Control device, inverter, apparatus with inverter and electric machine, method for operating an inverter, and computer program

Abstract

To provide an inverter in which an installation space, a weight, and a cost of an intermediate circuit capacitor, are reduced.SOLUTION: In an apparatus 1, a control device 8 for an inverter 2 that supplies a power to an electric machine 3 provides a carrier frequency for making a pulse duration modulation switching signal 15 operate a switching element 12 of the inverter 2. The control device 8 acquires voltage information 17 for writing a DC side voltage of the inverter 2, and determines the carrier frequency in accordance with the voltage information 17 so that the carrier frequency is increased as reduced the DC side voltage during an operation mode of at least control device 8 in a voltage interval of at least the DC side voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a control device for an inverter supplying an electric machine, the control device being arranged to provide a pulse width modulated switching signal at a carrier frequency for operating switching elements of the inverter.

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

[0003] Due to the growing importance of electrically powered vehicles, inverters and associated control devices for such applications have become the focus of industry development efforts. Such control devices are known and provide a constant carrier frequency pulse width modulated switching signal to operate the switching elements of the inverter. Summary of the Invention

[0004] An important element of the inverter is its intermediate circuit capacitor. It must provide an intermediate circuit voltage that is as constant as possible. The high-frequency switching operation of the switching elements causes high-frequency currents, which ideally flow through the intermediate circuit capacitor while the DC voltage source provides a current that is generally DC. The intermediate circuit capacitor therefore acts as a filter. However, the high-frequency capacitor currents generate high-frequency ripple voltages in the intermediate circuit capacitor. The higher the capacitance of the intermediate circuit capacitor and the lower the internal resistance of the intermediate circuit capacitor, the lower the ripple voltage. However, if the capacitance is increased, the space required for the intermediate circuit capacitor, its weight and manufacturing costs increase. This results in undesirably high costs, especially for use in the field of electromobility.

[0005] The present invention therefore addresses the problem of identifying more economical possibilities for realizing an inverter, in which in particular the installation space, weight and costs of the intermediate circuit capacitors are reduced.

[0006] According to the invention, this problem is solved in that a control device of the type mentioned in the introduction is designed to obtain voltage information describing the DC-side voltage of the inverter and to determine the carrier frequency as a function of the voltage information in such a way that, at least within the voltage interval of the DC-side voltage and at least during the operating mode of the control device, the carrier frequency increases with a decrease in the DC-side voltage.

[0007] The invention is based on the discovery that the peak-valley values ​​of the ripple voltage on the intermediate circuit capacitor of the inverter are determined to a very significant extent by the DC-side voltage and the carrier frequency of the pulse-width modulated switching signal. It has been found that, on the one hand, higher peak-valley values ​​of the ripple voltage occur at low DC-side voltages than at higher DC-side voltages due to the change in modulation index of the pulse-width modulation, and, on the other hand, lower peak-valley values ​​of the ripple voltage occur with an increase in the carrier frequency. The control device according to the invention is therefore designed to prescribe a higher carrier frequency with a decrease in the DC-side voltage, for example in the case of an advanced discharge of the battery supplying the inverter, thereby counteracting the increase in the peak-valley values ​​of the ripple voltage.

[0008] Therefore, when using the control device according to the invention, it is no longer necessary to design the capacitance of the intermediate circuit capacitor of the inverter for the occurrence of high peak-valley values ​​of the intermediate circuit voltage at low intermediate circuit voltages, resulting in the use of more space-saving, lighter and cheaper intermediate circuit capacitors compared to the use of conventional control devices, which advantageously allows for a more economical realization of the inverter.

[0009] It should be noted that in this situation, an increase in the carrier frequency indeed leads to an increase in the switching losses of the switching elements. However, these switching losses decrease again with a decrease in the DC-side voltage. Furthermore, the change in the DC-side voltage and the carrier frequency has only a small effect on the conduction losses in the inverter. Thus, at least in the case of practically relevant operations, as a result of the increase in the carrier frequency with a decrease in the DC-side voltage provided according to the invention, it is possible to achieve a reduction in the peak-to-valley value of the intermediate circuit voltage, without thereby increasing the overall losses, consisting of switching losses and conduction losses, beyond the values ​​occurring at the maximum intended DC-side voltage.

[0010] The control device according to the invention is preferably designed to determine the carrier frequency to a constant base frequency above the upper voltage range during the operating mode, so that the base frequency can be specified for a high DC side voltage until the voltage range falls below the upper voltage range, and the carrier frequency can be increased only after the voltage range falls below the upper voltage range.

