Method for detecting an electrical control variable, and device therefor

Abstract

The invention relates to a method for detecting an electrical control variable (IU, IV, IW) in a pulse-width-modulated, multi-phase electric motor (4), in which method: at least one pulse-width-modulated signal pulse (PU, PV, PW) is generated for each phase (U, V, W) of the electric motor (4) in the course of a pulse-width modulation within a period (T); and, during a measurement time interval (62), at least one minimum duty cycle is set for each phase (U, V, W), and a pulse position is selected for each phase (U, V, W) such that the pulse edges of the signal pulses (PU, PV, PW) do not overlap with the measurement time interval (62), and the control variable (IU, IV, IW) is measured during at least one pulse period (T).

Description

[0001]Page 1 2023 516 WO Description Method for detecting an electrical controlled variable The invention relates to a method for detecting an electrical controlled variable in a pulse-width modulated and multi-phase electric motor. The invention further relates to an electrical machine with an electric motor and software on a data carrier. Electric motor-driven or operated adjustment systems as motor vehicle components, such as window lifts, seat adjusters, door and sunroof drives or radiator fan drives as well as pumps and interior blowers, typically have an electric drive with a controlled electric motor. So-called brushless electric motors (brushless DC motors, BLDC motors) are increasingly being used for such electric motor drives, in which the wear-prone brush elements of a rigid (mechanical) commutator are replaced by electronic commutation of the motor current.The multi-phase motor current is usually generated by pulse width modulation (PWM) of a bridge circuit feeding the electric motor. With PWM, the width (duration) of the voltage pulses is varied to control the average voltage and thus the power delivered to the motor. This is achieved through a predetermined timing scheme in which the semiconductor switches of the bridge circuit alternate between a conducting and a blocking state in a rhythmic pattern, enabling efficient and precise control of the motor power. 2023516 WO Page 2 In practice, a duty cycle of the PWM is used to control the average power delivered to a load without directly changing the voltage. By adjusting the pulse width (and thus the duty cycle), the effective voltage applied to the load over time can be finely tuned.Electric motors in motor vehicles are often current-controlled. This means that the multi-phase (motor) current is used as the electrical control variable to regulate motor operation. In order to measure the current with sufficient quality, depending on the electric motor's equipment, there is a requirement that the PWM pulses must have a minimum length or pulse duration, and that no switching or pulse edge is located in the area around the measuring point (measurement time). If the current is measured, for example, via a total resistance in the ground path, the pulse pattern must not change during a measurement period (measurement window), and not all phases must have the same potential. Failure to meet this requirement will result in inaccurate current measurements. To meet these requirements, it is possible, for example, to widen one or more pulses, contrary to the controller requirement.However, such pulse widening can, among other things, lead to acoustic disturbances in motor operation. The invention is based on the object of specifying a particularly suitable method for detecting an electrical controlled variable in a pulse-width modulated and multi-phase electric motor. The invention is further based on the object of specifying a particularly suitable electrical machine and particularly suitable software. The method according to the invention is intended for detecting an electrical controlled variable in a pulse-width modulated and multi-phase electric motor 2023516 WO Page 3 and is suitable and designed therefor. The operation of the electric motor or the pulse width modulation (PWM) is controlled based on the controlled variable, wherein the electric motor is preferably current-controlled. The controlled variable is thus in particular a motor current or the individual phase currents of the electric motor.The electric motor is preferably part of a motor vehicle and is connected to an intermediate circuit of a (vehicle) electrical system. To detect or measure the controlled variable, a corresponding measuring circuit, for example in the form of a total resistance in the ground path of the intermediate circuit, is provided. During the PWM, at least one pulse-width modulated signal pulse (PWM pulse) is generated at a pulse position with a pulse duration for each of the phases of the electric motor during a period. The signal