Overvoltage protection for a motor vehicle electrical system in the event of a load dump

A motor vehicle electrical system, comprising:

• an electric machine;
• an active bridge rectifier;
• at least one control device configured for converting an alternating voltage which is output by the electric machine via a number of phase connections into a direct voltage by controlling active switching elements of the bridge rectifier;
• and
• an arrangement configured to initiate a short circuit of at least two of the phase connections as soon as a signal characterizing the direct voltage exceeds an upper threshold value, and to deactivate the short circuit as soon as the signal characterizing the direct voltage subsequently falls below a lower threshold value, the arrangement including:
• an evaluation element configured to detect a value of the direct voltage, to filtering the detected value, and to provide the filtered value as the signal characterizing the direct voltage, the evaluation element being configured to supply the signal characterizing the direct voltage to a comparator that is configured to compare the signal characterizing the direct voltage to the upper threshold value and to the lower threshold value;
• and
• a setting element configured to provide the upper threshold value and the lower threshold value in the form of a settable comparator threshold of the comparator, the setting element being configured to lower or deactivate the lower threshold value for a period of time as soon as the signal characterizing the direct voltage exceeds the upper threshold value and to raise or deactivate the upper threshold value for a period of time as soon as the signal characterizing the direct voltage falls below the lower threshold value.

A method for operating a motor vehicle electrical system which includes an electric machine, an active bridge rectifier, and at least one control device, in which an alternating voltage which is output by the electric machine at a number of phase connections is converted into a direct voltage with the aid of the at least one control device by controlling active switching elements of the bridge rectifier, and a short circuit of at least two of the phase connections is initiated as soon as a signal characterizing the direct voltage exceeds an upper threshold value, and the short circuit is deactivated as soon as the signal characterizing the direct voltage subsequently falls below a lower threshold value, the method comprising:

• detecting a value of the direct voltage;
• filtering the detected value;
• providing the filtered value as the signal characterizing the direct voltage;
• supplying the signal characterizing the direct voltage to a comparator;
• comparing, by the comparator the signal characterizing the direct voltage to the upper threshold value and to the lower threshold value, the upper threshold value and the lower threshold value being provided in the form of a settable comparator threshold of the comparator by a setting element;
• and
• lowering or deactivating, by the setting element, the lower threshold value for a period of time as soon as the signal characterizing the direct voltage exceeds the upper threshold value, and raising or deactivating the upper threshold value for a period of time as soon as the signal characterizing the direct voltage falls below the lower threshold value.

A processing unit for operating a motor vehicle electrical system which includes an electric machine, an active bridge rectifier, and at least one control device, in which an alternating voltage which is output by the electric machine at a number of phase connections is converted into a direct voltage with the aid of the at least one control device by controlling active switching elements of the bridge rectifier, and a short circuit of at least two of the phase connections is initiated as soon as a signal characterizing the direct voltage exceeds an upper threshold value, and the short circuit is deactivated as soon as the signal characterizing the direct voltage subsequently falls below a lower threshold value, the processing unit configured to:

• detect a value of the direct voltage;
• filter the detected value;
• provide the filtered value as the signal characterizing the direct voltage;
• compare the signal characterizing the direct voltage to the upper threshold value and to the lower threshold value, the upper threshold value and the lower threshold value being provided in the form of a settable comparator threshold of the comparator;
• and
• lower or deactivate the lower threshold value for a period of time as soon as the signal characterizing the direct voltage exceeds the upper threshold value, and raise or deactivate the upper threshold value for a period of time as soon as the signal characterizing the direct voltage falls below the lower threshold value.

A machine-readable memory medium storing a computer program for operating a motor vehicle electrical system which includes an electric machine, an active bridge rectifier, and at least one control device, in which an alternating voltage which is output by the electric machine at a number of phase connections is converted into a direct voltage with the aid of the at least one control device by controlling active switching elements of the bridge rectifier, and a short circuit of at least two of the phase connections is initiated as soon as a signal characterizing the direct voltage exceeds an upper threshold value, and the short circuit is deactivated as soon as the signal characterizing the direct voltage subsequently falls below a lower threshold value, the computer program, when executed by a processing unit, configured to cause:

• detecting a value of the direct voltage;
• filtering the detected value;
• providing the filtered value as the signal characterizing the direct voltage;
• comparing the signal characterizing the direct voltage to the upper threshold value and to the lower threshold value, the upper threshold value and the lower threshold value being provided in the form of a settable comparator threshold of the comparator;
• and
• lowering or deactivating the lower threshold value for a period of time as soon as the signal characterizing the direct voltage exceeds the upper threshold value, and raising or deactivating the upper threshold value for a period of time as soon as the signal characterizing the direct voltage falls below the lower threshold value.