Control device, inverter, assembly with inverter and electric machine, method for operating inverter and computer program - Patents.com

Abstract

A control device (8) for an inverter (2) supplying power to an electric machine (3), configured to provide a pulse-width modulated switching signal (15) having a carrier frequency for driving switching elements (12) of the inverter (2), the control device (8) determining the carrier frequency depending on operating point information describing an operating point defined by a rotational speed and torque of the electric machine (3), and configured to increase the carrier frequency within an operating region (22) extending within a rotational speed interval in which a lower limit rotational speed (23) is different from zero and an upper limit rotational speed (24) is in a power-limited operating region (21) or a field-weakening operating region as the rotational speed increases and the magnitude of the torque decreases.

Description

[Technical field]

[0001] The present invention relates to a controller for an inverter supplying an electric machine, the controller being arranged to provide pulse width modulated switching signals having a carrier frequency for driving switching elements of the inverter.

[0002] The invention further relates to an inverter, an assembly comprising an inverter and an electric machine, a method for operating the inverter and a computer program. [Background technology]

[0003] Due to the growing importance of electric vehicles, inverters and inverter-related controllers for such applications have become the focus of industry development efforts. Controllers of the type that provide pulse-width modulated switching signals having a constant carrier frequency for driving switching elements of an inverter are known.

[0004] Pulsed output voltages occur in such switching situations and can result in high total harmonic distortion (THD) of the phase currents of the electric machine, especially in certain regions of low torque. However, this results in undesirable mechanical vibrations in the electric machine. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is therefore based on the object of reducing the harmonic distortion in the operation of an inverter. [Means for solving the problem]

[0006] This object is achieved according to the invention by a control device of the type mentioned at the beginning, configured to determine the carrier frequency depending on operating point information describing an operating point defined by the rotational speed and torque of the electric machine, and to increase the carrier frequency as the rotational speed increases and the magnitude of the torque decreases within an operating region extending within a rotational speed interval whose lower rotational speed limit is different to zero and whose upper rotational speed limit is in the power limited operating region or in the field weakening operating region.

[0007] The invention is based on the recognition that the total harmonic distortion of the inverter output voltage depends on the carrier frequency, which, when increased, reduces the total harmonic distortion, on the one hand, and on the other hand, on the operating point of the electric machine. In the (first) operating region, if the carrier frequency is assumed to remain constant, only low switching losses still occur depending on the magnitude of the torque, but as the rotation speed increases and the magnitude of the torque decreases, the total harmonic distortion increases. Therefore, in order to reduce or limit the total harmonic distortion, there is room for an increase in the carrier frequency, since higher switching losses can be tolerated compared to operating with a constant carrier frequency. Thus, advantageously, the total harmonic distortion, and therefore the undesirable mechanical vibrations, are reduced.

[0008] The total harmonic distortion of the output voltage is typically described for the purposes of the present invention by a distortion measure that is a weighted combination of the frequency components of the inverter output voltage. In general, such a distortion measure m THD can be expressed by the following formula:

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[0009] In the formula, N AC is the electrical frequency of the electrical machine, f AC and the inverter output voltage u x The fundamental frequency f f represents the ratio of n is a weighting coefficient. The output voltage as a function of time t is described by the following equation:

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[0010] In the particularly practically relevant case of an inverter with three output phases, x∈{RS,ST,TR} will be set in terms of the usual phase identifiers R,S and T.

[0011] The distortion measure m, to which the present invention is not limited, THD As a possible special case of , the weighted total harmonic distortion (WTHD) should be considered as one in which the frequency components are weighted according to their order. In that case,

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[0012] In the case of a control device according to the invention, the lower rotational speed limit is preferably in the base rotational speed operating range.

[0013] Advantageously, for a control device according to the invention, the first boundary of the operating range can extend from a first operating point, the rotational speed of which corresponds to a lower limit rotational speed, to a second operating point, the rotational speed of which is greater than the lower limit rotational speed and the magnitude of the torque of which is greater than the magnitude of the torque of the first operating point. Alternatively or additionally, the second boundary of the operating range can extend from a first operating point, the rotational speed of which corresponds to an upper limit rotational speed, to a second operating point, the rotational speed of which is lower than the upper limit rotational speed and the magnitude of the torque of which is greater than the magnitude of the torque of the first operating point.

