Method of estimating a charge state for a battery cell

1. A computer-implemented method of estimating a charge state for a battery cell comprised with a vehicle, the vehicle comprising a battery management arrangement which comprises a control unit, the method comprising:

forming a first, a second and a third battery cell equivalent models for the battery cell, where the plurality of battery equivalent models relate to a first, a second and a third operational states for the battery cell, respectively;

measuring an intermediate electrical current value of the battery cell;

determining, by the control unit and based on the intermediate electrical current value, if the battery cell is in the first, the second or the third operational state for the battery cell;

estimating, by the control unit, the charge state for the battery cell based on the battery cell equivalent model corresponding to the determined operational state; and

identifying, by the control unit, a transition between operational states, wherein an output parameter from a previously applied battery cell equivalent model for estimating the charge state is provided as an input parameter for a subsequently applied battery cell equivalent model for estimating the charge state, wherein:

the first, the second and the third battery cell equivalent models correspond to a charge battery equivalent model, a discharge battery cell equivalent model and a relaxation battery cell equivalent model, respectively,

each of the battery equivalent models for the battery cell is represented by a circuit model, and

each of the circuit models is an RC based circuit model.

2. The method according to claim 1 , wherein the charge state is at least one of a state of charge (SOC) and a state of energy (SOE).

3. The method according to claim 1 , wherein a provision of the output parameter from the previously applied battery cell equivalent model as the input parameter for the subsequently applied battery cell equivalent model provides for hysteresis in the transition between operational states.

4. The method according to claim 1 , wherein the output/input parameter is based on an electrical current value for the battery cell.

5. The method according to claim 1 , wherein the RC based circuit model for the relaxation battery cell equivalent model is of a higher order as compared to the RC based circuit models for the charge battery equivalent model and the discharge battery cell equivalent model.

6. The method according to claim 1 , wherein each of the battery equivalent models for the battery cell is different from each other.

7. The method according to claim 1 , further comprising:

estimating an intermediate temperature of the battery cell.

8. The method according to claim 7 , further comprising:

determining a proportion rate based on the estimated charge state and the estimated temperature, and

using the proportion rate in relation to the subsequently applied battery cell equivalent model for estimating the charge state.

9. The method according to claim 1 , wherein the first, the second and the third operational states for the battery cell are arranged as a state machine.

10. The method according to claim 9 , further comprising determining if the battery cell is in a fourth operational state for the battery cell and forming a corresponding fourth battery cell equivalent model.

11. The method according to claim 10 , wherein the third operational state corresponds to a charge relaxation battery cell equivalent model and the fourth operational state corresponds to a discharge relaxation battery cell equivalent model.

12. A battery management arrangement for a vehicle, comprising a control unit adapted to estimating a charge state for a battery cell, wherein the control unit is configured to:

form a first, a second and a third battery cell equivalent models for the battery cell, where the battery equivalent models relate to a first, a second and a third operational states for the battery cell, respectively;

measure an intermediate electrical current value of the battery cell;

determine, based on the intermediate electrical current value, if the battery cell is in the first, the second or the third operational state for the battery cell;

estimate the charge state for the battery cell based on the battery cell equivalent model corresponding to the determined operational state;

identify a transition between operational states, wherein an output parameter from a previously applied battery cell equivalent model for estimating the charge state is provided as an input parameter for a subsequently applied battery cell equivalent model for estimating the charge state;

wherein the first, the second and the third battery cell equivalent models correspond to a charge battery equivalent model, a discharge battery cell equivalent model and a relaxation battery cell equivalent model, respectively,

each of the battery equivalent models for the battery cell is represented by a circuit model, and

each of the circuit models is an RC based circuit model.

13. The battery management arrangement according to claim 12 , wherein the charge state is at least one of a state of charge (SOC) and a state of energy (SOE).

14. A vehicle comprising the battery management arrangement according to claim 12 .

15. The vehicle according to claim 14 , wherein the vehicle is at least one of a pure electrical vehicle (PEV) and a hybrid electric vehicle (HEV).

16. A computer-implemented method of estimating a charge state for a battery cell comprised with a vehicle, the vehicle comprising a battery management arrangement which comprises a control unit, the method comprising:

forming a first, a second and a third battery cell equivalent models for the battery cell, where the battery equivalent models relate to a first, a second and a third operational states for the battery cell, respectively;

measuring an intermediate electrical current value of the battery cell;

determining by the control unit and based on the intermediate electrical current value, if the battery cell is in the first, the second or the third operational state for the battery cell;

estimating, by the control unit, the charge state for the battery cell based on the battery cell equivalent model corresponding to the determined operational state; and

identifying, by the control unit, a transition between operational states, wherein an output parameter from a previously applied battery cell equivalent model for estimating the charge state is provided as an input parameter for a subsequently applied battery cell equivalent model for estimating the charge state,

wherein:

the first, the second and the third battery cell equivalent models correspond to a charge battery equivalent model, a discharge battery cell equivalent model and a relaxation battery cell equivalent model, respectively,

wherein the method further comprises:

estimating an intermediate temperature of the battery cell,

determining a proportion rate based on the estimated charge state and the estimated temperature, and

using the proportion rate in relation to the subsequently applied battery cell equivalent model for estimating the charge state.