DE102010062334A1 - Method and device for operating an inverter-controlled electric machine in the event of a fault - Google Patents

Abstract

The invention relates to a method and a device for operating an electrical machine (1) controlled by an inverter (2) in the event of a fault, in which a short-circuit mode for the electrical machine (1) is implemented in that the electrical machine ( 1) is switched alternately into a first short-circuit mode and into a second short-circuit mode by a control unit (5; 7). In the first short-circuit mode, all switching elements (3a-3c) of the inverter (2) connected to a high supply voltage potential (T +) are closed and all of the switching elements (3a-3c) of the inverter (2) are open and in which second short-circuit mode, all switching elements (3a-3c) of the inverter (2) connected to the high supply voltage potential (T +) are open and all switching elements (3d-3f) of the inverter (2) connected to the low supply voltage potential (T-) are closed.

Description

The invention relates to a method and a device for operating an electric machine controlled by an inverter, in particular a pulse inverter, in the event of a fault.

State of the art

For the drive in hybrid or electric vehicles electrical machines in the form of induction machines are usually used, which in conjunction with inverters - often referred to as inverter - are operated. The electrical machines are operated either in motor or generator mode. During engine operation, the electric machine generates a drive torque which, when used in a hybrid vehicle, supports an internal combustion engine, for example in an acceleration phase. In generator mode, the electric machine generates electrical energy that is stored in an energy storage such as a battery or a super-cab. Operating mode and power of the electrical machine are set via the inverter.

Known inverters comprise a series of switching elements with which the individual phases (U, V, W) of the electric machine are selectively switched to a high supply voltage potential or to a low supply voltage potential. In each case, two series-connected switching elements form a half-bridge branch, wherein a first switching element with the high supply voltage potential and a second switching element with the low supply voltage potential are connected. Each phase of the electrical machine is then connected to one half-bridge branch each. The switching elements are controlled in normal operation, that is, without the occurrence of a fault, by an external control unit, which calculates a desired operating point for the electric machine depending on the driver's request (acceleration or braking). The inverter is connected to the control unit and receives from this the corresponding operating data or control commands.

In the case of a fault, the z. B. may arise from too high battery current or too high supply current, the inverter is switched to a safe state to prevent possible damage to electrical components. Essentially, two different turn-off methods are known from the prior art, which are used alternatively. In a first method, all switches connected to the low supply voltage potential (low-side switch) are closed and all switches (high-side switch) connected to the high supply voltage potential are opened. This mode is also referred to as a short circuit mode. In another shutdown procedure, all switches of the inverter are opened. This is also known as unlock mode.

From the DE 10 2006 003 254 A1 a method for operating an electrical machine with a pulse inverter in the event of a fault is known, in which the electrical machine is switched in the event of a malfunction first in a disconnection mode and subsequently in a short-circuit mode.

During normal operation, however, operating phases occur in which the electrical machine is not actively controlled by the inverter. During these phases of operation, the electric machine is often also switched to the short-circuit mode.

Disclosure of the invention

The invention provides a method for operating an electrical machine controlled by an inverter, in particular pulse-controlled inverter, in which a short-circuit mode for the electrical machine is realized by alternately switching the electrical machine into a first short-circuit mode and a second short-circuit mode. Mode is switched. In the first short circuit mode, all are high Supply voltage potential connected switching elements of the inverter closed and all connected to a low supply voltage potential switching elements of the inverter open. In the second short-circuit mode, all switching elements of the inverter connected to the high supply voltage potential are opened, and all switching elements of the inverter connected to the low supply voltage potential are closed.

The invention also provides an apparatus for operating an electric machine controlled by an inverter, in particular a pulse inverter, in the event of a fault. A control unit controls the inverter to implement a short circuit mode for the electrical machine so that it alternately switches the electrical machine in a first short-circuit mode and in a second short-circuit mode. In this case, in the first short-circuit mode all switching elements of the inverter connected to a high supply voltage potential are closed and all switching elements of the inverter connected to a low supply voltage potential are opened. In the second short-circuit mode, all switching elements of the inverter connected to the high supply voltage potential are opened, and all switching elements of the inverter connected to the low supply voltage potential are closed.