pulse has two pulse or switching edges, one each when switching on and off, with a constant level (voltage level) of the signal pulse present between the pulse edges. A "period" is understood here and below to mean in particular the time period of a complete PWM cycle repetition.A "pulse duration" (pulse width, pulse length, pulse width) is understood here and below to mean, in particular, a period of time during which the PWM pulse is held at a high (or low) level within the period. A "pulse position" is understood here and below to mean, in particular, the specific placement of the PWM pulse within the period, i.e., a temporal position of the PWM pulse relative to the beginning of the period. The pulse position refers, for example, to the middle of the PWM pulse. Alternatively, the pulse position can also refer to the beginning or end of the PWM pulse. 2023516 WO Page 4 A “duty cycle” of the PWM is to be understood here and in the following as a measure of the proportion of the time period during which a signal pulse is active, ie at a high signal level (voltage level), in relation to the total period of the cycle (period duration).The duty cycle is in particular the ratio of the pulse duration to the period duration and can be expressed as a percentage, for example. A duty cycle of 50%, for example, means that the signal pulse is connected to a positive supply voltage (high voltage potential) for half the period duration and to a negative supply voltage (low voltage potential) for the other half. In the following, a duty cycle is understood to mean in particular a standardized duty cycle, in which the duty cycle is expressed as a number between 0 and 1. According to the method, at least one minimum duty cycle is set for each phase during a measuring period, i.e. during a measuring window. In particular, a stored minimum pulse duration is set for a constant or changing period duration.Furthermore, for each phase, a pulse position is selected such that the pulse edges do not lie within the measurement period or do not overlap with it. In other words, the pulse positions are selected such that the pulse edges are not in the measurement range between the beginning and end of the measurement period. Preferably, the pulse edges also do not overlap with the beginning or end of the measurement period. This means that the pulse edges are arranged completely outside the measurement period. The controlled variable is then measured during at least one of the pulse durations. This realizes a particularly suitable method for measuring the controlled variable. In particular, the requirements for the most accurate and reliable measurement of the controlled variable, in particular of the individual (phase) currents, can thus be met, especially at low control levels or low duty cycles.2023516 WO Page 5 In contrast to the prior art, individual pulses are not extended here. According to the invention, all pulses are raised so that further (asymmetrical) widening is not necessary. If all phases are raised by the same amount (or the pulses are extended), the relative difference in the average voltage is maintained and the average current flow remains unchanged, so that no acoustic disturbances in motor operation occur. Preferably, the controlled variable is measured in each control period of the motor control. This means that, in particular, at least one measuring period is provided per control period. The measuring period corresponds, for example, to a period of the pulse width modulation. In other words, the controlled variable is measured at least once in each PWM period. Alternatively, the measuring period can also comprise only every second or third PWM period.In an advantageous embodiment, the minimum duty cycle is set in one phase, and in the other phases a duty cycle that is higher than the minimum duty cycle is set. In one conceivable embodiment, the duty cycles of the phases during the measurement period are each determined as a sum of the respective duty cycle of the phase outside the measurement period and a modulation function. The standardized phase voltage or the respective duty cycle at a time t can thus be expressed, for example, by the formula ^^^^^ ^^ௗ^^^^ ൌ ^^^^^ ^^^^^^ ^ ^^^^^^, where TV. i modthe modulated duty cycle for a phase i, i.e. the duty cycle during the measuring period, TVi is the initial, non-modulated, duty cycle for phase i, i.e. the duty cycle during normal motor operation outside the measuring period, and x is the modulation function. 