CONTROL DEVICE, INVERTER, ASSEMBLY HAVING AN INVERTER AND AN ELECTRICAL MACHINE, METHOD FOR OPERATING AN INVERTER, AND COMPUTER PROGRAM

Abstract

A control device (8) for an inverter (2) that feeds an electric machine (3), wherein the control device (8) is configured to provide pulse-width modulated switching signals (15) for driving switching elements (12) of the inverter (2), wherein the control device (8) is configured to determine a modulation type by means of which the pulse-width modulated switching signals (15) are generated depending on operating point information that describes an operating point defined by at least one operating parameter, and to use a first modulation type in at least one first operating region (21, 28, 30, 31) and a second modulation type in another operating region (32, 32a, 32b).

Claims

1. A control device for an inverter that feeds an electric machine, wherein the control device is configured to: provide pulse-width modulated switching signals for driving switching elements (12) of the inverter, determine a modulation type by which the pulse-width modulated switching signals are generated depending on operating point information that describes an operating point defined by at least one operating parameter, and to use a first modulation type in at least one first operating region and a second modulation type in another operating region.

2. The control device as claimed in claim 1, wherein the first modulation type is a continuous pulse-width modulation type and the second modulation type is a discontinuous pulse-width modulation type.

3. The control device as claimed in claim 1, wherein an operating parameter is a torque of the electric machine or a current magnitude of a machine current of the electric machine.

4. The control device as claimed in claim 3, wherein a first operating region, or a plurality of first operating regions, lies within an operating parameter interval defined by a lower operating parameter boundary and an upper operating parameter boundary.

5. The control device as claimed in claim 1, wherein an operating parameter is a rotation speed of the electric machine.

6. The control device as claimed in claim 5, wherein the at least one first operating region lies within a rotation speed interval defined by a lower rotation speed boundary and an upper rotation speed boundary.

7. The control device as claimed in claim 1, wherein an operating parameter is a DC link voltage of the inverter.

8. The control device as claimed in claim 1, wherein the operating regions are determined in such a way that a peak-to-peak value of a DC link voltage of the inverter does not exceed a predefined value.

9. The control device as claimed in claim 8, wherein operating regions in continuous load operation are determined in such a way that the peak-to-peak value of the DC link voltage does not exceed a predefined second value that is smaller than the first value.

10. The control device as claimed in claim 1, that is configured to provide the switching signals at a lower carrier frequency when the first modulation type is in use compared to when the second modulation type is in use.

11. The control device as claimed in claim 1, wherein the control device is configured to ascertain the modulation type that is to be used by means of a characteristic map that assigns one of the modulation types to the at least one operating parameter, or on the basis of a function that evaluates the at least one operating parameter.

12. An inverter, comprising: a DC link capacitor; switching elements that are interconnected to convert a DC link voltage present at the DC link capacitor into a single-phase or multi-phase AC voltage, depending on switching signals driving the switching elements; and a control device as claimed in claim 1.

13. An assembly comprising: an inverter as claimed in claim 12; and an electric machine that can be operated by the AC voltage.

14. A method for operating an inverter for the supply of an electric machine, comprising: determining, by a control device, a modulation type by which pulse-width modulated switching signals for driving switching elements of the inverter are generated depending on operating point information that describes an operating point defined by at least one operating parameter, wherein a first modulation type is used in at least one first operating region and a second modulation type is used in another operating region (32, 32a, 32b); and providing, by the control device, the switching signals.

15. A computer program, comprising commands which, when the program is executed by a computer, cause the latter to execute the steps, carried out by the control device, of the method as claimed in claim 14.

