METHOD FOR OPERATING AN INVERTER DEVICE OF AN ELECTRIC DRIVE DEVICE, CONTROL UNIT, ELECTRIC DRIVE DEVICE AND MOTOR VEHICLE

Abstract

An inverter device of an electric drive device may be configured to convert a direct voltage of an intermediate circuit of the electric drive device into a multi-phase alternating current to operate an electric motor of the electric drive device. A safety signal may be received by a control unit of the electric drive device, which instructs the control unit to operate the electric motor in a safe operating mode and to discharge the intermediate circuit at same time. If an active short circuit mode is preset, the inverter device is controlled to operate the electric motor in the active short circuit mode and to discharge the intermediate circuit in the discharge mode. If a freewheel mode is preset, the inverter device is controlled to operate the electric motor in the freewheel mode and, upon satisfaction of a current criterion, controlled to discharge the intermediate circuit in the discharge mode.

Claims

1. A method of operating an inverter device of an electric drive device, wherein the inverter device includes at least two half bridges with a respective low-side switch and a respective high-side switch and is configured to convert a direct voltage of an intermediate circuit of the electric drive device into a multi-phase alternating current to operate an electric motor of the electric drive device, the method comprising: by a control unit of the electric drive device, receiving a safety signal, which instructs the control unit to operate the electric motor in a safe operating mode and to discharge the intermediate circuit in a discharge mode at same time, if an active short circuit mode is preset as the safe operating mode, controlling the inverter device to operate the electric motor in the short circuit mode and to discharge the intermediate circuit in the discharge mode, if a freewheel mode is preset as the safe operating mode, controlling the inverter device to operate the electric motor in the freewheel mode, and examining a current strength captured by a sensor unit in the electric motor to determine a satisfaction of a current criterion, which indicates admissible discharge, and upon satisfaction of the current criterion, controlling the inverter device to terminate the operation of the electric motor in the freewheel mode and to discharge the intermediate circuit in the discharge mode.

2. The method according to claim 1, wherein in the active short circuit mode, at least two of the low-side switches of the inverter device are switched to conducting by the control unit to short-circuit at least two phase windings of the electric motor.

3. The method according to claim 1, wherein in the active discharge mode, at least one of the high-side switches and at least one of the low-side switches of the inverter device are switched to conducting by the control unit.

4. The method according to claim 1, wherein in the freewheel mode, each of the low-side switches of the inverter device and each of the high-side switches of the inverter device are switched to blocking by the control unit.

5. The method according to claim 1, wherein in the active short circuit mode, at least two of the high-side switches of the inverter device are switched to conducting by the control unit to short-circuit at least two phase windings of the electric motor.

6. The method according to claim 1, wherein upon satisfaction of the current criterion, the inverter device is controlled by the control unit for the active short circuit mode and in the discharge mode at same time.

7. A control unit to operate an inverter device comprising: a processing device to execute a process including, receiving a safety signal, which instructs the control unit to operate the electric motor in a safe operating mode and to discharge the intermediate circuit in a discharge mode at same time, if an active short circuit mode is preset as the safe operating mode, controlling the inverter device to operate the electric motor in the short circuit mode and to discharge the intermediate circuit in the discharge mode, if a freewheel mode is preset as the safe operating mode, controlling the inverter device to operate the electric motor in the freewheel mode, and examining a current strength captured by a sensor unit in the electric motor to determine a satisfaction of a current criterion, which indicates admissible discharge, and upon satisfaction of the current criterion, controlling the inverter device to terminate the operation of the electric motor in the freewheel mode and to discharge the intermediate circuit in the discharge mode.

8. The control unit according to claim 7, wherein in the active short circuit mode, at least two of the low-side switches of the inverter device are switched to conducting by the control unit to short-circuit at least two phase windings of the electric motor.

9. The control unit according to claim 7, wherein in the active discharge mode, at least one of the high-side switches and at least one of the low-side switches of the inverter device are switched to conducting by the control unit.

10. The control unit according to claim 7, wherein in the freewheel mode, each of the low-side switches of the inverter device and each of the high-side switches of the inverter device are switched to blocking by the control unit.

11. The control unit according to claim 7, wherein in the active short circuit mode, at least two of the high-side switches of the inverter device are switched to conducting by the control unit to short-circuit at least two phase windings of the electric motor.

12. The control unit according to claim 7, wherein upon satisfaction of the current criterion, the inverter device is controlled by the control unit for the active short circuit mode and in the discharge mode at same time.

13. An electric drive device, comprising: a control unit configured to execute a process including, receiving a safety signal, which instructs the control unit to operate the electric motor in a safe operating mode and to discharge the intermediate circuit in a discharge mode at same time, if an active short circuit mode is preset as the safe operating mode, controlling the inverter device to operate the electric motor in the short circuit mode and to discharge the intermediate circuit in the discharge mode, if a freewheel mode is preset as the safe operating mode, controlling the inverter device to operate the electric motor in the freewheel mode, and examining a current strength captured by a sensor unit in the electric motor to determine a satisfaction of a current criterion, which indicates admissible discharge, and upon satisfaction of the current criterion, controlling the inverter device to terminate the operation of the electric motor in the freewheel mode and to discharge the intermediate circuit in the discharge mode.

