Normally, such converters are created out of individual modules. To avoid early failure, each module has to be tested during a period of 12 h. These tests will be done in a climatic chamber with a temperature between 35°C and 40°C. During the test, current, voltage and frequency have to be changed. If it is possible to change the direction of current or energy, this will be done at minimum every 10 minutes. This test will be done during the production of the converter. A certificate is included in the documentation.