DE102018203739A1 - Method for detecting an error state of an electrical machine - Google Patents

Abstract

The invention relates to a method for detecting an error state of an electrical machine (100) having a rotor (120), a stator (110) and an inverter circuit (130) connected to the stator (110), wherein a first current intensity of a first phase current, a second current of a second phase current and a third current of a third phase current are detected, wherein for the first phase current, a theoretical first current from the detected second current and from the detected third current is determined, wherein from the detected first current and the theoretical first current Evaluation value is determined and it is evaluated depending on this evaluation value, whether or not an error state of the electric machine (100) is present.

Description

The present invention relates to a method for detecting an error state of an electrical machine as well as a computing unit and a computer program for its implementation.

State of the art

Electric machines can be used in motor vehicles as so-called starter generators in order to start the engine on the one hand in an engine operation and on the other hand to generate electricity for the vehicle electrical system and for charging the motor vehicle battery in a generator operation. Such electrical machines can be connected via a belt to the internal combustion engine or the crankshaft (so-called belt-driven starter generators, RSG).

By means of such an electric machine, for example, a boost recuperation system (BRS) can be realized. In generator mode, the electric machine absorbs a drive torque and converts mechanical energy into electrical energy. During engine operation, the electric machine converts electrical energy back into mechanical energy and generates a drive torque.

Disclosure of the invention

According to the invention, a method for detecting an error state of an electrical machine as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

The electric machine has a rotor, a stator and an inverter circuit connected to the stator. The rotor may in particular have an excitation winding (externally excited electrical machine) or permanent magnets (permanently excited electrical machine). The stator is in particular an n-phase stator with n stator phases, in particular with n≥3. In particular, the stator has three or five stator phases. However, the invention is particularly suitable for any number of stator phases. By means of the inverter circuit, it is expedient to rectify an n-phase AC voltage applied to the stator to a DC voltage, and vice versa, a DC voltage applied to the inverter circuit can be reversed to an n-phase AC voltage on the stator. In particular, the inverter circuit is also electrically connected to the rotor, e.g. via a carbon slip ring system.

As part of the method, a first current intensity of a first phase current, a second current intensity of a second phase current and a third current strength of a third phase current are now detected. In particular, a current into or out of a phase connection of the stator should be understood as a phase current. These three current strengths are detected in particular simultaneously or at least substantially simultaneously. In particular, a temporal course of the respective current intensities is detected.

For the first phase current then a theoretical first current from the detected second current and from the detected third current is determined. In particular, this theoretical first current intensity is determined analytically in accordance with theoretical principles or a theoretical mathematical model of the electrical machine. In particular, a theoretical time profile of the first current intensity is determined from the detected time profiles of the second and third current intensity. An evaluation value is determined from the detected first current value and the theoretical first current value. Depending on this evaluation value, it is judged whether or not there is an error state of the electric machine.

In the case of a fault-free electric machine in which there is no fault state, the phase currents of the individual phases are in particular symmetrical to each other or at least substantially symmetrical. In this context, symmetrical is to be understood in particular as meaning that the time profiles of the current strengths of the phase currents have the same or at least substantially the same amplitude and are phase-shifted relative to one another by a phase angle. For example, in a three-phase electric machine, the time courses of the three phase currents are phase-shifted by a phase angle of 120 ° and in a five-phase electric machine, the time profiles of the five phase currents are phase-shifted by a phase angle of 72 °.

In the case of a faulty electrical machine, in which there is thus an error state, this symmetry of the phase currents is no longer present. In particular, in the case of an error state, the amplitudes of the time profiles of the current strengths of the phase currents differ, and a regular phase shift about the respective phase angle is no longer given in particular.

This circumstance makes use of the invention to detect a fault condition of the electric machine. Due to the symmetry of the phase currents, the detected first current intensity and the theoretical first current intensity or their time profiles should coincide or at least substantially coincide in a fault-free electric machine.

The evaluation value is determined in particular by a comparison of the detected first current intensity and the theoretical first current intensity and in particular depends on a difference between the detected first current intensity and the theoretical first current intensity. Too great a difference between the detected first current intensity and the theoretical first current strength in particular indicates a non-given symmetry of the phase currents and thus an error state of the electric machine.

The invention thus provides a way to detect a fault of the electric machine in a simple, inexpensive and low-effort manner. In particular, the current intensities of the phase currents for the operation of the electric machine are detected anyway or are present anyway. Thus, in particular, it requires no additional measurement effort and no additional hardware. In particular, no structural changes to an electrical machine are necessary for carrying out the method. Appropriately, an electrical machine can thus be retrofitted in a simple manner to perform error detection of the electric machine in the context of the present method. In particular, the error detection in the context of the present invention can be implemented in software and implemented in a simple manner, for example, in a control unit of an electric machine for retrofitting.

