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TE Connectivity White Paper /// Thermal Modeling for High Power Charging (HPC) of Electric Vehicles Page 4 Thermal Modeling for High Power Charging (HPC) of Electric Vehicles which are involved, i.e. car makers (OEMs) and the energy sectors, in which the following applies: • The typical EV use case varies globally. While European EV driv- ers expect their car to be capable of occasional long-distance trips, Asian EV drivers tend to use their cars for short distances in mega cities. HPC DC would enable EVs to be used in all cases. • Simply expanding the inner-city AC charging station network would not be sufficient because lower power charging times would re- sult in prohibitively long waiting times and queues. • One potential advantage of AC charging stations is that they permit bi-directional use of the vehicles connected to the grid. While DC charging stations are mere energy sources, electric vehicles connected to an AC charging station for a longer time can serve as local energy source for the grid during peak demand times which could gen- erate an economic benefit for the vehicle owner. This makes both charging technologies meaning- ful. • Increasing battery capacities (equaling longer ranges) can only be exploited in a helpful way if "bigger" batteries do not lead to even longer charging times. • New EV use cases, such as fully autonomous robot taxis, will only be profitable if they are constantly on the road. Fast charging is es- sential to enable this. With a charging power of 350 kW, it would be possible to gain up to 300 km of additional range within up to minutes maximum. This would turn EV "re-fueling stops" into ac- ceptably short breaks (compara- ble with combustion engine driven cars) and the DC charging station will quickly be available for the next vehicle. However, 350 kW of charging power at currents of up to 500 amps are the peak load for the complete current path from the charging station to the vehicle battery. The high current, flowing along this path, causes high heat losses since the electric resistance of all com- ponents (connectors, cable) inevi- tably generates heat. This heat loss needs to be factored into the design and dimensioning of all electrically conductive components to avoid over-loading or over-heating or a controlled de-rating of the charging current, should the battery begin to overheat during charging. While de- rating protects the battery, it also prolongs the charging time. This di- vergence of objectives needs to be solved in an optimal way. Thermal management can do this by predicting the exact state of all components in every segment of the structure at any time. 3. The Challenge of HPC HPC DC represents a peak load state for the electrical system in an EV. There is no other operating con- dition in which there is such a con- stant and high energy flow between the charging point and the vehicle and subsequently within the vehicle. Even aggressive driving, when the driver demands lots of power, will not result in permanent currents of the same magnitude The high charging current of HPC DC causes a strong temperature in- crease in all components which is further exasperated when the vehi- cle is not moving, as there is no con- vection available for cooling. There- fore, in order to facilitate HPC DC, the complete electrical system from the charging point to the vehicle bat- tery, needs to be designed and di- mensioned electrically and thermally. A major contributor to this challenge is that the higher the current, the larger the required cable cross sec- tion to carry the power at the same level of voltage without over-heat- ing. Within the vehicle, this is pri- marily a matter of weight and avail- able space. For example, it makes a considerable difference, in terms of cost, weight and bulk, as to whether a 50 mm 2 cross section or a 95 mm 2 cross section conductor between the inlet and the battery will suffice. An attractive option is therefore to increase the voltage, so the same amount of power can be transmit- ted at a lower current level. This ex- plains why some OEMs are planning to move from 400V to 800V sys- tems. While dimensioning electrical components potentially accounts for unwanted additional mass in the vehicle, it also approaches weight limits in the case of fixed charging cables (mode 4 cables). If HPC DC is to be a realistic proposition, the over- dimensioning of the cable and all the other electrical components must be avoided. 4. Today's Electrical Component Design The way in which electrical compo- nents along the high-current path have been designed to date is based on assumptions that are not really suited for either the dynamic load profiles of driving or the require- ments of HPC DC. Existing standards are based on static load points orig- inally used for the design of relays and (switch) fuses, which are deter- mined by statistical methods reflect- ing the frequency at which they oc- cur and their importance. This leads to the root mean square (RMS) val- ues representing static conditions (Fig. 1). Electrical interconnection compo- nents are designed in accordance

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