On the design of a direct cell coupled hybrid energy storage system for plug-in hybrid electric vehicles

A pack design methodology is proposed to meet USABC PHEV-40 performance targets using battery and ultracapacitor energy storage elements in direct coupled topologies. Simulated responses of temperature dependent power capability and cold cranking requirements are embedded in the hybrid pack analysis and design process. A case study based on an 18650 NMC Lithium-ion battery cell and a non-aqueous symmetric ultracapacitor is presented to investigate replacement tradeoffs between the two energy storage components. Among the performance metrics in the case study, ultracapacitors give the greatest improvement for short term two second power. However, the 10-second discharge power requirement is shown to be a limiting design factor to which the replacement of battery cells with ultracapacitors is less effective.