For example, in an n = 5-phase electric machine with Drudenfußschaltung the theoretical time course of the first current I _{1_th} from the detected time histories of the second and third current I _{2_erfasst} and I _{3_erfasst} ) are determined according to the following formula: $${\text{I}}_{\text{1\_th}}=\left({\text{I}}_{\text{2\_erfasst}}+{\text{I}}_{\text{3\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\mathrm{\pi }/\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right)$$

The value 4 * π / n results from the "distance" or the geometry of the phases in the Drudenfußschaltung each other. For a five-phase machine, the distances between the phases are each 360 ° / n = 72 °. Thus, for example, the distance from the phase U to the phase V 72 °, from the phase U to the phase W according to 2 * 72 °, of the phase U to the phase X 3 * 72 ° and from the phase U to the phase Y 4 * 72 °.

According to an advantageous embodiment, the evaluation value determined is a difference between the detected first current intensity and the theoretical first current intensity. An excessively large difference between the detected and the theoretical first current strength in particular indicates a non-given symmetry of the phase currents and thus an error condition.

Advantageously, a statistical value is determined as the evaluation value, preferably a standard deviation between the detected first current intensity and the theoretical first current intensity. Too large a standard deviation means, in particular, too great a difference between the detected and the theoretical first current strength and indicates a present fault condition. Preferably, an average value, in particular the arithmetic mean or the median, between the detected first current value and the theoretical first current value can be determined as the evaluation value and / or a deviation, in particular an absolute deviation and / or an average absolute deviation between this mean value and the detected and / or or theoretical first current. Too great a deviation, in particular too great a mean absolute deviation of the mean from the detected or theoretical first current strength, in particular indicates a present fault condition.

Preferably, a threshold value comparison of the evaluation value is performed. If the evaluation value reaches or exceeds a threshold value, it is preferably evaluated that an error state of the electrical machine is present. For example, is the difference between the detected and theoretical first current determined as the evaluation value, this threshold may be, for example, 5%, 4%, 3%, 2% or 1% of the detected first current.

It should be noted at this point that the chosen nomenclature of the first, second and third phase current is not to be understood as limiting and is not intended to express an order or relevance of the phase currents. Rather, the three phases, whose phase currents are detected in the context of the method, are suitably selected.

Furthermore, it should be pointed out that in the case of a stator with more than three phases, for example in the case of a five-phase stator, in particular more than three phase currents can be determined simultaneously or essentially simultaneously, in particular four or five phase currents.

Advantageously, at least 3 and at most n current strengths of n phase currents are detected with n≥3. The first current of the first phase current, the second current of the second phase current and the third current of the third phase current are preferably selected from these detected currents of the n phase currents. In particular, current intensities can thus be detected for different appropriate combinations of three phase currents in each case and for one of these three phase currents in each case a theoretical current intensity can be determined from the detected current strengths of the two other phase currents. Thus, multiple pairs of detected and theoretical currents and, accordingly, multiple evaluation values may be determined. Thus, fault conditions with high security and low error rate can be detected.

The second phase current and the third phase current are preferably selected as a function of the first phase current on the basis of their electrical phase angles PHI _1, PHI ₂ and PHI ₃ . Preferably, the second and third phase currents are selected according to the following formula: $${\text{PHI}}_2={\text{PHI}}_1-720°/{\text{n and PHI}}_3={\text{<figure-callout id="1" label="PHI" filenames="DE102018203739A1\_0040.png" state="{{state}}">PHI</figure-callout>}}_1+720°/\text{n}$$

The second and third phase currents are selected according to this formula in particular when more than three phase currents are detected.

Alternatively, the second and third phase currents are selected on the basis of their electrical phase angles PHI ₂ and PHI _3, preferably according to the following formula: $${\text{PHI}}_2={\text{PHI}}_1-360°/{\text{n and PHI}}_3={\text{<figure-callout id="1" label="PHI" filenames="DE102018203739A1\_0040.png" state="{{state}}">PHI</figure-callout>}}_1+360°/\text{n}$$

In particular, the second and third phase currents are selected according to this formula when exactly three phase currents are detected.