[0014] In particular, a first preferred embodiment of the invention is described below in which the control device may be configured to generate pulse width modulated switching signals by continuous pulse width modulation, in particular space vector modulation.

[0015] In a first preferred embodiment, the second operating points of the first boundary and the second boundary may be identical and / or be in a power-limited or field-weakening operating region and / or be away from the maximum magnitude of the torque at the rotational speed of the respective operating point.

[0016] Furthermore, in the first preferred embodiment, the control device may be configured to increase the carrier frequency with increasing rotational speed, in particular independently of the torque, within a second operating range defined without overlapping with the first operating range, which comprises an operating point whose torque magnitude at the respective rotational speed is greater than the maximum torque magnitude in the first operating range at this rotational speed. It has been determined that the effect on the total harmonic distortion of the torque in the second operating range, whose carrier frequency value is advantageously adjacent to the carrier frequency value of the first operating range without interruption, is very small, if at all. In this respect, the definition of the second operating range allows the reduction of the total harmonic distortion to be extended up to operating points of higher loads of the electric machine, in particular full load operation. Full load operation in this case can be generally understood in the context of the present invention as an operating mode comprising an operating point with a maximum torque magnitude for the respective rotational speed.

[0017] Thus, the second operating region may lie entirely within the power limited or field weakening operating region and / or extend up to maximum full load operation.

[0018] In particular, a second preferred embodiment of the invention is described below in which the control device may be configured to generate a pulse width modulated switching signal by discontinuous pulse width modulation, in particular by generalized discontinuous pulse width modulation (GDPWM).

[0019] In a second preferred embodiment, it is advantageous if the control device is configured to increase the carrier frequency with decreasing rotational speed and decreasing torque within a second operating area defined without overlapping with the first operating area and including operating points whose torque magnitude at the respective rotational speed is greater than the maximum torque magnitude in the first operating area at this rotational speed.

[0020] Alternatively or additionally, the control device according to the invention in a second preferred embodiment is configured to increase the carrier frequency with increasing rotational speed and decreasing torque, or with increasing rotational speed independently of torque, within a third operating area defined without overlapping with the first operating area and including operating points whose torque magnitude at the respective rotational speed is greater than the maximum torque magnitude in the first operating area at this rotational speed.

[0021] The third operating region typically includes operating points whose torque magnitude at each rotational speed is greater than the maximum torque magnitude at that rotational speed in the second operating region.

[0022] In a second preferred embodiment, the first operating region and / or the second operating region and / or the third operating region may extend up to maximum full load operation and / or may extend from a base rotational speed operating region into a power limited operating region or a field weakening operating region.

[0023] In an advantageous development of the control device according to the invention, it can furthermore be configured not to determine a carrier frequency below a predefined or predefinable minimum value. In this way, the possibility that the carrier frequency at low values ​​of rotational speed and torque becomes so low that their ratio to the frequency of the respective phase current of the electric machine falls below a predefined minimum ratio is avoided. To that extent, the operating point at which the minimum value is specified can also be regarded as a further operating region.

[0024] In order to allow a particularly effortless implementation of the control device according to the invention, it is preferred that the control device is configured to select the carrier frequency from a characteristic map, which assigns carrier frequency values ​​to pairs of rotational speed values ​​and torque values. The characteristic map can be realized, for example, by means of a look-up table. The control device typically comprises a memory unit in which the characteristic map is stored.

[0025] Furthermore, the characteristic map may describe at least a piecewise linear assignment of the pairs and the carrier frequency values. Alternatively, it is also possible that the characteristic map is defined by the individual pairs and the control device is configured to determine the carrier frequency by, in particular, linear interpolation of the carrier frequency values ​​assigned to the individual pairs.

[0026] As an alternative to the use of characteristic maps, the control device according to the invention can also be configured to determine the carrier frequency by analytical calculation specifications, which make it possible to determine the carrier frequency depending on the operating point.

[0027] The characteristic map or calculation specifications may be determined, for example, by measurement or simulation for a particular configuration of inverter and electric machine.