Description

[0036] Further advantages and details of the present invention emerge from the exemplary embodiments described below and on the basis of the drawings. These are schematic illustrations in which:

[0037] FIG. 1 shows a block diagram of an exemplary embodiment of an assembly according to the invention with an exemplary embodiment of an inverter according to the invention and a first exemplary embodiment of a control device according to the invention;

[0038] FIG. 2 shows a torque-rotation speed diagram on which operating regions when operating the assembly with the first exemplary embodiment of the control device have been drawn;

[0039] FIG. 3 shows a torque-rotation speed diagram on which isolines of peak-to-peak values of a DC link voltage when operating the assembly with the first exemplary embodiment of the control device have been drawn;

[0040] FIG. 4 shows a torque-rotation speed diagram on which isolines of total losses when operating the assembly with the first exemplary embodiment of the control device have been drawn;

[0041] FIG. 5 shows a torque-rotation speed diagram on which isolines of percentage changes of total losses when operating the assembly with the first exemplary embodiment of the control device in comparison with an assembly according to the prior art have been drawn;

[0042] FIGS. 6 and 7 each show a torque-rotation speed diagram on which operating regions when operating the assembly according to FIG. 1 with further exemplary embodiments of the control device have been drawn;

[0043] FIG. 8 shows a diagram of a possible percentage reduction of a DC link capacitance against the carrier frequency of the second modulation type with a constant carrier frequency of the first modulation type;

[0044] FIG. 9 shows a diagram of a maximum percentage reduction of the total losses against the carrier frequency of the second modulation type with a constant carrier frequency of the first modulation type; and

[0045] FIGS. 10 and 11 each show a torque-rotation speed diagram on which operating regions when operating an assembly according to FIG. 1 with further exemplary embodiments of the control device have been drawn.

[0046] FIG. 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 that is configured to drive a vehicle that can be partially or fully electrically driven. The assembly 1 further comprises a DC voltage source 4 that is designed in the present case as a high-voltage battery.

[0047] The inverter 2 comprises a filter device 5 that is designed in the present case 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 converter device 11.

[0048] The power unit 7 comprises a plurality of switching elements 12 that are designed as semiconductor switching elements, for example as IGBTs or as power MOSFETs. The switching elements 12 are interconnected in pairs to form half-bridges. A driver 14 is connected upstream of a control input 13 of a respective switching element 12. For reasons of clarity, only one switching element 12 and one driver 14 have been given reference signs here. The drivers 14 receive pulse-width modulated switching signals 15 from the control device 8 that are provided in such a way that an output voltage for feeding the electric machine 3 is made available at a respective tap of the half-bridges. The power unit 7 therefore converts a DC link voltage, which is stabilized by the DC link capacitor 6, into an AC voltage, having three phases in the present case, depending on the switching signals 15. The voltage present at the DC link capacitor 6 is therefore to be considered the DC link voltage.

[0049] The first measuring device 9 is configured to acquire a machine current and to provide measurement signals to the analog-to-digital converter device 11 which converts the analog measurement signals of the first measuring device 9 into digital current information 16. The second measuring device 10 is accordingly configured to acquire a rotation speed of the electric machine 3 and to provide measurement signals to the analog-to-digital converter device 11, which converts the analog measurement signals of the second measuring device 10 into digital rotation speed information 17. The rotation speed information 17 can alternatively already be provided in digital form by the second measuring device 10. The control device 8 receives the current information 16 and the rotation speed information 17 at its input. From this, it ascertains torque information that describes the torque of the electric machine 3. The torque information can alternatively also be estimated in the context of a regulation for ascertaining the switching signals 15 by the control device 8.

[0050] A third measuring device 18 that acquires a DC link voltage present across the DC link capacitor 6 is also optionally provided at the inverter 2. The analog measurement signals of the third measuring device 18 are converted by the analog-to-digital converter device 11 into voltage information 19 which the control device 8 also receives at its input.

[0051] On the basis of the current information 16 and the rotation speed information 17, the control device 8 ascertains operating point information that describes an operating point defined by a tuple of operating parameters. In the present case, the operating parameters are the torque of the electric machine 3 and, furthermore, a rotation speed of the electric machine. In addition or as an alternative to the torque, a current magnitude of the machine current of the electric machine 3 ascertained on the basis of the current information 16 can be used as an operating parameter. The operating point information can optionally also comprise the DC link voltage as an operating parameter.