14. A motor vehicle including an electric drive device according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the examples, taken in conjunction with the accompanying drawings of which:

[0034] FIG. 1 a schematic representation of an electric drive device;

[0035] FIG. 2 a schematic representation of an electric drive device in a discharge mode;

[0036] FIG. 3 a schematic representation of an electric drive device in an active short circuit mode; and

[0037] FIG. 4 a schematic representation of a procedure of a method for operating an inverter device.

DESCRIPTION

[0038] The examples explained in the following are examples of an invention. In the examples, the described components of the examples each represent individual features to be considered independently of each other, which also each may develop the examples independently of each other. Therefore, the disclosure is to include also combinations of the features of the examples different from the illustrated ones. Furthermore, the described examples can also be supplemented by further ones of the already described features of the examples.

[0039] In the figures, identical reference characters each denote functionally identical elements.

[0040] FIG. 1 shows a schematic representation of an electric drive device. A motor vehicle 1 is shown, which may comprise the electric drive device 2. The electric drive device 2 may comprise a battery 3, which may be intended to provide energy for driving the electric drive device 2. The battery 3 may be designed as a lithium ion battery. The electric drive device 2 may comprise an intermediate circuit 4, which may be intended to connect the battery 3 to an inverter device 5 in electrically conducting manner. The inverter device 5 may be intended to convert a direct voltage provided on the intermediate circuit 4 into a multi-phase alternating current to operate a motor 6 by the multi-phase current. The multi-phase current may for example include two or three phases. The intermediate circuit 4 may comprise an intermediate circuit capacitor 7, which may be intended to buffer energy. The inverter device 5 may be controlled by a control unit 8 of the electric drive device 2 to be able to switch switching states of high-side switches 9 and low-side switches 10. Phase windings 11 may be connected to the inverter device 5 in electrically conducting manner. Therein, a respective high-side switch 9 and a respective low-side switch 10 of the inverter device 5 may form a half bridge 12, which may be intended for energizing a respective one of the phase windings 11 of the electric motor 6. Thereby, it may be possible to provide a respective phase by a respective one of the half bridges 12. The control unit 8 may be configured to switch the switching states of the low-side switches 10 and the high-side switches 9 during an operation of the electric motor 6 to provide the respective multi-phase current.

[0041] In certain situations, for example upon a malfunction or an accident, it may be provided that the motor 6 has to be set into a safe operating mode. Herein, it may in particular be required to avoid spontaneous torque changes in the electric motor 6. At the same time, it may be required for safety reasons to discharge the intermediate circuit 4. One of the safe operating modes is the so-called freewheel. In the freewheel, it is provided that each of the high-side switches 9 and each of the low-side switches 10 are open or switched to blocking to dissipate the current flow into the phase windings 11 of the electric motor 6 via a freewheel path of the antiparallel diodes 15, 16. Such a switching state is illustrated in FIG. 1. It may be effected by the control unit 8, when the control unit 8 receives a safety signal 13, which the control unit 8 receives for switching the freewheel mode and a discharge mode. Upon switching the inverter device 5 into the illustrated freewheel mode, however, the problem may arise that the intermediate circuit 4 cannot be discharged via the inverter device 5 because current cannot flow through the inverter device 5 due to the opened high-side switches 9 and the opened low-side switches 10. For this reason, it may be provided that a current flow is captured in the electric motor 6 by a sensor unit 14 and the captured current flow is compared to a predetermined current criterion by the control unit 8. The predetermined current criterion may for example preset that a current strength of the current through one or all of the phase windings 11 of the electric motor 6 has to be below a predetermined current threshold value. It may be provided that the intermediate circuit 4 may only be discharged if the current strength of the current is below the predetermined threshold value of the current strength. It may be provided that the inverter device 5 is controlled by the control unit 8 upon satisfaction of the current criterion and for example at least one of the high-side switches 9 and at least one of the low-side switches 10 are set to conducting or closed in order that the intermediate circuit 4 may be discharged via the inverter device 5. This switching state is also referred to as active discharge mode. It may additionally be provided that the inverter device 5 is set into an active short circuit mode at the same time for example in that two of the high-side switches 9 or two of the low-side switches 10 are set to conducting.

[0042] FIG. 2 shows a schematic representation of an electric drive device in a discharge mode. The discharge mode may for example be effected by switching a low-side switch 10 and a high-side switch 9 of a half bridge 12 such that a discharge may be effected via the inverter 5.

