Method for controlling an electric motor

Abstract

Title: Method for controlling an electric motor The invention relates to a method for controlling an electric motor (2), in particular of the three-phase type, in particular of the brushless direct current type, the electric motor (2) being in particular configured to rotate a rotating protection element (14) of a sensor (3), the method comprising the following step: commanding a rotation of the electric motor (2) at a given rotation frequency of the electric motor (2): by applying a first efficiency value (VE1) of the electric motor (2);or by applying a second efficiency value (VE2) of the electric motor (2) which is lower than the first efficiency value (VE1) of the electric motor (2), for the same rotational frequency of the electric motor (2), in order to generate, by applying this second efficiency value (VE2), more heat by Joule effect within the electric motor (2) than with the first efficiency value (VE1), so as to allow simultaneously rotation of the electric motor (2) and heating of this electric motor (2). Figure for the abbreviation: Fig. 2;

Description

Title of the invention: Method for controlling an electric motor

[0001] The present invention relates to a method for controlling an electric motor, in particular of the three-phase type, in particular of the brushless direct current type, the electric motor being in particular configured to rotate a rotary protection member of a sensor. The present invention applies in particular to integration on a vehicle, in particular an automobile.

[0002] Patent application FR 3 107 969 discloses a device for protecting a sensor, which comprises an electric motor arranged to rotate a transparent cover element which protects the sensor. The electric motor can be a heat source to provide a defrosting function for the transparent cover element. The heating function is implemented with specific magnetic fields, without rotating the electric motor.

[0003] The invention aims in particular to improve the cleaning of a protective element of a sensor.

[0004] The invention thus relates to a method for controlling an electric motor, in particular of the three-phase type, in particular of the brushless direct current type, the electric motor being in particular configured to rotate a rotary protection member of a sensor, the method comprising the following step: - control a rotation of the electric motor at a given rotation frequency of the electric motor: • by applying a first efficiency value of the electric motor; or • by applying a second efficiency value of the electric motor which is lower than the first efficiency value of the electric motor, for the same rotation frequency of the electric motor, in order to generate, by applying this second efficiency value, more heat by Joule effect within the electric motor than with the first efficiency value, so as to simultaneously allow rotation of the electric motor and heating of this electric motor.

[0005] The efficiency of an electric motor is equal to the ratio of the useful output power to the electrical input power, expressed either as a percentage or as a coefficient (eg 85% or 0.85).

[0006] Thanks to the invention, it is possible to simultaneously ensure a rotation frequency of the electric motor which is not degraded, and heating of this electric motor (the motor serving as a heat source). Thus it is in particular possible to ensure the defrosting (to remove frost, or remove fog from the lens or protective cover) of the rotating protective member at the same time as the rotation function (not degraded) thereof. Thanks to the invention, the heating of the engine (and therefore the defrosting function) can be carried out without having to reduce or forego cleaning by centrifugal force (rotation of the sensor protective member).

[0007] According to one aspect of the invention, the first efficiency value is at least 80%, preferably at least 90%.

[0008] According to one aspect of the invention, the second efficiency value is less than 70%, preferably less than 60%, more preferably less than 50%, and most preferably less than 40%.

[0009] When the electric motor is used to rotate a rotating protective member of a sensor, the first efficiency value to which the electric motor is commanded allows rotation of the electric motor with the least possible energy losses (in particular the least losses by Joule effect). In this case, the electric motor does not heat up or heats up very little, and there is no defrosting function. This mode of operation of the electric motor at the first efficiency value corresponds to a simple cleaning mode of the protective member, only with rotation of the protective member, without seeking to heat the electric motor.

[0010] When the electric motor is operated with the second efficiency value, the electric motor heats up to a desired level in order to serve as a heat source for defrosting the sensor protection member. This is particularly advantageous when the ambient temperature becomes negative (the vehicle being parked outside, in the open air in particular) and frost forms on the rotating protection member.

[0011] By using the second efficiency value, it is possible to operate the electric motor in a cleaning mode with heating. In this cleaning mode with heating, the electric motor is configured to rotate the rotating protection member at an optimal (non-degraded) speed while ensuring the heating of the rotating protection member due to the heat released by the Joule effect within the electric motor. In this cleaning mode with heating, it is deliberately sought to create losses by the Joule effect. In the invention, it is recommended to consume more energy to both maintain the rotation frequency and heat the electric motor more.