According to an advantageous embodiment, a fourth current of a fourth phase current is detected. For the second phase current, a theoretical second current intensity is preferably determined from the detected first current value and from the detected fourth current value. Preferably, a second evaluation value is determined from the detected second current value and the theoretical second current value, and depending on the evaluation value and the second evaluation value, it is preferably judged whether or not there is a fault state of the electric machine. In particular, in this case, four different phase currents in the regular operation of the electric machine can be detected simultaneously or at least substantially simultaneously, and in particular four low-side switches of the inverter circuit can be closed simultaneously or at least substantially simultaneously.

Advantageously, a fourth current of a fourth phase current and a fifth current of a fifth phase current are detected. For the fourth phase current, a theoretical fourth current is determined from the detected second current and from the detected fifth current. A second evaluation value is preferably determined from the detected fourth current value and the theoretical fourth current value, and depending on the evaluation value and the second evaluation value, it is advantageously judged whether or not there is a fault state of the electric machine. Such a determination of the first and second evaluation value is particularly suitable if during the regular operation of the electric machine five phase currents can be detected simultaneously or at least substantially simultaneously, in particular if five low-side switches of the inverter circuit can be closed simultaneously or at least substantially simultaneously ,

Advantageously, a fault condition is one or more of the following conditions: a short circuit of one or more switches of the inverter circuit to battery, a short circuit of one or more switches of the inverter circuit to ground, a short circuit in a phase winding of the stator, a short circuit between two or more phase windings of the stator , a short circuit of a phase winding of the stator after battery, a short circuit of a phase winding of the stator to ground, a fault condition in a measuring arrangement for detecting the currents of the phase currents.

Such switches of the inverter circuit may be used, for example, as passive switching elements, e.g. Diodes, be formed or as active switching elements, in particular as transistors, for example as a MOSFET or IGBT. In particular, the inverter circuit has half-bridges with so-called high-side switches and so-called low-side switches. As a respective high-side or low-side switch, in each case a single switching element can be used or in each case a plurality of switching elements, optionally of different design.

Such a measuring arrangement comprises in particular operational amplifier and / or analog-to-digital converter (ADC). An error state of the measuring arrangement may be, for example, a defect of one of the operational amplifiers or one of the analog-to-digital converters, for example a short circuit to ground or to battery.

Advantageously, the method is suitable for different types of electrical machines in various fields of application, e.g. for HV hybrid machines (high voltage). Particularly advantageously, the method is suitable for use as a starter generator, e.g. belt-driven starter generator (RSG) trained electric machine. As explained above, such a belt-driven starter generator can be used in a motor vehicle, on the one hand to start an internal combustion engine with the electric machine during engine operation and, on the other hand, to generate electricity for a vehicle electrical system and for charging a motor vehicle battery during generator operation. Accordingly, potential connections of the electrical machine can advantageously be connected to a vehicle electrical system and / or to a motor vehicle battery.

Such a starter generator is particularly preferably used in a boost recuperation system (BRS) or as a so-called boost recuperation machine (BRM). Such a boost recuperation machine (BRM) can in particular receive drive torque in generator operation and convert mechanical energy into electrical energy and, during engine operation, convert electrical energy back into mechanical energy and thus generate a drive torque.

In the course of operating such a boost recuperation system, the electric machine can be used for various functions, in particular for recuperation, ie energy recovery during braking, for torque assistance, in particular during startup and acceleration, for a start / stop function. in the course of which an internal combustion engine can be started after an automatic stop again, and / or for a sailing operation, for example when coasting or light downhill.

For use as such a starter generator are preferably foreign-excited three-phase synchronous machines, since their motor torque is particularly well regulated. A desired torque can be adjusted by appropriate control of the rotor winding (exciter coil) and / or the stator winding. A temporal modulation of the torque may be preferred in order to achieve as low a noise and low-vibration starting operation as possible.

An arithmetic unit according to the invention, e.g. a microcontroller or a control unit of a motor vehicle is, in particular programmatically, configured to perform a method according to the invention.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically by means of embodiments in the drawing and will be described below with reference to the drawing.

list of figures

• 1 schematically shows an electric machine with a preferred embodiment of a computing unit according to the invention, which is adapted to perform a preferred embodiment of a method according to the invention.
• 2 schematically shows a part of an electric machine with a preferred embodiment of a computing unit according to the invention, which is adapted to perform a preferred embodiment of a method according to the invention.
• 3 to 5 each show schematically a preferred embodiment of a method according to the invention as a block diagram.
• 6 schematically shows a current-time diagram, which can be detected in the course of a preferred embodiment of a method according to the invention.
• 7 schematically shows an evaluation value-time diagram, which can be detected in the course of a preferred embodiment of a method according to the invention.

