FR3145250A1 - DEVICE FOR CONTROLLING A SWITCHING CONVERTER, METHOD AND CORRESPONDING COMPUTER PROGRAM - Google Patents

Abstract

Control device (114) of a switching converter (110) designed to carry out voltage conversion between a direct voltage (E) and several phase voltages (Va, Vb, Vc) of an electrical machine (102), from respective pulse control signals (PWMa, PWMb, PWMc), the control device (114) comprising: - a signal generator (116), designed to generate the control signals (PWMa, PWMb, PWMc) at a frequency received; and - a frequency generation device (128), designed to provide the signal generator (116) with a so-called effective sequence of random frequencies for each control signal (PWMa, PWMb, PWMc), the frequencies of the same rank in the actual consequences being different. Figure for abstract: Fig. 1

Description

DEVICE FOR CONTROLLING A SWITCHING CONVERTER, METHOD AND CORRESPONDING COMPUTER PROGRAM Technical field of the invention

The present invention relates to a device for controlling a switching converter, a method and a corresponding computer program.

Technological background

It is known to use a switching inverter to drive an electric motor. To control the inverter, a control device generating pulse width modulated control signals is usually used.

Pulse width modulation is likely to cause EMC (electromagnetic compatibility) problems. Indeed, modulating a signal at a given frequency is likely to generate electromagnetic interference due to this frequency. In particular, pulse width modulation at a fixed frequency results in phase voltages generating electromagnetic waves at frequencies that are multiples of this fixed frequency. It has thus been observed that, for example, for HVAC (Heating Ventilation and Air Conditioning) fan motors controlled by pulse width modulation, electromagnetic interference in bands included in the range [0 MHz; 1 MHz] and more particularly in the band [0 kHz; 125 kHz] used by RFID chips associated with certain sensors, as well as in AM frequency bands, disrupting the reception of radio broadcasts.

In order to reduce such interference, it is known to vary randomly (or more precisely pseudo-randomly) the frequency of the pulse width modulated control signals. However, the frequency content of the phase voltages always contains peaks that can cause EMC problems.

It may thus be desirable to provide a control device for a switching converter which makes it possible to overcome at least some of the aforementioned problems and constraints.

• un générateur de signaux, conçu pour générer les signaux de commande à une fréquence reçue ; et
• un dispositif de génération de fréquence, conçu pour fournir au générateur de signaux une suite, dite effective, de fréquences aléatoires pour chaque signal de commande, les fréquences de même rang dans les suites effectives étant différentes.

There is therefore proposed a device for controlling a switching converter designed to carry out a voltage conversion between a direct voltage and several phase voltages of an electrical machine, from respective pulsed control signals, the control device being characterized in that it comprises:

• a signal generator, adapted to generate the control signals at a received frequency; and
• a frequency generating device, designed to provide the signal generator with a sequence, called effective, of random frequencies for each control signal, the frequencies of the same rank in the effective sequences being different.

The invention may further comprise one or more of the following optional features, in any technically possible combination.

Optionally, the control signals are pulse width modulated.

Also optionally, the frequency generating device comprises a random frequency generator for each control signal, the random frequency generators being independent of each other.

Also optionally, the frequency generation device comprises a random frequency generator for providing a so-called base sequence of random frequencies, the effective sequences being derived from the base sequence, one of the effective sequences possibly being equal to the base sequence.

Optionally, one of the effective sequences is taken equal to the basic sequence, each of the other effective sequences being obtained by adding or subtracting, at each rank, a predefined frequency from the frequency of the basic sequence.

Optionally also, the frequencies of one of the other effective sequences are obtained by adding a predefined frequency to the frequencies of the basic sequence and wherein the frequencies of another of the other effective sequences are obtained by subtracting a predefined frequency from the frequencies of the basic sequence.

Optionally also, the frequencies of one of the other effective sequences are obtained by alternately adding and subtracting a predefined frequency from the frequencies of the basic sequence, from one rank to the next.

