How to Control a Power Converter with Variable Switching Frequency

Abstract

The present invention relates to a method for controlling a power converter (I) having at least one switching cell (2) and a control unit (1) for controlling the at least one switching cell (2) with a switching frequency (fs) to deliver an output signal, by periodically adjusting (S1) the switching frequency (fs) via the control unit (1) to vary the switching frequency (fs) within a period (T) of the output signal (Sout), the switching frequency (fs) being selected from a set (11) of at least two switching frequencies.

Description

[Technical Field]

[0001] The present invention relates to the field of electrical systems that use electrical power to control the power supply of electrical devices mounted on automobiles, in particular electric vehicles (EVs), hybrid vehicles (HVs), etc. Such electrical systems are designed as power converters.

[0002] More particularly, the present invention relates to a method for controlling a power converter using a variable switching frequency. [Background technology]

[0003] As is known, an electric or hybrid vehicle includes an electric drive system that includes an electric motor and other electrical devices, such as a power converter, that must be supplied by either a high-voltage or low-voltage power source. In this context, a power converter is configured to convert an input voltage into an output voltage. For example, an inverter converts a direct current (DC) voltage from a high-voltage power supply battery into an alternating current (AC) voltage to power the electric motor and drive the vehicle.

[0004] Typically, such power converters comprise switching elements that are controlled by a control unit according to a switching pattern to achieve a desired voltage. For example, a conventional method of controlling the switching elements uses pulse width modulation (PWM) signals, where the switching frequency of the switching elements is kept constant and the time ratio between the open and closed states of each switching element, the so-called duty cycle, is variable.

[0005] When establishing a switching pattern, optimizing the switching losses and current ripple during the switching operation are important issues to address. Switching losses can cause heating of the power stage of the power converter, thereby shortening the lifespan of the power converter. Meanwhile, the switching pattern must comply with several constraints, especially the operating capacity of the switching elements and control unit, the allowable current ripple, and the acoustic and vibration requirements. Summary of the Invention [Problem to be solved by the invention]

[0006] In this regard, it is a primary object of the present invention to provide a method for controlling a power converter and a power converter that reduces switching losses and current ripple. [Means for solving the problem]

[0007] More precisely, the invention relates to a method for controlling a power converter having at least one switching cell and a control unit for controlling the at least one switching cell with a switching frequency to deliver an output signal, the method further comprising periodically adjusting the switching frequency via the control unit to vary the switching frequency within a period of the output signal, the switching signal being selected from a set of at least two switching frequencies.

[0008] The switching frequencies of the set of at least two switching frequencies are selected in a sorted manner, in particular such that the lower the switching frequency of the set of at least two switching frequencies, the higher the amplitude range corresponding to the output signal. In other words, the method according to the present invention advantageously allows adjusting the switching frequencies to lower the switching frequencies at the peaks and valleys of the output signal and to raise the switching frequencies near the zero crossings of the output signal. This provides the substantial benefit of reducing switching losses and / or current ripple in the switching elements, and thus enabling the lifetime of the inverter to be extended.

[0009] Furthermore, the method according to the invention allows for optimizing switching losses while facilitating the implementation of a switching pattern of the inverter that is adapted to the operating conditions of the control unit and the switching elements, for example, the invention allows for keeping the average switching frequency substantially constant over the period of the output signal and adapting to the operating conditions.

[0010] According to one embodiment, adjusting the switching frequency via the control unit is performed periodically, each switching frequency of the set of at least two switching frequencies having an associated preset time interval ti, and the control unit controls the at least one switching cell continuously at each switching frequency of the set of at least two switching frequencies for the associated preset time interval ti. This embodiment of the invention provides the advantage that the adjustment of the switching frequency is pre-arranged and therefore can be easily implemented via the control unit.

[0011] According to another embodiment, the method comprises: - periodically receiving an output signal by a control unit; - adjusting or maintaining the switching frequency via the control unit based on a comparison of a representative value of the output signal with at least one threshold value; It comprises successive steps.

[0012] This embodiment allows for effective monitoring of when it is appropriate to adjust the switching frequency.

[0013] Advantageously, the set of at least two switching frequencies comprises a first switching frequency and a second switching frequency, the first switching frequency being lower than the second switching frequency. Using two switching frequencies allows for a more limited number of switching frequency changes over a period of the output signal while reducing switching losses.

