METHOD FOR OPERATING AN AT LEAST GENERATOR-OPERABLE ELECTRIC MOTOR AND MEANS FOR THE IMPLEMENTATION THEREOF

Abstract

A method for controlling a multi-phase electric machine, whose phase terminals in an active bridge rectifier are respectively connected, via controllable first current valves, to a first DC voltage terminal and via second current valves to a second DC voltage terminal. The method includes switching on the first current valves when an output voltage between the first DC voltage terminal and the second DC voltage terminal has exceeded an upper threshold value at an exceedance point in time, and shutting off the first current valves again only once the output voltage has subsequently fallen below a lower threshold value at a shortfall point in time. The first current valves are shut off again after the shortfall point in time individually, and each only when a respective indication value, which characterizes a current flow in the phase terminal associated with the respective current valve, exhibits a predetermined property.

Claims

1-12. (canceled)

13. A method for controlling a multi-phase electric machine, operable at least in generator mode, whose phase terminals in an active bridge rectifier are respectively connected, via controllable first current valves capable of being switched on and shut off, to a first DC voltage terminal and via second current valves to a second DC voltage terminal, the method comprising: in a generator mode of the electric machine, switching on the first current valves when an output voltage between the first DC voltage terminal and the second DC voltage terminal has exceeded an upper threshold value at an exceedance point in time, and shutting off the first current valves again only once the output voltage has subsequently fallen below a lower threshold value at a shortfall point in time; wherein the first current valves are shut off again after the shortfall point in time individually, and each only when a respective indication value, which characterizes a current flow in the phase terminal associated with the respective current valve, exhibits a predetermined property, the predetermined property encompassing the indication value exhibiting a minimum determined by way of a determination specification.

14. The method as recited in claim 13, wherein the predetermined property encompasses the indication value being below a maximum value, the maximum value being elevated during a time span that is after the shortfall point in time.

15. The method as recited in claim 14, wherein the maximum value at the shortfall point in time initially corresponds to a zero value of a current flow in the phase terminal associated with the respective current valve.

16. The method as recited in claim 15, wherein the maximum value is elevated, starting from the zero value, at the earliest after a predefined waiting time after the shortfall point in time has elapsed.

17. The method as recited in claim 16, wherein the waiting time is predefined as a function of a rotation speed of the electric machine.

18. The method as recited in claim 14, wherein elevation of the maximum value occurs at least intermittently linearly with a predefined steepness, and/or in the form of a nonlinear function.

19. The method as recited in claim 18, wherein the steepness and/or at least one parameter of the nonlinear function is set as a function of a difference between the indication value and the maximum value.

20. The method as recited in claim 13, wherein the indication value is at least one of a measured current value, a voltage drop across the respective first current valve, and a value derived therefrom.

21. A control unit designed to control a multi-phase electric machine, operable at least in generator mode, whose phase terminals in an active bridge rectifier are respectively connected, via controllable first current valves capable of being switched on and shut off, to a first DC voltage terminal and via second current valves to a second DC voltage terminal, the control unit designed to: in a generator mode of the electric machine, switch on the first current valves when an output voltage between the first DC voltage terminal and the second DC voltage terminal has exceeded an upper threshold value at an exceedance point in time, and shut off the first current valves again only once the output voltage has subsequently fallen below a lower threshold value at a shortfall point in time; wherein the first current valves are shut off again after the shortfall point in time individually, and each only when a respective indication value, which characterizes a current flow in the phase terminal associated with the respective current valve, exhibits a predetermined property, the predetermined property encompassing the indication value exhibiting a minimum determined by way of a determination specification.