[0052] The control device 8 is configured to ascertain a modulation type by means of which the pulse-width modulated switching signals 15 are generated depending on the operating point information. For this purpose, the control device 8 comprises a memory unit 20 in which a characteristic map, realized in the form of a lookup table, which assigns a modulation type to pairs of rotation speed values and torque values, is stored. The control device 8 selects a corresponding modulation type with reference to the operating point information from the characteristic map.

[0053] A consistent carrier frequency of, for example, 10 kHz was used in the preceding exemplary embodiment for both modulation types.

[0054] FIG. 2 is a torque-rotation speed diagram on which operating regions when operating the assembly 1 shown in FIG. 1 have been drawn, wherein, in general, a torque is indicated with M and a rotation speed is indicated with frot.

[0055] The characteristic map has a first operating region 21 that lies between a positive lower torque boundary 22 and an upper torque boundary 23, also positive, and is limited by the upper torque boundary 23. The first operating region 21 furthermore lies between a lower operating parameter boundary 24 and an upper operating parameter boundary 25 which, in the present case, are rotation speed boundaries. The first operating region 21 here extends from base rotation speed operation 26 up to power-limiting operation 27. A further first operating region 28 can also be seen in FIG. 2 that extends from a full load line 29 at which a torque with a maximum value is present, toward torques with lower values. Further first operating regions 30, 31 are defined for negative torques. Other operating points lie in a second operating region 32.

[0056] The control device is configured to use a continuous pulse-width modulation type, in this case space vector modulation (SVM), in the first operating regions 21, 28, 30, 31, and a discontinuous pulse-width modulation, in this case generalized discontinuous pulse-width modulation (GDPMW), in the second operating region 32 to generate the switching signals 15. The operating regions 21, 28, 30 to 32 are determined here in such a way that a peak-to-peak value of a DC link voltage of the inverter does not exceed a predefined first value if the electric machine 3 is in high-load operation 33, 34, and does not exceed a second value that is, for example, smaller than the first value by a factor of 2, if the electric machine 3 is in continuous load operation 35. Boundaries between high-load operation 33, 34 and continuous load operation 35 are illustrated by lines 36, 37 in FIG. 2, and in sections also form higher torque boundaries such as the upper torque boundary 23. The demarcation between high-load operation 33, 34 and continuous load operation 35 occurs here with reference to a predefined amplitude î.sub.AC of the motor current, wherein, in the present exemplary embodiment, î.sub.AC≤√{square root over (2)}.Math.300 A is assumed for the continuous load operation.

[0057] In the present exemplary embodiment, the first value is 23.7 V and the second value is 13.65 V. It can be seen from a torque-rotation speed diagram in FIG. 3, on which isolines of peak-to-peak values of the DC link voltage during operation of the assembly 1 have been drawn, that, as a result of the operating-point-dependent specification of the modulation types, these values are not exceeded. FIG. 4 is a torque-rotation speed diagram on which isolines of total losses, defined as a sum of switching losses and conduction losses in the inverter 2 during operation of the assembly 1, have been drawn. In this connection, FIG. 5 shows a-rotation speed diagram on which isolines of percentage changes of the total losses in comparison with an assembly corresponding to the assembly 1 according to the prior art, where only SVN is used, have been drawn. It can be seen from FIG. 5 that, in comparison with an exclusive use of SVM, a significant reduction in the total losses is found in the second operating region 32.

[0058] The following table 1 shows operating properties of this assembly according to the prior art as a reference in a column “SVM 10 kHz”, corresponding operating properties with the exclusive use of GDPWM for comparison in a column “GDPWM 10 kHz”, and corresponding operating properties when operating the assembly 1 according to the present exemplary embodiment in a column “SVM 10 kHz and GDPWM 10 kHz”. This is illustrated for three DC link voltages, namely 270 V, 350 V and 450 V, at a constant carrier frequency of 10 kHz. A value of 650 μF is assumed as the DC link capacitance. In general here, u.sub.DC,pp identifies the peak-to-peak value of the DC link voltage, P.sub.tot the total losses, max(u.sub.DC,pp) the maximum peak-to-peak value of the DC link voltage in the given operating region, and max(P.sub.tot) the maximum total losses in the given operating region.

