Method and battery management system for monitoring a battery system by determining impedance
A method for monitoring a battery system is proposed. The method includes providing a sequence of pairs of measured current and voltage values that follow one another in time. The pairs of current and voltage values indicate the current flowing through the battery system and the voltage present at the battery system. The method also provides for an electrical equivalent model of the battery system to be provided. The equivalent electrical model has several impedances connected in series. Initial impedance parameter values are provided for the impedances of the equivalent electrical model. The method provides for adjusting a first impedance parameter of an impedance of the equivalent electrical model based on the difference between a first voltage value simulated based on the initial impedance parameter values and the first current value of the finite sequence and the first measured voltage value of the finite sequence. An optimized first impedance parameter value is thereby obtained. By minimizing the deviation of a sequence of simulated voltage values obtained on the basis of the electrical equivalent model and the first sequence of measured current values from the sequence of measured voltage values by adapting at least one further impedance parameter of the impedances of the electrical equivalent model, at least one optimized further impedance parameter value of the at least one further impedance parameter is obtained. A battery management system for carrying out the method is also proposed.
1. A method for determining one or more impedance parameters of a battery system, comprising:
providing a finite sequence of pairs of measured current and voltage values (I meas,k ; U meas,k ) that follow one another in time, the pairs of current and voltage values (I k : U k ) indicating the current (I L ) flowing through the battery system and the voltage (U L ) present at the battery system at the corresponding point in time;
providing an electrical equivalent model of the battery system, wherein the electrical equivalent model has series-connected impedances (Z 1 , Z 2 , Z 3 , Z 4 );
providing initial impedance parameter values (R ohm,initial ; R ct,initial ; R eldiff,initial ; R soldiff,initial ) of the impedances of the equivalent electrical model;
adapting a first impedance parameter (R soldif ) of an impedance (Z 4 ) of the equivalent electrical model based on the difference between a first impedance parameter based on the initial impedance values (R ohm,0 ; R ct,0 ; R eldiff,0 ; R soldiff,0 ) and the first current value (I 1 ) of the finite sequence of simulated voltage values (U sim,1 ) and the first measured voltage value (U meas,1 ) of the finite sequence, whereby an optimized first impedance parameter value (R soldif,optimated ) is obtained;
minimizing the deviation of a sequence of simulated voltage values (U sim,k ) obtained on the basis of the equivalent electrical model and the first sequence of measured current values (I meas,k ) and the sequence of measured voltage values (U meas,k ) by adapting at least one further impedance parameter (R ohm ; R ct ; R eldiff ) of the impedances (Z 0 , Z 1 , Z 2 , Z 3 , Z 4 ) of the equivalent electrical model, whereby an optimized further impedance parameter value (R ohm,optimal ; R ct,optimal ; R eldiff,optimal ) of the at least one further impedance parameter is obtained,
wherein the optimized first impedance parameter and the optimized further impedance parameters are used as initial impedance parameter values of a subsequent finite sequence, thereby improving subsequent determinations of impedance parameters.
2. The method of claim 1 ,
wherein the first impedance parameter (R soldif ) is adjusted by adding a product of the difference with the initial first impedance parameter value and a constant to the initial first impedance parameter value.
3. The method of claim 1 ,
wherein, when minimizing the deviation, a correction voltage is used which is calculated on the basis of the initial parameter values, the first measured current value and the first measured voltage value.
4. The method of claim 1 ,
wherein at least one impedance has a current-dependent resistance.
5. The method of claim 1 ,
wherein a trust region method is used to minimize the deviation.
6. The method of claim 5 ,
wherein the finite sequence comprises a subsequence of predetermined length for which the magnitude of the quotient of the current value and the nominal capacity of the battery system is higher than a predetermined minimum C-rate (C min ).
7. The method of claim 1 ,
wherein the finite sequence is selected from a longer sequence of pairs of measured current and voltage values (I meas,k ; U meas,k ), and
wherein as the first pair of the finite sequence a pair of the longer sequence is selected after a predetermined number of pairs of the longer sequence in which the current value remains substantially constant or the magnitude of the quotient of the current value and a nominal capacity of the battery system is less than a predetermined maximum C-rate (CR max ).
8. The method of claim 1 ,
wherein the optimized first impedance parameter and the optimized further impedance parameters are used as initial impedance parameter values of a subsequent finite sequence.
9. A battery management system, wherein the battery management system is set up to carry out a method according to claim 1 .
10. The battery management system of claim 9 , wherein the battery management system has
means for measuring the pairs of measured current and voltage values (I meas,k ; U meas,k ); and
a memory for storing the finite sequence of pairs.
11. The battery management system of claim 10 , wherein the memory has a ring memory.