Method for balancing states of charge of an electrical energy store

1. A method for balancing states of charge of an electrical energy store with a plurality of battery cells, the method comprising:

a) acquiring a voltage magnitude U mess,i that represents an electric voltage of a battery cell;

b) determining a maximum positive electric charge Q i,Pos of the battery cell with respect to an electric reference voltage level U BalLevel of all the battery cells of the electrical energy store with balanced states of charge according to

Q i,Pos =OCV PosErr ( U mess,i +U PosErr )− OCV PosErr ( U BalLevel ),

wherein OCV PosErr represents a no-load voltage curve with a positive capacity estimation error and U PosErr represents a sensor tolerance of the acquired voltage magnitude U mess,i and a modeled positive battery cell voltage error;

c) determining a maximum negative electric charge Q i,Neg of the battery cell with respect to the electric reference voltage level U BalLevel of all the battery cells of the electrical energy store with balanced states of charge according to

Q i,Neg =OCV NegErr ( U mess,i −U NegErr )− OCV NegErr ( U BalLevel ),

wherein OCV NegErr represents a no-load voltage curve with a negative capacity estimation error and U NegErr represents a sensor tolerance of the acquired voltage magnitude U mess,i and a modeled negative battery cell voltage error;

d) determining an electric charge ΔQ i to be balanced of the battery cell according to

Δ Q i =Q i −Q min ,

wherein Q i represents an electric charge of the battery cell with respect to the reference voltage level U BalLevel and Q min represents a minimum electric charge of all the battery cells located in a series circuit with respect to the reference voltage level U BalLevel ;

e) determining a charge error ΔQ i,Err , of the electric charge ΔQ i to be balanced according to

Δ Q i,Err =Q i,Pos −Q min,Neg ,

wherein Q min,Neg represents an electric charge Q i,Neg of the battery cell with the minimum electric charge Q min ;

f) determining an electric charge ΔQ i,use to be balanced of the battery cell according to

Δ Q i,use =ΔQ i −W*ΔQ i,err ,

wherein W represents a predefinable weighting factor;

g) calculating a duration t i,bal for balancing the state of charge of the battery cell on the basis of the electric charge ΔQ i,use that is to be balanced when the electric charge ΔQ i,use to be balanced exceeds a predefined threshold value, according to

t

i

,

b

⁢

a

⁢

l

=

Δ

⁢

Q

i

*

R

B

⁢

a

⁢

l

U

mess

,

i

,

wherein R Bal represents an ohmic resistance assigned to the battery cell;

h) balancing the state of charge of the battery cell for the duration t i,bal .

2. The method according to claim 1 , wherein the full charge error ΔQ i,err is subtracted from the electric charge ΔQ i that is to be balanced if the weighting factor W adopts the value 1, and the charge error ΔQ i,err is not taken into consideration if the weighting factor W adopts the value 0.

3. The method according to claim 1 , wherein the no-load voltage curve, the sensor tolerance, and/or the capacity estimation errors are determined statically and/or dynamically in order to determine the maximum positive charge Q i,Pos and/or the maximum negative charge Q i,Neg .

4. The method according to claim 1 , wherein the electric reference voltage level U BalLevel of the battery cells of the electrical energy store with balanced states of charge of all the battery cells is 3.7 V.

5. The method according to claim 1 , wherein the capacity estimation error of the no-load voltage curve OCV is a maximum of ±4%.

6. An electrical energy store comprising:

a plurality of battery cells;

at least one voltage sensor; and

at least one electronic battery control device, the at least one electronic battery control device configured to carry out the steps of the method according to claim 1 .

7. The electrical energy store according to claim 6 , further comprising:

discharge resistors for the selective discharge of individual battery cells.

8. A non-transitory, machine-readable storage medium containing instructions that, when executed by a computer, cause the computer to

a) acquire a voltage magnitude U mess,i that represents an electric voltage of a battery cell;

b) determine a maximum positive electric charge Q i,pos of the battery cell with respect to an electric reference voltage level U BalLevel of all the battery cells of the electrical energy store with balanced states of charge according to

Q i,Pos =OCV PosErr ( U mess,i +U PosErr )− OCV PosErr ( U BalLevel ),

wherein OCV PosErr represents a no-load voltage curve with a positive capacity estimation error and U PosErr represents a sensor tolerance of the acquired voltage magnitude U mess,i and a modeled positive battery cell voltage error;

c) determine a maximum negative electric charge Q i,Neg of the battery cell with respect to the electric reference voltage level U BalLevel of all the battery cells of the electrical energy store with balanced states of charge according to

Q i,Neg =OCV NegErr ( U mess,i −U NegErr )− OCV NegErr ( U BalLevel ),

wherein OCV NegErr represents a no-load voltage curve with a negative capacity estimation error and U NegErr represents a sensor tolerance of the acquired voltage magnitude U mess,i and a modeled negative battery cell voltage error;

d) determine an electric charge ΔQ i to be balanced of the battery cell according to

Δ Q i =Q i −Q min ,

wherein Q i represents an electric charge of the battery cell with respect to the reference voltage level U BalLevel and Q min represents a minimum electric charge of all the battery cells located in a series circuit with respect to the reference voltage level U BalLevel ;

e) determine a charge error ΔQ i,Err of the electric charge ΔQ i to be balanced according to

Δ Q i,Err =Q i,Pos −Q min,Neg ,

wherein Q min,Neg represents an electric charge Q i,Neg of the battery cell with the minimum electric charge Q min ;

f) determine an electric charge ΔQ i,use to be balanced of the battery cell according to

Δ Q i,use =ΔQ i −W*ΔQ i,err ,

wherein W represents a predefinable weighting factor;

g) calculate a duration t i,bal for balancing the state of charge of the battery cell on the basis of the electric charge ΔQ i,use that is to be balanced when the electric charge ΔQ i,use to be balanced exceeds a predefined threshold value, according to

t

i

,

b

⁢

a

⁢

l

=

Δ

⁢

Q

i

*

R

B

⁢

a

⁢

l

U

mess

,

i

,

wherein R Bal represents an ohmic resistance assigned to the battery cell; and

balancing the state of charge of the battery cell for the duration t i,bal .