[0028] The control device according to the invention may further be configured to determine an updated carrier frequency upon receipt of the updated operating point information and / or after a predefined or predefinable period has elapsed and / or after completion of an electrical period of the electric machine and / or after completion of a period of the respective switching signal, so that the carrier frequency can be adapted to the instantaneous operating point at an advantageous time.

[0029] Furthermore, the control device according to the invention can be configured to determine operating point information from torque information received at an input and / or rotational speed information received at an input and / or in dependence on current information received at an input describing the phase currents supplying the electric machine and / or to estimate the operating point information in the context of a control for determining switching signals. The torque can in particular be determined from the current information.

[0030] The object on which the invention is based is further achieved by an inverter comprising switching elements interconnected to convert a voltage present on the input side into an alternating current for operating an electric machine in response to switching signals controlling the switching elements, and a control device according to the invention.

[0031] The inverter may further comprise a specially designed DC link capacitor, either as a single capacitor element or as multiple capacitor elements connected in parallel and / or in series.

[0032] The inverter may further comprise an analog-to-digital converter designed to convert the analog measurement signal into current information and / or rotational speed information and / or torque information.

[0033] The object on which the invention is based is further achieved by an assembly comprising an inverter according to the invention and an electric machine that can be operated by the inverter.

[0034] It is now preferred if the determination of the carrier frequency represents the following relationship:

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[0035] During the ceremony, f PWM (M,f rot ) is the torque M and the rotational speed f rot Describes the carrier frequency to be determined in dependence on m THD describes the distortion measure of the total harmonic distortion of the inverter output voltage, f PWM,min describes the minimum carrier frequency that is predefined or can be predefined, f PWM,losses (M,f rot ) is the minimum carrier frequency

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[0036] If WTHD is used as the distortion measure, the following can be applied:

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[0037] The object on which the invention is based can further be achieved by a method for operating an inverter for supplying power to an electric machine, comprising the steps of determining, executed by a control device, a carrier frequency of a pulse width modulated switching signal for operation of the inverter in dependence on operating point information describing an operating point defined by the rotational speed and torque of the electric machine, such that as the rotational speed increases and the magnitude of the torque decreases, the carrier frequency increases within an operating region whose lower rotational speed limit is different to zero and whose upper rotational speed limit is in the power limited operating region or the field weakening operating region; and supplying switching signals to switching elements of the inverter.

[0038] The object on which the invention is based is finally achieved by a computer program comprising commands which, when said program is executed by a computer, cause the computer to carry out the steps of the method according to the invention executed by a control device.

[0039] All statements relating to the control device according to the invention, the inverter according to the invention and the assembly according to the invention are equally applicable to the method according to the invention and the computer program according to the invention, so that the above-mentioned advantages can also be achieved by means of these.

[0040] Further advantages and details of the invention emerge from the exemplary embodiments described below on the basis of the drawings, which are schematic diagrams: [Brief description of the drawings]

[0041] [Figure 1] 1 is a block diagram of an exemplary embodiment of an assembly according to the present invention comprising an exemplary embodiment of an inverter according to the present invention and an exemplary embodiment of a control device according to the present invention; [Diagram 2] FIG. 2 is a torque / rotational speed diagram illustrating operating regions for operation of the assembly shown in FIG. 1. [Diagram 3] FIG. 1 is a torque speed diagram plotting WTHD for a prior art assembly. [Figure 4] FIG. 2 is a torque-speed diagram illustrating the total losses of the inverter of a prior art assembly; [Diagram 5] FIG. 6 is a torque rotational speed diagram plotted with carrier frequency values ​​when operating a further exemplary embodiment of an assembly according to the invention; [Figure 6] FIG. 11 is a torque / rotation speed diagram plotted with WTHD for a further exemplary embodiment; [Figure 7] FIG. 11 is a torque-speed diagram illustrating total inverter losses of an inverter of a further exemplary embodiment; [Figure 8] 2 is a torque rotational speed diagram illustrating an operating region for the operation of a further exemplary embodiment of the assembly shown in FIG. 1; [Figure 9] FIG. 13 is a torque / rotational speed diagram plotting the WTHD of a further assembly according to the prior art. [Figure 10] FIG. 2 is a torque-speed diagram in which the total inverter losses of a further assembly according to the prior art are plotted; [Figure 11] FIG. 6 is a torque rotational speed diagram plotted with carrier frequency values ​​when operating a further exemplary embodiment of an assembly according to the invention; [Figure 12] FIG. 11 is a torque / rotation speed diagram plotted with WTHD for a further exemplary embodiment; [Figure 13] FIG. 11 is a torque-speed diagram illustrating total inverter losses of an inverter of a further exemplary embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] 1 is a block diagram of an exemplary embodiment of an assembly 1 comprising an exemplary embodiment of an inverter 2 and an electric machine 3 configured to drive a vehicle that may be partially or fully electric. The assembly 1 further comprises a DC voltage source 4, in this example designed as a high-voltage battery.