Optionally also, the effective sequences are obtained by shifting the basic sequence, with different shifts from one effective sequence to another, the shift being able to be zero for one of the effective sequences.

Also optionally, for each control signal, each frequency of the effective sequence is used for an integer number of pulses.

• une génération d’une suite, dite effective, de fréquences aléatoires pour chaque signal de commande, les fréquences de même rang dans les suites effectives étant différentes ; et
• une génération des signaux de commande aux fréquences des suites effectives respectives.

There is also provided a method of controlling a switching converter designed to perform a voltage conversion between a DC voltage and several phase voltages of an electrical machine, from respective pulsed control signals, the control method being characterized in that it comprises:

• a generation of a sequence, called effective, of random frequencies for each control signal, the frequencies of the same rank in the effective sequences being different; and
• a generation of control signals at the frequencies of the respective effective sequences.

Also provided is a computer program downloadable from a communications network and/or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of a method according to the invention, when said program is executed on a computer.

Brief description of the figures

• la est une vue schématique d’un système d’entraînement électrique dans lequel l’invention est mise en œuvre, et
• la est un chronogramme illustrant des changements de fréquences de signaux de commande d’un convertisseur à commutation de la , générés par un dispositif de commande de la ,
• la est une vue schématique d’une variante du dispositif de commande de la ,
• la est un chronogramme illustrant des changements de fréquences de signaux de commande généré par le dispositif de commande de la ,
• la est une vue schématique d’une variante du dispositif de commande de la ,
• la est un chronogramme illustrant des changements de fréquences de signaux de commande généré par le dispositif de commande de la ,
• la est une vue schématique d’une variante du dispositif de commande de la ,
• la est un chronogramme illustrant des changements de fréquences de signaux de commande généré par le dispositif de commande de la ,
• la illustre des tensions de phase sinusoïdales obtenues dans l’état de la technique,
• la est un spectre fréquentiel de puissance des tensions de phase de la ,
• la illustre différents signaux obtenus dans un dispositif de commande selon l’invention, en particulier les signaux de commande du convertisseur à commutation,
• la est un spectre fréquentiel de puissance des tensions de phase sinusoïdales résultant des signaux de commande de la ,
• la illustre des tensions de phase en full SVM obtenues dans l’état de la technique,
• la est un spectre fréquentiel de puissance des tensions de phase de la ,
• la illustre différents signaux obtenus dans un dispositif de commande selon l’invention, en particulier les signaux de commande du convertisseur à commutation,
• la est un spectre fréquentiel de puissance des tensions de phase full SVM résultant des signaux de commande de la ,
• la illustre des tensions de phase en flat bottom SVM obtenues dans l’état de la technique,
• la est un spectre fréquentiel de puissance des tensions de phase de la ,
• la illustre différents signaux obtenus dans un dispositif de commande selon l’invention, en particulier les signaux de commande du convertisseur à commutation, et
• la est un spectre fréquentiel de puissance des tensions de phase flat bottom SVM résultant des signaux de commande de la .

The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which:

• there is a schematic view of an electric drive system in which the invention is implemented, and
• there is a timing diagram illustrating frequency changes of control signals of a switching converter of the , generated by a control device of the ,
• there is a schematic view of a variant of the control device of the ,
• there is a timing diagram illustrating changes in frequencies of control signals generated by the control device of the ,
• there is a schematic view of a variant of the control device of the ,
• there is a timing diagram illustrating changes in frequencies of control signals generated by the control device of the ,
• there is a schematic view of a variant of the control device of the ,
• there is a timing diagram illustrating changes in frequencies of control signals generated by the control device of the ,
• there illustrates sinusoidal phase voltages obtained in the state of the art,
• there is a power frequency spectrum of the phase voltages of the ,
• there illustrates different signals obtained in a control device according to the invention, in particular the control signals of the switching converter,
• there is a power frequency spectrum of the sinusoidal phase voltages resulting from the control signals of the ,
• there illustrates phase voltages in full SVM obtained in the state of the art,
• there is a power frequency spectrum of the phase voltages of the ,
• there illustrates different signals obtained in a control device according to the invention, in particular the control signals of the switching converter,
• there is a power frequency spectrum of the full SVM phase voltages resulting from the control signals of the ,
• there illustrates flat bottom SVM phase voltages obtained in the state of the art,
• there is a power frequency spectrum of the phase voltages of the ,
• there illustrates different signals obtained in a control device according to the invention, in particular the control signals of the switching converter, and
• there is a power frequency spectrum of the flat bottom SVM phase voltages resulting from the control signals of the .