Embodiment (s) of the invention

In 1 is an electrical machine shown schematically and with 100 designated. The electric machine 100 For example, it may be designed as a belt-driven starter generator (RSG) and used in a motor vehicle in a boost recuperation system (BRS) as a so-called boost recuperation engine (BRM).

The electric machine 100 is in this example designed as a five-phase electric machine, wherein stator inductances (phases) of a stator 110 are connected to a Pentagrammschaltung and a rotor 120 a field winding 121 having.

The electric machine 100 also has one with the stator 110 connected inverter circuit 130 on that between a DC voltage connection 141 and a mass connection 142 is switched. For example, an electrical system and / or a motor vehicle battery with these connections 141 . 142 be connected. By means of the inverter circuit 130 can one on the stator 110 adjacent rectified five-phase AC voltage can be rectified into a DC voltage and vice versa, one at the terminals 141 . 142 applied DC voltage in a five-phase AC voltage are reversed.

The inverter circuit 130 has five half bridges, each with a highside switch 131 and a lowside switch 132 on. The highside and lowside switches 131 . 132 are each formed as MOSFETs in this example. Each half bridge points between its highside and lowside switches 131 . 132 each have a center tap, via which the respective half-bridge with a phase connection U . V, W X, Y of the stator 110 connected is.

Between each of the lowside switches 132 and the mass connection 142 is each a measuring resistor 133 or shunt resistor switched. These measuring resistors 133 are each designed in particular as low-resistance, electrical resistance elements and are used in particular for measuring electrical currents. Alternatively or additionally, it is also conceivable to each have a measuring resistor between each of the highside switches 131 and the DC voltage connection 141 to switch. Alternatively or additionally, it is also conceivable to each have a measuring resistor between each of the highside switches 131 and the lowside switch 132 to switch.

It is envisaged to use alternative current measuring devices instead of measurement resistors (e.g., LEM converters).

An arithmetic unit 150 is for driving the electric machine 100 intended. For example, the arithmetic unit 150 be designed as a microcontroller of a control device of the corresponding motor vehicle.

A part of the electric machine 100 out 1 is in 2 shown schematically. As in 2 can be seen, a measuring arrangement may be provided which, for example, with the measuring resistors 133 connected operational amplifiers 134 which can with analog-to-digital converters 135 of the microcontroller 150 are connected.

Current levels of the measuring resistors can be measured via this measuring arrangement 133 flowing currents as phase currents of the phases of the stator 110 be detected metrologically. For detecting the current intensity of a phase current in this way, in particular, the low-side switch connected to the phase connection of this particular phase is provided 132 closed. In particular, as the respective phase current, a current intensity of a current is detected, which is detected by the closed-circuit lowside switch 132 connected measuring resistor 133 flows.

The microcontroller 150 is adapted to detection of fault conditions of the electric machine 100 perform. For this purpose, the microcontroller 150 in particular programmatically, adapted to carry out a preferred embodiment of a method according to the invention, as described below with reference to FIGS 3 to 7 is explained.

In 3 a preferred embodiment of the method according to the invention is shown schematically as a block diagram.

In one step 201 are doing so with the help of the measuring resistors 133 a first current of a first phase current, a second current of a second phase current and a third current of a third phase current detected. In particular, temporal courses of these current intensities are detected, in particular as long as the low-side switch connected to the respective phase is closed.

und $${\text{PHI}}_3={\text{PHI}}_1+360°/\text{n}\text{.}$$

In particular, phase currents of three phases are detected, their respective low-side switches 132 are closed simultaneously or at least substantially simultaneously in the course of operation of the electric machine. In particular, the electrical phase angles of the first phase current PHI _1, the second phase current PHI ₂ and the third phase current PHI _{3 are} related to one another as follows: $${\text{PHI}}_2={\text{PHI}}_1-360°/\text{n}$$

and $${\text{PHI}}_3={\text{PHI}}_1+360°/\text{n}\text{,}$$

und $${\text{PHI}}_3={\text{PHI}}_1+720°/\text{n}\text{.}$$

Alternatively, it is also conceivable that the electrical phase angles are related to one another in the following way: $${\text{PHI}}_2={\text{PHI}}_1-720°/\text{n}$$

and $${\text{PHI}}_3={\text{PHI}}_1+720°/\text{n}\text{,}$$

In one step 202 For the first phase current, a theoretical first current intensity is determined from the detected second current value and from the detected third current value. In particular, a theoretical time course of the first current is determined.

For example, in step 201 Amperages of the phase currents of the phases U . V and W be recorded. For the phase current of the phase V as the first phase current can in step 202 the theoretical first current from the detected currents of the phase U be determined as the second phase current and the phase Wals third phase current.