Advantages of the invention

The invention is based on the basic idea of avoiding excessive loading of components of the inverter and / or busbars in uncontrolled short-circuit mode by switching between two short-circuit modes, the short-circuit current being exceeded in the first short-circuit mode via the high-side mode. Side switch and in the second short-circuit mode flows through the low-side switch. In this way, the current load and thus the thermal load of the components and the busbars are distributed over several components, so that a one-sided load of the inverter components in the short-circuit mode is avoided. This has a positive effect both on the dimensioning of the power units of the inverter and on their service life.

It can be changed with a predetermined switching frequency between the first and the second short-circuit mode. The switching frequency can be specified such that in each case after a predefined period of time between the two short-circuit mode is changed. In order to achieve a particularly effective protection against permanent damage due to thermal overloads, it is advantageous to specify the switching frequency as a function of a thermal behavior of at least one module to be protected. For this purpose, a corresponding sensor system can be used which detects a variable characterizing the thermal behavior of the at least one module to be protected. The control unit can then set the switching frequency between the first and the second short-circuit mode depending on the thermal behavior of the at least one module to be protected. The thermal load of the components is determined essentially by the corresponding current load. As an alternative to a sensor system, the thermal behavior of a module to be protected can also be determined model-based.

In this case, the sensor system can comprise one or more temperature sensors which directly detect the temperature in the region of the components to be protected, that is to say in particular of the switching elements. The detected temperatures can then be evaluated by an evaluation unit to the effect that is switched when a predeterminable temperature threshold to the other short circuit mode is exceeded.

A required switching frequency but also z. B. be determined by counting a number of zero crossings of at least one of the phase currents of the electric machine and the switching frequency is predetermined in dependence on the number of zero crossings. Specifically, it can be switched between the two short-circuit mode, as soon as a predetermined number of zero crossings is reached. It makes use of the fact that the phase current oscillates at an active short circuit around the zero point.

The application of the method and the device according to the invention is basically useful and advantageous in all operating phases in which the electric machine is operated in a short-circuit mode. In particular, this includes cases of failure and operating phases in which the electrical machine is not actively controlled by the inverter.

In order to ensure the functionality of the controller even in case of failure, it is advantageous to provide two separate control units, of which a first control unit controls the inverter in normal operation and a second control unit controls the inverter in case of failure. Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying figure, which shows a schematic block diagram of an inverter controlled by an electric machine.

Description of the embodiments

1 shows a schematic representation of a three-phase electric machine 1 which can be designed, for example, as a synchronous, asynchronous or reluctance machine with a pulse inverter connected thereto 2 , The pulse inverter 2 includes switching elements 3a - 3f in the form of circuit breakers, which with individual phases U, V, W of the electric machine 1 are connected and the phases U, V, W switch either against a high supply voltage potential T + or a low supply voltage potential T-. The switching elements connected to the high supply voltage potential T + 3a - 3c are also called "high-side switch" and connected to the low supply voltage potential T- switch 3d - 3f referred to as "low-side switch" and can be embodied for example as Insulated Gate Bipolar Transistor (IGBT) or as Metal Oxide Semiconductor Field-Effect Transistor (MOSFET). Of the Pulse inverter 2 further includes a plurality of free-wheeling diodes 4a - 4f , which in each case parallel to one of the switching elements 3a - 3f are arranged. The switching elements 3a and 3d . 3b and 3e such as 3c and 3f each form a half bridge 10a . 10b respectively. 10f , which in each case one of the phases U, V, W of the electrical machine 1 assigned.

The pulse inverter 2 determines the power and operating mode of the electric machine 1 and is of a first control unit shown only schematically 5 which also in the inverter 2 can be integrated, driven accordingly. The electric machine 1 can be operated either in motor or generator mode.

Parallel to the pulse inverter 2 is a so-called DC link capacitor 6 arranged, which also in the pulse inverter 2 can be integrated and which essentially serves to stabilize a voltage of an energy storage, so for example a battery voltage.

The electric machine 1 is designed in the illustrated embodiment, three-phase, but may also have fewer or more than three phases.

In a fault of the system, the z. B. may be due to too high current or voltage values or in too high a temperature, the pulse inverter switches 2 triggered by a second control unit 7 , the electric machine 1 automatically in a first short circuit mode to damage the electric machine 1 or voltage-sensitive components. In the first short-circuit mode, all are high-side switches 3a - 3c of the pulse inverter 2 closed and all low-side switches 3d - 3f of the pulse inverter 2 open.