TABLE-US-00001 TABLE 1 SVM 10 kHz and SVM 10 kHz GDPWM 10 kHz GDPWM 10 kHz max(u.sub.DC, pp) in 13.23 V (270 V) 17.04 V (270 V) 13.65 V (270 V) continuous load 13.65 V (350 V) 17.41 V (350 V) 13.65 V (350 V) operation 13.55 V (450 V) 17.87 V (450 V) 13.65 V (450 V) max(u.sub.DC, pp) in 26.21 V (270 V) 28.05 V (270 V) 27.30 V (270 V) high-load 25.24 V (350 V) 27.86 V (350 V) 27.29 V (350 V) operation 26.52 V (450 V) 28.27 V (450 V) 27.30 V (450 V) max(P.sub.tot) in high- 3.00 kW (270 V) 2.55 kW (270 V) 3.00 kW (270 V) load operation 3.34 kW (350 V) 2.77 kW (350 V) 3.33 kW (350 V) 3.80 kW (450 V) 3.05 kW (450 V) 3.80 kW (450 V) Highest relative — 0.0% (270 V) 0.0% (270 V) increase in P.sub.tot 0.0% (350 V) 0.0% (350 V) compared to SVM 0.0% (450 V) 0.0% (450 V) Highest relative — 29.5% (270 V) 29.5% (270 V) reduction in P.sub.tot 32.4% (350 V) 32.4% (350 V) compared to SVM 35.4% (450 V) 35.4% (450 V)

[0059] It can be seen from table 1 that, in comparison with the exclusive use of SVM in the assembly 1, the predefined first or second values of the peak-to-peak value of the DC link voltage are not exceeded, and at the same time there is a significant reduction in the total losses in the operating region 32. The exclusive use of GDPWN would indeed permit lower maximum losses in high-load operation. Due, however, to the significantly higher peak-to-peak values of the DC link voltage in the continuous mode operating region, a 30.9% increase in the DC link capacitance would be necessary; bearing in mind the associated costs and increased space requirements, this is unwanted.

[0060] Further exemplary embodiments of the assembly 1 are described below, differing from the first exemplary embodiment in that the control device 8 is configured to provide the switching signals at a different carrier frequency when the continuous modulation type is in use compared to when the discontinuous modulation type is in use.

[0061] In the following table 2, the columns “SVM 10 kHz” and “SVM 10 kHz and GDPWM 10 kHz”correspond to those in table 1. The column “SVM 10 kHz and GDPWM 13.5 kHz” relates to an exemplary embodiment in which, when using SVM in the same way as in the first exemplary embodiment, a carrier frequency of 10 kHz is used, and, when using GDPWN, a carrier frequency is 13.5 kHz is used. The structure of the rest of table 2 corresponds to table 1.

TABLE-US-00002 TABLE 2 SVM 10 kHz and SVM 10 kHz and SVM 10 kHz GDPWM 10 kHz GDPWM 13.5 kHz max(u.sub.DC, pp) in 13.23 V (270 V) 13.65 V (270 V) 12.50 V (270 V) continuous load 13.65 V (350 V) 13.65 V (350 V) 12.50 V (350 V) operation 13.55 V (450 V) 13.65 V (450 V) 12.50 V (450 V) max(u.sub.DC, pp) in 26.21 V (270 V) 27.30 V (270 V) 20.78 V (270 V) high-load 25.24 V (350 V) 27.29 V (350 V) 20.64 V (350 V) operation 26.52 V (450 V) 27.30 V (450 V) 20.94 V (450 V) max(P.sub.tot) in high- 3.00 kW (270 V) 3.00 kW (270 V) 2.80 kW (270 V) load operation 3.34 kW (350 V) 3.33 kW (350 V) 3.10 kW (350 V) 3.80 kW (450 V) 3.80 kW (450 V) 3.48 kW (450 V) Highest relative — 0.0% (270 V) 0.0% (270 V) increase in P.sub.tot 0.0% (350 V) 0.0% (350 V) compared to SVM 0.0% (450 V) 0.0% (450 V) Highest relative — 29.5% (270 V) 19.1% (270 V) reduction in P.sub.tot 32.4% (350 V) 21.0% (350 V) compared to SVM 35.4% (450 V) 23.0% (450 V)

[0062] As can be seen in table 2, through increasing the carrier frequency when GDPWM is used, a reduction in the maximum peak-to-peak values of the DC link voltage can be achieved both in continuous load and in high-load operation, as can a reduction in the maximum total losses max(Ptot). This reduction in the maximum peak-to-peak values advantageously provides scope for reducing the DC link capacitance by, in the present case, 8.4%, which in effect enables a saving in cost and space.

