Patent ID: 11892517
Assignee: DEKRA SE
Field: Measurement (Instruments)
Classification: CPC B  G  Y | IPC B  G

Claim 11:
12. A method for determining a state of health (SoH) value of a traction battery of an electric vehicle, which characterizes the ageing state of the traction battery, comprising:
loading the traction battery by a test load;
at at least one point in time, acquiring a respective output voltage and load current value pair of the traction battery;
establishing an ohmic internal resistance of the traction battery on the basis of the acquired output voltage and load current value pair;
establishing the state of health value of the traction battery on the basis of the established ohmic internal resistance;
establishing at least one normalisation variable which characterizes the traction battery;
on the basis of the established ohmic internal resistance and the at least one normalisation variable, establishing a normalised internal resistance based on a reference value of the normalisation variable;
wherein the state of health value of the traction battery is established on the basis of the normalised internal resistance;
wherein the test load proceeds in a such a way that, on connection of the test load, the load current has a step change in current or a ramped profile;
wherein a measurement sequence of output voltage and load current value pairs is acquired starting with the connection of the test load;
wherein the measurement sequence comprises a plurality of output voltage and load current value pairs acquired at succeeding points in time;
wherein parameters of a compensation function, which models a profile of the measurement sequence, are established for the determination of the internal resistance by means of a mathematical adjustment calculus;
wherein an optimization calculation of the compensation function is carried out in such a way that a coefficient of determination which describes a goodness of fit of the adjustment calculus, is maximized,
wherein:
at least one output voltage and load current reference value pair is additionally acquired before the test load is connected, on the basis of which an open-circuit voltage and a closed-circuit current are established;
the ohmic internal resistance for a respective value pair of the measurement sequence is established as a quotient of a difference of the acquired output voltage and the open-circuit voltage and a difference of the acquired load current and the closed-circuit current;
parameters of a logarithmic function, which models a profile of the measurement sequence, are established for the measurement sequence by means of a mathematical adjustment calculus; and
on a basis of the logarithmic function, the ohmic internal resistance is established at the time of the step change in current, or at a corresponding frequency.