2023516 WO Page 6 For a three-phase electric motor with phases U, V, and W, for example, the following results: ^^^^^ ^^ௗ^^^^ ൌ ^^^^^ ^^^^^^ ^ ^^^^^^^^^^^ ^^ௗ^^^^ ൌ ^^^^^ ^^^^^^ ^ ^^^^^^^^^^^ ^^ௗ^^^^ ൌ ^^^^^ ^^^^^^ ^ ^^^^^^^^^^^ ^^ௗ^^^^ ൌ ^^^^^ ^^^^^^ ^ ^^^^^^In a possible further development, the modulation function x is determined by a difference between the minimum duty cycle and the minimum duty cycle of the phases during the measuring period. The minimum duty cycle is therefore in particular the minuend, with the minimum phase duty cycle being subtracted as the subtrahend.The modulation function at time t for the three-phase electric motor can thus be expressed, for example, as ^^^^^^ ൌ ^^^^ெ^^ െ min ^^^^^^ ^^ௗ^^^^,^^^^^^ ^^ௗ^^^^,^^^^^^ ^^ௗ^^^^^. Here, TVMin is the stored minimum duty cycle. This ensures that each phase has at least a duty cycle equal to the minimum duty cycle TV during the measurement period. Min In other words, a constant minimum pulse width is ensured for all phases. In particular, one phase has the minimum duty cycle TVMin, and the other phases each have a pulse width that is lower than the minimum duty cycle TV Min increased duty cycle. By appropriate selection of the minimum duty cycle TV MinThis ensures that a reliable and precise measurement of the controlled variable can be carried out. In an alternative, equally possible further development, the modulation function is determined by the maximum of a difference between a first minimum duty cycle required for measuring the controlled variable and the median of the duty cycles of the phases during the measurement period, and a difference between a second minimum duty cycle of the smallest pulse and the minimum duty cycle of the phases during the measurement period. This further development assumes that, due to Kirchhoff's rules, it is sufficient to forgo a measurement in the phases, since this can be calculated based on the other measurements. For example, with a three-phase motor current as the controlled variable, two current measurements are sufficient.It is therefore sufficient for two phases to have a minimum pulse width (first minimum duty cycle) to perform the current measurement, and for the third phase to have a minimum pulse width (second minimum duty cycle). The minimum pulse width of the shortest signal pulse, i.e. the second minimum duty cycle, is dimensioned to be greater than or equal to zero. In particular, the minimum pulse width is dimensioned to be greater than a dead time of the semiconductor switches controlled by the PWM, so that distortions in an output stage do not have a disruptive effect. In a preferred embodiment, the increased duty cycles, i.e. the first minimum duty cycle, are dimensioned such that they are greater than or equal to a stored threshold value. The threshold value is expediently a minimum pulse duration or a minimum duty cycle for which a reliable measurement of the controlled variable is possible.For example, if the phases have a duty cycle of U = 0.05 (5%) and V = 0.1 (10%) as well as W = 0.1 (10%), and for reliable current measurement at least a duty cycle of 0.15 (15%) is required, the duty cycles of the phases are each increased by 0.05 (i.e. U = 0.1 and V = 0.15 as well as W = 0.15), and the current in phases V and W is measured. The current value for phase U is then calculated using a known input current and the measured phase currents for V and W. For a three-phase system, the modulation function x at time t can be expressed, for example, as follows: 2023516 WO Page 8. ^^^^ெ^^ଶ െ min ^^^^^^ ^^ௗ^^^^, ^^^^^ ^^ௗ^^^^,^^^^^ ^^ௗ^^^^^^Here TVMin1 is the first minimum duty cycle for a reliable measurement of the controlled variable, and TVMin2 is the second minimum duty cycle for the smallest or shortest signal pulse of the modulated PWM. Thus, one phase has the second minimum duty cycle TVMin2, and the other phases each have at least the first minimum duty cycle TV Min1 Preferably, the second minimum duty cycle is greater than or equal to zero, and the first minimum duty cycle is dimensioned greater than or equal to the second minimum duty cycle, so that the first minimum duty cycle TV Min1 compared to the second minimum duty cycle TV Min2 is increased (0 ≤ TV Min2 ≤TV Min1). The above statements refer in particular to comparatively small control levels or small or low duty cycles (≤ 0.5). For large duty cycles outside the measurement period, the procedure can be carried out accordingly with reference to the supply voltage (off state, Off). The following then applies to the modulation function for a three-phase system: or 1െ ^^^^ெ^^ை^^ଶ െ max ^^^^^^ ^^ௗ^^^^,^^^^^ ^^ௗ^^^^, ^^^^^ ^^ௗ^^^^^^where TVMinOff to the minimum duty cycle TVMin, TVMinOff1 to the minimum duty cycle TV Min1 , and TV MinOff2 to the minimum duty cycle TV Min2 corresponds, and where 0 ≤ TV MinOff2 ≤TV MinOff1applies. 