Detailed description of the invention

Subsequently, the term “random” will be synonymous with “pseudo-random”.

In reference to the , an example of an electric drive system 100 in which the invention is implemented, will now be described.

The system 100 first comprises an electric machine 102 comprising a stator 104 with several stator phases X, Y, Z and a rotor 106. The electric machine 102 is designed to have alternating phase voltages Va, Vb, Vc. The electric machine 102 can be an electric motor or an electric generator. The electric machine 102 can be brushed or brushless. The electric machine 102 drives, for example, a fan of an HVAC system.

The system 100 further comprises a direct voltage source 108 designed to provide a direct voltage E.

The system 100 further comprises a switching converter 110 connected between the DC voltage source 108 and the stator phases X, Y, Z of the electric machine 102. The switching converter 110 is designed to perform a voltage conversion between the DC voltage E and the phase voltages Va, Vb, Vc.

The switching converter 110 comprises a switching circuit 112 with, for example, as many switching arms a, b, c as there are phase voltages Va, Vb, Vc of the electric machine 102. Each switching arm a, b, c comprises, for example, two controllable switches connected to each other at a midpoint and together at the terminals of the DC voltage source 108. The midpoint is intended to present the phase voltage Va, Vb, Vc of the electric machine 102.

Each controllable switch is preferably a semiconductor controllable switch, such as a metal-oxide gate field effect transistor (also referred to by the acronym MOSFET) or a silicon metal-oxide gate field effect transistor (also referred to by the acronym Si MOSFET) or a silicon carbide metal-oxide gate field effect transistor (also referred to by the acronym SiC MOSFET) or an insulated gate bipolar transistor (also referred to by the acronym IGBT) or a gallium nitride field effect transistor (also referred to by the acronym GaN FET), etc.

The switching converter 110 further comprises a device 114 for controlling the switching circuit 112.

The control device 114 comprises, for example, at least one computer system comprising a data processing unit (such as a microprocessor) and a main memory (such as a RAM memory, from the English “Random Access Memory”) accessible by the processing unit. Each computer system further comprises, for example, a local medium (such as a local hard disk). A computer program containing instructions for the processing unit(s) is recorded on the local medium(s). This computer program is for example intended to be loaded into the main memory(ies), so that the processing unit(s) executes its instructions. To facilitate the description of the computer program, the instructions will be described below as organized into software modules. However, this presentation does not prejudge the form of the computer program, which may be arbitrary.

Alternatively, all or part of these modules could be implemented in the form of hardware modules, that is to say in the form of an electronic circuit, for example micro-wired, not involving a computer program.

The control device 114 firstly comprises a control generator 116 designed to generate control signals PWMa, PWMb, PWMc with pulse width modulation. Thus, each control signal PWMa-c alternately takes a high value (corresponding to a pulse) and a low value. The control signals PWMa-c are generated at respective frequencies Fa, Fb, Fc received.

These PWMa-c control signals are for example respectively applied to the switching arms a, b, c to control the two switches of this switching arm in opposition to each other: when the PWMa-c control signal takes the high value, one of the switches is open and the other closed, and vice versa for the low value.

To avoid a simultaneous closing of both switches of the switching arm a, b, c, the control generator 116 can further be designed to insert dead times into the PWMa-c control signals, as is known per se.