[0012] According to one aspect of the invention, the method comprises a step of selecting between: a simple cleaning mode in which the electric motor is operated with the first efficiency value, and a cleaning mode with heating in which the electric motor is put operating with the second efficiency value.

[0013] The rotating protective member is placed at a location chosen so as to be able to receive heat from the electric motor.

[0014] According to one aspect of the invention, the method comprises the following step: - operating the electric motor by controlling the ratio V / f where V is the voltage applied to the electric motor and f is the rotational frequency of the electric motor, by applying a first value (V / f)i to the control of the electric motor for operation of the motor at the first efficiency value and by applying a second value (V / f)2 to the control of the electric motor for operation of the motor at the second efficiency value, the value (V / f)2 being greater than the value (V / f)i at a given value f.

[0015] An increase in the V / f ratio leads to an increase in Joule effect losses, and therefore to heating of the electric motor.

[0016] According to one aspect of the invention, the value (V / f)2 is at least 20%, preferably at least 30% and more preferably at least 40% greater than the value (V / f)i.

[0017] According to one aspect of the invention, the second value (V / f)2 is constant, namely the voltage V is an increasing linear function of the frequency f, for example over the entire operating frequency range of the electric motor.

[0018] Alternatively, the second value (V / f)2 is constant over at least two operating frequency ranges of the electric motor, with different values ​​over each frequency range.

[0019] According to one aspect of the invention, the first value (V / f)i is constant over at least two operating frequency ranges of the electric motor, with different values ​​over each frequency range.

[0020] In this exemplary embodiment of the invention, it is a scalar control in which the speed of the motor is adjusted by modifying the frequency and the voltage of the supply current. This makes it possible to regulate the speed of the motor depending for example on the load and other conditions. This exemplary embodiment of the invention requires an increase in the power absorbed by the motor, for the same rotation frequency.

[0021] According to another aspect of the invention, the method comprises the following step: - operating the electric motor by controlling a mechanical angle Alpha between the rotor field and the stator field of the electric motor, by applying a first value Alpha 1 to the control of the electric motor for operation of the motor at the first efficiency value and by applying a second value Alpha2 to the control of the electric motor for operation of the motor at the second efficiency value, the value Alpha2 being

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[0030] greater than the Alpha 1 value. According to one aspect of the invention, the value Alphal is chosen to be substantially equal to 90°. According to one aspect of the invention, the Alpha2 value is chosen to be at least 20%, preferably at least 30%, more preferably at least 40% and most preferably at least 50% smaller than the Alphal value. According to one aspect of the invention, the value Alpha2 is chosen to be substantially equal to 45°. When an electric motor is operating, the stator field is in front of the rotor field. By reducing the angle Alpha, the stator field is closer to the rotor field. The smaller the Alpha angle, the greater the engine heating. By monitoring the rotor position, the system is therefore able to adapt the voltages applied to the 3 phases of the motor in order to create the desired stator magnetic field, with a defined amplitude and angle. The Alpha angle can therefore be reduced to a minimum, and motor heating maximized accordingly. According to one aspect of the invention, the method comprises the following steps: - triggering the operation of the engine at the second efficiency value for a predetermined duration (NB: sufficient to carry out defrosting), or a duration determined according to surrounding weather conditions; and - if necessary, once heating is complete, switch to the operating mode at the first efficiency value. According to one aspect of the invention, upon receipt of an order to clean the rotating protection member, and in particular depending on the ambient temperature, the method comprises the following step: - trigger the simple cleaning mode of the rotating protection member; or - trigger the cleaning mode with heating of the protective device rotary. The invention also relates to a control unit for an electric motor, in particular of the three-phase type, in particular of the brushless direct current type, the electric motor being in particular configured to rotate a rotary protection member of a sensor, the control unit being configured to control rotation of the electric motor at a given rotation frequency of the electric motor: - by applying a first efficiency value of the electric motor; or - by applying a second efficiency value of the electric motor which is lower than the first efficiency value of the electric motor, for the same rotation frequency of the electric motor, in order to generate, by applying this second efficiency value, more heat by Joule effect within the electric motor than with the first efficiency value, so as to simultaneously allow rotation of the electric motor and heating of this electric motor.

[0031] The invention also relates to an electrical system comprising: - a sensor with a rotating sensor protection member; - an electric motor configured to rotate the rotating protection member; and - a control unit as mentioned above, configured to control the electric motor.

[0032] According to one aspect of the invention, the sensor may be of the type that emits and receives electromagnetic waves, in particular the visible light spectrum.