22. A non-transitory machine-readable memory medium on which is stored a computer program for controlling a multi-phase electric machine, operable at least in generator mode, whose phase terminals in an active bridge rectifier are respectively connected, via controllable first current valves capable of being switched on and shut off, to a first DC voltage terminal and via second current valves to a second DC voltage terminal, the computer program, when executed by a processor, causing the processor to perform: in a generator mode of the electric machine, switching on the first current valves when an output voltage between the first DC voltage terminal and the second DC voltage terminal has exceeded an upper threshold value at an exceedance point in time, and shutting off the first current valves again only once the output voltage has subsequently fallen below a lower threshold value at a shortfall point in time; wherein the first current valves are shut off again after the shortfall point in time individually, and each only when a respective indication value, which characterizes a current flow in the phase terminal associated with the respective current valve, exhibits a predetermined property, the predetermined property encompassing the indication value exhibiting a minimum determined by way of a determination specification.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 is a simplified schematic depiction of an assemblage having a generator and an active bridge rectifier.

[0036] FIG. 2 shows signal curves to explain the principles of a method according to an embodiment of the present invention.

[0037] FIG. 3 illustrates, in the form of a diagram, a method according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0038] In the Figures, elements corresponding to one another are labeled with identical reference characters and are not explained repeatedly.

[0039] FIG. 1 schematically illustrates an assemblage, having a generator 1 and an active bridge rectifier 2, that can be the basis of an embodiment of the present invention.

[0040] Generator 1 encompasses a stator 11 configured with five phases and as a pentagram circuit, and a rotor 12. The individual windings of stator 11 and of rotor 12 are not labeled separately. Generator 1 is connected at five phase terminals U to Y, via respective controllable current valves capable of being switched on and shut off (here labeled UL to YL and UH to YH), respectively to first DC voltage terminal B and to a second DC voltage terminal B+. The method according to the present invention will be described below with reference to initiation of a phase short circuit in current valves UL to YL of a low-side rectifier branch, but can also be carried out with current valves UH to YH in the high-side rectifier branch. The current valves participating in each case are referred to in the context of this Application as first current valves; at least these are controllable and capable of being switched on and shut off, for example are MOSFETs. The controllable current valves UL to YL and UH to YH that are capable of being switched on and shut off are illustrated in simplified fashion in the Figure as switches having Zener diodes connected in parallel. The Zener diodes here symbolize both the typical breakdown property of a MOSFET above a specific drain-source voltage and the reverse diode present in a MOSFET.

[0041] Current valves UH to YH and UL to YL are respectively controllable by way of decentralized control devices 21 to 25, as illustrated here by dashed addressing arrows. A generator regulator 13 evaluates a voltage present between DC voltage terminals B+ and B (DC voltage terminal B can be connected to ground) and regulates the power output of generator 1, for example by pulse width modulated application of current to the excitation winding of rotor 12.

[0042] FIG. 2 illustrates signal curves of phase currents in an assemblage having a generator and an active bridge rectifier, for example in accordance with FIG. 1, in order to explain the principles of a method in accordance with an embodiment of the invention. The phase currents are plotted on the ordinate (in amperes) against time (in milliseconds) on the abscissa. The example shows the effects that result when one of the phases is permanently short-circuited to ground (see B in FIG. 1) (the corresponding current curve is labeled 201), while the other phases (the corresponding current curves are labeled 202) are in ordinary rectification mode, i.e., continuously switching between the potential of B+ and of B. As explained, such an effect can occur, for example, when a switching threshold for shutting off a corresponding current valve can no longer be reached because of an excessively high DC proportion in the corresponding phase. The result is that the current of the phase short-circuited to ground (current curve 201) is permanently positive.

[0043] If such an effect occurs, switching under load can no longer be avoided. In order to minimize stress on the current valves, however, switching should not occur at the maximum if at all possible.

[0044] The present invention deals with this problem as illustrated in FIG. 3. FIG. 3 depicts a corresponding phase current, highly enlarged and labeled 310. The phase current 310 is plotted (in amperes) on the ordinate against a time (in milliseconds) on the abscissa. In the example depicted, it oscillates between a value of 50 and a value of 250 amperes, i.e., it no longer reaches the zero value.

[0045] A maximum value, used according to the present invention, with which the phase current 310 is compared is labeled 320. This value is equal to 0 amperes at the beginning and is elevated in ramp fashion, i.e., here in the form of a linear function, starting at a time of 2.5 milliseconds. At a time of, for example, 6 milliseconds, the phase current 310 is below the maximum value 320 for the first time, and a corresponding current valve can be shut off.