The control generator 116 is for example designed to generate the control signals PWMa-c, from respective reference signals Sa, Sb, Sc which the phase voltages Va, Vb, Vc are intended to follow.

For example, the control generator 116 comprises, to generate each control signal PWMa-c, a triangular generator 118a, 118b, 118c designed to generate a triangular signal at the received frequency Fa, Fb, Fc. The control generator 116 further comprises a comparator 120a, 120b, 120c, designed to compare the triangular signal Ta, Tb, Tc to the reference signal Sa, Sb, Sc. The control signal PWMa-c takes a first value when the triangular signal Ta, Tb, Tc is higher, and a second value when the triangular signal is lower Ta, Tb, Tc.

To determine the reference signals Sa, Sb, Sc, the control device 114 comprises for example a regulator 122 designed to provide the reference signals Sa, Sb, Sc from an angular speed setpoint ω* of the rotor 106, an angular position θ of the rotor 106 and phase currents ia, ib, ic flowing between the switching circuit 112 of the switching converter 110 and the stator phases X, Y, Z of the electric machine 102. To obtain these last two pieces of information, the system 100 comprises for example a sensor 124 of the angular rotation θ of the rotor 106 and a sensor 126 of the phase currents ia, ib, ic.

The control device 112 further comprises a frequency generation device 128, designed to provide the frequencies Fa, Fb, Fc to the signal generator 116. More precisely, from an initial time t0, for example from the start of the switching converter 110, the frequency generation device 128 is designed to provide, for each frequency Fa, Fb, Fc, a sequence, called effective {Fa}, {Fb}, {Fc}, of random frequencies. Thus, each frequency Fa, Fb, Fc successively takes the values of the associated effective sequence {Fa}, {Fb}, {Fc}. In order to avoid that the PWMa-c control signals do not have, at any instant, the same frequency, which would produce a frequency peak in the spectrum of the phase voltages Va, Vb, Vc, the frequency generation device 128 is designed so that the effective sequences {Fa}, {Fb}, {Fc} are different from each other, that is to say so that the frequencies of the same rank in the effective sequences {Fa}, {Fb}, {Fc} are different.

In the context of the present invention, the term “different” is to be understood from a probabilistic point of view, that is to say that it is always possible, in certain of the embodiments which will be described later, that frequencies of the same rank are equal by chance.

To obtain different effective sequences, the frequency generation device 128 may for example comprise a random frequency generator 130a, 130b 130c for each PWMa-c control signal, the random frequency generators 130a-c being independent of each other. This embodiment is illustrated in FIG. . In order for the random frequency generators 130a-c to be independent, they may, for example, implement the same random generation algorithm, but starting from a different initial value. The random frequency generators 130a-c may also implement different random generation algorithms.

For example, for each PWMa-c control signal, each frequency of the associated effective series is provided every N pulses of the PWMa-c control signal, N being greater than or equal to one. This number of pulses N can be the same for all PWMa-c control signals or different from one PWMa-c control signal to another.

The number N of pulses can be fixed, or can vary over time, for example randomly to further improve the EMC.

In reference to the , an example of frequency succession in the PWMa-c control signals is illustrated, with effective sequences provided by the device 128 of the .

Thus, from time t0, the random frequency generator 130a successively provides the frequencies Fa ⁽¹⁾ , Fa ⁽²⁾ , Fa ⁽³⁾ , Fa ⁽⁴⁾ , Fa ⁽⁵⁾ , etc. The first N pulses are therefore generated at the frequency Fa ⁽¹⁾ , the following N at the frequency Fa ⁽²⁾ , and so on. On the , each block thus represents a set of N pulses, and the frequency of these pulses is indicated in the block. Each block thus has a more or less long duration depending on the frequency used for the N pulses of this block.