In an analogous way, in step 201 for example, currents of the phases V . W and X be recorded. The theoretical first current of the phase W can in step 202 for example, from the detected currents of the phases V (as a second phase current) and X (as the third phase current).

For example, in step 201 also current levels of the phases W . X and Y be recorded. For the phase X can in step 202 the theoretical first current from the detected currents of the phases W (as a second phase current) and Y (as the third phase current).

It is also conceivable, for example, in step 201 Currents of the phases X . Y and U capture. In this case, in step 202 for example for the phase Y the theoretical first current from the detected currents of the phases X (as a second phase current) and U (as the third phase current).

Furthermore, it is conceivable, for example, in step 201 Currents of the phases Y . U and V to capture and in step 202 for the phase U the theoretical first current from the detected currents of the phases Y (as a second phase current) and V (as the third phase current).

In step 203 An evaluation value is determined from the detected first current value and the theoretical first current value. For example, a difference between the detected and theoretical first currents is determined as this evaluation value.

In step 204 a threshold comparison of the evaluation value is performed. If the evaluation value does not exceed a limit value of, for example, 5% of the detected first current value or of, for example, 5% of the amplitude of the detected first current value, in step 205 rated that no fault condition of the electric machine 100 is present. On the other hand, if the evaluation value exceeds the limit value, in step 206 rated that a fault condition of the electric machine 100 is present. In this case, in step 207 a measure is performed, for example, an error message can be issued.

According to a preferred embodiment, more than three phase currents can be detected simultaneously. Such a preferred embodiment of the method according to the invention is in 4 shown schematically as a block diagram.

In this case, in step 301 with the help of the measuring resistors 133 For example, the first current, the second current, the third current and a fourth current of a fourth phase current are detected.

In step 302 In this case, in addition to the theoretical first current intensity, a theoretical second current intensity from the detected first current intensity and from the recorded fourth current intensity is determined for the second phase current.

For example, in step 301 the currents of the phase currents of the phases V . W . X and Y be recorded. For example, the current intensity of the phase can be used as the first current V , as the second current, the current of the phase Y , as the third current, the current of the phase X and the fourth current strength, the current intensity of the phase W are detected.

In step 302 is for the first phase current of the phase V is the theoretical first current intensity I _{V_th} from the detected second current I _{Y_erfasst} the phase Y and the detected third current I _{X_erfasst} the phase X determined, for example, according to the following formula: $${\text{I}}_{\text{V\_TH}}=\left({\text{I}}_{\text{X\_erfasst}}+{\text{I}}_{\text{Y\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

Furthermore, for the second phase current of the phase Y the theoretical second current intensity I _{Y_th} from the detected first current intensity I _{V_ detects} the phase V and from the detected fourth current intensity I _{W_records} the phase W determined, for example according to the formula: $${\text{I}}_{\text{Y\_th}}=\left({\text{I}}_{\text{V\_erfasst}}+{\text{I}}_{\text{W\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

und $${\text{PHI}}_3={\text{PHI}}_1+720°/\text{n}\text{.}$$

The electrical phase angle of the first phase current PHI _1, the second phase current PHI ₂ and the third phase current PHI ₃ are in particular in the following relationship to each other: $${\text{PHI}}_2={\text{PHI}}_1-720°/\text{n}$$

and $${\text{PHI}}_3={\text{PHI}}_1+720°/\text{n}\text{,}$$

und $${\text{PHI}}_4={\text{PHI}}_2-720°/\text{n}\text{.}$$

Analogously, the electrical phase angles of the second phase current PHI ₂ , the first phase current PHI ₁ and the fourth phase current PHI _{4 are} in particular in the following relationship: $${\text{<figure-callout id="1" label="PHI" filenames="DE102018203739A1\_0040.png" state="{{state}}">PHI</figure-callout>}}_1={\text{PHI}}_2+720°/\text{n}$$

and $${\text{PHI}}_4={\text{PHI}}_2-720°/\text{n}\text{,}$$

und $${\text{PHI}}_3={\text{PHI}}_1+360°/\text{n}$$

bzw. $${\text{PHI}}_1={\text{PHI}}_2+360°/\text{n}$$

und $${\text{PHI}}_4={\text{PHI}}_2-360°/\text{n}\text{.}$$

Alternatively, the phase angles could expediently also be in the following relationship to one another: $${\text{PHI}}_2={\text{PHI}}_1-360°/\text{n}$$

and $${\text{PHI}}_3={\text{<figure-callout id="1" label="PHI" filenames="DE102018203739A1\_0040.png" state="{{state}}">PHI</figure-callout>}}_1+360°/\text{n}$$

respectively. $${\text{<figure-callout id="1" label="PHI" filenames="DE102018203739A1\_0040.png" state="{{state}}">PHI</figure-callout>}}_1={\text{PHI}}_2+360°/\text{n}$$

and $${\text{PHI}}_4={\text{PHI}}_2-360°/\text{n}\text{,}$$

It is also conceivable, for example, in step 301 the currents of the phases U . W . X . Y capture. For example, while the first current of the phase W be detected, the second current of the phase U , the third current of the phase Y and the fourth current of the phase X ,