[0043] The inverter 2 comprises a filter device 5, which in this example is designed as an EMC filter, a DC link capacitor 6, a power unit 7, an exemplary embodiment of a control device 8, a first measuring device 9, a second measuring device 10 and an analog-to-digital conversion device 11.

[0044] The power unit 7 comprises a number of switching elements 12 designed as semiconductor switching elements, for example IGBTs or power MOSFETs. The switching elements 12 are connected in pairs to form a half-bridge. A drive circuit 14 is connected in front of a control input 13 of each switching element 12. For the sake of clarity, only one switching element 12 and one drive circuit 14 are labeled here. The drive circuit 14 receives a pulse-width modulated switching signal 15 from the control device 8, which is provided such that a voltage for supplying the electric machine 3 is provided at each tap of the half-bridge. The power unit 7 thus converts the DC link voltage, smoothed by the DC link capacitors 6, into a voltage having, in this case, three phases, in response to the switching signal 15.

[0045] The first measuring device 9 is configured to acquire the phase currents and to provide measurement signals to an analog-to-digital conversion device 11, which converts the analog measurement signal of the first measuring device 9 into digital current information 16. The second measuring device 10 is thus configured to acquire the rotational speed of the electric machine 3 and to provide measurement signals to an analog-to-digital conversion device 11, which converts the analog measurement signal of the second measuring device 10 into digital rotational speed information 17. The control device 8 receives the current information 16 and the rotational speed information 17 at its inputs.

[0046] Based on the current information 16 and the rotational speed information 17, the controller 8 determines operating point information describing an operating point defined by the rotational speed and torque of the electric machine 3. The controller 8 is configured to determine a carrier frequency of the pulse-width modulated switching signal 15. For this purpose, the controller 8 comprises a memory unit 18 in which a characteristic map is stored, which assigns carrier frequency values ​​to pairs of rotational speed and torque values. Based on the operating point information, the controller 8 selects a corresponding carrier frequency value from the characteristic map.

[0047] FIG. 2 is a torque-rotational speed diagram illustrating the operating region when operating the assembly shown in FIG. 1, where the torque is indicated by M and the rotational speed is f rot In this exemplary embodiment, the switching signal 15 is determined by continuous space vector modulation (SVM).

[0048] The figure shows a characteristic map describing the association between each pair and the carrier frequency value. In Fig. 2, a corner operating point 19 is first shown, describing the magnitude of the maximum torque when passing from the base speed operating region 20 into the power limited operating region 21 or into the field weakening operating region. Selected contours of the carrier frequency values ​​are shown by dashed and dotted lines.

[0049] The first operating region 22 extends within a rotational speed interval in which the lower rotational speed limit 23 is different from zero and the upper rotational speed limit 24 is in the power limited operating region 21 or in the field weakening operating region. A first boundary 25 of the first operating region 22 extends from a first operating point 26 in the basic rotational speed operating region, whose rotational speed corresponds to the lower rotational speed limit 23, to a second operating point 27, whose rotational speed is greater than the lower rotational speed limit 23 and whose torque magnitude is greater than the torque magnitude of the first operating point 26. The second operating point 27 is in the power limited operating region 21 or in the field weakening operating region and is spaced apart from the maximum amplitude of the torque at the rotational speed of the second operating point 27.

[0050] A second boundary 28 of the first operating region 22 extends from a first operating point 29 , the rotational speed of which corresponds to the upper rotational speed limit, to a second operating point identical to the second operating point 27 of the first boundary 25 .