2023516 WO Page 9 An additional or further aspect of the invention provides that the pulse positions of the signal pulses during the measurement period for each phase are selected or set such that the pulse intervals between the pulses of the phases are of equal dimension. In other words, the pulses are evenly distributed in the measurement period or in the PWM period. Alternatively, the centers of the pulses are equidistant from one another. In a three-phase electric motor, the signal pulses of the phases are thus generated with a temporal offset from one another of, for example, one third of the period. Due to the temporal distribution of the signal pulses, they can be measured individually particularly well, wherein the uniform distribution is particularly unobtrusive acoustically with regard to motor operation.Alternatively, it is also conceivable, for example, for the signal pulses to be sequentially arranged, i.e., for the pulse positions to be set such that the end of a pulse (off-pulse edge) coincides with the start of the subsequent pulse (on-pulse edge). At least a certain overlap of the signal pulses is permissible, i.e., the on-pulse edge of the subsequent pulse is temporally before the off-pulse edge of the previous pulse, as long as the respective measurement of the controlled variable is free of pulse edges. By sequencing or overlapping the signal pulses in this way, a "burst" mode is realized during the measurement period, which is shorter and asymmetrical, but can be advantageous with regard to power loss (depending on the equipment of the electric motor). The electric machine according to the invention is intended in particular as an electric motor drive in a motor vehicle, and is suitable and configured for this purpose.In principle, however, the application is not limited to the automotive sector. The electric machine has a pulse-width modulated and multi-phase electric motor which is designed to be brushless and has a stator and a rotor mounted so as to be rotatable relative to the stator. The electric machine also has a bridge circuit connected or coupled to the electric motor and a controller, i.e. a 2023516 WO Page 10 control unit. The bridge circuit is preferably part of a power converter, in particular an inverter. The controller is, for example, part of the power converter. The stator has a number of phase windings which are led to the bridge circuit on the one hand and are connected in a star connection on the other hand, for example at a common connection point (star point). The operation of the electric motor is regulated by the controller.For this purpose, the controller detects or evaluates a controlled variable, which is detected by a corresponding sensor. The electric motor is preferably current-controlled, with the multi-phase motor current or the individual phase currents in the phase windings of the stator being detected as the controlled variable. The sensor is designed, in particular, as a total resistor in the ground path of the power converter, with the corresponding current value being determined based on a voltage drop across the total resistor. The controller is generally suitable and configured—in terms of programming and / or circuitry—to carry out the method described above.The controller is therefore specifically designed to change the pulse width modulation of the electric motor during motor operation during a measurement period in such a way that at least a minimum duty cycle is set for each phase, and that a pulse position is selected for each phase in such a way that the pulse edges do not overlap with the beginning or end of the measurement period: Furthermore, the controller is intended and set up to carry out and evaluate a measurement of the controlled variable, wherein the controlled variable is measured during at least one pulse duration.In a preferred embodiment, the controller is formed at least in its core by a microcontroller with a processor and a data memory in which the functionality for carrying out the method according to the invention is implemented in the form of operating software (firmware) so that the method is carried out automatically when the operating software is executed in the microcontroller - if necessary in interaction with a user. 2023516 WO Page 11 Within the scope of the invention, the controller can alternatively also be formed by a non-programmable electronic component, for example an ASIC (application-specific integrated circuit), in which the functionality for carrying out the method is implemented using circuitry. The electrical machine operated with the method therefore has particularly reliable and precise detection of the controlled variable.An additional or further aspect of the invention provides software on a medium or data carrier for carrying out or executing the method described above. This means that the software is stored on a data carrier and is intended for carrying out the method described above, as well as being suitable and designed for this purpose. This results in particularly suitable software for operating an electric motor, with which the functionality for carrying out the method according to