[0011] Alternatively or additionally, the control device according to the present invention may be designed to determine the carrier frequency during the operating mode to a constant maximum frequency below the lower limit of the voltage range. As a result, a maximum frequency can be specified for low DC side voltages after the voltage range falls below the lower limit of the voltage range. This prevents the carrier frequency from reaching an undesirably high level at very low DC side voltages.

[0012] Of course, it is also contemplated that the voltage interval can cover a range from zero volts to the maximum intended DC side voltage.

[0013] To allow a particularly economical implementation of the control device according to the invention, the latter may preferably be designed to select the carrier frequency from a characteristic map which assigns carrier frequency values ​​to values ​​of the DC-side voltage. The characteristic map may for example be provided by means of a look-up table. Typically, the control device has a memory unit in which the characteristic map is stored.

[0014] It may be provided that the characteristic map describes an at least partially linear relationship between values ​​of the DC side voltage and values ​​of the carrier frequency. Alternatively, it is possible to design the characteristic map to be defined by reduced values ​​of the DC side voltage and the control device to determine the carrier frequency by partially linear interpolation of the carrier frequencies associated with the reduced values.

[0015] As an alternative to the use of characteristic maps, the control device according to the invention may also be designed to determine the carrier frequency by means of analytical calculation rules which make it possible to determine the carrier frequency depending on the DC side voltage.

[0016] The characteristic maps or calculation rules may, for example, be determined by measurements or simulations for a specific configuration of the inverter and the electric machine.

[0017] Advantageously, the control device according to the invention is designed to assume a second operating mode describing a part-load operation different from the first operating mode depending on operating point information describing an operating point defined by the speed and torque of the electric machine, and to set the carrier frequency in the second operating mode either invariably or depending on the operating point. In this way, it is possible to prevent the part-load efficiency of the inverter or the electric machine from decreasing at low DC-side voltages.

[0018] As a general rule, the carrier frequency may be determined in the first operating mode as a function of the operating point.

[0019] The control device according to the invention may be designed to determine an updated carrier frequency when updated voltage information is received and / or after a predetermined or predeterminable period of time has elapsed and / or after an electrical period of the electric machine has been completed and / or after a period of the switching signal has been completed. In this way, the carrier frequency can be adapted to the DC side voltage at the appropriate time.

[0020] The DC side voltage may be the intermediate circuit voltage or the output voltage of a direct current voltage source, in particular a battery, which supplies the inverter.

[0021] The control device may in general principle be equipped with a measuring device designed to detect the DC side voltage and provide voltage information, but preferably the control device has an input by which voltage information can be made available from an external measuring device.

[0022] The problem addressed by the invention is further solved by an inverter comprising an intermediate circuit capacitor, switching elements interconnected to convert a voltage applied to the intermediate circuit capacitor into a single-phase or multi-phase alternating voltage depending on switching signals that actuate the switching elements, and a control device according to the invention.

[0023] The intermediate circuit capacitor may be formed by a single capacitor element or by a number of capacitor elements interconnected in parallel and / or in series.

[0024] The inverter may also include an analog-to-digital converter designed to convert the analog measurement signal into digital voltage information.

[0025] The problem addressed by the invention is also solved by an arrangement comprising an inverter according to the invention and an electric machine operable with an alternating voltage.

[0026] Preferably, the carrier frequency is determined during operation of the device so as to satisfy the following relationship:

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[0027] The problem addressed by the present invention is further solved by a method of operating an inverter to power an electric machine, the method comprising the following steps executed by a control device: obtaining voltage information describing a DC side voltage of the inverter; determining a carrier frequency of a pulse width modulated switching signal for operating the inverter in response to the voltage information such that the carrier frequency increases with decreasing DC side voltage; and providing switching signals to switching elements of the inverter.

[0028] The method according to the present invention may also include the following steps: checking whether the DC side voltage is within the voltage interval, and then determining the carrier frequency according to the voltage information if the DC side voltage is within the voltage interval. If the DC side voltage is above the upper limit of the voltage interval, the carrier frequency can be determined to a constant base frequency. Alternatively or additionally, if the DC side voltage is below the lower limit of the voltage interval, the carrier frequency can be determined to a constant maximum frequency.

