Improvement of Available Battery Capacity in Electric Vehicles

Abstract

This paper proposes a new method to improve the available battery capacity in electric vehicles by connecting lead-acid batteries with lithium-ion battery in parallel to supply power. In addition, this method combines the discharge characteristics of batteries to improve their efficiency and lower their cost for electric vehicles. A lithium-ion battery set is used to connect with N sets of lead-acid batteries in parallel. The lead-acid battery supplies the initial power. When the lead-acid battery is discharged by the load current until its output voltage drops to the cut-off voltage, the power management unit controls the lead-acid battery and changes it to discharge continuously with a small current. This discharge can be achieved by connecting the lead-acid battery to a lithium-ion battery in parallel to supply the load power or to discharge its current to another lead-acid or lithium-ion battery. Experimental results demonstrates that the available capacity can be improved by up to 30% of the rated capacity of the lead-acid batteries.

Development of Battery Parallel Operation for Improving Battery Service Life and Flexibility in Electric Vehicles

“…A bi-directional dc-dc converter shown in Fig. 3 is employed [3]. The difference between a bi-directional converter and a general power converter is there is no fixed output and input terminal in its circuit operation but it needs to follow the power flow direction to define its output and input positions.…”

“…However, even if we connect the same type of batteries in parallel, it may still generate circulating current due to different internal impedance of the cells [1]. Therefore, there is a need to overcome such circulating current problem [2], [3]. There are literatures indicating the exploration of intermittent current discharge method using parallel-connected batteries to supply power.…”