To the current load on the high-side switches 3a - 3c as well as other components lying in a resulting short-circuit circuit but not to be too large, a second short-circuit mode is provided, in which all high-side switch 3a - 3c of the pulse inverter 2 open and all low-side switches 3d - 3f of the pulse inverter 2 are closed. The second control unit 7 then controls the pulse inverter 2 so on, that this is the electric machine 1 alternately in a first short-circuit mode and in a second short-circuit mode switches. In this respect, of course, initially also be switched to the second short-circuit mode.

The switching frequency is by the second control unit 7 given as a function of the current load of the electrical components to be protected. To determine the current load and thus the thermal load phase currents with the aid of a sensor in the form of current sensors 11-U . 11-V and 11-W detected. In the second control unit 7 then zero crossings of the phase currents or at least one phase current are counted and a change of the short circuit mode is initiated as soon as the number of zero crossings reaches a predetermined threshold value.

Alternatively or in addition to the detection of the phase currents, the temperature at the electrical components to be protected can also be measured. Through the second control unit 7 then a change of the short circuit mode can be initiated as soon as a predeterminable temperature threshold is exceeded.

To ensure the availability of the control even in case of failure, is the second control unit 7 separate to the first control unit 5 realized, which the pulse inverter 2 in normal operation controls. In principle, the second control unit 7 also in the first control unit 5 be integrated.

Also, it is irrelevant to the applicability of the invention, whether the electric machine 1 is switched immediately after detection of a malfunction in a short-circuit operation or whether the short-circuit operation another mode, such as, a freewheeling operation is connected upstream.

Even in normal operation, operating phases occur in which the electrical machine is not actively controlled by the inverter. During these operating phases, the electric machine is also switched to the short-circuit mode. Analogous to the second control unit 7 in case of failure then controls the first control unit 5 the pulse inverter 2 so on, that this is the electric machine 1 alternately in the first short-circuit mode and in a second short-circuit mode switches.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102006003254 A1 [0005]

Claims (8)

Method for operating an inverter ( 2 ), in particular pulse-controlled inverter, controlled electrical machine ( 1 ), in which a short circuit mode for the electric machine ( 1 ) is realized by alternately switching the electric machine into a first short-circuit mode and a second short-circuit mode, wherein in the first short-circuit mode all switching elements (A +) connected to a high supply voltage potential (T +) 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to a low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are open and in the second short-circuit mode all switching elements connected to the high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to the low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are closed. The method of claim 1, wherein is switched with a predetermined switching frequency between the first and the second short-circuit mode. The method of claim 2, wherein the switching frequency is predetermined in dependence on a thermal behavior of at least one module to be protected. The method of claim 3, wherein the switching frequency is predetermined in dependence on a temperature at least one module to be protected. Method according to claim 3, wherein the switching frequency is dependent on a number of zero crossings of at least one of the phase currents of the electrical machine ( 1 ) is given. Device for operating an inverter ( 2 ), in particular pulse-controlled inverter, controlled electrical machine ( 1 ) with a control unit ( 5 ; 7 ), which the inverter ( 2 ) for realizing a short circuit mode for the electric machine ( 1 ) so that this the electric machine ( 1 ) alternately switches into a first short-circuit mode and a second short-circuit mode, wherein in the first short-circuit mode all switching elements connected to a high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to a low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are open and in the second short-circuit mode all switching elements connected to the high supply voltage potential (T +) ( 3a - 3c ) of the inverter ( 2 ) and all switching elements connected to the low supply voltage potential (T-) ( 3d - 3f ) of the inverter ( 2 ) are closed. Apparatus according to claim 6, wherein a sensor system ( 11a - 11c ) is provided for detecting a characterizing the thermal behavior of at least one module to be protected size and the control unit ( 5 ; 7 ) sets a switching frequency between the first and the second short-circuit mode depending on the thermal behavior of the at least one module to be protected. Device according to one of claims 6 or 7, wherein a second control unit ( 7 ), which the inverter ( 2 ) in the event of a fault, separately from a first control unit ( 5 ) is realized, which the inverter ( 2 ) in normal operation.

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