[0033] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and several exemplary embodiments given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

[0034] [Fig-1] [Fig.l] is a simplified diagram of a motor-driven electrical system for motor vehicle conforming to an example of implementation of the invention;

[0035] [Fig.2] [Fig.2] is a sectional view of the motor and sensor of the system of the [Fig.l];

[0036] [Fig.3] [Fig.3] shows curves of voltage versus frequency of rotation for the motor of the system of [Fig.l];

[0037] [Fig.4] [Fig.4] is a representation of the mechanical angle Alpha between the field rotor field VBr and stator field VBs of the electric motor 2 of the system of [Fig.l].

[0038] The features, variants and different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0039] [Fig. 1] shows a simplified diagram of an electrical system 1 with a motor, for a motor vehicle, in accordance with an example of implementation of the invention.

[0040] The electrical system 1 comprises a three-phase, four-pole electric motor 2.

[0041] In the example described, the electric motor 2 is capable of delivering a nominal rotation speed of 10,000 rpm (revolutions / min).

[0042] The electric motor 2, provided with a stator with electromagnetic excitation coils and a rotor with magnets, is of the brushless type, also called a BLDC motor (“Brushless Direct Current”).

[0043] The electrical system 1 further comprises a control circuit 3 configured to control the supply of the electrical phases Iphase A, Iphase B and Iphase C to the electric motor 2.

[0044] The control circuit 3 comprises switches, here transistors 5 of the MOSFET type (or “Metal-oxide-semiconductor field effect transistor”) which are six in number, with two transistors 5 for each phase Iphase A, Iphase B and Iphase C. The transistors 5 are arranged in an H-bridge configuration. These transistors 5 form an inverter.

[0045] The control circuit 3 also comprises an electronic control unit 7 formed by a microcontroller and a system (also called “Bridge driver” in English) making it possible to control power components such as MOSFETS (also called “Bridge driver” in English).

[0046] The electronic control unit 7 is configured to generate a sinusoidal excitation to rotate the electric motor 2.

[0047] The electronic control unit 7 is configured to receive rotation speed instructions for the electric motor 2 and / or data concerning the desired operating mode of this electric motor 2.

[0048] The electronic control unit 7 is configured to provide PWM (Pulse Width Modulation) or MLI (Pulse Width Modulation) type control signals to the switches 5 of the control circuit 3 to control them (the PWM signal passage lines are symbolized by the lines 17 in [Fig.l]). The electronic control unit 7 is thus configured to carry out the variation of the duty cycle of the PWM signals.

[0049] The electrical system 1 is configured to be powered by a direct current battery (for example 12V), and the electronic control unit 7 is configured to deliver PWM signals with a frequency of 20Khz (Kilohertz) or any other modulation frequency, with a variable duty cycle in order to vary the voltage between 0 and the maximum battery voltage Vbat.

[0050] The electrical system 1 also comprises circuits 15 for detecting current on the phases Iphase A, Iphase B and Iphase C and a temperature measuring circuit 16, for more precise control of the three-phase motor.

[0051] As illustrated in [Fig.2], the electrical system 1 further comprises a sensor 3 with a rotating protection member 14 to protect the sensor 3, the motor electric 2 being configured to rotate the rotary protection member 14. The sensor 3 is housed in a housing 4. The sensor 3 is for example part of a vehicle driving assistance system, arranged for example at the front or rear of the vehicle.

[0052] In the invention, a sensor designates a device for emitting and receiving electromagnetic waves at predetermined wavelengths.

[0053] The electric motor 2 is configured to rotate the rotary protection member 14 of the sensor 3.

[0054] The protective member 14 is a protective cover transparent to the operating lengths of the sensor 3 or a lens, being for example made of PMMA or other plastic materials.

[0055] The invention allows cleaning of the protection member 14 by centrifugal effect which is arranged opposite the sensor 3.

[0056] The rotary protection member 14 has an axis of rotation X.

[0057] The sensor 3 is here a camera-type optical sensor, with an optical part 6, a electronic block 8 and a sheath 10 housing power and communication cables. This sensor 3 is mounted on a support member 12 helping to form a fixed part.

[0058] Sensor 3 makes it possible to acquire images of the road scene.

[0059] The housing 4 is mounted to rotate about the axis of rotation X, and comprises a first end 15 and a second end 17 longitudinally opposite. The first end 15 is turned towards the road scene and carries the rotary protection member 14 while the second end 17 is integral with the electric motor 18.