[0014] Advantageously, the at least one threshold value comprises a first threshold value, the method comprising: adjusting the switching frequency to a first switching frequency when the representative value is greater than or equal to a first threshold value; adjusting the switching frequency to a second switching frequency when the representative value is less than a first threshold value; This includes:

[0015] Advantageously, the set of at least two switching frequencies further comprises a third switching frequency, the second switching frequency being lower than the third switching frequency. It should be noted that the present invention is not limited to three switching frequencies, and more switching frequencies can be considered. The number of switching frequencies can be selected as a compromise between not having to change the switching frequency too frequently throughout one period of the output signal and reducing switching losses and / or current ripple.

[0016] Advantageously, the at least one threshold comprises a first threshold and a second threshold greater than the first threshold, and the method further comprises: adjusting the switching frequency to the first switching frequency when the representative value is greater than or equal to the second threshold value; adjusting the switching frequency to a second switching frequency when the representative value is greater than or equal to the first threshold value and less than a second threshold value; adjusting the switching frequency to a third switching frequency when the representative value is less than the first threshold value; Be prepared.

[0017] Advantageously, each of the set of at least two switching frequencies is a multiple of the fundamental frequency, which makes the method easy to implement, in particular by allowing simple and low-cost operations such as integer multiplication to be configured.

[0018] Advantageously, the first switching frequency is the same as the fundamental switching frequency, the second switching frequency is twice the fundamental switching frequency, and the third switching frequency is four times the fundamental switching frequency.

[0019] Advantageously, adjusting or maintaining the switching frequency via the control unit is performed periodically, preferably at a switching frequency intermediate a set of at least two switching frequencies.

[0020] Advantageously, the output signal is the output current of the power converter. The advantage of using the output current to adjust the switching frequency is that no additional means for measuring the output current are required, but the current setpoint is directly available.

[0021] Advantageously, the method comprises dynamically adjusting said at least one threshold via a regulator circuit of the power converter to maintain an average switching frequency of at least one switching cell substantially constant over said period of the output signal.

[0022] The invention also relates to a power converter comprising at least one switching cell and a control unit for controlling the at least one switching cell in accordance with any of the methods described above.

[0023] According to one aspect of the present invention, the power converter is an inverter that converts a DC voltage output from a high-voltage power supply battery into an AC voltage to drive an electric motor of an electric or hybrid vehicle. The AC voltage may be a polyphase AC voltage, in particular a three-phase voltage.

[0024] Advantageously, the at least one switching cell has three switching cells and supplies a three-phase AC voltage to the electric motor, and the power converter adjusts the switching frequency of each of the three switching cells independently of the other switching cells, thereby reducing switching losses in an optimized manner for each of the at least one switching cell.

[0025] Another aspect of the present invention is an electric drive device including an electric motor and the aforementioned inverter that converts a DC voltage to an AC voltage to drive the electric motor.

[0026] A further aspect of the invention is a vehicle comprising an electric drive for driving the vehicle, which may comprise a high voltage power supply battery, preferably a rechargeable battery, for supplying DC voltage to an inverter, if appropriate.

[0027] These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the accompanying drawings, which disclose preferred embodiments of the invention. [Brief explanation of the drawings]

[0028] The invention will be better understood by reading the following description and by referring to the accompanying drawings, given by way of non-limiting example, in which like objects have been given like references: [Figure 1] 1 is a circuit diagram showing an outline of an example of an inverter according to an embodiment of the present invention; [Figure 2] 3 is a flowchart of a first example of a method for controlling an inverter according to the present invention. [Figure 3] 5 is a flowchart of a second example of a method for controlling an inverter according to the present invention. [Figure 4] 3A and 3B are schematic diagrams illustrating an example of time intervals associated with an output signal and a switching frequency of an inverter according to an embodiment of the present invention; [Figure 5] 4 is a schematic diagram illustrating an example of time intervals associated with an output signal and a switching frequency of an inverter according to another embodiment of the present invention. [Figure 6] 1 is a circuit diagram showing an example of a control unit for an inverter according to the present invention; [Figure 7] 1 is a diagram illustrating a schematic of an electric or hybrid vehicle equipped with an inverter according to an aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Selected embodiments of the present invention will now be described with reference to the drawings. Those skilled in the art will appreciate from this disclosure that the following descriptions of embodiments of the present invention are provided for illustrative purposes only and are not intended to limit the invention, which is defined by the appended claims and equivalents thereof.