[0051] The controller 8 is configured to increase the carrier frequency in the first operating region 22 with increasing rotational speed and decreasing torque magnitude, which is represented by the arrows in the remainder of the figure.

[0052] The second operating region 30, defined so as not to overlap with the first operating region 22, includes operating points whose torque magnitude at the respective rotational speed is greater than the maximum torque magnitude at this rotational speed in the first operating region. The second operating region 30 lies entirely within the power-limited operating region 21 or the field-weakening operating region and extends up to a full-load operation 30a described by a line in the characteristic map, where the maximum possible torque magnitude exists for the respective rotational speed. The control device 8 is configured to increase the carrier frequency in the second operating region 30 with increasing rotational speed, independent of the torque.

[0053] The control device 8 is finally configured not to determine a carrier frequency below a predefined minimum value. In this respect, a further operating region 31 is depicted in which a minimum value is specified. The further operating region 31 includes an operating point on the low rotation speed side of the first boundary 25 and the boundary 28a of the second operating region 30.

[0054] In summary, the characteristic maps of the operating regions 22, 30, 31 form the following relationships:

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[0055] During the ceremony, f PWM (M,f rot ) is the torque M and the rotational speed f rot Describes the carrier frequency to be determined in dependence on WTHD describes the weighted total harmonic distortion as an exemplary distortion measure of the total harmonic distortion of the output voltage of inverter 2; f PWM,min describes the minimum carrier frequency, f PWM,losses (M,f rot ) is the minimum carrier frequency

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[0056] The control device 8 is configured to periodically update the carrier frequency, for example upon receipt of updated operating point information, after a predefined or predefinable period has elapsed, after completion of an electrical cycle of the electric machine 3 or after completion of the period of the respective switching signal 15. Combinations of the above mentioned update events are also possible.

[0057] Figures 3 and 4 relate to an assembly corresponding to Figure 1 according to the prior art, in which an SVM is used, but in which the carrier frequency is specified as a constant 10 kHz for all operating points of the torque-speed diagram.

[0058] Figure 3 shows a torque-speed diagram plotting the WTHD of an assembly according to the prior art. The WTHD is shown in Figure 3 as a contour line where the value of the WTHD is given in percentage. It can be seen that the WTHD essentially rises with increasing rotational speed and the magnitude is particularly noticeable at low torques. Here, high values ​​of WTHD can cause unwanted vibrations in the electric machine 3.

[0059] Figure 4 shows a torque-speed diagram plotting the total losses of the inverter of a prior art assembly. The total losses are shown in Figure 4 as contour lines where the value of the total losses is given in kW. As a rule of thumb, the total losses at a constant carrier frequency of 10 kHz increase with increasing torque magnitude and are almost independent of the rotation speed.

[0060] Figures 5, 6 and 7 relate to further exemplary embodiments of the assembly 1 corresponding to the exemplary embodiments of Figures 1 and 2 described above. The specific design of the assembly 1 here is for a maximum of 12000 min -1 The characteristic map covers a range of rotational speeds from 0.1 to 1.5 rpm and a torque range of approximately -250 to 250 Nm. The determination of the carrier frequency depends on the operating point. The switching signal 15 is determined by the SVM.

[0061] 5 shows a torque-rotational speed diagram plotting carrier frequency values ​​during operation of a further exemplary embodiment. The characteristic maps have been determined here on an experimental basis or by simulation. The operating regions 22, 30, 31 and the corner operating point 19 are shown.

[0062] Figure 6 is a torque-rotation speed diagram plotted with WTHD, which corresponds to Figure 3. Comparing Figure 6 with Figure 3, it can be seen that by determining the carrier frequency depending on the operating point, a maximum WTHD value of 1.3% is achieved, which is significantly lower than the maximum WTHD value of over 3.0% with a fixed carrier frequency specification according to the prior art.