[0060] The four-pole electric motor 2 comprises a rotor 26 and a stator 28. The stator 28 comprises a winding and the rotor 26 comprises permanent magnets.

[0061] The stator 28, the support 12 and the sensor 3 represent a fixed part.

[0062] The rotor 26, the housing 4 and the rotary protection member 14 represent a part mobile in rotation around the X axis.

[0063] A bearing 32, here a ball bearing, is placed between the moving part and the fixed part.

[0064] The rotor 26 is configured to drive the housing 4 and the rotary protection member 14 in rotation and the rotation of the rotary protection member 14 makes it possible to remove by centrifugal force the dirt present on the rotary protection member 14.

[0065] The electronic control unit 7 is configured to control the electric motor 2 according to the following steps: - command a rotation of the electric motor 2 at a given rotation frequency of the electric motor 2: • by applying a first efficiency value VEi of the electric motor 2; or • by applying a second efficiency value VE2 of the electric motor 2 which is lower than the first efficiency value VEi of the electric motor 2, for the same rotation frequency of the electric motor 2, in order to generate, by applying this second efficiency value VE2, more heat by Joule effect within the electric motor 2 than with the first efficiency value VEi, so as to simultaneously allow rotation of the electric motor 2 and heating of this electric motor 2.

[0066] The efficiency of an electric motor 2 is equal to the ratio of the useful output power to the electrical input power, expressed as a percentage.

[0067] Thanks to the invention, it is possible to simultaneously ensure a rotation frequency of the electric motor 2 which is not degraded, and heating of this electric motor 2 (the motor serving as a heat source). Thus it is in particular possible to ensure defrosting, to remove frost, or remove mist, on the rotary protection member 14 at the same time as the rotation function (not degraded) thereof. Thanks to the invention, the heating of the motor (and therefore the defrosting function) can be carried out without having to reduce or forego cleaning by centrifugal force (rotation of the sensor protection member 3).

[0068] The first efficiency value VEi is at least 80%, in particular at least 90%.

[0069] The second efficiency value VE2 is less than 70%, in particular less than 60%, in particular less than 50%, or in particular less than 40%.

[0070] When the electric motor 2 is used to rotate the rotary protection member 14 of a sensor 3, the first efficiency value VEi to which the electric motor 2 is commanded allows rotation of the electric motor 2 with the least possible energy losses (in particular the least losses by Joule effect). In this case, the electric motor 2 does not heat up or heats up very little, and there is no defrosting function. This mode of operation of the electric motor 2 at the first efficiency value VEi corresponds to a simple cleaning mode of the protection member, only with rotation of the protection member 14, without seeking to heat the electric motor 2.

[0071] When the electric motor 2 is operated with the second efficiency value VE2, the electric motor 2 heats up to a desired level in order to serve as a heat source for defrosting the sensor protection member 3. When speaking of a desired heating level, it will be understood that this is a heating level suitable not only for the implementation in question (e.g. the size of the sensor and its positioning in / on the vehicle), but also suitable for the specific conditions of its use (e.g. the rolling speed and / or the weather conditions observed at the time). This is particularly advantageous when the ambient temperature becomes negative (the vehicle being parked outside, in the open air) and frost forms on the rotating protection member 14.

[0072] The heating of the protective member 14 can be generated by conduction and / or convection of heat from the electric motor 2 to the protective member 14. The rotating protective member 14 is placed at a location chosen so as to be able to receive heat from the electric motor 2, for example to receive hot air blown by the rotation of the electric motor 2, or by conduction through the various parts.

[0073] By using the second efficiency value VE2, it is possible to operate the electric motor 2 in a cleaning mode with heating. In this cleaning mode with heating, the electric motor 2 is configured to rotate the rotary protection member 14 at an optimal (non-degraded) speed while ensuring the heating of the rotary protection member 14 due to the heat released by the Joule effect within the electric motor 2. In this cleaning mode with heating, it is deliberately sought to create losses by the Joule effect. In the invention, it is recommended to consume more energy to both maintain the rotation frequency and heat the electric motor 2 more.

[0074] The method described comprises a step of selection between: - a simple cleaning mode in which the electric motor 2 is operated with the first efficiency value VEi, and - a cleaning mode with heating in which the electric motor 2 is operated with the second efficiency value VE2.

[0075] This selection can be made manually or automatically, for example depending on the ambient air temperature.