[0029] The method according to the invention may also comprise the following steps: obtaining operating point information describing an operating point defined by a speed and a torque of the electric machine and checking whether the operating point describes a part-load operation of the electric machine. It may be provided that in the absence of a part-load operation, a first operating mode is assumed which comprises determining a carrier frequency as a function of the voltage information and / or in the presence of a part-load operation, a second operating mode is assumed in which the carrier frequency is fixedly specified or is determined as a function of the operating point.

[0030] Finally, the problem addressed by the present invention is further solved by a computer program comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to the invention executed by a control device.

[0031] All the descriptions relating to the control device according to the invention, the inverter according to the invention and the apparatus according to the invention can likewise be converted into 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.

[0032] Further advantages and details of the invention will become apparent from the exemplary embodiments described hereinafter and on the basis of the drawings, which are schematic representations. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a block diagram of an exemplary embodiment of an apparatus according to the invention, together with an exemplary embodiment of an inverter according to the invention and an exemplary embodiment of a control device according to the invention. [Diagram 2] Figure 2 is a graph of carrier frequency versus DC side voltage. [Diagram 3] FIG. 3 is a graph of the peak-valley value of the intermediate circuit voltage versus speed in a prior art device. [Figure 4]FIG. 4 is a graph of peak-to-valley intermediate circuit voltage against speed for the exemplary form of the apparatus shown in FIG. 1, at the carrier frequency shown in FIG. 2; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] 1 is a block diagram of an exemplary embodiment of an apparatus 1, designed to drive a vehicle capable of partial or full electric drive, including an exemplary embodiment of an inverter 2 and an electric machine 3. The apparatus 1 further comprises a direct current voltage source 4, in this case formed as a high-voltage battery.

[0035] The inverter 2 comprises a filter device 5, in this case formed as an EMC filter, an intermediate circuit capacitor 6, a power supply 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, which is represented by two blocks for clarity.

[0036] The power supply unit 7 comprises a number of switching elements 12, which are formed as semiconductor switching elements, for example IGBTs or power MOSFETs. The switching elements 12 are connected in pairs to form a half-bridge. A driver 14 is connected upstream of a control input 13 of each switching element 12. For the sake of clarity, only one switching element 12 and one driver 14 are labeled with reference numbers. The driver 14 receives a pulse-width modulated switching signal 15 from the control device 8. The pulse-width modulated switching signal 15 is provided such that the voltage for supplying the electric machine 3 is supplied to the corresponding tap of the half-bridge. The power supply unit 7 thus converts the intermediate circuit voltage 16, which is smoothed by the intermediate circuit capacitor 6, into an alternating voltage, in this case a three-phase alternating voltage, depending on the switching signal 15.

[0037] The first measuring device 9 is designed to detect the intermediate circuit voltage as the DC side voltage of the inverter 2 and to provide an analog measurement signal to the analog-digital conversion device 11. This converts the analog measurement signal into digital voltage information 17. The second measuring device 10 is accordingly designed to detect the phase currents and to provide a measurement signal to the analog-digital conversion device 11. The analog-digital conversion device 11 converts the analog measurement signal of the second measuring device 10 into digital current information 18. Finally, the third measuring device 10a is designed to detect the speed of the electric machine 3 and to provide a measurement signal to the analog-digital conversion device 11. The analog-digital conversion device 11 converts the analog measurement signal of the third measuring device 10a into digital speed information 18a. The control device 8 receives the voltage information 17, the current information 18 and the speed information 18a on the input side.

[0038] Using the current information 18 and the speed information 18a, the control device 8 determines operating point information describing an operating point defined by the speed and torque of the electric machine 3. If it can be concluded from the operating point that the electric machine 3 is not operating at part load operation, the control device 8 assumes a first operating mode. On the other hand, if the operating point information indicates that the electric machine is in part load operation, the control device 8 assumes a second operating mode, in which case the carrier frequency of the pulse width modulation is fixedly specified or otherwise determined depending on the operating point.

[0039] The control device 8 is designed to determine the carrier frequency of the pulse width modulated switching signal 15 in the first operating mode as a function of the voltage information 17, such that the carrier frequency increases with a decrease in the DC-side voltage. For this purpose, the control device 8 comprises a memory unit 19, in which a characteristic map is stored which associates carrier frequency values ​​with values ​​of the DC-side voltage.

[0040] Figure 2 shows the DC side voltage U in for carrier frequency f PWM1 is a graph of a characteristic map describing a piecewise linear relationship between the value of the DC side voltage and the value of the carrier frequency.

