Method for determining a state value of a traction battery

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:
• a first normalisation variable is a temperature of the traction battery during acquisition of the output voltage and load current values;
• and
• the reference value of the first normalisation variable is a reference temperature;
• the temperature of the traction battery is established in that;
• in a first measurement step, a first ambient temperature and a first ohmic internal resistance of the traction battery are established at a first point in time;
• in a second measurement step after a predetermined period of time has elapsed, a second ambient temperature and a second ohmic internal resistance of the traction battery is established at a second point in time;
• on a basis of a difference of the first and second ohmic internal resistance and the specified period of time, a rate of change in internal resistance is established;
• on a basis of the rate of change in internal resistance, a differential temperature between the ambient temperature and the temperature of the traction battery is established;
• and
• the temperature of the traction battery is established by addition of a reference ambient temperature established from the first and/or second ambient temperature and the established differential temperature.

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.