[0043] FIG. 3 shows a schematic representation of an electric drive device in an active short circuit mode. The inverter device 5 may be switched into the active short circuit mode by the control unit 8 in that all of the high-side switches 9 are set to conducting and the low-side switches 10 are set to blocking. It would also be possible to allow an active short circuit in that all of the low-side switches 10 are set to conducting and all of the high-side switches 9 are blocked.

[0044] FIG. 4 shows a schematic representation of a procedure of a method for operating an inverter device.

[0045] In a step S1, a safety signal 13 may be received by a control unit 8 of the electric drive device 2, which instructs the control unit 8 for operating the electric motor 6 in a predetermined safe operating mode and for discharging the intermediate circuit 4 in a predetermined discharge mode at the same time.

[0046] In a step S2, a case distinction may be performed by the control unit 8, wherein it is examined by the control unit 8 if the predetermined safe operating mode is an active short circuit mode or a freewheel mode. For this purpose, the control unit 8 may ascertain via a captured current course which type the electric motor is. If the electric motor is an asynchronous motor, the freewheel mode may be selected as the safe operating mode. If the electric mode is a permanent magnet synchronous motor, the active short circuit mode may be selected as the safe operating mode.

[0047] In case that the predetermined safe operating mode is an active short circuit mode, the inverter device 5 may be controlled by the control unit 8 for operating the electric motor 6 in the predetermined active short circuit mode and for discharging the intermediate circuit 4 in the predetermined discharge mode in a method step S3a.

[0048] If the predetermined safe operating mode is a predetermined freewheel mode, the inverter device 5 may be controlled by the control unit 8 for operating the electric motor 6 in the predetermined freewheel mode in a method step S3b.

[0049] In a method step S4b, a current strength in the electric motor 6 may be captured by the sensor unit 14 and a satisfaction of a predetermined current criterion based upon the captured current strength may be examined by the control unit 8. For example, the current strength may be below a predetermined threshold value for satisfying the predetermined current criterion. The measurement may be effected at least once.

[0050] If the current criterion is satisfied, the inverter device 5 may be controlled by the control unit 8 in a method step S5b to terminate the freewheel mode and to set the inverter device 5 into an active discharge mode.

[0051] In addition, it may be provided in a step S6b that the control unit 8 controls the inverter device 5 to switch the inverter device 5 into the active discharge mode and an active short circuit mode at the same time.

[0052] In defined fault cases, for example in load shedding or crash case, the high-voltage powertrain attempts to transition into a safe state. This usually means shutting down the high voltage and the electrical machine, wherein it is attempted to avoid jumps in the torque as well as abrupt braking torques. For discharging the high-voltage intermediate circuit, either discharge resistors specially provided thereto are connected in parallel with the high-voltage on-board power supply. Or alternatively thereto, as far as possible, the energy may for example also be dissipated via the power semiconductors of the drive converter.

[0053] At the same time, the electrical machine is transitioned into a safe state according to machine type (for example permanent magnet synchronous motor or asynchronous motor), for example active short circuit (AKS) or freewheel.

[0054] Since it may, for example, be mandatory for a freewheel that the power semiconductors of the pulse inverter are not turned on, an active discharge cannot be effected via the present power semiconductors without further measures in this operating state.

[0055] The examples describes an operation strategy of how a safe state of the electrical machine may be taken and an active discharge is possible via the power semiconductors independently of machine type.

[0056] A separate active discharge via additional components may be omitted, which reduces cost and installation space requirement and makes the fault strategy independent of machine type at least to a certain extent.

[0057] If the pulse inverter transitions into the safe state and the active discharge is to be controlled at the same time, it is proceeded as follows. If the active short circuit is taken as the safe state, thus, it may be begun with the active discharge at the same time since the active short circuit may for example be implemented by controlling the low-side switches and the active discharge may be effected by switching on one or more high-side switches. Therein, it does not matter if the high-side switch(es) is (are) controlled in pulsed manner or for example operated in the linear operation.

[0058] In case that the freewheel is to be taken, for example in an asynchronous motor, thus, the requested operating state is initially taken. The freewheel is maintained until the current in the machine has decreased to zero or at least below a certain value, which usually may take few 100 ms. During this time, the active discharge remains inactive in order that an undesired erratic torque change does not occur. If the current has correspondingly decreased, the active discharge may be activated. Therein, at least one high-side switch 9 and one low-side switch 10 are controlled. Since the current in the machine is very small and/or equal to 0 at this point of time, an undesired torque does not arise. Optionally, an active short circuit mode may be taken in addition thereto, which may be switched via the high-side switches or the low-side switches.

[0059] In an example, it may be be considered that the period of time until the current has decreased below the desired value and subsequently the active discharge has discharged the intermediate circuit to a harmless voltage, does not take longer than the period of time requested in standards. The active discharge and optionally also the electrical machine are to be accordingly considered.

[0060] Overall, the examples show, how a discharge of an intermediate circuit may be allowed.

[0061] A description has been provided with particular reference to examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims, which may include the phrase “at least one of A, B and C” as an alternative expression that refers to one or more of A, B or C, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).