METHOD FOR OPERATING AN ELECTRIC MACHINE

Abstract

A method for checking an operation of an electric machine, which has three phases. For pulses of a first electric variable of the three phases, a pulse width modulation is carried out. Depending in each case on a positioning of electromechanical components of the electric machine with respect to one another, the first electric variable has a pulse with a longest pulse width for a first of the three phases, a pulse with an intermediate pulse width for a second of the three phases, and a pulse with a shortest pulse width for a third of the three phases. A cycle of the pulse width modulation is delimited by two points in time.

Claims

1-11. (canceled)

12. A method for checking an operation of an electric machine, which has three phases, comprising: for pulses of a first electric variable of the three phases, a pulse width modulation is carried out, wherein, depending in each case on a positioning of electromechanical components of the electric machine with respect to one another, a first electric variable has a pulse with a longest pulse width for a first of the three phases, a pulse with an intermediate pulse width for a second of the three phases, and a pulse with a shortest pulse width for a third of the three phases, wherein a cycle of the pulse width modulation is delimited by two points in time, including, a point in time at the beginning of the cycle and a point in time at the end of the cycle, wherein a first pulse of the three phases is shifted with respect to a first of the two points in time that delimit the cycle and a second pulse of the three phases is shifted with respect to a second of the two points in time that delimit the cycle, wherein at least one value of a second electric variable is measured during the cycle within at least one measurement window.

13. The method according to claim 12, wherein the at least one value of the second electric variable is measured for an intermediate circuit of the electric machine.

14. The method according to claim 12, wherein a point in time that delimits the at least one measurement window is placed on one of the two points in time that delimit the cycle.

15. The method according to claim 12, which is carried out for an electric machine (49) designed as an electric motor.

16. The method according to claim 12, wherein, as the second electric variable, a current flowing through the electric machine is checked, wherein, for a voltage as the first electric variable, two pulses designed as voltage pulses of the three phases respectively are shifted and the current is measured within at least one of these voltage pulses within the at least one measurement window.

17. The method according to claim 12, wherein the pulse with the longest pulse width is shifted with respect to the first of the two points in time that delimit the cycle, and the pulse with the shortest pulse width is shifted with respect to the second of the two points in time that delimit the cycle.

18. The method according to claim 12, wherein an operation of the electric machine (49) is checked taking into consideration the at least one measured value.

19. A system for checking an operation of an electric machine, which has three phases, comprising a microcontroller and at least one sensor, wherein the microcontroller is designed such that, for pulses of a first electric variable of the three phases, a pulse width modulation is carried out, wherein, depending on a positioning of electromechanical components of the electric machine with respect to one another in each case, the first electric variable has a pulse with a longest pulse width for a first of the three phases, a pulse with an intermediate pulse width for a second of the three phases, and a pulse with a shortest pulse width for a third of the three phases, wherein a cycle of the pulse width modulation is delimited by two points in time, including a point in time at the beginning and a point in time at the end of the cycle, wherein the microcontroller is designed such that a first pulse of the three phases is shifted with respect to a first of the two points in time that delimit the cycle, and a second pulse of the three phases is shifted with respect to a second of the two points in time that delimit the cycle, wherein the at least one sensor is designed such that at least one value of a second electric variable is measured during the cycle within at least one measurement window.

20. The system according to claim 19, further comprising: a sensor for measurement of the at least one value of the second electric variable.

21. The system according to claim 15, wherein the at least one sensor is designed as a measuring resistor.

22. The system according to one of claim 19, wherein the microcontroller is designed such that the pulses are to be shifted asynchronously.

Description

[0022] The invention is illustrated schematically in the drawings on the basis of embodiments and is described schematically and in detail with reference to the drawings.

[0023] FIG. 1 shows a schematic space vector drawing for a voltage vector of an electric machine.

[0024] FIG. 2 shows a diagram with an example of the arrangement of measurement windows for measurement of a current as electric variable in accordance with prior art.

[0025] FIG. 3 shows a diagram with measurement windows for measurement of the current as electric value, as said measurement windows are arranged in an embodiment of the method according to the invention.