[0063] FIG. 7 is a torque-rotation speed diagram in which the total losses of the inverter 2 are plotted, the diagram corresponding to FIG. 4. Comparing FIG. 7 with FIG. 4, it can be seen that the total losses in the region where high WTHD values ​​occur at a constant carrier frequency specification increase slightly above the previous losses of the prior art. However, the maximum total losses are particularly noteworthy, since the thermal durability of the switching elements 12 must be especially directed to this. Advantageously, they remain practically unchanged. Thus, the operating point-dependent carrier frequency specification allows a significant reduction in the total harmonic distortion over a wide operating range of the electric machine 3, without thereby increasing the maximum total losses.

[0064] Fig. 8 is a torque-rotational speed diagram with operating regions plotted for the operation of a further exemplary embodiment of the assembly 1 shown in Fig. 1. In this exemplary embodiment, the switching signal 15 is determined by Generalized Discontinuous Pulse Width Modulation (GDPWM), i.e. using a discontinuous modulation scheme.

[0065] 8 again shows a first operating region 22, within which the carrier frequency increases with increasing rotational speed and decreasing torque magnitude, stretching between a lower rotational speed limit 23 and an upper rotational speed limit 24, which is in the power-limited operating region 21 or field-weakening operating region. A first boundary 25 of the first operating region 22 extends from a first operating point 26, which is in the base speed operating region 20 and whose rotational speed corresponds to the lower rotational speed limit 23, to a second operating point 27, whose rotational speed is greater than the lower rotational speed limit 23 and whose torque magnitude is greater than that of the first operating point 26. However, the second operating point 27 is also in the base speed operating region 20, and the first boundary 27 extends into the full-load operating region 30a.

[0066] The second boundary 28 of the first operating region 22 extends from a first operating point 29, whose rotational speed corresponds to the upper rotational speed 24, but which is within the base rotational speed operating region 20 and the full load operating region 30a, to a second operating point 32 having a higher rotational speed than the second operating point 27 of the first boundary 25.

[0067] 8 further shows a second operating region 33 of the characteristic map, defined so as not to overlap with the first operating region 22, which includes operating points whose torque magnitude at the respective rotational speed is greater than the maximum torque magnitude at this rotational speed in the first operating region 22. The second operating region 33 is directly adjacent to the first operating region 22. One boundary 34 of the second operating region 33 extends from an upper rotational speed limit 35 in the power-limited operating region 21 or in the field-weakening operating region to the full-load operating region 30a in the maximum, base rotational speed operating region 20. The control device 8 is configured to increase the carrier frequency in the second operating region 33 with decreasing rotational speed and decreasing torque.

[0068] A third operating area 36 is also defined in the characteristic map and comprises operating points whose torque magnitude at the respective rotational speed is greater than the maximum torque magnitude at this rotational speed in the operating areas 22, 33. The third operating area 36 lies beyond the border 34 of the second operating area 33 in the basic rotational speed operating area 20 and in the power-limited operating area 21 or in the field-weakening operating area. The control device 8 is configured to increase the carrier frequency in the third operating area 36 with increasing rotational speed and decreasing torque or, alternatively, independently of the torque, with increasing rotational speed.

[0069] Otherwise, this exemplary embodiment corresponds to the first exemplary embodiment as described with reference to FIGS.

[0070] Figures 9 and 10 relate to an assembly corresponding to Figure 1 according to the prior art, but in this assembly the carrier frequency is specified as a constant 15.9 kHz for all operating points of the torque-speed diagram and GDPWM is used.

[0071] Figure 9 is a torque-speed diagram plotted with the WTHD of an assembly according to the prior art. The WTHD is shown in Figure 9 as a contour line where the value of the WTHD is given in percentage. It can be seen that due to the different type of modulation, the WTHD is distributed differently than when the SVM according to Figure 3 is used. As an approximation, it can be defined here that the WTHD takes on higher values ​​for small values ​​of torque. However, the global maximum of the WTHD is present at a torque of 0 Nm in the power-limited or field-weakening operating region.

[0072] Figure 10 shows a torque-speed diagram plotting the total losses of the inverter of an assembly according to the prior art. The total losses are shown in Figure 10 as contour lines, where the value of the total losses is given in kW. The distribution of the total losses corresponds approximately to the distribution according to the SVM according to Figure 4.

