Method and control unit for regulating a fill level of a storage of a catalytic converter for an exhaust gas component

A control unit for regulating a filling of an exhaust gas component storage of a catalytic converter in an exhaust gas of an internal combustion engine, comprising:

• an arrangement for ascertaining an actual fill level of the exhaust gas component storage using a first system model;
• an arrangement for feeding to the first system model a signal of a first exhaust gas sensor projecting into an exhaust gas flow upstream from the catalytic converter and detecting a concentration of the exhaust gas component;
• an arrangement for predefining in the first system model a base lambda setpoint value for a first control loop, the predefining being performed by a second control loop;
• an arrangement for converting, in the second control loop, an initial value for the base lambda setpoint value into a fictitious fill level by a second system model identical to the first system model;
• an arrangement for comparing the fictitious fill level with a setpoint value for a fill level, the comparing producing a comparison result;
• and
• an arrangement for iteratively changing the base lambda setpoint value as a function of the comparison result, if the comparison result indicates a difference between the setpoint value for the fill level and the fictitious fill level that is greater than a predefined degree, wherein the base lambda setpoint value is not changed if the comparison result indicates no difference between the setpoint value for the fill level and the fictitious fill level.