Methods and apparatus for detecting battery cell imbalance
Various embodiments of the present technology may provide methods and apparatus for detecting battery cell imbalance. The apparatus may provide a fuel gauge circuit to detect imbalance in a battery pack with two series-connected battery cells and determine the amount of imbalance using only the positive and negative terminal of the battery pack.
1. An apparatus capable of connecting to a battery pack, wherein the battery pack includes a first battery cell connected in series with a second battery cell, and has a first terminal and a second terminal, comprising:
a fuel gauge circuit configured to connect to the first terminal and the second terminal, and comprising:
a voltage detector configured to measure a total voltage of the battery pack;
a memory configured to store a first battery characteristic data indicating a relationship between open circuit voltage and capacity; and
a processor, in communication with the voltage detector and the memory, and configured to detect imbalance between the series-connected battery cells, comprising:
determine a first capacity based on the measured total voltage and the first battery characteristic data;
compute a first actual resistance of the battery pack using the measured total voltage and a first load current;
determine whether the computed first actual total resistance is equal to a theoretic resistance;
generating a first signal if the computed first actual total resistance is equal to the theoretic resistance, wherein the first signal indicates that the first and second battery cells are balanced;
generating a second signal if the computed first actual total resistance is not equal to the theoretic resistance, wherein the second signal indicates that the first and second battery cells are imbalanced;
compute a second actual resistance of the battery pack using the measured total voltage and a second load current; and
compute a second capacity of the first battery cell and a third capacity of the second battery cell using the computed first actual resistance, the computed second actual resistance, and a set of equations.
2. The apparatus according to claim 1 , wherein the memory is further configured to store a second battery characteristic data indicating a relationship between capacity, internal resistance, and current.
3. The apparatus according to claim 2 , wherein the theoretic resistance is selected from the second battery characteristic data.
4. The apparatus according to claim 1 , wherein the total voltage is the sum of a first voltage of the first battery cell and a second voltage of the second battery cell.
5. The apparatus according to claim 1 , wherein determining the first capacity comprises selecting a capacity from the first battery characteristic data that corresponds to the measured total voltage.
6. The apparatus according to claim 1 , wherein the set of equations comprises:
a first function describing a first resistance versus capacity curve with a first current parameter; and
a second function describing a second resistance versus capacity curve with a second current parameter.
7. The apparatus according to claim 1 , wherein the set of equations comprises an equation that describes a total capacity as the sum of the second capacity and the third capacity.