[0030] 7, one aspect of the present invention is an electric or hybrid electric vehicle EV comprising wheels and an electric drive unit configured to at least indirectly drive at least one wheel of the vehicle. The vehicle may also comprise a high-voltage power supply battery B, preferably a rechargeable battery, for powering the electric drive unit.

[0031] Another aspect of the invention is an electric drive device comprising an electric motor M and an inverter I for converting a direct current (DC) voltage from a high-voltage power supply battery B into an alternating current (AC) voltage for driving the electric motor M. The electric motor M may in particular be a three-phase electric motor. In this connection, the inverter I generates three output voltages with a phase shift of 120 degrees relative to each other.

[0032] A further aspect of the invention is an inverter I. The invention is not limited to the aforementioned applications but can be applied to power converters supplying an AC voltage from a power source to a load. The inverter I comprises in particular a power stage PW, an electromagnetic interference (EMI) filtering stage F, an intermediate circuit capacitor C and a dielectric forming a busbar.

[0033] FIG. 1 shows a schematic circuit diagram of an example of an inverter I according to the present invention. The inverter I comprises at least one switching cell 2 in a power stage, in particular three switching cells, and is controlled to provide a three-phase AC voltage for driving an electric motor M from a power source Vin. Each of the three switching cells is associated with one of the three phases. Each of the at least one switching cell 2 may be arranged, for example, in a half-bridge configuration with upper and lower switching elements K. The switching elements K may be, for example, IGBTs or MOSFETs.

[0034] The inverter I further comprises a control unit 1 for controlling at least one switching cell 2 at a switching frequency fs to transmit an output signal. In particular, at the switching frequency fs, the at least one switching cell 2 is preferably controlled using pulse width modulation (PWM), in which the time ratio between the open state and the closed state of each switching element, the so-called duty cycle, is variable. The PWM signal may be, for example, center-aligned. For this purpose, the inverter I may comprise a PWM generator 3.

[0035] According to one aspect of the invention, the invention relates to a method for controlling an inverter. The method according to this aspect of the invention comprises periodically adjusting a switching frequency fs via a control unit 1 and varying the switching frequency fs within a period T of an output signal Sout. The output signal Sout is preferably the output current, or the output voltage, or the output power of the inverter, or a combination thereof. The advantage of adjusting the switching frequency using the output current is that no additional means for measuring the output current are needed, and the current setpoint is directly available.

[0036] The switching frequency fs is further selected from a set 11 of at least two switching frequencies, the at least two sets 11 of switching frequencies being different from one another, in other words the switching frequency is selected from a discrete set of possible switching frequencies.

[0037] In particular, the switching frequencies are selected such that the lowest value of the set of at least two switching frequencies corresponds to a high amplitude range of the output signal and the highest value of the set of at least two switching frequencies corresponds to a low amplitude range of the output signal. The switching frequencies of the set of at least two switching frequencies are selected in a sorted manner such that the lower the switching frequency of the set of at least two switching frequencies, the higher the corresponding amplitude range of the output signal. Thus, the present invention makes it possible to adjust the switching frequency so that the switching frequency is lowered at the peaks and valleys of the output signal and the switching frequency is raised near the zero crossings of the output signal. This makes it possible to reduce switching losses and / or current ripple in the switching elements.

[0038] More precisely, by adjusting the switching frequency to match the peaks and valleys of the output current, switching losses can be optimized, and similarly, by adjusting the switching frequency to match the peaks and valleys of the output voltage, current ripple can be optimized.

[0039] Furthermore, the method according to the present invention can reduce switching losses while facilitating the implementation of inverter switching patterns that are compatible with the operating conditions of the control unit and the switching elements. For example, the set of at least two switching frequencies advantageously corresponds to the minimum and maximum allowable frequencies of the switching elements, respectively. Furthermore, the present invention allows the average switching frequency to be kept substantially constant over a period of the output signal to maintain the operating conditions. For example, the average switching frequency can be preset. The lowest frequency of the set of at least two switching frequencies can be equal to or less than the desired minimum average switching frequency. Similarly, the highest frequency of the set of at least two switching frequencies can be equal to or greater than the desired maximum average switching frequency.

