Depending on the car model and manufacturer, electric cars require very different charging voltages depending on the battery voltage selected. Charging columns must be correspondingly flexible and cover a wide voltage range. Common systems are based on three power levels to convert the output voltage into the required final voltage.
»We have succeeded in doing without one power stage by integrating a kind of 'gear shift' in the second stage. This translates the output value of 680 to 840 V into the desired voltage,« explains project manager Prof. Dr. Christian Dick from the Institute for Automation Technology at the Technical University of Cologne. Doing without the third stage enables cost savings to be made on semiconductors and passive components. Due to the increasing charge level of the battery, more and more voltage must be provided during the course of a charging process to complete the process.
»Therefore, it may be necessary to shift into a higher gear during the charging process, which can lead to a risk of overcurrent. This is why we continuously measure the current amplitude. If the peak values become too high, we automatically switch off the power supply for a few microseconds until the values have normalized. In this way we protect the system and the battery without slowing down the charging process noticeably,« explains Dick.
Function for bidirectional loading
To increase the application possibilities of the rapid charging system, the research team has also integrated a function for the bidirectional flow of energy. This means that the new technology can not only be used to charge, but also to extract energy from a battery and supply it to another system. For example, the technology could be used to move energy back and forth between the household storage tank and a car battery.