Similarly, from time t0, the random frequency generator 130b successively provides the frequencies Fb ⁽¹⁾ , Fb ⁽²⁾ , Fb ⁽³⁾ , Fb ⁽⁴⁾ , Fb ⁽⁵⁾ , etc. for the successive blocks of N pulses, and the random frequency generator 130c successively provides the frequencies Fc ⁽¹⁾ , Fc ⁽²⁾ , Fc ⁽³⁾ , Fc ⁽⁴⁾ , Fc ⁽⁵⁾ , etc. for the successive blocks of N pulses.

Since the random frequency generators 130a, 130b, 130c are independent, it is very unlikely that the PWMa-c control signals will have the same frequency at the same time.

In reference to the , in other embodiments, the frequency generation device 128 may for example comprise a single random frequency generator 302 designed to provide a base frequency F. More precisely, the random frequency generator 302 is designed to provide a sequence, called base {F}, of random frequencies. Thus, the base frequency F successively takes the values of the base sequence {F}. The frequency generation device 128 further comprises a derivation module 304, designed to derive the effective sequences {Fa}, {Fb}, {Fc} from the base sequence {F}, one of the effective sequences being able to be taken equal to the base sequence. In the latter case, each of the other effective sequences may for example be obtained by adding, at each rank, a predefined frequency of the frequency of the base sequence {F}. For example, as is the case in the , the effective sequence {Fa} is taken equal to the basic sequence {F}, the effective sequence {Fb} is taken equal to the basic sequence {F} plus a predefined frequency f, and the effective sequence Fc is taken equal to the basic sequence {F} minus the predefined frequency f. In other embodiments, the predefined frequency could be different between the effective sequence {Fb} and the effective sequence {Fc}.

In reference to the , an example of frequency succession in the PWMa-c control signals is illustrated, with effective sequences {Fa}, {Fb}, {Fc} provided by the frequency generation device 128 of the .

Thus, from time t0, the random frequency generator 302 successively provides the frequencies F ⁽¹⁾ , F ⁽²⁾ , F ⁽³⁾ , F ⁽⁴⁾ , F ⁽⁵⁾ , etc. For the control signal PWMa, the first N pulses are therefore generated at the frequency F ⁽¹⁾ , the next N at the frequency F ⁽²⁾ , and so on. For the control signal PWMb, the first N pulses are generated at the frequency F ^{( 1)} + f, the next N at the frequency F ⁽²⁾ + f, and so on. For the control signal PWMc, the first N pulses are generated at the frequency F ⁽¹⁾ - f, the next N at the frequency F ⁽²⁾ - f, and so on.

In this way, it is still very unlikely that the PWMa-c control signals will have the same frequency at the same time.

In reference to the , in other embodiments, the derivation module 304 can be configured so that the frequencies of one of the effective sequences other than the one equal to the basic sequence {F}, the effective sequence {Fb} in the illustrated example, are obtained by alternately adding a predefined frequency and subtracting a predefined frequency from the basic sequence, from one rank to the next. Thus, the pulses of the control signal PWMb remain on average temporally aligned with those of the control signal PWMa, instead of drifting temporally more and more as in the case of the .

Preferably, the frequencies of the other of the effective sequences other than that equal to the basic sequence, the effective sequence {Fc} in the illustrated example, are also obtained by alternately adding a predefined frequency and subtracting a predefined frequency from the basic sequence, from one rank to the next, but opposite the first effective sequence {Fb}. Thus, the pulses of the control signal PWMc also remain on average temporally aligned with those of the control signal PWMa, while having frequencies different from the control signals PWMa, PWMb.

In reference to the , an example of frequency succession in the PWMa-c control signals is illustrated, with actual sequences provided by the frequency generation device 128 of the .

Thus, from time t0, the random frequency generator 302 successively provides the frequencies F ⁽¹⁾ , F ⁽²⁾ , F ⁽³⁾ , F ⁽⁴⁾ , F ⁽⁵⁾ , etc. For the control signal PWMa, the first N pulses are therefore generated at the frequency F ⁽¹⁾ , the next N at the frequency F ⁽²⁾ , and so on. For the control signal PWMb, the first N pulses are generated at the frequency F ^{( 1)} + f, the next N at the frequency F ⁽²⁾ - f, and so on. For the control signal PWMc, the first N pulses are generated at the frequency F ^{( 1)} - f, the next N at the frequency F ⁽²⁾ + f, and so on.