[0040] In short, the present invention has the inherent advantage of being able to adjust the switching frequency between a discrete range of switching frequencies to optimize switching losses and current ripple, thereby extending the life of the inverter.

[0041] For example, the set 11 of at least two switching frequencies includes a first switching frequency fs1 and a second switching frequency fs2, where the first switching frequency fs1 is lower than the second switching frequency fs2. Using two switching frequencies can limit the number of times the switching frequency is changed over a period of the output signal while reducing switching losses.

[0042] In another preferred example, the set of at least two switching frequencies 11 includes the first switching frequency fs1 and the second switching frequency fs2 according to the above example, and further includes a third switching frequency fs3, where the second switching frequency fs2 is lower than the third switching frequency fs3. It should be noted that the present invention is not limited to three switching frequencies, and more switching frequencies can be considered. The number of switching frequencies can be selected based on a compromise between not having to change the switching frequency too frequently over a period of the output signal and reducing switching losses and / or current ripple.

[0043] Furthermore, each of the set of at least two switching frequencies 11 is preferably a multiple of the fundamental switching frequency fsb. This makes it possible to set simple and inexpensive operations such as integer multiplication, making the method easy to implement. In particular, the fundamental switching frequency is advantageously set according to hardware, acoustic, thermal and control speed constraints.

[0044] For example, the first switching frequency fs1 is equal to the basic switching frequency fsb, the second switching frequency fs2 is twice the basic switching frequency fsb, and the third switching frequency fs3 is four times the basic switching frequency fsb. For example, the first switching frequency, the second switching frequency, and the third switching frequency are 4 kHz, 8 kHz, and 16 kHz, respectively.

[0045] As another example, the first switching frequency fs1 is equal to the fundamental switching frequency fsb, the second switching frequency fs2 is twice the fundamental switching frequency fsb, and the third switching frequency fs3 is three times the fundamental switching frequency fsb.

[0046] Furthermore, the step S1 of adjusting the switching frequency fs of each of the three switching cells can be performed independently of the others of the three switching cells, thereby enabling an optimized reduction of switching losses for each of at least one switching cell, although the switching frequencies can be adjusted between the three switching cells, for example for task synchronization or noise and vibration management purposes.

[0047] According to one embodiment of the present invention, FIG. 4 illustrates a diagram of an output signal Sout and a time interval during which one of the at least one switching cell 2 is controlled at a corresponding switching frequency. Here, three switching frequencies are illustrated. According to this embodiment of the present invention, adjusting the switching frequency fs (S1) is periodically performed via the control unit 1. Each switching frequency of the set 11 of at least two switching frequencies has an associated preset time interval ti, and the control unit 1 is configured to continuously control the at least one switching cell 2 at each switching frequency for the associated preset time interval ti. In the example of FIG. 4, each switching frequency fs1, fs2, and fs3 has an associated preset time interval t1, t2, and t3, respectively. This embodiment of the present invention has the advantage that the adjustment of the switching frequency is preset and therefore easily implemented via the control unit 1.

[0048] According to another embodiment of the invention, the adjustment of the switching frequency is controlled in an event-driven manner, for example after each modulator cycle of the PWM generator 3 or after measuring the output signal, which allows to effectively monitor when an adjustment of the switching frequency is appropriate.

[0049] Figure 5 discloses a diagram of the output signal Sout and the time intervals during which one of the at least one switching cell 2 is controlled with the corresponding switching frequency according to this embodiment of the invention, where a special case with three switching frequencies is shown. Figure 6 discloses the control unit 1 according to this embodiment of the invention. Next, as shown in Figures 2 and 3, the method proceeds with the following sequence of operations: periodic reception S01 of an output signal Sout by the control unit 1; - adjusting S1 or maintaining S1' the switching frequency fs via the control unit 1 based on a comparison between the representative value RV of the output signal Sout and at least one threshold value 12; Equipped with.

[0050] Therefore, in this embodiment, the switching frequency is adjusted directly according to the output signal, allowing for further optimization of switching losses.

[0051] Next, the control unit may further comprise an S02 comparator 13 for comparing the representative value RV with at least one threshold value 12 to decide whether to adjust S1 or maintain S1' the current value of the switching frequency fs as shown in FIG. 6.

[0052] Advantageously, the decision to adjust S1 or maintain S1' the switching frequency fs is carried out periodically via the control unit 1, preferably at an intermediate switching frequency of the set of at least two switching frequencies, as needed.

