DE102020207856A1 - Inverter for an electrical machine, electrical machine with such an inverter and steering system with such an electrical machine - Google Patents

Abstract

The invention relates to an inverter (10) for an electrical machine (100), the inverter (10) having a half-bridge circuit (20) with switches (22) and a control unit (30) for driving the switches (22) of the half-bridge Circuit (20), and wherein the control unit (30) is adapted to detect a fault in the electrical machine (100) and / or the inverter (10). One aspect of the invention is that the control unit (30) is set up to switch the half-bridge circuit (20) to a multiple short circuit in the event of a fault, and the inverter (30) also has a disconnect switch (40) to disconnect the Inverter (10), in particular the half-bridge circuit (20), from a supply voltage (50), and wherein the control unit (30) is set up to switch the isolating switch (40 ).The invention also relates to an electrical machine (100) with an inverter (10) according to the invention and a steering system with an electrical machine (100) according to the invention.

Description

State of the art

The invention relates to an inverter for an electrical machine, the inverter having a half-bridge circuit with switches and a control unit for controlling the switches of the half-bridge circuit, and the control unit being configured to detect a fault in the electrical machine and / or the inverter to recognize.

Such an inverter is for example in the laid-open specification DE 102015108691 A1 disclosed. There, in the event of a fault, the half-bridge circuit is switched into a simple active short circuit. In particular, either the low-side switches or the high-side switches of the half-bridge circuit can be short-circuited. However, this type of short circuit creates a very high or even permanent current in individual switches, which is why the switches have to be oversized compared to a configuration for normal operation in order to be able to cope with such currents as well.

The invention also relates to an electrical machine with such an inverter and a steering system with such an electrical machine.

Disclosure of the invention

The invention relates to an inverter for an electrical machine, the inverter having a half-bridge circuit with switches and a control unit for controlling the switches of the half-bridge circuit, and the control unit being configured to detect a fault in the electrical machine and / or the inverter to recognize.

One aspect of the invention is that the control unit is set up to switch the half-bridge circuit to a multiple short circuit in the event of a fault, and the inverter also has an isolating switch for separating the inverter, in particular the half-bridge circuit, from a supply voltage , and wherein the control unit is set up to open the isolating switch before switching the multiple short-circuit of the half-bridge circuit.
The advantage here is that, in the event of a fault, overvoltages and uncontrollable currents can be avoided due to the multiple short circuit. In addition, the switch-on resistance of the half-bridge circuit can be reduced by the multiple short-circuits. This in turn reduces the power loss that is converted in the half-bridge circuit during short-circuiting. Furthermore, by dividing the current over a large number of switches, the cooling surface, which can absorb the heat generated by the power loss, is increased. In particular, as a result of the division, the respective current intensity which flows through the individual switches can be reduced, whereby the longevity of the switches can be improved or else the overdimensioning of the switches can also be reduced. Since the switches only have to be dimensioned for normal operation, manufacturing and material costs can also be saved and the robustness of the system can be increased.
Such multiple short-circuits are only possible if the isolating switch has been opened beforehand in order to disconnect the supply voltage.
If the circuit breaker is not opened, the source, for example the battery, is short-circuited. This can destroy the inverter.

The electric machine can in particular be designed as an electric motor, for example as a permanently excited synchronous machine, as an electrically excited synchronous machine, or also as an asynchronous machine. This electric motor has, for example, a stator and a rotor. In addition, the electric motor has an inverter in order to control the machine accordingly in order to generate a rotating magnetic field in the stator coils.

An inverter is to be understood here as an electronic circuit which can be used to convert direct current into alternating current, the direct current being supplied by a supply voltage.
In particular, a corresponding control of stator coils is implemented by means of a half-bridge circuit by means of the inverter in order to generate a rotating magnetic field. The switches of the half-bridge circuit can be opened or closed by the control unit as required. This rotating magnetic field in turn drives the rotor and ultimately the rotor shaft in interaction with magnetic components of the rotor.
The half-bridge circuit has several half-bridges for this purpose, a half-bridge being constructed from a low-side switch and a high-side switch and the center tap between the switches each leading to a stator coil. A half bridge with the associated stator coil forms a corresponding phase of the motor. If the half-bridge circuit has three half-bridges, for example, this corresponds to a total of six switches, which then form what is known as a B6 bridge, in order in turn to form a three-phase electrical machine.
Such an electrical machine can be used, for example, in a steering system in order to move the steering axis accordingly. In particular, however, an electrical machine is conceivable in any type of electrical drive, for example also in a vehicle drive.