[0041] For a maximum DC side voltage 20, a fundamental frequency 21 is specified in the first operating mode. in However, if the DC voltage source 4 is discharged, for example, and the voltage drops to the upper limit 22 of the voltage section 23, the DC side voltage U in The characteristic map for decreasing values ​​of the carrier frequency f PWM The DC side voltage U in falls below the lower limit 24, the characteristic map provides a constant maximum frequency 25 as the carrier frequency.

[0042] In the voltage section 23, the characteristic map corresponds to the following relationship during operation of the device 1:

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[0043] The control device 8 is designed to update the carrier frequency periodically, for example upon receipt of updated voltage information, after a predetermined or predeterminable period of time, after completion of an electrical period of the electric machine 3 or after completion of a period of the corresponding switching signal 15. Combinations of the above mentioned update events are also possible.

[0044] According to a further exemplary embodiment of the control device 8, the characteristic map is defined by discrete values ​​of the DC-side voltage, and the control device 8 is designed to determine the carrier frequency by linear interpolation of the carrier frequency values ​​associated with the discrete values. According to a further exemplary embodiment, instead of using the characteristic map, the control device 8 is designed to determine the carrier frequency by analytical calculation rules, which allow the carrier frequency to be determined as a function of the DC-side voltage. Finally, according to a further exemplary embodiment, it is provided that the output voltage 16a of the direct current voltage source 4 is used as the DC-side voltage. In this case, instead of the first measuring device 9, a first measuring device 9a is provided which provides a corresponding measuring signal of the analog-to-digital conversion device 11. According to a further exemplary embodiment, the torque as part of the operating point information is not determined on the basis of the current information 18, but is estimated by the control device 8 within the scope of the control system which determines the switching signal 15.

[0045] In the following, the functioning of the device 1 will be described in more detail on the basis of an exemplary embodiment.

[0046] For this purpose, first, FIG. 3 shows the speed f rot Peak and valley values ​​of intermediate circuit voltage u DC,pp Figure 3 shows the peak-valley value u when the intermediate circuit voltage is 270V, where the carrier frequency is always set to a constant 10kHz. DC,pp The curve 26 and the peak-valley value u when the intermediate circuit voltage is 350V DC,pp The curve 27 and the peak-valley value u when the intermediate circuit voltage is 450V DC,pp 2 and a curve 28.

[0047] Approximately 4000 min before the electric machine goes into field weakening operation or goes into power limiting at maximum torque -1 It can be seen that the peak-valley value at speeds around 1000 rpm is highest at a low intermediate circuit voltage of 270 V and lowest at an intermediate circuit voltage of 450 V. This means that the capacitance of the intermediate circuit capacitors must be adapted to the maximum of curve 26.

[0048] The following table 1 shows the different intermediate circuit voltages U DC and carrier frequency f PWM = 10 kHz, the maximum peak-to-valley value of the voltage applied to the intermediate circuit capacitor 6 of the prior art device u DC,pp,max and the maximum value of the inverter switching loss P S,max and the maximum value of the inverter line loss P L,max and the maximum value of the overall loss of the inverter P L,max This shows that: [Table 1]

[0049] FIG. 4 shows the speed f of an exemplary embodiment of the device 1 with a variably predefined carrier frequency. rot Peak and valley values ​​of intermediate circuit voltage u DC,pp Figure 4 shows the peak-valley value u when the intermediate circuit voltage is 270V. DC,pp The curve 29 and the peak-valley value u when the intermediate circuit voltage is 350V DC,pp The curve 30 and the peak-valley value u when the intermediate circuit voltage is 450V DC,pp The curves 31 and 32 are shown.

[0050] Approximately 4000 minutes -1It can be seen that the maxima of curves 29, 30, 31 at speeds around 1000 Hz are essentially adapted to the level of curve 28 in figure 3. This means that the intermediate circuit capacitor 6 can be chosen to have a much lower capacitance than when using a constant carrier frequency.

