Fundamentals of EV Battery Pack Thermal Management
Designing a high-voltage battery pack for electric vehicles involves complex scaling from individual electrochemical cells up to modules, and finally to the complete pack structure. A critical aspect of this scaling is managing the electrical and thermal loads simultaneously to prevent accelerated degradation or catastrophic thermal runaway.
Series and Parallel Topologies (NsNp)
The topology of the battery pack determines its overarching electrical characteristics. Cells placed in series (Ns) increase the nominal Pack Voltage, crucial for driving high-power traction motors efficiently. Cells placed in parallel (Np) increase the Pack Capacity (Ah). The total pack energy in kWh is essentially the product of the scaled voltage and capacity. Understanding this cell-to-pack ratio directly dictates the overall internal resistance of the system.
Heat Generation and Steady-State Temperature
As current flows through the battery pack, the inherent internal resistance of the cells (Rcell) leads to Joule heating (I²R). During high C-rate discharging or fast charging, this heat generation (Q) can be immense. The pack's cooling system—often utilizing liquid cold plates—is quantified by its Thermal Resistance (Rth). By evaluating the heat generation against the thermal resistance, engineers can estimate the Steady-State Temperature (Tss). Maintaining this temperature below 45-50°C is strictly required in modern EV design to ensure longevity and safety.