The control unit can be designed, for example, as one or more microcontrollers. In particular, there can be various separate control circuits or control partitions within the control unit. For example, a control circuit or partition can be set up to detect faults by means of appropriate aids or protective devices. Another control circuit or partition can be responsible for controlling the switches of the half-bridge circuit in normal operation and in turn another control circuit or partition for controlling the isolating switch and short-circuiting the switches of the half-bridge circuit in the event of a fault. Here, the control circuit for the active multiple short circuit can be designed both as a master and as a slave. As the master, another control circuit is no longer able to intervene in the control of the half-bridge circuit until this is released again by the master. As a slave, the multiple short-circuit is carried out in addition to or after a normal control.

An error case can be understood to mean, for example, a short circuit error, an open circuit error, an offset error, an overvoltage or other disturbances.

A simple active short circuit is to be understood as meaning that, in the half-bridge circuit, the low-side switches or the high-side switches of the half-bridges are actively controlled in order to short-circuit them. In this case, several or all switches of the same type, that is to say low-side or high-side switches, can be actively short-circuited. A multiple short circuit, on the other hand, is to be understood as meaning that, in the half-bridge circuit, low-side switches and high-side switches of the half-bridges are actively activated in order to short-circuit them. Here one or more of the respective switch types can be short-circuited. In this case, the multiple short-circuit is maintained, in particular, until the fault no longer exists.

The isolating switch is also a switch that can be opened or closed by the control unit. By opening the isolating switch, in particular the supply voltage, which is supplied, for example, from a vehicle electrical system or a corresponding battery, can be decoupled so that it is no longer applied to the half-bridge circuit.

One embodiment of the invention provides that the control unit is set up to close all switches of the half-bridge circuit in the event of a fault.

It is advantageous here that, on the one hand, the switch-on resistance is minimized and, on the other hand, the cooling surface for dissipating the power loss generated by the switches is maximized.

It must be taken into account here that the control unit must be set up to control all the switches of the half-bridge circuit in a corresponding manner, in particular, for example, to close them essentially at the same time.

A further embodiment of the invention provides that the control unit is set up to detect an overvoltage in the supply voltage and to short-circuit the half-bridge circuit and / or open the disconnector as a function of the overvoltage. It is advantageous here that if there is an overvoltage in the supply voltage such as the battery, the generator is disconnected from the power supply, so that destruction of the inverter can be avoided.

Overvoltage is an electrical voltage that exceeds the nominal voltage of an electrical system.

According to a further embodiment of the invention, it is provided that the control unit is set up to switch the half-bridge circuit to a simple short circuit in the event of a fault before the disconnector is opened. The advantage here is that the inverter can first be put into a safe state through the simple short circuit. The isolating switch can then open in order not to short-circuit the supply voltage (battery). The load on the output stage can then be started by switching on the complementary switches.

According to a further embodiment of the invention, it is provided that the switches of the half-bridge circuit and / or the isolating switch are configured as semiconductor switches. The advantage here is that this type of switch is low-wear, has a high switching speed and is easy to control.

In particular, the switches and / or the isolating switch are designed as MOSFETs. However, a combination of an IGBT with a diode as a switch would also be conceivable.

Semiconductor switches are understood to mean switches whose functional principle is based on the semiconductor properties of the components.

According to a further embodiment of the invention it is provided that the control unit is set up to short-circuit a Detect the intermediate circuit of the inverter and, depending on this, carry out the short-circuiting of the switches of the half-bridge circuit and / or the opening of the isolating switch.
It is advantageous here that an increased availability of the inverter can be made possible. The short circuit in the intermediate circuit can lead to a short circuit in the supply voltage (battery), which in turn can lead to two scenarios. For example, a fire can occur in the inverter if the short circuit does not resolve itself.
Furthermore, it would be possible that the fuse of the battery is destroyed, which under certain circumstances can lead to other consumers being cut off from the supply.

An intermediate circuit is to be understood as an electrical device which, as an energy store, electrically couples several electrical networks on an interposed current or voltage level via converters. In this case, the intermediate circuit can have a capacitor, for example.

The invention also relates to an electrical machine with an inverter according to the invention. The electrical machine can in particular be designed as an electric motor, for example as a permanently excited synchronous machine, as an electrically excited synchronous machine or also as an asynchronous machine.

The invention also relates to a steering system with an electrical machine according to the invention.

Figure list

• 1 shows an embodiment of an electrical machine according to the invention with an inverter according to the invention.

Description of exemplary embodiments

1 shows an exemplary embodiment of an electrical machine according to the invention in a sectional view.