[0053] Furthermore, the representative value RV compared with the at least one threshold value 12 can be, for example, the absolute value of the induced output current, i.e., the ratio of the absolute value of the phase current setpoint to the size of the current setpoint vector. Each of the at least one threshold value 12 can then be set equal to a predetermined percentage. However, other parameters can also be used as the representative value RV.

[0054] The method further includes dynamically adjusting the at least one threshold 12 via a regulator circuit 14 of the inverter, as shown in Figure 6. The at least one threshold 12 is preferably adjusted such that the average switching frequency fsa of the at least one switching cell 2 remains essentially constant over the period T of the output signal Sout. This means that the limit on the average switching frequency can be easily tightened.

[0055] It should be noted that by adjusting the at least one threshold 12, a wide range of values ​​of the average switching frequency can be obtained, particularly between the lowest and highest switching frequencies of the set of at least two switching frequencies.

[0056] The control unit 1 may further comprise a counter for each phase and a switching frequency controller. After each switching frequency adjustment step, the counter is incremented by the number of switching events during the time interval of the corresponding switching frequency. The number of switching events is then periodically checked by the switching frequency controller, and the suitability between the counted number of switching events and the desired average switching frequency is checked, and at least one threshold is adjusted accordingly to achieve the desired average switching frequency.

[0057] Furthermore, adjustment of the at least one threshold 12 can be performed for the entire power stage or for each switching cell independently of the other switching cells.

[0058] Figure 2 discloses a first example of a method according to the embodiment of the invention described above. In this example, the at least one threshold 12 comprises a first threshold A. The method then comprises: - adjusting the switching frequency fs to a first switching frequency fs1 when the typical value RV is equal to or greater than a first threshold value A S11; - adjusting the switching frequency fs to a second switching frequency fs2 when the typical value RV falls below a first threshold A S12; Includes:

[0059] 3 discloses a second example of a method according to the aforementioned embodiment of the present invention. In this example, the at least one threshold 12 comprises a first threshold A and a second threshold B higher than the first threshold A. The method then comprises: - adjusting the switching frequency fs to the first switching frequency fs1 when the typical value RV is equal to or greater than the second threshold value B; - adjusting the switching frequency fs to the second switching frequency fs2 when the typical value RV is greater than or equal to the first threshold value A and less than the second threshold value B; adjusting the switching frequency fs to a third switching frequency fs3 when the typical value RV falls below a first threshold A (S13'); Includes:

[0060] In a second example, as described above, the first switching frequency fs1, the second switching frequency fs2, and the third switching frequency fs3 may be 4 kHz, 8 kHz, and 16 kHz, respectively, and the decision to adjust S1 or maintain S1' the switching frequency fs may be performed periodically, in particular at a frequency of 8 kHz.

[0061] In such a case, the phase controlled by the first switching frequency fs1, corresponding to the lowest switching frequency, here 4 kHz, can either operate for half a cycle until the next decision, or use left-aligned PWM for the next cycle after the next decision. The phase controlled by the second switching frequency fs2, here 8 kHz, operates for one cycle before the next decision. The phase controlled by the third switching frequency fs3, here 16 kHz, operates for two cycles before the next decision.

[0062] In both examples, the switching frequency is gradually adjusted so that the higher the value of the output signal, the lower the switching frequency. Therefore, for the output signal that is the output current, switching losses are advantageously reduced, thereby extending the inverter's lifespan. However, if other aspects of the inverter need to be optimized, other output signals can be used to adjust the switching frequency.

[0063] Furthermore, the method may further comprise controlling the inverter at a fixed switching frequency during some time periods corresponding to a fixed frequency mode, in addition to controlling the inverter at a variable switching frequency during other time periods corresponding to a variable frequency mode. Thus, the inverter may be advantageously controlled at a fixed switching frequency for certain operations. The variable frequency mode may be implemented according to any of the aforementioned features and embodiments of the present invention. To facilitate implementation of such a method, the fixed switching frequency may be one of a set of at least two switching frequencies. If there are three possible switching frequencies, the fixed switching frequency may preferably correspond to an average switching frequency of the three possible switching frequencies.

