Active Battery Balancing

General Procedure

• Redistributes charge between battery cells during the charge and discharge cycles

• Increasing system run time by increasing the total useable charge in the battery stack

• Decreasing charge time compared with passive balancing

• Decreasing heat generated while balancing, and less power waste than passive

• Uses inductive charge shuttling or capacitive charge shuttling to transfer the charge between the cells. 

Example Method (Buck-Boost)

• The charge from the high voltage cell is pumped into the inductor and then discharged into the low voltage cell by using the buck-boost converter.

• The charge is transferred from cell 1 to cell 2 by switching the MOSFETS sw1 and sw2. in the following manner.

1. SW1 is closed, allowing charge from cell 1 to flow into the inductor with current I-charge. Once the inductor is fully charged the switch SW1 is opened and the switch sw2 is closed.

2. The inductor is fully charged and will reverse its polarity and begin to discharge. Charge from the inductor flows into cell 2 with current I-discharge.

3. Once the inductor is fully discharged the switch SW2 is opened and the switch SW1 is closed to repeat the process. 

Active Cell Balancing During Discharge

• While discharging, some cells may become weaker and rain quicker, see picture below

• This leads to limiting the runtime of the system. Active balancing allows the distribution of charges from stronger cells to weaker cells. See the result below

Active Cell Balancing While Charging

• Without balancing, the weak cells reach full capacity prior to the stronger batteries, which limits how much total charge our system can hold. See the picture below.

• With active balancing, the stack can reach its full capacity.