In reference to the , in other embodiments, the derivation module 304 may for example be configured to shift the frequencies of the basic sequence {F} to obtain the effective sequences {Fa}, {Fb}, {Fc}, with different shifts from one effective sequence to another. The shift may be zero for one of the effective sequences {Fa}, {Fb}, {Fc}.

In reference to the , an example of frequency succession in the PWMa-c control signals is illustrated, with effective sequences {Fa}, {Fb}, {Fc} provided by the frequency generation device 128 of the .

Thus, from time t0, the random frequency generator 302 successively provides the frequencies F ⁽¹⁾ , F ⁽²⁾ , F ⁽³⁾ , F ⁽⁴⁾ , F ⁽⁵⁾ , etc. For the control signal PWMa, the offset is zero: the first N pulses are therefore generated at the frequency F ⁽¹⁾ , the next N at the frequency F ⁽²⁾ , and so on. For the control signal PWMb, the offset is +1: the first N pulses are generated at the frequency F ^{( 2 )} , the next N at the frequency F ^{( 3 )} , and so on. For the control signal PWMc, the offset is +2: the first N pulses are generated at the frequency F ^{( 3 )} , the next N at the frequency F ^{( 4 )} , and so on.

There represents the voltages Va, Vb, Vc when the reference signals Sa, Sb, Sc are sinusoidal and in the absence of the invention, that is to say when the three effective sequences {Fa}, {Fb}, {Fc} are identical: Fa ⁽ⁱ⁾ = Fb ⁽ⁱ⁾ = Fc ⁽ⁱ⁾ , changed randomly every six pulses.

There is the power frequency spectrum of the voltages Va, Vb, Vc of the . This frequency spectrum includes in particular a first peak (15.8 kHz, -35 dB), a second peak (35.7 kHz, -45 dB) and a third peak (68.3 kHz, -55 dB).

There illustrates the reference signals Sa-c, the triangular signals Ta-c and the control signals PWMa-c of the device 116 of the , with the sinusoidal Sa-c reference signals. Each frequency is changed every six pulses.

There is the power frequency spectrum of the voltages Va-c with the effective sequences {Fa}, {Fb}, {Fc} obtained by the frequency generation device 128 of the . As is apparent, in relation to the , the peaks were attenuated: the first peak went to -38 dB, the second peak went to -47 dB, and the third peak went to -56 dB.

There represents the voltages Va-c when the reference signals Sa-c are full space vector modulation (Full SVM) and in the absence of the invention, that is to say when the three effective sequences {Fa}, {Fb}, {Fc} are identical: Fa ⁽ⁱ⁾ = Fb ⁽ⁱ⁾ = Fc ⁽ⁱ⁾ .

There is the power frequency spectrum of the Va-c voltages of the . This frequency spectrum includes in particular a first peak (15.8 kHz, -35 dB), a second peak (35.7 kHz, -45 dB) and a third peak (68.3 kHz, -55 dB).

There illustrates the reference signals Sa-c, the triangular signals Ta-c and the control signals PWMa-c of the device 116 of the , with the Sa-c Full SVM reference signals. Each frequency is changed every six pulses.

There is the power frequency spectrum of the voltages Va-c with the effective sequences {Fa}, {Fb}, {Fc} obtained by the frequency generation device 128 of the . As is apparent, in relation to the , the peaks were attenuated: the first peak went to -38 dB, the second peak went to -47 dB, and the third peak went to -56 dB.

There represents the voltages Va, Vb, Vc when the reference signals Sa-c are flat bottom space vector modulation (SVM) and in the absence of the invention, that is to say when the three effective sequences {Fa}, {Fb}, {Fc} are identical: Fa ⁽ⁱ⁾ = Fb ⁽ⁱ⁾ = Fc ⁽ⁱ⁾ .