An electrical machine is shown 100 , for example for a steering system not shown in the figure. The electric machine 100 is designed here as an electric motor and has a rotor-stator unit 105 on which a rotor shaft, not shown, is arranged. Furthermore, the electrical machine 100 an inverter 10 on which electrically with the rotor-stator unit 105 connected is.

The inverter 10 again has a half-bridge circuit 20th and a control unit 30th on. The half-bridge circuit 20th assigns switch 22nd on which as low-side switch-23 and as high-side switch 24 are arranged and connected in such a way that they form a B6 bridge, which can drive a three-phase electric motor. However, this would depend on the type of electrical machine 100 any number of further half bridges is also conceivable.
The control unit 30th is electrical with the switches 22nd the half-bridge circuit 20th connected in order to be able to control them accordingly, here two control paths are illustrated as an example. The control unit 30th is set up, especially in normal operation, to switch the switch 22nd to be controlled in such a way that a magnetic rotating field is generated by means of coils of the stator, which drives the permanent magnetic rotor.
Furthermore, the inverter 10 a circuit breaker 40 on. The control unit 30th is electrical with the disconnector 40 connected in order to be able to control this as well.

The switches 22nd the half-bridge circuit 20th and / or the circuit breaker 40 can be designed in particular as semiconductor switches, for example as MOSFETs.

The control unit 30th is set up to deal with a fault in the electrical machine 100 and / or the inverter 10 to recognize. Such a fault can, for example, be an overvoltage in the supply voltage 50 of the inverter 10 or an undesired short circuit in the inverter 10 being. Furthermore is the control unit 30th set up for this purpose, the half-bridge circuit in the event of a fault 20th to switch into a multiple short circuit, i.e. any number of low-side switches 23 as well as high-side switches 24 to close, and before switching the multiple short circuit of the half-bridge circuit 20th the circuit breaker 40 to open. In particular, the control unit 30th set up to do this, all switches in the event of an error 22nd the half-bridge circuit 20th close.

Furthermore, the control unit 30th be set up to avoid an overvoltage of the supply voltage 50 to detect and short-circuit the half-bridge circuit 20th and / or opening the circuit breaker 40 to be carried out depending on the overvoltage. Such an overvoltage can represent a particularly critical fault situation for the inverter.

In addition, the control unit 30th be set up to do this, in the event of a fault, before the disconnector is opened 40 the half-bridge circuit 20th to switch into a simple short circuit.

Additionally or alternatively, the control unit 30th to be set up a short circuit of an intermediate circuit 60 of the inverter 10 to detect and, depending on this, the short-circuiting of the half-bridge circuit 20th and / or opening the circuit breaker 40 perform.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102015108691 A1 [0002]

Claims (8)

Inverter (10) for an electrical machine (100), the inverter (10) being a half-bridge circuit (20) with switches (22) and a control unit (30) for controlling the switches (22) of the half-bridge circuit (20) and wherein the control unit (30) is set up to detect a fault in the electrical machine (100) and / or the inverter (10), characterized in that the control unit (30) is set up to open the half bridges in the event of a fault To switch the circuit (20) into a multiple short circuit, and wherein the inverter (30) also has an isolating switch (40) for separating the inverter (10), in particular the half-bridge circuit (20), from a supply voltage (50), and wherein the control unit (30) is set up to open the isolating switch (40) before switching the multiple short-circuit of the half-bridge circuit (20). Inverter (10) Claim 1 , characterized in that the control unit (30) is set up to close all switches (22) of the half-bridge circuit (20) in the event of a fault. Inverter (10) Claim 1 or 2 , characterized in that the control unit (30) is set up to detect an overvoltage in the supply voltage (50) and to short-circuit the half-bridge circuit (20) and / or to open the isolating switch (40) as a function of the overvoltage. Inverter (10) according to one of the preceding claims, characterized in that the control unit (30) is set up to switch the half-bridge circuit (20) to a simple short circuit in the event of a fault before the isolating switch (40) is opened. Inverter (10) according to one of the preceding claims, characterized in that the switches (22) of the half-bridge circuit (20) and / or the isolating switch (40) are designed as semiconductor switches. Inverter (10) according to one of the preceding claims, characterized in that the control unit (30) is set up to detect a short circuit in an intermediate circuit (60) of the inverter (10) and, as a function thereof, the short circuit of the half-bridge circuit (20) and / or to open the circuit breaker (40). Electrical machine (100) with an inverter (10) according to one of the preceding claims. Steering system with an electric machine (100) according to Claim 7 .

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