Method for controlling an inverter

Abstract

The invention relates to a method for controlling an inverter which is electrically connected to an electric motor, having the following steps: defining a modulated voltage (S1) for the inverter, said voltage being based on a first switching frequency, for operating the electric motor with a current, wherein the current has an electric frequency; determining the electric frequency (S2); changing the first switching frequency (S4) on which the modulated voltage is based to a second switching frequency if a value pair consisting of electric frequency and first switching frequency, or a value pair consisting of electric frequency and a sideband of the first switching frequency, is within at least one defined disturbance range (S3).

Claims

1. A method for controlling an inverter that is electrically connected to an electric motor, the method comprising the steps: stipulating a modulated voltage (S1), based on a first switching frequency, for the inverter in order to operate the electric motor using a current, wherein the current has an electrical frequency; determining the electrical frequency (S2); and changing the first switching frequency (S4), on which the modulated voltage is based, to a second switching frequency when a value pair comprising electrical frequency and first switching frequency or a value pair comprising electrical frequency and a sideband of the first switching frequency lies within at least one defined interference range (S3).

2. The method as claimed in claim 1, wherein the sideband comprises all the value pairs comprising electrical frequency and first switching frequency that satisfy formula 1: $f_{\mathrm{WPM},}\left(f_{\mathrm{el}}\right)=\left(f_{\mathrm{WPM},0}\pm k_{1^{*}}{f}_{\mathrm{el}},k_1▯N\right).$

3. The method as claimed in claim 1, wherein the defined interference range is formed by virtue of an integer multiple of the electrical frequency being equal to the first switching frequency.

4. The method as claimed in claim 1, wherein the defined interference range is stipulated by formula 2: $\begin{array}{cc}{f}_{\mathrm{WPM}}={\left(k_2\pm \Delta \right)}^{*}{f}_{\mathrm{el}}& k_2▯N.\end{array}$

5. The method as claimed in claim 1, wherein the interference range is defined by stored value pairs comprising electrical frequency and first switching frequency.

6. The method as claimed in claim 1, wherein the first switching frequency is changed to the second switching frequency when a sensor signal from a component of a unit to which the inverter is assigned leaves a certain target value range or reaches a critical value range.

7. The method as claimed in claim 1, wherein the first switching frequency is changed to the second switching frequency when, on the basis of present driving states of a vehicle to which the inverter is assigned, it is expected through predictive calculations that the value pair comprising electrical frequency and first switching frequency or the value pair comprising electrical frequency and a sideband of the first switching frequency will lie within an interference range.

8. The method as claimed in claim 1, wherein the second switching frequency is derived, in accordance with a rule, from the value pair comprising the first switching frequency and the electrical frequency.

9. The method as claimed in claim 8, wherein, before the first switching frequency is changed, a check is performed to determine whether the value pair comprising electrical frequency and second switching frequency or the value pair comprising electrical frequency and a sideband of the first switching frequency lies within an interference range.

10. The method as claimed in claim 1, wherein the second switching frequency is determined from the first switching frequency by increasing or decreasing the first switching frequency by a predefined value.

11. The method as claimed in claim 1, wherein the second switching frequency is selected depending on a change in successive different switching frequencies over time.

12. A non-transitory, computer-readable storage medium comprising commands that, during execution by a computer, cause the latter to control an inverter that is electrically connected to an electric motor by: stipulating a modulated voltage (S1), based on a first switching frequency, for the inverter in order to operate the electric motor using a current, wherein the current has an electrical frequency; determining the electrical frequency (S2); and changing the first switching frequency (S4), on which the modulated voltage is based, to a second switching frequency when a value pair comprising electrical frequency and first switching frequency or a value pair comprising electrical frequency and a sideband of the first switching frequency lies within at least one defined interference range (S3).

13. A control unit (31) for controlling an inverter (37) that is electrically connected to an electric motor (38), wherein the control unit (31) has a voltage modulator (32) that is configured to provide a modulated voltage for the inverter (37), by means of a first switching frequency, for operating the electric motor (38) using a current that has an electrical frequency; has a computing unit (33) for determining the electrical frequency; and has a changeover switch (34), wherein the changeover switch (34) is configured to change the first switching frequency for the voltage modulator (32) to a second switching frequency when the value pair comprising electrical frequency and first switching frequency lies within at least one defined interference range.