[0073] Figures 11, 12 and 13 relate to further exemplary embodiments of the assembly 1 corresponding to the exemplary embodiments of Figures 1 and 8 described above. The specific design of the assembly 1 is again for a maximum of 12000 min -1 The characteristic map covers a range of rotational speeds from 0.1 to 1.5 rpm and a torque range from approximately -250 to 250 Nm. The determination of the carrier frequency depends on the operating point. The switching signal 15 is determined by GDPWM.

[0074] 11 shows a torque-rotational speed diagram plotting carrier frequency values ​​during operation of a further exemplary embodiment. The characteristic maps have been determined here on an experimental basis or by simulation. The operating regions 22, 31, 33, 36 as well as the corner operating point 19 are shown.

[0075] Fig. 12 is a torque-rotation speed diagram plotted with WTHD, which corresponds to Fig. 9. Comparing Fig. 12 with Fig. 9, it can be seen that by determining the carrier frequency depending on the operating point, a maximum WTHD value of 0.9% is achieved, which is significantly lower than the maximum WTHD value of over 2.5% with a fixed carrier frequency specification according to the prior art.

[0076] Fig. 13 is a torque-speed diagram in which the total losses of the inverter 2 are plotted, and corresponds to Fig. 10. From a comparison of Fig. 13 with Fig. 10, it can be seen that the advantages described with reference to Figs. 4 and 7 are also achieved by the use of GDPWM.

[0077] The following further exemplary embodiments may be based on any of the previous exemplary embodiments, according to further exemplary embodiments of the control device 8, the characteristic map is defined by individual pairs and the control device 8 is configured to determine the carrier frequency by interpolation, in particular linear interpolation, of the carrier frequency values ​​assigned to the individual pairs. According to further exemplary embodiments, the control device 8 is configured to determine the carrier frequency by analytical calculation specification, which allows the carrier frequency to be determined in dependence on the operating point instead of based on the characteristic map. According to further exemplary embodiments, the torque information is not obtained with reference to the current information 16, but is estimated or measured by the control device 8 in the context of the control for determining the switching signal 15.

Claims

1. A control device (8) for an inverter (2) supplying an electric machine (3), configured to provide a pulse width modulated switching signal (15) having a carrier frequency for driving switching elements (12) of the inverter (2), comprising: determining said carrier frequency in dependence on operating point information describing an operating point defined by a rotational speed and a torque of said electric machine (3); configured to increase the carrier frequency within a first operating region (22) that extends within a rotational speed interval whose lower limit rotational speed (23) is different from zero and whose upper limit rotational speed (24) is in a power limited operating region (21) or a field weakening operating region as the rotational speed increases and the magnitude of the torque decreases; configured to increase the carrier frequency with increasing rotational speed, in particular independently of the torque, within a second operating region (30) defined without overlapping with the first operating region (22) and including an operating point where the magnitude of the torque at each rotational speed is greater than the maximum magnitude of the torque in the first operating region (22) at this rotational speed. A control device comprising:

2. a first boundary (25) of the first operating region (22) extends from a first operating point (26) at which the rotational speed corresponds to the lower limit rotational speed (23) to a second operating point (27) at which the rotational speed is greater than the lower limit rotational speed (23) and at which the magnitude of the torque is greater than the magnitude of the torque of the first operating point (26); and / or a second boundary (28) of the first operating region extends from a first operating point (29) where the rotational speed corresponds to the upper rotational speed (24) to a second operating point (27) where the rotational speed is lower than the upper rotational speed (29) and where the magnitude of the torque is greater than the magnitude of the torque of the first operating point (29); The control device according to claim 1 .

3. The second operating point (27) of the first boundary (25) and the second boundary (28) is are identical and / or in the power-limited operating region (21) or the field-weakening operating region; and / or each said second operating point (27) being spaced apart from a maximum magnitude of said torque at said rotational speed; The control device according to claim 2.

4. the second operating region (30) extends entirely within the power limited operating region (21) or the field weakening operating region and / or up to maximum full load operation (30a); A control device according to any one of claims 1 to 3.

5. configured to generate said pulse width modulated switching signal (15) by continuous pulse width modulation, in particular space vector modulation, A control device according to any one of claims 1 to 4.