[0026] FIG. 4 shows, in schematic illustration, an embodiment of an electric system with which the embodiment of the method according to the invention is to be carried out as well as diagrams relating to the plot of a voltage as electric variables.

[0027] The figures will be described in connection with one another and in an overarching manner, with identical reference signs referring to identical components.

[0028] The space vector drawing 10 of FIG. 1 for illustration of a course of a voltage vector 12 of a voltage as first electric variable of an electric machine comprises here a hexagon, which is divided into a first sector 1, which here spans angular positions from 0 to 60, a second sector 2, which here spans angular positions from 60 to 120, a third sector 3, which here spans angular positions from 120 to 180, a fourth sector 4, which here spans angular positions from 180 to 240, a fifth sector 5, which here spans angular positions from 240 to 300, and a sixth sector 6, which here spans angular positions from 300 to 360. The angular positions given here relate to electric angles. The voltage vector 12, which, during an operation of the electric machine rotates, as indicated by the curved arrow 14, and, in the process, passes through the six sectors 1, 2, 3, 4, 5, 6 in succession at regular intervals, extends from a center of the hexagon. A positionhere, an angular position of the voltage vectordepends on a relative position or angular position of two electromechanical components of the electric machine.

[0029] For measurement of a current as second electric variable of the electric machine with a single measuring resistor or single shunt and accordingly only one sensor for current measurement in an intermediate circuit of a three-phase electric machine, designed here as an electric motor, either one phase or two phases is or are to be engaged in parallel for the actuation thereof. The current thereby measured in or by the measuring resistor as second electric variable corresponds to the current of one of the three phases in each case. The power electronics of the electric machine comprise a plurality of electronic switch elementshere, three highside switch elements and three lowside switch elements. In the case that either all three highside or all three lowside switch elements are engaged, no current flows in the intermediate circuit. The electronic switch elements are designed either as MOSFETS or metal oxide semiconductor field effect transistors or else as IGBTs or bipolar transistors. Accordingly, the power electronics comprise, for example, three highside and three lowside MOSFETS or three highside and three lowside IGBTs.

[0030] Shown in Table 2 in a right column are values of a current I.sub.z, which flows through the intermediate circuit, as a function of the three currents flowing through the phases, namely, I.sub.1 (for a first phase), I.sub.2 (for a second phase), I.sub.3 (for a third phase), for different switching possibilities, which are given in a left column of Table 2 by a switching vector (a, b, c). In this case, a unit vector a is assigned to a first phase, a unit vector b to a second phase, and a unit vector c to a third phase. In the case that, for a value of a unit vector a, b, c in the left column, the value 1 is given, a highside switch element associated with the respective phase is engaged. In the case that, for a unit vector a, b, c in the left column, the value 0 is given, a lowside switch element associated with the respective phase is engaged. Accordingly, Table 2 shows an example for switching possibilities of electronic switch elements and the resulting values of the current I.sub.z flowing through the intermediate circuit, said current corresponding here, depending on the positioning of the electronic switch elements, to a positive or negative value of one of the three phase currents I.sub.1, I.sub.2, I.sub.3. In the case that the electric motor is designed as a direct current motor, the current I.sub.z through the intermediate circuit is also a direct current I.sub.dc.

TABLE-US-00002 TABLE 2 Switching vector (a, b, c) Current I.sub.z of the intermediate circuit (1, 1, 1) or (0, 0, 0) 0 (1, 0, 0) I.sub.1 (1, 1, 0) I.sub.3 (0, 1, 0) I.sub.2 (0, 1, 1) I.sub.1 (0, 0, 1) I.sub.3 (1, 0, 1) I.sub.2

[0031] When an electronic switch element is engaged, the current flowing through the intermediate circuit and accordingly an intermediate circuit current oscillates, usually because of the inherent capacitance and inherent inductance of the respective electronic switch element. Alternatively or additionally, other effects, such as, reverse recovery effects, can also lead to oscillations in the intermediate circuit. However, in order to be able to measure correctly a value of the intermediate circuit current, a control element (controller) provided for this has to wait until the oscillations of the intermediate circuit current have died out. Only then can the current be measured precisely. In the process, there exists at all times only a minimal measurement window in order to be able to measure the current correctly, that is, precisely and free of oscillations.