Accordingly, in step 302 the theoretical first current I _{W_th of} the phase W from the detected second current I _{U_erfasst} the phase U and from the detected third current I _{Y_ detects} the phase Y be determined, in particular according to the formula: $${\text{I}}_{\text{W\_th}}=\left({\text{I}}_{\text{Y\_erfasst}}+{\text{I}}_{\text{U\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

The theoretical second current I _{U_th of} the phase U can in step 302 doing so from the detected first current I _{W_erfasst} the phase W and from the detected fourth current ix captures the phase X be determined, for example, as follows: $${\text{I}}_{\text{U\_th}}=\left({\text{I}}_{\text{W\_erfasst}}+{\text{I}}_{\text{X\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

For example, in step 301 also the currents of the phases U . V . X . Y be recorded. In this case, for example, the first current of the phase X be detected, the second current of the phase V , the third current of the phase U and the fourth current of the phase Y ,

In step 302 may be, for example, the theoretical first current I _{X_th} the phase X from the detected second current intensity I _{V_ detects} the phase V and from the detected third current intensity I _{U_ detects} the phase U are determined, in particular according to the formula: $${\text{I}}_{\text{X\_th}}=\left({\text{I}}_{\text{U\_erfasst}}+{\text{I}}_{\text{V\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

Furthermore, in step 302 the theoretical second current I _{V_th of} the phase V from the detected first current I _{x_erfasst} the phase X and from the detected fourth current I _{Y_ detects} the phase Y be determined, in particular as follows: $${\text{I}}_{\text{V\_TH}}=\left({\text{I}}_{\text{X\_erfasst}}+{\text{I}}_{\text{Y\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

In an analogous way, in step 301 eg also the currents of the phases U . V . W . Y be recorded. For example, this is the first current of the phase Y detected, the second current of the phase W , the third current of the phase V and the fourth current of the phase U ,

In step 302 For example, the theoretical first current I _{Y_th of} the phase Y from the detected second current I _{W_erfasst} the phase W and from the detected third current intensity I _{V_,} the phase V is determined as follows: $${\text{I}}_{\text{Y\_th}}=\left({\text{I}}_{\text{V\_erfasst}}+{\text{I}}_{\text{W\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

Further, the theoretical second current I _{W_th of} the phase W from the detected first current I _{Y_erfasst} the phase Y and from the detected fourth current I _{U_ detects} the phase U determined as follows: $${\text{I}}_{\text{W\_th}}=\left({\text{I}}_{\text{Y\_erfasst}}+{\text{I}}_{\text{U\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

Likewise, it is conceivable the currents of the phases U . V . W . X in step 301 to capture, for example, the first current of the phase U is detected, the second current of the phase X , the third current of the phase W and the fourth current of the phase V ,

Accordingly, in step 302 For example, the theoretical first current I _{U_th of} the phase U from the detected second current I _{x_erfasst} the phase X and from the detected third current I _{W_erfasst} the phase W determined as follows: $${\text{I}}_{\text{U\_th}}=\left({\text{I}}_{\text{W\_erfasst}}+{\text{I}}_{\text{X\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

The theoretical second current I _{X_th of} the phase X is, for example, from the detected first current I _{U_erfasst} the phase U and from the detected fourth current intensity I _{V_,} the phase V is determined as follows: $${\text{I}}_{\text{X\_th}}=\left({\text{I}}_{\text{U\_erfasst}}+{\text{I}}_{\text{V\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

In step 303 a first evaluation value is determined from the detected first current value and the theoretical first current value, and a second evaluation value is determined from the detected second current value and the theoretical second current value, for example by determining the difference between the respective detected current value and the respective theoretical current value.

Analogous to step 204 out 3 will be in step 304 in each case a threshold value comparison of the first and the second evaluation value is performed. For example, the threshold for the first evaluation value may be 5% of the amplitude of the detected first current and the threshold for the second evaluation may be 5% of the amplitude of the detected second current.