the invention is implemented in programming terms. The software is thus in particular operating software (firmware), with the data carrier being, for example, a data memory of the controller. An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. In these, schematic and simplified representations: Fig.1 shows an electrical machine with a power source and with an electric motor and with a power converter connected in between, Fig. 2 shows three phase windings of a three-phase electric motor of the machine in a star connection, Fig. 3 shows a bridge module of a bridge circuit of the power converter for controlling a phase winding of the electric motor, Fig. 4 shows an equivalent circuit diagram for the power source, Fig. 5 shows a block diagram for pulse width modulation during a measuring period in a first embodiment, 2023516 WO page 12 Fig. 6 shows a block diagram for pulse width modulation during a measuring period in a second embodiment, and Fig. 7 shows a block diagram for pulse width modulation during a measuring period in a third embodiment. The invention is explained below by way of example using a drive with a B6 circuit and a three-phase electric motor. However, the invention can also be applied to other arrangements.In particular, the following statements can also be applied analogously to multi-phase electric motors in general. Corresponding parts and sizes are always provided with the same reference numerals in all figures. Fig. 1 shows an electric machine 2 for an electric motor drive of a vehicle (not shown in detail), for example a motor vehicle or an electrically powered or drivable bicycle (e-bike). The machine 2 comprises a three-phase brushless electric motor 4, which is connected to a power source (voltage supply) 8 by means of a power converter (converter, inverter) 6. In this exemplary embodiment, the power source 8 comprises an internal vehicle energy storage device in the form of a (motor vehicle) battery 10, as well as a (DC voltage) intermediate circuit 12 connected thereto as part of an on-board electrical system, which extends at least partially into the power converter 6.The intermediate circuit 12 is essentially formed by a forward line (supply line) 12a and a return line (ground line) 12b, by means of which the power converter 6 is connected to the battery 10. The lines 12a and 12b are at least partially routed into the power converter 6, in which an intermediate circuit capacitor 14 and a bridge circuit 16 are connected between them. 2023516 WO Page 13 During operation of the machine 2, an input current IE supplied to the bridge circuit 16 is converted into a three-phase output current (motor current, three-phase current) IU, I. V , I Wfor the three phases U, V, W of the electric motor 4. The output currents IU, IV, IW, also referred to below as phase currents, are fed to the corresponding phases (windings) U, V, W (Fig. 2) of a stator not shown in detail. Fig. 2 shows a star connection 18 of the three phase windings U, V, W. The phase windings U, V and W are each connected with a (phase) end 20, 22, 24 to a respective bridge module 26 (Fig. 3) of the bridge circuit 16, and are interconnected with the opposite end at a star point 28 as a common connection terminal. In the illustration in Fig. 2, the phase windings U, V and W are each shown by means of an equivalent circuit in the form of an inductance 30 and an ohmic resistor 32 as well as a respective voltage drop 34, 36, 38.The voltage drop 34, 36, 38 across the phase windings U, V, W is represented schematically by arrows and results from the sum of the voltage drops across the inductance 30 and the ohmic resistance 32 as well as the induced voltage 40. The voltage 40 (electromagnetic force, EMF) induced by a movement of a rotor of the electric motor 4 is shown in Fig. 2 using a circle. The star connection 18 is controlled by means of the bridge circuit 16. The bridge circuit 16 is designed with the bridge modules 26 in particular as a B6 circuit. In this embodiment, during operation, each of the phase windings U, V, W is switched at a high switching frequency between a high (DC) voltage level of the forward line 12a and a low voltage level of the return line 12b. The high voltage level is in particular an intermediate circuit voltage U. ZKof the intermediate circuit 12, whereby the low voltage level is preferably an earth potential (ground) U G This clocked control is implemented as a PWM control – 2023516 WO Page 14 in Fig.1 by means of arrows – by a controller 42, with which a control and / or regulation of the speed, the power and the direction of rotation of the electric motor 4 is possible. The bridge modules 26 each comprise two semiconductor switches 44 and 46, which are shown in Fig.2 only schematically and as an example for the phase W. The bridge module 26 is connected, on the one hand, with