[0064] The switching pattern can then be adjusted to achieve a smooth transition between the fixed frequency mode and the variable frequency mode. For example, in embodiments in which at least one threshold is used to trigger adjustments to the switching frequency, the at least one threshold can be adjusted gradually over multiple periods of the output signal to smooth the transition. A smooth transition has the advantage of preventing sudden acoustic and vibration changes.

[0065] While the embodiments have been described with reference to a number of exemplary embodiments, it will be understood that those skilled in the art may devise other modifications and embodiments that fall within the scope and principles of the present disclosure.

Claims

1. A method for controlling a power converter (I) having at least one switching cell (2) and a control unit (1) for controlling the at least one switching cell (2) at a switching frequency (fs) to deliver an output signal, comprising: adjusting (S1) the switching frequency (fs) periodically via the control unit (1) to vary the switching frequency (fs) within a period (T) of the output signal (Sout), the switching frequency (fs) being selected from a set (11) of at least two switching frequencies; The method comprises: The control unit (1) periodically receives the output signal (Sout) (S01); adjusting (S1) or maintaining (S1') the switching frequency (fs) via the control unit (1) based on a comparison between a representative value (RV) of the output signal (Sout) and at least one threshold value (12); With a series of steps, dynamically adjusting the at least one threshold (12) via a regulator circuit (14) of the power converter (I) to maintain a constant average switching frequency of the at least one switching cell (2) over the period (T) of the output signal (Sout); method.

2. The adjusting (S1) of the switching frequency (fs) via the control unit (1) is performed periodically; Each switching frequency of the set of at least two switching frequencies (11) has an associated preset time interval ti, and the control unit (1) controls the at least one switching cell (2) continuously at each switching frequency of the set of at least two switching frequencies (11) for the associated preset time interval ti. The method of claim 1.

3. the set of at least two switching frequencies (11) comprises a first switching frequency (fs1) and a second switching frequency (fs2); The first switching frequency (fs1) is lower than the second switching frequency (fs2). The method according to claim 1 or claim 2.

4. The at least one threshold (12) comprises a first threshold (A), When the representative value (RV) is equal to or greater than the first threshold value (A), the switching frequency (fs) is adjusted to the first switching frequency (fs1) (S11); When the representative value (RV) is less than the first threshold value (A), the switching frequency (fs) is adjusted to the second switching frequency (fs2) (S12); The method of claim 3.

5. The set of at least two switching frequencies (11) further comprises a third switching frequency (fs3); The second switching frequency (fs2) is lower than the third switching frequency (fs3). The method of claim 3.

6. the at least one threshold (12) comprises a first threshold (A) and a second threshold (B) greater than the first threshold (A); When the representative value (RV) is equal to or greater than the second threshold value (B), the switching frequency (fs) is adjusted to the first switching frequency (fs1) (S11'); When the representative value (RV) is equal to or greater than the first threshold value (A) and less than the second threshold value (B), the switching frequency (fs) is adjusted to the second switching frequency (fs2) (S12'); When the representative value (RV) becomes less than the first threshold value (A), adjusting the switching frequency (fs) to the third switching frequency (fs3). The method of claim 5.

7. Each of the set of at least two switching frequencies (11) is a multiple of a fundamental switching frequency. The method of claim 1.

8. each of the set of at least two switching frequencies (11) is a multiple of a fundamental switching frequency; the first switching frequency (fs1) is the same as the basic switching frequency, the second switching frequency (fs2) is twice the fundamental switching frequency; The third switching frequency (fs3) is four times the fundamental switching frequency. The method of claim 5.

9. each of the set of at least two switching frequencies (11) is a multiple of a fundamental switching frequency; adjusting (S1) or maintaining (S1') the switching frequency (fs) via the control unit (1) is periodically performed at a switching frequency (fs) intermediate the set (11) of at least two switching frequencies; The method of claim 1.

10. The output signal (Sout) is the output current of the power converter (I); The method of claim 1.

11. At least one switching cell (2); a control unit (1) for controlling at least one said switching cell (2) according to the method of claim 1; A power converter (I).

12. An inverter converts the DC voltage output from a high-voltage power battery (B) into AC voltage to drive an electric motor (M). A power converter (I) according to claim 11.

13. The at least one switching cell (2) has three switching cells and supplies a three-phase AC voltage to the electric motor (M); adjusting (S1) the switching frequency (fs) of each of the three switching cells is performed independently of the other cells of the three switching cells; A power converter (I) according to claim 12.

Images