Abstract
This paper proposes a fast cell-to-cell balancing circuit for lithium-ion battery strings. The proposed method uses only one push-pull converter to transfer energy between high- and low-voltage cells directly for a fast balancing speed. The switch network for selecting a certain pair of cells is implemented using relays to achieve a low cost. The control circuit is composed of a battery-monitoring IC and a digital signal processor (DSP) to monitor the cell voltage and to protect the batteries. In order to prove the validity of the proposed method, a prototype circuit is built with twelve lithium-ion batteries in a string. The experimental results show that it takes only 50 min to balance twelve lithium-ion batteries during the charge with 89.5% maximum efficiency. The outstanding performance of the proposed cell balancing circuit is verified through its comparison with other methods in terms of several factors, such as the balancing time and the implementation cost.
Highlights
Nowadays, lithium-ion batteries are being used increasingly for automotive applications
A battery string with a large number of cells connected in series and in parallel is necessary for many applications that require high power and high voltage, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and energy storage systems (ESSs) [1]
The balancing circuit needs to work in three modes, such as relaxation mode, charging mode, and discharging mode for fast and high efficiency balancing
Summary
Lithium-ion batteries are being used increasingly for automotive applications. A battery string with a large number of cells connected in series and in parallel is necessary for many applications that require high power and high voltage, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and energy storage systems (ESSs) [1]. The weakest cell undergoes overdischarge and undercharge and eventually reaches failure. The normal cell may experience overcharge because the charge operation continues until the string voltage reaches the nominal value. In this case the voltage of the normal cell may exceed the maximum charge voltage and it may cause an early failure due to the accelerated degradation [1]. The cell balancing circuit is crucial for the battery strings or modules [3]
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