Page 60 - NEW Armstrong Book - 2

generation EVs to travel farther and be safer and more reliable.
Powertrain bus voltages
Today’s EV main power bus is typically 400 V, but there are 800-V powertrains in development — a level that is fast approaching Formula E’s own 900-V bus. High-voltage, wide- bandgap components such as SiC increase power density and allow smaller motors to be used, which will speed up the realization and adoption of higher-voltage buses.
Higher battery voltages also help in the volt/amp problem of fast charging. For the installed base of EV chargers, how- ever, changing battery voltages may be problematic. Future chargers will likely be digitally controlled to accommodate multiple voltages. Also, EVs will have to be flexible on charg- ing rates, as the rate will be based on the charger’s output capabilities.
The 12-V bus system will be around for the foreseeable future for both Formula E and EVs. This is because 12 V provides power to everything from sensors to infotainment systems to comfort and convenience. However, this does not necessarily imply a need for 12-V batteries. High-voltage DC/DC convert- ers, such as 400 V/800 V to 12 V and 48 V to 12 V, can address this issue.
Increasingly, 48-V bus systems are becoming a require- ment. Many motors, such as those driving the park assist and eTurbo, need a higher voltage to satisfy increased torque requirements. A solution to get to 48 V is to use two 12-V bat- teries and then boost one to 48 V. In the future, there will likely be one high-voltage battery with multiple voltage rails to support the different requirements of each of the elec- tronic loads around the vehicle.
Fast charging
Consumers expect commercial EV charging times to be similar to the time it takes to fill a gasoline-powered car at the pump. Although Formula E charging for third- generation cars will be 600 kW, delivering 4 kWh in 30 seconds, it is unlikely that these speeds will be available to consumers in the foreseeable future.
Most electrical grids are not designed for massive power transfers on the scale required for Formula E–style fast charging. Other limiting factors to the charging speed include the current capacity of the charger/cable, the impedance of the battery, and battery balancing.
As higher voltages reduce charge currents and transmis- sion loss, there will likely be higher battery voltages in the future. It is reasonable to envisage charging stations, similar
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ASPENCORE GUIDE TO SILICON CARBIDE