Battery management for maximum performance in plug-in electric and hybrid vehicles

Battery energy and power density are limiting factors in the design of electric and hybrid vehicle systems, particularly in the context of wide-range cycling needed for plug-in systems. Many commercial hybrid designs are controlled around specific operating conditions for long battery life. In this paper, battery management aspects for long operating life are discussed. Electrical considerations in valve-regulated lead-acid batteries, nickel-metal-hydiride batteries, and lithium-ion batteries are described. Emphasis is provided on charge balancing requirements and state-of-charge operating ranges. The role of ultracapacitors for power buffering is addressed briefly. It is shown that lithium-ion cells offer considerable promise because of their high input-output energy efficiency and possibility of relatively wide operating range. Charge balancing is known to be a vital aspect, and balancing requirements are quantified for sample systems.