a potential connection 48 to the forward line 12a and thus to the intermediate circuit voltage UZK. On the other hand, the bridge module 26 is connected with a second potential connection 50 to the return line 12b and thus to the ground potential U GThe respective phase end 20, 22, 24 of phase U, V, W is connected via the semiconductor switches 44, 46 either to the intermediate circuit voltage U ZK or with the earth potential U G connectable. If the semiconductor switch 44 is closed (conductive) and the semiconductor switch 46 is opened (non-conductive, blocking), the phase end 20, 22, 24 is connected to the potential of the intermediate circuit voltage UZK. Accordingly, when the semiconductor switch 44 is opened and the semiconductor switch 46 is closed, the phases U, V, W are connected to the ground potential U Gcontacted. This makes it possible to apply two different voltage levels to each phase winding U, V, W using the PWM control. A single bridge module 26 is shown in simplified form in Fig. 3. In this exemplary embodiment, the semiconductor switches 44 and 46 are implemented as MOSFETs (metal-oxide semiconductor field-effect transistors), which each switch between a conductive state and a non-conductive state using the PWM control. For this purpose, the respective gate connections are connected to corresponding control voltage inputs 52, 54, by means of which the PWM control signals of the controller 42 are transmitted. Fig. 4 shows an equivalent circuit diagram for the current source 8. During operation, the battery 10 generates a battery voltage U Bat and a corresponding battery current I Batfor operating the power converter 6. In Fig. 4, the internal resistance 2023516 WO Page 15 of the battery 10 is shown as an ohmic resistor 56 and the self-inductance of the battery 10 as an inductance 58. A shunt resistor 60 is connected in the return line 12b. Depending on the switching states of the (power) semiconductor switches 44, 46, the phase current I flows. U , I V , I W across the shunt resistor 60. The voltage drop across the shunt resistor 60 is amplified and evaluated. Using measurements and the knowledge of the switching states of the semiconductor switches 44, 46, the phase currents I U , I V , I W reconstructed by the controller 42. Other measurement methods can also be used to determine the motor currents (e.g., direct phase current measurement). Together with the measured and / or calculated phase voltages (U U , U V , U W) the controller 42 has the phase voltages (U U , U V , U W ) and the phase currents I U , I V , I W available. The electric motor 4, or its motor operation, is in particular current-controlled. This means that the motor current or the phase currents IU, IV, IW are recorded as controlled variables during motor operation. The phase currents IU, IV, IW are therefore also referred to below as controlled variables IU, IV, IW. The controller 42 controls and / or regulates the motor operation based on the controlled variables, in particular based on the recorded phase currents I U , I V , I W and the calculated phase voltages U U , U V , U W, as well as other variables (e.g., motor resistance, motor inductance, duty cycle of the PWM voltage). For example, a field-oriented control for the electric motor 4 is implemented here. For reliable and safe motor operation, the controlled variable is recorded at least once per control period. For this purpose, a measurement window, i.e., a measurement period 62, is provided, during which the phase currents I U , I V , I W detected or measured by means of the shunt resistor 60. The measuring time 62 corresponds, for example, to a period T of the pulse width modulation, which means that during one pulse period the phase currents I U , I V , I Wbe measured. 2023516 WO Page 16 In order to ensure the most accurate determination of the phase currents IU, IV, IW, the pulse width modulation is changed during the measurement period. In particular, the duty cycles or pulse widths of the signal pulses in the individual phases U, V, W as well as their pulse position are changed during the measurement period. A method for operating the electrical machine 2 or the electric motor 4 is explained in more detail below with reference to Figures 5 to 8. Figures 5 to 8 each show a schematic time-voltage diagram for the PWM curve, in which the time t is plotted along the abscissa axis (X-axis), and the switching or voltage state for the PWM, i.e. a signal for the control voltage inputs, is plotted along the vertical ordinate axis (Y-axis) (not shown in detail).Figures 5 to 8 show four exemplary embodiments for changing the pulse width modulation or for improving the current measurement, wherein in each case a single PWM period is shown with one signal pulse PU, PV, PW per phase U, V, W. According to the method, at least one minimum duty cycle