[0063] FIGS. 6 and 7 each show, in a torque-rotation speed diagram, the boundaries of first operating regions, represented by lines 38 to 42, with further exemplary embodiments for a carrier frequency of 10 kHz when SVM is used and a different carrier frequency when GDPMW is used, compared to the boundaries of first operating regions, represented by lines 44, in the first exemplary embodiment in which the carrier frequency for GDPWM is also 10 kHz. Lines 38 relate here to a carrier frequency of 6 kHz, lines 39 to a carrier frequency of 8 kHz, lines 40 to a carrier frequency of 11 kHz, lines 41 to a carrier frequency of 12 kHz, and line 42 to a carrier frequency of 13 kHz. It can be seen that when GDPWM is used the first operating regions become smaller as the carrier frequency rises.

[0064] The choice of the carrier frequency when GDPWM is used affects the global maximum of the peak-to-peak value of the DC link voltage, and thereby the possible reduction in the DC link capacitance, the maximum total losses and the efficiency at partial load. It can be stated generally that, when the carrier frequency rises while using GDPWM, the global maximum of the peak-to-peak value of the DC link voltage falls, which permits a reduction in the DC link capacitance.

[0065] FIG. 8 shows in this connection a diagram of the possible percentage reduction of the DC link capacitance against the carrier frequency of the second modulation type with a constant carrier frequency of the first modulation type with reference to a line 49. For comparison, a line 50 is furthermore drawn, showing the maximum possible reduction in the DC link capacitance with the exclusive use of GDPWM, as compared with the exclusive use of SVM.

[0066] FIG. 9 finally shows a diagram of the maximum percentage reduction of the total losses against the carrier frequency of the second modulation type with a constant carrier frequency of the first modulation type. Here, a line 51 shows the maximum relative reduction in the total losses at a DC link voltage of 270 V, a line 52 shows the maximum relative reduction of the total losses at a DC link voltage of 350 V, and a line 53 shows the maximum relative reduction in the total losses at a DC link voltage of 450 V.

[0067] FIGS. 10 and 11 are each a torque-rotation speed diagram on which operating regions for an assembly 1 according to FIG. 1 with further exemplary embodiments of the control device 8 have been drawn. FIGS. 10 and 11 here show qualitatively the assembly of first operating regions 21, 30 and second operating regions 32, 32a, 32b. These exemplary embodiments can be implemented particularly easily, and enable, at least in sections, similarly advantageous effects to the more complex exemplary embodiments described previously.

[0068] In the first exemplary embodiment according to FIG. 10, the first operating region 21 for positive torques, independently of the rotation speed, is only limited by the lower torque boundary 22 and the upper torque boundary 23. The further first operating region 30 for negative torques is also, independently of the rotation speed, limited by a lower torque boundary 22a and an upper torque boundary 23a.

[0069] In the first exemplary embodiment according to FIG. 11, the first operating region 21 for positive torques is limited by the lower torque boundary 22 and the upper torque boundary 23 as well as by the lower torque boundary 24 and the upper torque boundary 25. The first operating region 30 for negative torques is limited by the lower torque boundary 22a and the upper torque boundary 23a as well as by the lower torque boundary 24a and the upper torque boundary 25a.

[0070] According to further exemplary embodiments which in other respects correspond to one of the exemplary embodiments described previously, the control device 8 can alternatively be configured, as an alternative to using a characteristic map, to ascertain the modulation type to be used on the basis of a function that evaluates the at least one operating parameter.