

After assembly the power electronics has to undergo particular security tests. For this purpose SOMA has constructed a HV-test cell which has been integrated into the Zollner assembly system separate from the large function test system.

Lighthouse project

The realisation of the test system for integrated automotive vehicle power electronics was one of the largest projects SOMA was involved in and has been successfully finalized with the official acceptance in December 2014.

For further information on SOMA and SOMA’s testing systems please refer to www.soma.de

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