TV is measured for each phase U, V, W during the measurement period 62. Min In particular, at least a minimum pulse duration τ Min with a constant period T. In other words, TVMin = τMin / T. Furthermore, for each phase, a pulse position U, V, W is selected or set such that the pulse edges of the respective signal pulse PU, PV, PW do not overlap with the beginning or end of the measurement period 62. The controlled variable or the phase currents I U , I V , I Ware then measured during the pulse durations. In the embodiment shown in Fig.5, at least the duty cycle TV is measured for all phases U, V, W. Min or for each signal pulse P U , P V , P W 2023516 WO Page 17 at least the pulse duration τMin is set. In other words, the following applies to the pulse durations τU, τV, τW of the signal pulses PU, PV, PW: τMin, τV, ≥ τMin, and τW ≥ τMin. For this purpose, a modulated duty cycle TVi mod is set for each phase U, V, W: where i is the phase U, V, W and TVi in the initial, non-modulated, duty cycle for phase i, i.e. the duty cycle during normal engine operation outside of the measurement period 62. This ensures that each phase U, V, W has at least the minimum duty cycle TVMin or each signal pulse PU, PV, PW has at least the minimum pulse duration τMin. In the embodiment of Fig. 5, the pulse positions of the signal pulses PU, PV, PW during the measurement period 62 are set such that no switching or pulse edge overlaps with the beginning or end of the measurement period 62. In particular, the pulse positions of the signal pulses P U , P V , P W evenly distributed in the pulse period T. In other words, the pulse positions of the signal pulses P U , P V , P W are arranged offset from each other by one third of the period T. This allows the individual phase currents IU , I V , I W during the respective pulse durations τU, τV, τW can be measured reliably and accurately. In the embodiments of Fig.6 and Fig.7, the duty cycles or pulse durations τU, τV, τW are set as explained above for the embodiment of Fig.5 such that each pulse duration τU, τV, τW is greater than the minimum pulse duration τ Minis dimensioned. The key distinguishing feature here is the arrangement of the pulse positions during the measurement time 62 or in the pulse period T. In both the embodiment of Fig. 6 and the embodiment of Fig. 7, the signal pulses PU, PV, PW or their pulse positions are arranged in the period T or the measurement time 62 2023516 WO Page 18 such that the individual phase currents IU, IV, IW can be recorded as part of a burst mode measurement. In the embodiment of Fig. 6, the signal pulses PU, PV, PW are arranged in a row, i.e. the pulse positions are set such that the end of a pulse (off-pulse edge) essentially coincides with the start of the following pulse (on-pulse edge). The phase currents IU, IV, IW are recorded or measured in burst mode during the respective pulse durations τU, τV, τW. The embodiment shown in Fig.7 shows a variant for the burst mode, in which at least two of the signal pulses PU, PV, PW – here the signal pulses PU and P. V – overlap with each other. In other words, phases U and V are energized simultaneously, at least temporarily. The controlled variables or phase currents IU, IV, IW are also recorded or measured during the respective pulse durations τU, τV, τW, but the measurements are carried out in such a way that no pulse or switching edge falls within the measurement period and could therefore influence the measurement. Fig. 8 shows an embodiment in which only two of the phase currents I U , I V , I W – in the example shown the phase currents I V and I W – are measured or recorded, and the third phase current – ​​here IU – is determined by the controller 42 based on the input current I E and the measured phase currents I V and I Wis determined or calculated. It is therefore sufficient that only the phases V, W to be measured have a minimum pulse width to carry out the current measurement, with the third phase having a minimum pulse width greater than or equal to zero, in particular greater than a dead time of the semiconductor switches 44, 46. For this purpose, the maximum of a difference between a first minimum duty cycle TV required for measuring the controlled variable is used as the modulation function. Min1 and the median of the duty cycles of the phases TV U mod , TV V mod , TV W mod during the measurement period 62, and a difference of a second minimum duty cycle TV Min2of the smallest pulse and the minimum duty cycle of the phases U, V, W during the measuring period 62. Preferably, the second 2023516 WO Page 19 minimum duty cycle is greater than or equal to zero, and the first minimum duty cycle is greater than or equal to the second minimum duty cycle, so that the first minimum duty cycle TV Min1 compared to the second minimum duty cycle TV Min2 is increased (0 ≤ TVMin2 ≤TVMin1). The duty cycle of a phase i at time t is thus ^^^^ெ^^ଶ െ min ^^^^^^ ^^ௗ^^^^,^^^^^^ ^^ௗ^^^^, ^^^^^ ^^ௗ^^^^^^expressible. If, for example, the phases have a duty cycle of U = 0.2 and V = 0.4 as well as W = 0.4, and for reliable current measurement at least a duty cycle of 0.5 is required, the duty cycles of the phases are each increased by 0.1, for example (i.e. U = 0.3 and V = 0.5 as well as W = 0.5), and the current in phases V and W is measured. The current value for phase U is then calculated based on a known input current and the measured phase currents for V and W. The claimed invention is not limited to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by a person skilled in the art within the scope of the disclosed claims, without departing from the subject matter of the claimed invention.In particular, all of the individual features described in connection with the various exemplary embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the subject matter of the claimed invention. 2023516 WO Page 20 List of reference symbols 2 electric machine 4 electric motor 6 power converter 8 voltage supply 10 battery 12 intermediate circuit 12a forward line 12b return line 14 intermediate circuit capacitor 16 bridge circuit 18 star connection 20, 22, 24 phase end 26 bridge module 28 star point 30 inductance 32 resistor 34, 36, 38 voltage drop 40 voltage 42 controller 44, 46 semiconductor switch 48, 50 potential connection 52, 54 control voltage inputs 56 resistor 58 inductance 60 shunt resistor 62 measuring time period I. E Input current IU, IV, IW phase current, controlled variable U, V, W phase U ZKIntermediate circuit voltage 2023516 WO Page 21 UG Earth potential UBat Battery voltage T Period duration PU, PV, PW Signal pulse τU, τV, τW Pulse duration 2023516 WO

Claims

Page 22 Claims 1. Method for detecting an electrical controlled variable (I U , I V , I W ) in a pulse-width modulated and multi-phase electric motor (4), in which, in the course of a pulse-width modulation, at least one pulse-width modulated signal pulse (PU, PV, PW) is generated for each phase (U, V, W) of the electric motor (4) during a period (T), and in which, during a measuring period (62), a) at least one minimum duty cycle is set for each phase (U, V, W), b) a pulse position is selected for each phase (U, V, W) such that the pulse edges of the signal pulses (P U , P V , P W) do not overlap with the measurement period (62), and c) the controlled variable (IU, IV, IW) is measured during at least one pulse duration (T).

2. Method according to claim 1, characterized in that the minimum duty cycle is set in one phase (U, V, W), and that in the other phases (U, V, W) a duty cycle that is increased compared to the minimum duty cycle is set.

3. Method according to claim 2, characterized in that the increased duty cycles are dimensioned such that they are greater than or equal to a stored threshold value.

4. Method according to one of claims 1 to 3, characterized in that the pulse positions in the phases (U, V, W) are selected such that the pulse intervals between the signal pulses (PU, PV, PW) are of equal dimensions. 2023516 WO Page 23 5. The method according to one of claims 1 to 4, characterized in that the duty cycles of the phases (U, V, W) during the measurement period (62) are each formed as a sum of the respective duty cycle of the phase (U, V, W) outside the measurement period (62) and a modulation function.

6. The method according to claim 5, characterized in that the modulation function is determined by a difference between the minimum duty cycle and the minimum duty cycle of the phases (U, V, W) during the measurement period (62). 7.Method according to claim 5, characterized in that the modulation function is determined by the maximum of - a difference between a first minimum duty cycle required for measuring the controlled variable (IU, IV, IW) and the median of the duty cycles of the phases (U, V, W) during the measuring period (62), and - a difference between a second minimum duty cycle of the smallest pulse and the minimum duty cycle of the phases (U, V, W) during the measuring period (62).

8. Method according to claim 7, characterized in that the second minimum duty cycle is selected to be greater than or equal to zero, and the first minimum duty cycle is selected to be greater than or equal to the second minimum duty cycle.

9. Electrical machine (2), comprising a pulse-width-modulated and multi-phase electric motor (4) and a bridge circuit (16) as well as a 2023516 WO. Page 24, the bridge circuit (16) controlling the controller (42) for carrying out a method according to one of claims 1 to 8.

10. Software on a data carrier for carrying out a method according to one of claims 1 to 8, when the software runs on a computer. 2023516 WO

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