Model-Based Analysis of a 12V Dual-Battery System for Design Optimization of Microhybrid Vehicles

12V microhybrid (MHEV) technology has potential to deliver 5-10% fuel economy improvement over traditional gasoline vehicles without adding excessive cost to the consumer. Parallelizing the traditional lead acid battery with a high-power lithium ion battery has the potential to enable critical microhybrid function such as regenerative braking.  Enabling a low-cost passive connection between the lead-acid and lithium-ion batteries requires compatibility between the two batteries, including design factors such as battery size, resistance, and open-circuit voltage (OCV).

In this work we have developed a dual-battery model that couples an electrochemical model of a lithium ion battery and an equivalent circuit model of a lead acid battery in order to perform design optimization of a passively-connected dual-battery MHEV system. We analyzed the dynamic responses of the two batteries upon high power charge and discharge pulses, with and without simulated vehicle accessory loads. The current split between the two batteries is explored in detail as a function of pulse characteristics, operating voltage, and accessory load.  Finally, a simulated vehicle regulatory drive cycle, specifically the New European Driving Cycle (NEDC), is implemented for analysis of contributions of two batteries.