If the two evaluation values do not exceed their respective limits, in step 305 rated that no fault condition of the electric machine 100 is present. If at least one of the evaluation values exceeds the respective limit value, in step 306 rated that a fault condition of the electric machine 100 is present and an error message is in step 307 output.

According to a preferred embodiment, also five phase currents can be detected simultaneously. Such a preferred embodiment of the method according to the invention is in 5 shown schematically as a block diagram.

In this case, in step 401 with the help of the measuring resistors 133 in addition to the first, second, third and fourth current, a fifth current of a fifth phase current are detected. In step 402 In addition to the theoretical first current strength, a theoretical fourth current intensity from the detected second current intensity and from the detected fifth current value is furthermore determined for the fourth phase current.

und $${\text{PHI}}_3={\text{PHI}}_1+720°/\text{n}\text{.}$$

In particular, the electrical phase angles of the first phase current PHI _1, the second phase current PHI ₂ and the third phase current PHI _{3 are} in the following relationship to one another: $${\text{PHI}}_2={\text{PHI}}_1-720°/\text{n}$$

and $${\text{PHI}}_3={\text{PHI}}_1+720°/\text{n}\text{,}$$

und $${\text{PHI}}_3={\text{PHI}}_1+360°/\text{n}\text{.}$$

Alternatively, the phase angles may, for example, also be related to each other as follows: $${\text{PHI}}_2={\text{PHI}}_1-360°/\text{n}$$

and $${\text{PHI}}_3={\text{PHI}}_1+360°/\text{n}\text{,}$$

und $${\text{PHI}}_5={\text{PHI}}_4-720°/\text{n}\text{.}$$

Analogously, the electrical phase angles of the fourth phase current PHI ₄ , the second phase current PHI ₂ and the fifth phase current PHI _{5 are} in particular in the following relationship: $${\text{PHI}}_2={\text{PHI}}_4+720°/\text{n}$$

and $${\text{PHI}}_5={\text{PHI}}_4-720°/\text{n}\text{,}$$

und $${\text{PHI}}_5={\text{PHI}}_4+360°/\text{n}\text{.}$$

Alternatively, the relationship would be conceivable: $${\text{PHI}}_2={\text{PHI}}_4-360°/\text{n}$$

and $${\text{PHI}}_5={\text{PHI}}_4+360°/\text{n}\text{,}$$

For example, in step 401 the first current of the phase U be detected, the second current of the phase X , the third current of the phase W , the fourth current of the phase V and the fifth current of the phase Y ,

Accordingly, in step 402 the theoretical first current intensity I _{U_th of} the phase U from the detected second current intensity I _{X_ detects} the phase X and the detected third current I _{W_ detects} the phase W determined, for example, according to the formula: $${\text{I}}_{\text{U\_th}}=\left({\text{I}}_{\text{W\_erfasst}}+{\text{I}}_{\text{X\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

Further, the theoretical fourth current I _{V_th of} the phase V from the detected second current I _{x_erfasst} the phase X and the detected fifth current I _{Y_ detects} the phase Y for example, determined as follows: $${\text{I}}_{\text{V\_TH}}=\left({\text{I}}_{\text{X\_erfasst}}+{\text{I}}_{\text{Y\_erfasst}}\right)/\left(\text{cos}\left(4*\mathrm{\pi }/\text{n}\right)-\text{sin}\left(4*\pi /\text{n}\right)/\text{tan}\left(-4*\mathrm{\pi }/\text{n}\right)\right),$$

Analogous to step 303 be in step 403 a first evaluation value as a difference of the detected and the theoretical first current strength and a second evaluation value as a difference of the detected and the theoretical fourth current determined.

Analogous to the steps 304 to 307 will be in step 404 a threshold comparison of this first and second evaluation value performed. In this case, the limit value for the first evaluation value may be 5% of the amplitude of the detected first current value and the limit value for the fourth evaluation value 5% of the amplitude of the detected fourth current value.

If both evaluation values do not exceed their respective limits, in step 405 evaluates that no fault condition exists. If at least one evaluation value exceeds its limit, it will be in step 406 evaluates that an error condition exists and an error message is issued in step 407.

In 6 schematically a current-time diagram is shown. In this case, time profiles of the current strengths of the five phase currents I _U , I _V , I _W , I _X and I _Y are shown, as can be seen for example in step 401 be recorded.

As in 6 It can be seen have the waveforms of the currents I _U, I _V, I _W, up to a time of 0.2 has substantially the same amplitude and are phase shifted I _X and I _Y s to each other by a phase angle of 72 °. The phase currents I _U, I _V, I _W, I _X and I _Y of the individual phases are thus up to the time of 0.2 s to each other symmetrically. Up to this time of 0.2 s there is no fault state of the electrical machine.

