AUTOMOTIVE DESIGNSECTION TITLE
of standard-compliant charging communication during the DC charging process has been achieved by Innolectric. Te greatest challenge in this project was found in the high voltage battery. Several approaches have been analysed in deep detail, like optimisation of the charging strategy (eg. so-called boost-charging) and external cooling for heat exchange with an external cooling system integrated in charging station. But these approaches result in extremely high power losses of up to 40kW and in greatly reduced battery lifetime.
Te optimal solution for the battery has been found in optimisation of the power to energy ratio, thus enabling an efficient compromise between heat generation, service life, and range. In the same cell format and chemistry a li-ion cell can be optimised for highest energy density or for higher power by variation of parameters like particle sizes, porosity, conductive additives and anode and cathode thickness. Te various cell formats that made it to
the shortlist were tested by the high-voltage test service provider Voltavision. Te appropriate battery was developed by hofer powertrain and the University of Bochum. Te final battery prototype uses cells with a P/E ratio of 3.5 and an energy density of 210Wh/kg. Te new high power prototype battery with Li-ion technology has a voltage of 645-903V and can be charged at a constant rate of 460A.
THE RESULTS In this project, the entire energy flow chain from grid to the vehicle was optimised, built and validated using a prototype vehicle and charging system. In the final charging test a constant charge rate of 460A
Charging Power of the Porsche Taycan 4S over State-of-Charge
was applied to the vehicle, resulting in 392kW charging power. After exactly 15 minutes, 98.1kWh had been charged by this. Due to the optimally chosen P/E ratio, the battery temperature increased by 26°C only, so that no extensive cooling was necessary. To proof the amount of energy
stored, the vehicle was discharged at 70kW, which is far more than average driving requires. Even so, 90.3kWh could be discharged. By this, 103% of the project target was reached. Te overall efficiency of charging plus discharging process is at a very high 92%. Tese 90.3kWh result in either
Measured charging current, voltage, power and temperature
410km real-world driving or 560+km WLTP range is it is communicated by vehicle manufacturers, charged in only 15 minutes.
Charging 400km real-world range in only 15 minutes is possible today. By the results of this project, such high charging rates will come at definite costs like reduced efficiency, reduced battery lifetime, convenience losses and increased production costs. As a solution, we suggest increasing the P/E ratio moderately, so that a minor reduction in EV range enables for fast recharging without the mentioned disadvantages.
Prof. Dr. Kai André Böhm is at hofer powertrain.
www.hofer.de
Charging Power of the Porsche Taycan 4S over State-of-Charge
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