[0032] The non-measurable range of the current is cross-hatched in FIG. 1. The voltage applied at the machine is illustrated with the rotating voltage vector 12, the length of which depends on the applied voltage and the rotational speed of which depends on the rotational speed with which the electromechanical components of the electric machine rotate in relation to one another. At a low rotational speed, the applied voltage is small and, in this case, the voltage vector 12 is situated for the most part in the cross-hatched region, in which no measurement of the current is possible. The smaller the required voltage is, the smaller the voltage vector 12 is, with no measurement of the current being possible when the voltage vector 12 drops below a minimal length. In this case, the voltage vector is situated in the cross-hatched region the entire time.

[0033] The diagram of FIG. 2 comprises three abscissas 16a, 16b, 16c, along each of which the time is plotted. Plotted along a first ordinate 18a are values of the voltage as first electric value, that is, a voltage U.sub.1 of the first phase, along a second ordinate 18b values of a voltage U.sub.2 of the second phase, and, along a third ordinate 18c values of a voltage U.sub.3 of the third phase. Furthermore, a first original voltage pulse 20a of the first phase, a second original voltage pulse 20b of the second phase, and a third original voltage pulse 20c of the third phase are illustrated. In this case, the first original voltage pulse 20a has a shortest pulse width, the second original voltage pulse 20b has an intermediate pulse width, and the third original voltage pulse 20c has a longest pulse width. Illustrated in the diagram, moreover, are an old measurement window 22 for measurement of the current as second electric variable of the second phase to be employed in accordance with prior art and an old measurement window 24 for measurement of the current as second electric variable of the third phase. Further illustrated in the diagram by a double arrow 26 is a cycle of a pulse width modulation for the electric machine, which begins at a point in time 25 at the beginning of the cycle and ends at a point in time 27 at the end of the cycle 26.

[0034] On account of the position in time of the old measurement windows 22, 24 in relation to the voltage pulses 20a, 20b, 20c, a measurement of the currents is possible only within limits by means of a single measuring resistor, for which reason the machine can be regulated securely at low rotational speeds, for example. At high rotational speeds, the measurement of the current is also not possible in some regions. Accordingly, the measurement of the current of a respective phase and thus the required reconstruction of the current is imprecise and this, in turn, has consequences on the ability to regulate the electric machine. As a rule, two measurements are possible for a field-oriented regulation within the cycle of the pulse width modulation.

[0035] The diagram of FIG. 3 for illustration of the embodiment of the method according to the invention is based on the diagram of FIG. 2. Illustrated to this end in this diagram, in addition to the original voltage pulses 20a, 20b, 20c and the old measurement windows 22, 24, are a first voltage pulse 28a shifted to the right in the direction of a first arrow 30a in the scope of the invention, said first voltage pulse originating here from the first original voltage pulse 20a with the shortest pulse width, a third voltage pulse 28c shifted to the left in the direction of a second arrow 30c in the scope of the invention, said third voltage pulse originating here from the third original voltage pulse 20c with the longest pulse width, a new measurement window 32 for measurement of the current I.sub.1 of the first phase, the length of which in time is indicated by a double arrow 34, a first new measurement window 40 for measurement of the current I.sub.3 of the third phase, the length of which in time is indicated by a double arrow 42, and a second new measurement window 44 for measurement of the current I.sub.3 of the third phase, the length of which in time is indicated by a double arrow 46.

[0036] In order to make possible at all times a useable measurement of the current, at least two of the original voltage pulses 20a, 20b, 20c are shifted within the cycle of the pulse width modulation (double arrow 26) depending on an angular position of the voltage vector 12 of FIG. 1, with the first and the third shifted voltage pulse 28a, 28c ensuing here for the first and third phase, whereas the original second voltage pulse 20b of the second phase, which has the intermediate pulse width, remains unchanged.

