TE - White Papers

TE Connectivity White Paper /// Thermal Modeling for High Power Charging (HPC) of Electric Vehicles Page 7 Thermal Modeling for High Power Charging (HPC) of Electric Vehicles of charging time (combined AC and DC) over the service life of the vehi- cle, systemic simulation offers a po- tential solution for the comprehen- sive testing profiles. The Challenge of HPC It is therefore necessary to find a dif- ferent tool for a timely definition of a safe, and economically feasible de- sign of a current path for HPC DC – and to provide proof of its safety. Us- ing a proven systemic thermal simu- lation makes it easy to test automat- ically an almost unlimited number of possible load profiles in advance. This will reveal potential thermal bot- tlenecks in the system that can be addressed via design changes. Using this methodology can reduce subsequent troubleshooting effort. The reduced investigative effort can be considerable because the thermal system is so complex and the exact root cause may not be in the orig- inally diagnosed component but in an adjacent component along the heat path. 6. Systemic Simulation Method This advanced systemic simulation methodology calculates heat losses along the high voltage path under dynamically changing load condi- tions and is based on Kirchhoff's cir- cuit laws. His "point rule" and "loop rule", known within electrical engineering, state that the sum of all currents at a "point" and the sum of all voltag- es in a "loop" has to be zero. At the same time, the rule states that ener- gy is always conserved. That means that the current that is transformed into heat (heat loss) due to the elec- trical resistance is not lost. Instead this heat energy is exactly equal to the difference between the electri- cal energy flowing into the circuit and the energy that is available at the target system. Equivalent circuit diagrams exploit the immediate and linear relationship between electrical and thermal behavior (Fig. 4). Consequently, equivalent circuit di- agrams (Fig. 5) serve to simulate the linked electrical and thermal be- havior. In the same way, a voltage sends a current through a resistor, a temperature difference causes heat transport. The different phys- ical forms of transport (conduction, convection, radiation) are each rep- resented by a resistor. Stored alge- braic equations in the component model continually calculate the heat generation depending on the ap- plied current and voltage as well as the ambient temperature. Based on this heat generation, the different possibilities for heat dissipation are represented by resis- tors (thermal barriers) and thermal masses/capacities in the equivalent circuit diagram representing the heat transport resolved over space via conduction within the material, via radiation and via convection. Using this fairly simple method, it is possible to simulate individual components (e.g. a contact), whole products (e.g. a connector, such as in Fig. 6) or a high voltage path, as heat generation and heat dissipation are predictable through loop-formation. Once cable models are made avail- able from the cable manufacturers, the intermediate sections can also be calculated. It is also possible to integrate components from different manufacturers (as per the on-board net), as all it requires is to enter the manufacturer-specific electrical pa- Electrical Thermal Current I P Heat Flow Voltage U T Temperature Resistance R R th Thermal Resistance Capacity C C th Heat Capacity Fig. 4: Correlation between electrical and thermal values form the basis for equivalent circuit diagrams. Fig. 5: Equivalent circuit diagram for thermal simulation: Resistors represent the three ways of heat dissipation.

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