14. A vehicle having an electric motor (38), an inverter (37) for operating the electric motor (38) that is electrically connected to the electric motor, and a control unit (31) for controlling the inverter (37), wherein the control unit (31) has a voltage modulator (32) that is configured to provide a modulated voltage for the inverter (37), by means of a first switching frequency, for operating the electric motor (38) using a current that has an electrical frequency; a computing unit (33) for determining the electrical frequency; and a changeover switch (34), wherein the changeover switch (34) is configured to change the first switching frequency for the voltage modulator (32) to a second switching frequency when the value pair comprising electrical frequency and first switching frequency lies within at least one defined interference range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are depicted in FIGS. 1 and 2 and are explained in more detail below. In the figures:

(2) FIG. 1a shows an example of a sideband overlapping an interference range;

(3) FIG. 1b shows an example of the switching frequency changing when a sideband reaches an interference range;

(4) FIG. 2 shows different interference ranges;

(5) FIG. 3 shows the sequence of a method; and

(6) FIG. 4 shows a vehicle having an electric motor and an inverter.

DETAILED DESCRIPTION

(7) FIG. 1a shows, based on the switching frequency when the value of the electrical frequency is zero 11, how the sidebands 10 shown diverge and overlap the interference range 12. The interference range can be a natural frequency band of an electric drivetrain, for example. In this case, the switching frequency ωfs is plotted against the electrical frequency ωel. The characteristic of the sidebands can be described by formula 1: f.sub.WPM,(f.sub.el)=(f.sub.WPM, 0±k.sub.1*f.sub.el, k.sub.1N). In said formula, f.sub.WPM,(f.sub.el) is the value pair comprising electrical frequency f.sub.el and switching frequency f.sub.WPM that lies on the straight line described by: f.sub.WPM, 0±k.sub.1*f.sub.el. Here, f.sub.WPM, 0 is the switching frequency 11 itself and k1 is a whole number k.sub.1N.

(8) FIG. 1b shows how the switching frequency f.sub.WPM, 0 14 can be varied in order to prevent the sidebands from overlapping the interference range. As can be seen, the switching frequency can be increased, which results in a family of curves 15 above the interference range 13, or also decreased, as can be seen in the family of curves 16. When the relevant sidebands 17 of the original switching frequency 14 have left the interference range 13, it is possible to return to the original switching frequency 14 again.

(9) This method can therefore be used to avoid interference in the form of oscillations or sound emissions, for example, or even electrical interference that is caused by the electrical frequencies or switching frequencies.

(10) In addition to the constant interference range 21 that is in the form of a band and known from FIG. 1, FIG. 2 also shows an interference range 22 that increases in a manner proportional to the electrical frequency and defines an angle. This interference range can be described by formula 2:

(11) $\begin{array}{cc}{f}_{\mathrm{WPM}}={\left(k_2\pm \Delta \right)}^{*}{f}_{\mathrm{el}}& k_2▯N.\end{array}$

(12) The factor k.sub.2N represents a natural number and the Δ forms the angle of the interference range. Interference ranges of this kind can arise from vibratory systems with a multiple of a fundamental frequency, for example.

(13) FIG. 3 shows the sequence of the method. In step S1, a modulated voltage, based on a first switching frequency, for the inverter is stipulated that is used to operate the electric motor using a current that has an electrical frequency.

(14) In step S2 the electrical frequency of the current of the electric motor is determined.

(15) In S3 a check is performed to determine whether the value pair comprising electrical frequency and first switching frequency or the value pair comprising electrical frequency and a sideband of the first switching frequency lies within at least one defined interference range.

(16) If the check in S3 is true, in step S4 the first switching frequency, on which the modulated voltage was previously based, is changed to a second switching frequency. Otherwise, the first switching frequency remains the same. In both cases the method can start again at S1.

(17) FIG. 4 shows a vehicle 30 having an electric motor 38 and an inverter 37 for operating the electric motor 38 that is electrically connected to the electric motor 38. The vehicle 30 also contains a control unit 31 for controlling the inverter 37. The control unit 31 has a voltage modulator 32 that is configured to provide a modulated voltage for the inverter 37, by means of a first switching frequency, for operating the electric motor 38 using a current with an electrical frequency.

(18) Furthermore, the control unit 31 has a computing unit 33 for determining the electrical frequency. A changeover switch 34 of the control unit 31 is configured to change the first switching frequency for the voltage modulator 32 to a second switching frequency when the value pair comprising electrical frequency and first switching frequency lies within at least one defined interference range.