[0037] In the process, it is provided that the first shifted voltage pulse 28a begins at the point in time 27 at the end of the cycle and the third shifted voltage pulse 28c at the point in time 25 at the beginning of the cycle. The two shifted voltage pulses 28a, 28c are accordingly edge-aligned. The intermediate original voltage pulse 20b remains unchanged in time and is accordingly center-aligned. The first new measurement window 32 begins at the point in time 25 at the beginning of the cycle. The third new measurement window 44 ends at the point in time 27 at the end of the cycle. Usually, measurement windows 32, 40, 44 are arranged overlapping in time with respect to the shifted voltage pulses 28a, 28e.

[0038] In each sector 1, 2, 3, 4, 5, 6, a voltage pulse 20a or 28a, 20b, 20c or 28c of a first of the three phasesin the diagram of FIG. 3, currently the voltage pulse 20a or 28a of the first phasehas a shortest pulse width, a voltage pulse 20a or 28a, 20b, 20c or 28c of a second of the three phasesin the diagram of FIG. 3 currently the voltage pulse 20b of the second phasehas an intermediate pulse width, and a voltage pulse 20a or 28a, 20b, 20c or 28c of a third of the three phasesin the diagram of FIG. 3, currently the voltage pulse 20c or 28c of the third phasehas a longest pulse width.

[0039] The following Table 3 shows an assignment of a length of the pulse widths to the voltage pulses 20a or 28a, 20b, 20c or 28c of the three phases in a respective sector 1, 2, 3, 4, 5, 6 (FIG. 1):

TABLE-US-00003 TABLE 3 Pulse width of Pulse width of the voltage pulse Pulse width of the voltage pulse of the second the voltage pulse Sector of the first phase phase of the third phase 1 long intermediate short 2 intermediate long short 3 short long intermediate 4 short intermediate long 5 intermediate short long 6 long short intermediate

[0040] When the embodiment of the method is carried out, the originally longest voltage pulse 20a, 20b, 20c with the longest pulse widthhere, the third original voltage pulse 20cis shifted to the left up to the point in time 25 at the beginning of the cycle of the pulse width modulation (left edge-aligned). The originally intermediate voltage pulse 20a, 20b, 20c with the intermediate pulse widthhere, the second original voltage pulse 20bremains unshifted (center-aligned). The originally shortest voltage pulse 20a, 20b, 20c with the shortest pulse widthhere, the first voltage pulse 20ais shifted to the right up to the point in time 27 at the end of the cycle of the pulse width modulation (right edge-aligned).

[0041] Variants for the shift of the original voltage pulses 20a, 20b, 20c are presented as a function of a respective pulse width in the following Table 4:

TABLE-US-00004 TABLE 4 Edge-aligned (right) Center-aligned (middle) Edge-aligned (left) long intermediate short intermediate short long short long intermediate long short intermediate intermediate long short short intermediate long

[0042] In the presented embodiment of the method, new measurement windows 32, 40, 44 are provided for two of the three phases. Through shift of two of the three original voltage pulses 20a, 20b, 20c, from which the two shifted voltage pulses 28a, 28c result here, a sensor has available to it larger measurement windows 32, 40, 42 for measurement of values of the currentshere, the new measurement window 32 for the current I.sub.1 of the first phase as well as two new measurement windows 40, 44 for the current I.sub.3 of the third phase. Usually, two scans and thus measurements of the current per cycle of pulse width modulation are adequate in order to measure the current securely. A value of the current I.sub.2 of a second phase (not measured here) is calculated from the values of the current I.sub.1, I.sub.3 of the two other phases by way of the equation I.sub.1+I.sub.2+I.sub.3=0, which states that the sum of all three currents is zero at a point in time.

[0043] A voltage as first electric variable remains the same at each phase. In addition, the pulse width is neither lengthened nor altered for any of the voltage pulses 20a, 20b, 20c, 28a, 28b of the voltage in order to make possible measurement of the current as second electric variable. The method is easy to implement and requires no additional load for the electronics of the electric machine as well as no asymmetry in an actuation. For the measurement of a current as second electric variable in each case, a single measuring resistor is employed for the measurement in the case of a sinus commutation and/or field-oriented regulation, without any power limitations.

