Medium-voltage charging station
In the “MS-Tankstelle” project, Fraunhofer ISE worked with industrial partners to develop the medium-voltage system technology for future fast-charging stations that will enable peak loads of several megawatts.
The number of e-vehicles in Germany is increasing the need for fast charging stations that can serve a large number of vehicles simultaneously, similar to today’s charging stations. These are particularly necessary on freeways, but also in urban parking garages and parking lots.
The average output of a fast-charging system for a car is 150 kW, for buses, vans and small trucks it currently rises to 350 kW. As electric charging is slower than the refueling process, in future charging stations will need around 15 to 25 charging points instead of eight to serve the same number of vehicles in the same amount of time. With parallel fast charging, the electric filling station calls up around 1.5 to 3.5 megawatts of power. This means that future fast-charging stations can no longer be supplied via the low-voltage grid – even if the charging station is not fully utilized, the power required would exceed 300 kW. Distribution within the filling station or parking lot should also not take place in the low-voltage grid, as the long cable runs (100 meters or more for 25 charging points) and the high power lead to high installation costs and high losses in the cables.
Charging at the medium voltage
The power electronic system for charging stations developed in the project with partners Sumida Components & Modules GmbH, Infineon Technologies AG and AEG Powersolutions GmbH therefore relies on a medium-voltage network that is operated with a rectifier at a voltage of 1500 VDC. The higher voltage level leads to a higher output with the same current strength, without the need to increase the cable cross-section. The significantly lower copper consumption makes a significant contribution to protecting the environment and conserving resources. The value of 1500 VDC was chosen as this is the limit of low voltage and other standards apply above this value. There are plans to increase the voltage beyond this in subsequent projects.
Modular approach for charging stations of different sizes
An electrically isolated converter couples the direct current (DC) distribution network to the vehicle battery and controls the fast charging process. The DC converters, each with an output of 175 kW, are designed so that they can be easily connected in parallel in the system. This modular approach makes it possible to build both lower-power charging stations for cars and higher-power stations for trucks.
For an uncomplicated charging process, the station should be fully compatible with the CCS1 and CCS2 (Combined charging system) standards that dominate in Europe, i.e. for currents of up to 500 A and a voltage of up to 1000 V in the vehicles. In addition, the concept should also support the Megawatt Charging System (MCS) standard. A second inverter module variant is planned for this, for which only a few components need to be adapted.
“The topology we developed in the project can be used not only for charging stations, but potentially also in renewable hybrid power plants or for the integration of stationary battery storage systems,” explains Andreas Hensel, Group Manager High Power Electronics and System Technology at Fraunhofer ISE.
A demonstrator of a charging point can be seen at the Fraunhofer Energy Alliance stand (Hall 5, D126) during E-World (February 11-13, Essen). (pq)
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