US-20260128690-A1 - METHOD FOR OPERATING AN INVERTER, INVERTER, AND ELECTRIC DRIVE SYSTEM

Abstract

The invention relates to a change from an active short circuit to the freewheel in an inverter of an electric drive system. For this purpose, a switching state corresponding to the switching state of the freewheel is temporarily set in a half-bridge of the inverter. The current curve in this half-bridge is then evaluated in order to check whether a change to the freewheel is permissible or not.

Inventors

• Daniel Schweiker
• Ekard Grossmann
• Kay Hindorf
• Mark Damson

Assignees

• ROBERT BOSCH GMBH

Dates

Publication Date

20260507

Application Date

20230712

Priority Date

20220930

Claims (8)

1. 1 . A method for operating an inverter ( 1 ) for an electric drive system, wherein the inverter ( 1 ) comprises a plurality of half-bridges, each having two switching elements (S 1 -S 6 ), and wherein the method comprises the following steps: setting ( 100 ) an active short circuit in the inverter ( 1 ); opening ( 200 ) the switching elements in a first half-bridge of the inverter ( 1 ); determining ( 300 ) an electrical parameter that characterizes a curve of a phase current in the direction of the first half-bridge in which the two switching elements are opened; setting ( 400 ) a freewheel mode in the inverter, in which all switching elements (S 1 -S 6 ) of all half-bridges are opened if the curve of the phase current in the direction of the first half-bridge satisfies a predetermined change condition.
2. 2 . The method according to claim 1 , wherein the active short circuit is switched to the freewheel mode if the amount of the phase current in the direction of the first half-bridge starting from a current zero pass does not exceed a specified threshold value.
3. 3 . The method according to claim 1 , wherein the two switching elements in a half-bridge of the inverter are opened when a curve of the phase current in the direction of the first half-bridge is at least approximately in the range of a zero pass.
4. 4 . The method according to claim 1 , wherein, in order to set ( 400 ) the freewheel mode in the inverter ( 1 ), the switching elements in the first half-bridge, in which both switching elements have previously been opened, remain open, and then the switching elements in the further half-bridges of the inverter ( 1 ) are opened.
5. 5 . The method according to claim 1 , wherein, after determining ( 300 ) the electrical parameter, a switching element in the first half-bridge is first closed again to set an active short circuit; and the curve of the phase current in the direction of the first half-bridge is then evaluated, and, after the evaluation, a freewheel mode is set in the inverter ( 1 ) if the curve of the phase current in the direction of the first half-bridge satisfies the predetermined change condition.
6. 6 . The method according to claim 1 , having a step for determining a rotational speed of an electric machine ( 2 ) connected to the inverter ( 1 ), wherein the steps of opening ( 200 ) the two switching elements, subsequently determining ( 300 ) the electrical parameter, and setting ( 400 ) to the freewheel mode are only performed if the determined rotational speed of the electric machine ( 2 ) falls below a specified threshold value.
7. 7 . An inverter ( 1 ), having: a plurality of half-bridges, each comprising two switching elements (S 1 -S 6 ), wherein a diode is provided parallel to each switching element (S 1 -S 6 ); and a control device ( 10 ) designed so as to provide control signals for the switching elements (S 1 -S 6 ) in the plurality of half-bridges; wherein the control device ( 10 ) is designed to perform a method according claim 1 .
8. 8 . An electric drive system, having: an electric machine ( 2 ); and an inverter ( 1 ) according to claim 7 ; wherein the inverter ( 1 ) is connected to the electric machine ( 2 ) at an AC voltage terminal, and wherein the inverter ( 1 ) is designed to be connected to a DC voltage source at a DC voltage terminal.

Description

BACKGROUND The invention relates to a method for operating an inverter, in particular an inverter of an electric drive system. The present invention further relates to an inverter in which such a method is implemented, as well as an electric drive system having such an inverter. Electric drive systems are used in numerous applications. Such electric drive systems are used, for example, in fully or at least semi-electrically driven vehicles. Electrical energy from a power source, for example the traction battery of an electric vehicle, can be converted by means of a inverter into an electric voltage, which is suitable for driving an electric machine. In addition, so-called safe operating states can also be set in the inverter, for example an active short-circuit in which the switching elements are controlled such that the terminals of the electric machine are short-circuited. Furthermore, a so-called freewheel can be provided, in which all switching elements in the half-bridges of the inverter are opened. For example, publication DE 10 2014 222 256 A1 describes a method for switching an operating state of an electric machine from a freewheel into an active short circuit. Here, it is proposed that in a multi-phase electric machine, the individual phases are successively shifted into the corresponding switching states. SUMMARY The present invention provides a method for operating an inverter, an inverter, and an electric drive system having the features of the disclosure. Further advantageous embodiments are the subject matter of the dependent claims. The following is therefore provided: A method for operating an inverter, in particular for operating an inverter for an electric drive system. The inverter comprises a plurality of half-bridges, each having two switching elements. The method comprises a step of setting an active short circuit in the inverter. In such an active short circuit, either the upper switching elements of all half-bridges or the lower switching elements of all half-bridges are closed. In this way, all phase terminals of an electrical machine connected to the inverter are electrically connected to one another, i.e. short-circuited. The method further comprises a step of opening the two switching elements in a first half-bridge of the inverter. In other words, in a first of the half-bridges of the inverter, a switching state corresponding to the switching state for a freewheel mode is set. Furthermore, the method comprises a step of determining an electrical parameter that characterizes a curve of a phase current in the direction of the first half-bridge, in which both switching elements are opened. Furthermore, the method comprises a step for setting a freewheel mode in the inverter, in which all switching elements of all half-bridges are opened when a curve of the phase current in the direction of the first half-bridge satisfies a predetermined change condition. The determination of an electrical parameter that characterizes a curve of a phase current in the direction of the first half-bridge can be done for example using at least one current measuring device. Of course, the phase current can take on positive and negative values, so that the phrase “phase current in the direction of the first half-bridge” is not to be construed as being restrictive in any way to the extent that only the current flowing in the direction of the first half-bridge is determined, but rather the phase current is of course also considered in the opposite direction, flowing away from the first half-bridge. Preferably, one or more current measuring devices are used in order to determine the electrical parameter, depending on the arrangement within the inverter, which allow the determination of a parameter that characterizes the curve of a phase current in the direction of the first half-bridge. Preferably, such a current measuring device can be arranged within a switching element of the half-bridge, which in particular detect currents through an intrinsic parallel-connected diode or a body diode of a switching element. Preferably, such a current measuring device is arranged in a supply line or discharge line of the current through a switching element of a half-bridge, preferably at the phase current terminal of a half-bridge. The following is furthermore provided: An inverter having a plurality of half-bridges and a control device. The plurality of half-bridges each comprise two switching elements. In particular, two semiconductor switching elements can be provided in each half-bridge, wherein a diode is provided parallel to each semiconductor switching element. The control device is designed so as to provide control signals for the switching elements in the plurality of half-bridges. Furthermore, the control device is designed so as to carry out a method according to the invention for operating the inverter. Finally, the following is provided: An electric drive system having an electric machine and an inverter ac