Life estimation and Thermal management for a 48V mild Hybrid battery pack 2019-01-1001
The cycle and/or calendar life of a battery pack depends on its operating limits, usage pattern and environmental conditions. The operating limits depend on the operating SOC window and temperature boundaries. The driving pattern changes according to the vehicle class and user profile. Drive profile and usage can be estimated in terms of the energy throughput derived from the battery pack (Wh/km or Wh/year) or in terms of root mean square power, Prms (kW) for a single cycle.
Since, 48V m-Hybrid technology is a low-cost mass market solution developed by OEMs for meeting / reducing fleet CO2 emission targets, the 48V battery pack is most often preferred to be a passively cooled system. A passively cooled battery pack witnesses a rapid increase in temperature particularly in case of aggressive drives with high ambient temperatures. If maintained within the operating boundaries, the mild hybrid functionalities are severely compromised resulting in compromised fuel consumption improvement benefits. On the other hand, relaxing the operating boundaries will negatively impact the battery life due to exposure of the battery pack to intense thermal stress.
A lifetime estimation is provided for a passively cooled 48V battery pack for a aggressive Indian drive cycle. The impact on the battery life is then analyzed in terms of different End-Of-Life (EOL) criteria.
Further, various active-air cooling strategies have been evaluated at the vehicle level and the performances have been compared against a passively cooled battery pack. An actively cooled battery pack shows significant improvement in terms of availability of hybrid functions. The trade-offs between designing for thermal optimization, vehicle integration and battery life is discussed.