[0076] In a first exemplary embodiment of the invention, the method comprises the following step: - operating the electric motor 2 by controlling the ratio V / f where V is the voltage applied to the electric motor 2 and f is the rotation frequency of the electric motor 2, by applying a first value (V / f)i to the control of the electric motor 2 for the operation of the motor at the first efficiency value VEi and by applying a second value (V / f)2 to the control of the electric motor 2 for the operation of the motor at the second efficiency value VE2, the value (V / f)2 being greater than the value (V / f)i at a given value f.

[0077] An increase in the V / f ratio, at a given value f, leads to an increase in the losses due to Joule effect, and therefore heating of the electric motor 2.

[0078] The value (V / f)2 is at least 20% or 30% or 40% greater than the value (V / f)b at a given value f.

[0079] The second value (V / f)2 is constant (as illustrated on the curve of [Fig.3]), namely the voltage V is a linear increasing function of the frequency f, for example over the entire operating frequency range of the electric motor 2.

[0080] Alternatively (not shown), the second value (V / f)2 is constant over at least two operating frequency ranges of the electric motor 2, with different values ​​over each frequency range.

[0081] In the example illustrated on the curve of [Fig.3], the first value (V / f)i is represented by at least two operating ranges of the electric motor 2, with different values ​​(V / f)ia and (V / f)ib on each range. Consequently, the coast corresponding to the value (V / f)ib is greater than the coast corresponding to the value (V / f)ia. This inflection is obtained for example by a variation in the operating frequency of the electric motor.

[0082] In this exemplary embodiment of the invention, it is a scalar control in which the speed of the motor is adjusted by modifying the frequency and the voltage of the supply current. This makes it possible to regulate the speed of the motor depending for example on the load and other conditions. This exemplary embodiment of the invention requires an increase in the power absorbed by the motor, for the same rotation frequency.

[0083] In a second exemplary embodiment of the invention, the method comprises the following step: - operating the electric motor 2 by controlling a mechanical angle Alpha between the rotor field VBr and the stator field VBs of the electric motor 2 (see [Fig.4]), by applying a first value Alphal to the control of the electric motor 2 for the operation of the motor at the first efficiency value VEi and by applying a second value Alpha2 to the control of the electric motor 2 for the operation of the motor at the second efficiency value VE2, the value Alpha2 being greater than the value Alphal.

[0084] The value Alphal is chosen to be substantially equal to 90°.

[0085] The Alpha2 value is chosen at least 20%, preferably at least 30%, more preferably preferably at least 40% and most preferably at least 50% smaller than the Alphal value.

[0086] The value Alpha2 is chosen to be substantially equal to 45°.

[0087] In operation of the electric motor 2, the stator field is in front of the rotor field. By reducing the angle Alpha, it is ensured that the stator field is more close to the rotor field.

[0088] The smaller the Alpha angle, the greater the engine heating.

[0089] By monitoring the rotor position, the system is therefore able to adapt the voltages applied to the 3 phases of the motor in order to create the desired stator magnetic field, with a defined amplitude and angle. The Alpha angle can therefore be reduced to a minimum, and motor heating maximized accordingly.

[0090] In all cases, it is possible to trigger the operation of the engine at the second efficiency value VE2 for a predetermined fixed duration, in particular a time sufficient to carry out defrosting, or a duration determined according to surrounding weather conditions, for example the outside temperature.

[0091] If necessary, once heating is complete, the process switches to the operating mode at the first efficiency value VEi.

[0092] Upon receipt of an order to clean the rotary protection member 14, an order which is in particular a function of the ambient temperature or of metrological data or of data coming from a frost or mist sensor, the method comprises the following step: - trigger the simple cleaning mode of the rotating protection member 14; Or - trigger the cleaning mode with heating of the rotating protection member 14.

[0093] In summary, the control unit 7 of the electric motor 2 is configured to control a rotation of the electric motor 2 at a given rotation frequency of the electric motor 2: - by applying a first efficiency value VEi of the electric motor 2; or - by applying a second efficiency value VE2 of the electric motor 2 which is lower than the first efficiency value VEi of the electric motor 2, for the same rotation frequency (for example 10,000 rpm) of the electric motor 2, in order to generate, by applying this second efficiency value VE2, more heat by Joule effect within the electric motor 2 than with the first efficiency value VEi, so as to simultaneously allow rotation of the electric motor 2 and heating of this electric motor 2.

[0094] The sensor 3 may be of the type that emits and receives electromagnetic waves, in particular the visible light spectrum.