[0051] The following Table 2 shows the relationship between the different intermediate circuit voltages U according to an exemplary embodiment. DC and the maximum peak-valley value u of the voltage applied to the intermediate circuit capacitor 6 of the device 1 for the adapted carrier frequency. DC,pp,max and the maximum value of the inverter switching loss P S,max and the maximum value of the inverter line loss P L,max and the maximum value of the overall loss of the inverter P tot,max This shows that: [Table 2]

[0052] As can be seen from a comparison of Tables 1 and 2, the lower the intermediate circuit voltage, the more advantageously the use of a higher carrier frequency can be achieved with the highest possible intermediate circuit voltage U DC = 450V. [Explanation of symbols]

[0053] 2 Inverter 3. Electrical machinery 4 DC voltage source 6 Intermediate circuit capacitor 8 Control Devices 12 Switching elements 15 Pulse Width Modulated Switching Signals 16 Intermediate circuit voltage 16a Output voltage 17 Digital voltage information 22 upper limit 23 Voltage Section 24 lower limit

Claims

1. A control device (8) for an inverter (2) supplying an electric machine (3), the control device (8) being designed to provide a pulse width modulated switching signal (15) at a carrier frequency for operating switching elements (12) of the inverter (2), The control device (8) assuming a first operating mode and a second operating mode different from the first operating mode and describing a part load operation in response to operating point information describing an operating point defined by a speed and a torque of the electric machine (3); obtaining voltage information (17) describing a DC side voltage of the inverter (2); In the first operation mode, the carrier frequency is determined according to the voltage information (17) such that the carrier frequency increases as the DC side voltage decreases, at least within a voltage section (23) of the DC side voltage; In the second operation mode, the carrier frequency is specified to be invariant or is determined depending on the operation point. A control device, characterized in that it is designed to

2. During the operational mode, the carrier frequency is above the upper limit (22) of said voltage interval (23), at a constant fundamental frequency (21); and / or Below the lower limit (24) of the voltage section (23), a constant maximum frequency (25) is The control device of claim 1 , adapted to determine

3. 3. A control device according to claim 1 or 2, which is designed to select the carrier frequency from a characteristic map which associates carrier frequency values ​​with values ​​of the DC-side voltage.

4. the characteristic map describes an at least partially linear relationship between the value of the DC side voltage and the value of the carrier frequency, or 4. The control device according to claim 3, wherein the characteristic map is defined by discrete values ​​of the DC-side voltage, and the control device (8) is designed to determine the carrier frequency by piecewise linear interpolation of the carrier frequency values ​​associated with the discrete values.

5. 3. The control device according to claim 1 or 2, which is designed to determine the carrier frequency by analytical calculation rules that allow to determine the carrier frequency depending on the DC side voltage.

6. When updated voltage information (17) is received, and / or after a predetermined or predeterminable period of time has elapsed, and / or After an electrical cycle of the electric machine (3) is completed, and / or After a period of the switching signal (15) is completed, A control device according to any one of claims 1 to 5, designed to determine an updated carrier frequency.

7. 7. The control device according to claim 1, wherein the DC side voltage is an intermediate circuit voltage (16) or an output voltage (16a) of a direct current voltage source (4) supplying the inverter (2).

8. An inverter (2), An intermediate circuit capacitor (6); switching elements (12) interconnected to convert a voltage applied to the intermediate circuit capacitor (6) into a single-phase or multi-phase AC voltage in response to a switching signal (15) that operates the switching elements (12); A control device (8) according to any one of claims 1 to 7, An inverter comprising:

9. 9. An apparatus (1) comprising an inverter (2) according to claim 8 and an electric machine (3) operable with said alternating voltage.

10. The carrier frequency is determined during operation of the device according to the following relationship: [0010] Fulfilling Where: [0025] is the carrier frequency f PWM,n Describe the peak and valley values ​​of the voltage applied to the intermediate circuit capacitor (6) when (n=1, 2), f PWM,1 describes a first carrier frequency, f PWM,2 The apparatus of claim 9 , wherein: describes a second carrier frequency.

11. A method of operating an inverter (2) for powering an electric machine (3), comprising the steps of: The following steps are carried out by a control device (8): obtaining operating point information describing an operating point defined by a speed and a torque of the electric machine; determining whether the operating point describes part load operation of the electric machine; obtaining voltage information (17) describing a DC side voltage of the inverter (2); determining a carrier frequency of a pulse width modulated switching signal (15) for operating the inverter (2) in a first operating mode, which is assumed when there is no partial load operation, in response to the voltage information (17) such that the carrier frequency increases with a decrease in DC side voltage; In a second operating mode, which is assumed when a partial load operation is present, the carrier frequency is fixed or determined depending on the operating point; providing said switching signal (15) to a switching element (12) of said inverter (2); The method comprises:

12. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to claim 11, which are carried out by the control device (8).

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