A novel battery cell balancing circuit using an auxiliary circuit for fast equalization

Abstract

This paper proposes an improved cell balancing circuit for fast equalization among the lithium ion (Li-ion) batteries. Usually, the battery cell balancing circuit uses the sensor to estimate the accurate SOC (state of charge) of each battery cell and to operate the switch selectively [1], but it makes the system bulky and expensive. A simple voltage sensorless charge balancing circuit has been proposed in [2]. This cell balancing circuit automatically transfers the energy from the high-voltage battery cell to the low-voltage battery cell. But it needs the switch which has low on-resistance, since the balancing speed is limited by the on-resistance of the switch. Also, as the voltage difference among the battery cells is decreased, the balancing speed is decreased. To ensure that the battery can operate in the safety state, the fast balancing speed must be obtained. In this paper, the balancing speed of the cell balancing circuit is enhanced by using the auxiliary circuit. Switching operation of the proposed circuit is controlled by the comparator and the flip-flop, gate devices. So there is no need for the complicated algorithm to control the switching operation. The simulation results are provided to verify the validity of the proposed cell balancing circuit.