From the time of 0.2 s in the illustrated example is an error state of the electric machine 100 in front. As can be seen, the symmetry of the phase currents I _U, I _V, I _W, I _X and I _Y no longer given from this point on, the amplitudes of the waveforms of the currents I _U, I _V, I _W, I _X and I _{Y are} different and a regular phase shift is no longer given. This circumstance makes use of the invention to a fault condition of the electric machine 100 to recognize.

In 7 schematically an evaluation value-time diagram is shown. In this case, for example, a temporal course of the first evaluation value Δ ₁ and the second evaluation value Δ ₂ as shown in step 403 be determined.

As in 7 can be seen, are the evaluation values Δ ₁ and Δ ₂ until the time of 0.2 s, and are below their respective limits in this area. From the time of 0.2 s, to which a fault condition of the electric machine 100 occurs, are the evaluation values Δ ₁ and Δ ₂ significantly higher and are each above their respective limit, thereby recognizing that a fault condition exists.

Claims (14)

A method of detecting a fault condition of an electric machine (100) having a rotor (120), a stator (110) and an inverter circuit (130) connected to the stator (110), wherein a first current of a first phase current, a second current of a second phase current and a third current of a third phase current are detected (201, 301, 401), wherein for the first phase current a theoretical first current intensity is determined from the detected second current value and from the detected third current value (202, 302, 402), wherein an evaluation value is determined (203, 303, 403) from the detected first current value and the theoretical first current value and (204, 304, 404) is evaluated in dependence on this evaluation value, whether an error state of the electrical machine (100) is present ( 206, 306, 406) or not (205, 305, 405). Method according to Claim 1 , wherein as the evaluation value, a difference between the detected first current value and the theoretical first current value is determined (203, 303, 403). Method according to Claim 1 or 2 , where the evaluation value is a statistical value. Method according to Claim 3 in which the evaluation value is a standard deviation and / or a mean value and / or a deviation between an average value and the detected first current intensity and / or a deviation between an average value and the theoretical first current value. The method of any one of the preceding claims, wherein it is judged that an error condition of the electric machine is present when the evaluation value reaches a threshold (206, 306, 406). Method according to one of the preceding claims, wherein at least three and at most n current strengths of n phase currents are detected with n≥3 and wherein the first current of the first phase current, the second current of the second phase current and the third current of the third phase current of the detected currents of the n phase currents are selected. Method according to Claim 6 in which the second phase current and the third phase current are selected as a function of the first phase current on the basis of their electrical phase angles PHI _1, PHI ₂ and PHI ₃ , where PHI ₂ = PHI ₁ - 720 ° / n and PHI ₃ = PHI ₁ + 720 ° or PHI ₂ = PHI ₁ - 360 ° / n and PHI ₃ = PHI ₁ + 360 ° / n. Method according to one of the preceding claims, wherein a fourth current of a fourth phase current is detected (301), wherein for the second phase current a theoretical second current is determined from the detected first current and from the detected fourth current (302), wherein a second evaluation value is determined (303) from the detected second current value and the theoretical second current value and (304) is evaluated depending on the evaluation value and the second evaluation value, whether an error state of the electrical machine is present (306) or not (306) 305). Method according to one of Claims 1 to 7 , wherein a fourth current of a fourth phase current and a fifth current of a fifth phase current are detected (401), wherein for the fourth phase current, a theoretical fourth current from the detected second current and the detected fifth current is determined (402), wherein from the a second evaluation value is determined (403) and, depending on the evaluation value and the second evaluation value, it is judged (404) whether there is an error state of the electric machine (406) or not (405). The method of any one of the preceding claims, wherein an error condition is one or more of the following conditions: a short circuit of one or more switches (131, 132) of the inverter circuit (130) to the battery (141), a short circuit of one or more switches (131, 132) of the inverter circuit to ground (142), a short circuit in a phase winding of the stator (110), a short circuit between two or more phase windings of the stator (110), a short circuit of a phase winding of the stator (110) to battery (141), a short circuit of a phase winding of the stator (110) to ground (142), a fault condition in a measuring arrangement for detecting the currents of the phase currents. Method according to one of the preceding claims, wherein the electric machine (100) is a starter generator, in particular a boost recuperation machine. Arithmetic unit (150) adapted to perform a method according to any one of the preceding claims. Computer program that causes a computing unit (150) to perform a method according to any one of Claims 1 to 11 when executed on the arithmetic unit (150). Machine-readable storage medium with a computer program stored thereon Claim 13 ,

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