Claims

Claims

1. Method for controlling an electric motor (2), in particular of the three-phase type, in particular of the brushless direct current type, the electric motor (2) being in particular configured to rotate a rotary protection member (14) of a sensor (3), the method comprising the following step: - controlling rotation of the electric motor (2) at a given rotation frequency of the electric motor (2): • by applying a first efficiency value (VEi) of the electric motor (2);or • by applying a second efficiency value (VE2) of the electric motor (2) which is lower than the first efficiency value (VEi) of the electric motor (2), for the same rotation frequency of the electric motor (2), in order to generate, by applying this second efficiency value (VE2), more heat by Joule effect within the electric motor (2) than with the first efficiency value (VEi), so as to simultaneously allow rotation of the electric motor (2) and heating of this electric motor (2).;

2. Method according to the preceding claim, wherein the first efficiency value (VEi) is at least 80%, preferably at least 90%, and the second efficiency value (VE2) is less than 70%, preferably less than 60%, more preferably less than 50%, and most preferably less than 40%.

3. Method according to one of the preceding claims, in which the method further comprises a step of selecting between: - a simple cleaning mode in which the electric motor (2) is operated with the first efficiency value (VEi), and - a cleaning mode with heating in which the electric motor (2) is operated with the second efficiency value (VE2).

4. Method according to one of the preceding claims, wherein the method further comprises the following step: - operating the electric motor (2) by controlling the ratio V / f where V is the voltage applied to the electric motor (2) and f is the rotation frequency of the electric motor (2), by applying a first value (V / f)i to the control of the electric motor (2) for the operation of the motor at the first efficiency value and by applying a second value (V / f)2 to the control of the electric motor (2) for the operation of the motor at the second efficiency value, the value (V / f)2 being greater than the value (V / f)i at a given value f.

5. Method according to the preceding claim, wherein the value (V / f)2 is at least 20%, preferably at least 30% and more preferably at least 40% greater than the value (V / f)i.

6. Method according to claim 4 or 5, in which the second value (V / f)2 is constant, namely the voltage V is a linear increasing function of the frequency f, in particular over the entire operating frequency range of the electric motor (2), or the second value (V / f) 2 is constant over at least two operating frequency ranges of the electric motor (2), with different values ​​over each frequency range.

7. Method according to one of claims 4 to 6, in which the first value (V / f)i is constant over at least two operating frequency ranges of the electric motor (2), with different values ​​over each frequency range.

8. Method according to one of claims 1 to 3, wherein the method further comprises the following step: - operating the electric motor (2) by controlling a mechanical angle Alpha between the rotor field and the stator field of the electric motor (2), by applying a first value Alpha 1 to the control of the electric motor (2) for the operation of the motor at the first efficiency value (VEi) and by applying a second value Alpha2 to the control of the electric motor (2) for the operation of the motor at the second efficiency value (VE2), the value Alpha2 being greater than the value Alpha 1.

9. Method according to the preceding claim, in which the value Alpha 1 is chosen to be substantially equal to 90°, and in particular the value Alpha2 is at least 20%, preferably at least 30%, more preferably at least 40% and most preferably at least 50% smaller than the value Alpha 1, in particular the value Alpha2 being chosen to be substantially equal to 45°.

10. Method according to one of the preceding claims, in which the method further comprises the following steps: - triggering the operation of the engine at the second efficiency value (VE2) for a predetermined duration, or a duration determined according to surrounding weather conditions; and - where appropriate, once the heating is finished, switching to the operating mode at the first efficiency value (VEi)•

11. Control unit of an electric motor (2), in particular of the three-phase type, in particular of the brushless direct current type, the electric motor (2) being in particular configured to rotate a rotary protection member (14) of a sensor (3), the control unit being configured to control a rotation of the electric motor (2) at a given rotation frequency of the electric motor (2): - by applying a first efficiency value (VEi) of the electric motor (2);or - by applying a second efficiency value (VE2) of the electric motor (2) which is lower than the first efficiency value (VEi) of the electric motor (2), for the same rotation frequency of the electric motor (2), in order to generate, by applying this second efficiency value (VE2), more heat by Joule effect within the electric motor (2) than with the first efficiency value (VEi), so as to simultaneously allow rotation of the electric motor (2) and heating of this electric motor (2).;

12. Electrical system comprising: - a sensor (3) with a rotating protection member (14) of the sensor (3); - an electric motor (2) configured to rotate the rotating protection member (14); and - a control unit according to claim 12, configured to control the electric motor (2).

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