There is the power frequency spectrum of the Va-c voltages of the This frequency spectrum includes in particular a first peak (16 kHz, -38 dB), a second peak (34 kHz, -47 dB) and a third peak (73 kHz, -56 dB).

There illustrates the reference signals Sa-c, the triangular signals Ta-c and the control signals PWMa-c of the device 116 of the , with the reference signals Sa, Sb, Sc flat bottom SVM. Each frequency is changed every six pulses.

There is the power frequency spectrum of the voltages Va-c with the effective sequences {Fa}, {Fb}, {Fc} obtained by the frequency generation device 128 of the . As is apparent, in relation to the , the peaks were attenuated: the first peak went to -40 dB, the second peak went to -50 dB, and the third peak went to -57 dB.

In conclusion, it appears clearly that a switching converter control device, such as that described previously, makes it possible to reduce peaks in the power frequency spectrum.

It will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents the prediction of which is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching just disclosed to them.

Claims (11)

Control device (114) of a switching converter (110) designed to perform a voltage conversion between a direct voltage (E) and several phase voltages (Va, Vb, Vc) of an electric machine (102), from respective pulsed control signals (PWMa, PWMb, PWMc), the control device (114) being characterized in that it comprises:

• a signal generator (116), adapted to generate the control signals (PWMa, PWMb, PWMc) at respective received frequencies; and
• a frequency generation device (128), designed to provide the signal generator (116) with a sequence, called effective, of random frequencies for each control signal (PWMa, PWMb, PWMc), the frequencies of the same rank in the effective sequences being different.

The control device (114) of claim 1, wherein the control signals (PWMa, PWMb, PWMc) are pulse width modulated. A control device (114) according to claim 1 or 2, wherein the frequency generating device (128) comprises a random frequency generator (130a, 130b, 130c) for each control signal (PWMa, PWMb, PWMc), the random frequency generators (130a, 130b, 130c) being independent of each other. Control device (114) according to claim 1 or 2, in which the frequency generation device (128) comprises a random frequency generator (302) for providing a sequence, called a base, of random frequencies, the effective sequences being derived from the base sequence, one of the effective sequences possibly being equal to the base sequence. Control device (114) according to claim 4, in which one of the effective sequences is taken equal to the basic sequence, each of the other effective sequences being obtained by adding or subtracting, at each rank, a predefined frequency to the frequency of the basic sequence. A control device (114) according to claim 5, wherein the frequencies of one of the other effective sequences are obtained by adding a predefined frequency to the frequencies of the basic sequence and wherein the frequencies of another of the other effective sequences are obtained by subtracting a predefined frequency from the frequencies of the basic sequence. A control device (114) according to claim 5, wherein the frequencies of one of the other effective sequences are obtained by alternately adding and subtracting a predefined frequency from the frequencies of the basic sequence, from one rank to the next. Control device (114) according to claim 4, in which the effective sequences are obtained by shifting the basic sequence, with different shifts from one effective sequence to another, the shift possibly being zero for one of the effective sequences. A control device (114) according to any one of claims 1 to 8, wherein, for each control signal (PWMa, PWMb, PWMc), each frequency of the effective sequence is used for an integer number of pulses. Method for controlling a switching converter (110) designed to perform a voltage conversion between a direct voltage (E) and several phase voltages (Va, Vb, Vc) of an electrical machine (102), from respective pulsed control signals (PWMa, PWMb, PWMc), the control method being characterized in that it comprises:

• a generation of a sequence, called effective, of random frequencies for each control signal (PWMa, PWMb, PWMc), the frequencies of the same rank in the effective sequences being different; and
• a generation of the control signals (PWMa, PWMb, PWMc) at the frequencies of the respective effective sequences.

Computer program downloadable from a communications network and/or recorded on a computer-readable medium, characterized in that it comprises instructions for executing the steps of a method according to claim 10, when said program is executed on a computer.