6. and configured to increase the carrier frequency with decreasing rotation speed and decreasing torque within a second operating region (33) defined without overlapping with the first operating region (22) and including an operating point in which the magnitude of the torque at each rotation speed is greater than a maximum magnitude of the torque in the first operating region (22) at the rotation speed. The control device according to claim 1 or 2.

7. configured to increase the carrier frequency with increasing rotational speed with increasing rotational speed and decreasing torque or independently of torque within a third operating region (36) defined without overlapping with the first operating region (22) and including an operating point where the magnitude of the torque at each rotational speed is greater than a maximum magnitude of the torque in the first operating region (22) at that rotational speed.

7. A control device according to claim 1, 2 or 6.

8. the third operating region (36) includes operating points at which the magnitude of the torque at each rotational speed is greater than a maximum magnitude of the torque at this rotational speed in the second operating region (33), The control device according to claim 7.

9. The first operating area (22) and / or the second operating area (30) and / or within the full load operating region (30a); ranging from a base rotation speed operating region (20) to within the power limited operating region (21) or the field weakening operating region; The control device according to claim 1 or 2.

10. The first operating area (22) and / or the second operating area (33) and / or the third operating area (36) and / or within the full load operating region (30a); ranging from a base rotation speed operating region (20) to within the power limited operating region (21) or the field weakening operating region; A control device according to any one of claims 7 and 8.

11. configured to generate said pulse width modulated switching signal (15) by discontinuous pulse width modulation, in particular by generalized discontinuous pulse width modulation, A control device according to claim 1 or 2 or according to any one of claims 7 to 10.

12. a switching element (12) configured to convert a voltage present on the input side into an alternating current for operating an electric machine (3) in response to a switching signal controlling said switching element (12); A control device (8) according to any one of claims 1 to 11, An inverter (2).

13. Assembly (1) comprising an inverter (2) according to claim 12 and an electric machine (3) capable of being driven by said inverter (2).

14. wherein the determination of the carrier frequency represents the following relationship: [0010] [0025] and [0030] During the ceremony, f ＰＷＭ (M, f ｒｏｔ ) is the torque M and the rotational speed f ｒｏｔ Describing the carrier frequency to be determined in dependence on m ＴＨＤ describes a distortion measure of the total harmonic distortion of the output voltage of the inverter (2); f ＰＷＭ，ｍｉｎ describes a predefined or predefinable minimum carrier frequency, f ＰＷＭ，ｌｏｓｓｅｓ (M, f ｒｏｔ ) is the minimum carrier frequency [0045] The maximum value of the total loss of the inverter (2) at the minimum carrier frequency [0050] The switching losses at ｃ Taking into account the torque M and the rotational speed f ｒｏｔ Describe the carrier frequency that depends on, [006] is the minimum carrier frequency [0070] and the carrier frequency dependent on the distortion measure at [0080] The torque M and the rotational speed f, taking into account the maximum value of the distortion measure at ｒｏｔ Describe the carrier frequency that depends on, [0097] but, [0089] 、 ##EQU00011## and f ＰＷＭ，ｍｉｎ , in particular describing a function determined by simulation or measurement, 14. The assembly of claim 13.

15. A method for operating an inverter (2) for powering an electric machine (3), carried out by a controller (8), comprising the steps of: determining a carrier frequency of a pulse width modulated switching signal (15) for the operation of the inverter (2) in dependence on operating point information describing operating points defined by the rotational speed and the torque of the electric machine (3) such that the carrier frequency increases as the rotational speed increases and the magnitude of the torque decreases within a first operating region (22) extending within a rotational speed interval whose lower limit rotational speed (23) is different from zero and whose upper limit rotational speed (24) is in a power limited operating region (21) or in a field weakening operating region, wherein the carrier frequency increases with increasing rotational speed, in particular independently of the torque, within a second operating region (30) defined without overlapping with the first operating region (22) and including operating points whose magnitude of the torque at the respective rotational speed is greater than the maximum magnitude of the torque in the first operating region (22) at this rotational speed; providing said pulse width modulated switching signal (15) to a switching element (12) of said inverter (2); A method comprising:

16. A computer program comprising commands which, when said computer program is executed by a computer, cause said computer to carry out the steps executed by the control device (8) of the method according to claim 15.

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