[0044] FIG. 4a shows an example of an electric machine 49, which is designed here as an electric motor and has the electromechanical components 50, the power electronics 52, and a control unit 54. In this case, the power electronics 52 comprise three highside switch elements 56a, 56b, 56b* and three lowside switch elements 57a, 57b, 57c and accordingly a total of six electronic switch elements, which are designed as MOSFETs or metal [oxide]** semiconductor field effect transistors or as IGBTs. The control unit 54 comprises a microcontroller 58 and a driver 60, with it being possible via the control unit 54, even independently of the embodiment of the method presented here, to implement a pulse width modulation, designed as a power pulse wide modulation, for a current and/or a voltage as at least one electric variable of the three phases 62a, 62b, 62c of the electric machine 49. * sic; 56c?Translator's note** The word oxide is omitted from the German text.

[0045] To this end, reference is made to the diagrams from the two FIGS. 4b and 4c, each of which comprises an abscissa 64 along which the time is plotted. The diagram of FIG. 4b comprises a curve 66a of a first actuation signal for the first pulse-width-modulated electric variable (here, the voltage) of the first phase 62a, a curve 66b of a second actuation signal for the pulse-width-modulated voltage of the second phase 62b, and a curve 66c of a third actuation signal for the pulse-width-modulated voltage of the third phase 62c of the electric machine 49. There results from this the curves 68a, 68b, 68c, shown in the diagram from 4c, for the voltages of the phases 62a, 62b, 62c. In this case, a curve 68a of the voltage of the first phase 62a corresponds to the curve 66a of the actuation signal predetermined for the first phase, a curve 68b of the voltage of the second phase 62b corresponds to the curve 66b of the actuation signal predetermined for the second phase, and a curve 68c of the voltage of the third phase 62c corresponds to the curve 66c of the actuation signal predetermined for the third phase.

[0046] The embodiment of the system 70 according to the invention presented here or a corresponding arrangement comprises only one sensor 72, designed as a measuring resistor, for measurement of a value of a second electric variable, designed here as the current 74 I.sub.z of at least one phase 62a, 62b, 62c of the electric machine 49here, in an intermediate circuit 76 of the electric machine 49as well as an amplifier 80, whereby the current I.sub.z to be measured may also be referred to as an intermediate circuit current.

[0047] Furthermore, in this case, at least the microcontroller 58, too, is designed as a component of the system 70. The driver 60 and accordingly the control unit 54 are also designed as a component of the system 70 in this case, with the driver 60 being controlled by the microcontroller 58 in the embodiment.

[0048] The microcontroller 58, which is already designed, in an operation of the electric machine 40 independent of the method, for supplying the actuation signals, illustrated on the basis of the curves 66a, 66b, 66c, for implementation of the pulse width modulation, is additionally designed for shifting in time the curves 66a, 66b, 66c and thus the pulse of the actuation signals when the embodiment of the method is carried out, with the shape of the curves 66a, 66b, 66c and accordingly of the pulses being retained. The actuation signals are transmitted from the microcontroller 58 to the driver 60, which is designed here as a power amplifier, and, from there, the actuation signals are used for actuation of the MOSFETs 56a, 56b, 56c, 57a, 57b, 57c of the power electronics 52. The pulses for two of the three actuation signals and accordingly two of three pulses at least of an electric variable of the phases 62a, 62b, 62c of the electric machine 50, that is, the original voltage pulses 20a, 20b, 20c of the voltage, are shifted asynchronously by the microcontroller 58. In each case, such an asynchronous shift is carried out for actuation signals with the longest pulse width and the shortest pulse width, as a result of which, as already explained on the basis of the diagrams of FIG. 3 by way of example, the original voltage pulse 20a with the shortest pulse width as well as the original voltage pulse 20c with the longest pulse width are shifted, resulting in the voltage pulses 28a, 28b that are shifted for carrying out the measurement.