DEVICE AND METHOD FOR REGULATING THE SPEED OF A BRUSHLESS DC MOTOR

Abstract

Method for regulating the speed of a motor, the motor being a brushless DC motor comprising a stator and a rotor, the motor being intended to drive a load up and down. The method is implemented by a motor control unit and comprises, when a driving load phenomenon is detected, applying braking by applying (406) an angular offset to the stator magnetic field relative to an optimal stator magnetic field orientation corresponding to the current angular position of the rotor, the angular offset being applied in the opposite direction to the direction of rotation of the motor. Figure to be published with the abstract: Fig. 4

Description

Title of the invention: DEVICE AND METHOD FOR REGULATING THE SPEED OF A BRUSHLESS DC MOTOR technical field

[0001] The present invention relates to the field of brushless DC motors and more particularly to a method for regulating the speed of the motor when the motor is driven by an object. STATE OF PRIOR ART

[0002] Brushless direct current (BLDC) motors generate more power and are more efficient than conventional brushed DC motors of similar size. Such a motor has a stator comprising sequentially energized coils and a rotor comprising at least one permanent magnet. The use of battery-powered motors is now commonplace. BLDC motors are one example.

[0003] It is sometimes necessary to regulate the speed of a BLDC motor, particularly when a mechanical load that could be driven by the BLDC motor becomes a driving load. In this case, the mechanical load drives the BLDC motor, and not the other way around, which creates a risk of damage to the motor's electronic components due to an increase in voltage across the motor terminals, as it becomes a generator. Furthermore, a driving load phenomenon can damage the mechanical load, which might be, for example, a shutter.

[0004] Various methods of braking BLDC motors are known.

[0005] For example, one braking method involves injecting a braking current into the motor. However, such a method requires a high current consumption, which is not environmentally friendly. This is also the case with battery power, since injecting a braking current leads to a risk of rapid battery discharge and therefore an inability to operate the motor.

[0006] When the mechanical load is driving, another braking method involves drawing current from the motor to the power source, which allows the motor to be braked while energy is recovered. However, current cannot be drawn to a fully charged battery. Such a braking method is therefore incompatible with battery power or is not environmentally friendly.

[0007] A third method consists of replacing the BLDC motor's power supply with a resistor when motor braking is desired, for example using an electronic system. However, the size of the required resistor is generally too large relative to the engine volume and the heat produced is too great to be easily dissipated without harming the engine's operation.

[0008] In some cases, motor braking is achieved by cyclically short-circuiting the stator coils. However, such a braking method requires oversizing the coil power supply transistors, is likely to generate noise, and does not allow for optimal braking control.

[0009] It is therefore desirable to overcome these drawbacks of the prior art.

[0010] It is particularly desirable to provide a solution which allows the motor to be braked while being compatible with a battery power supply.

[0011] It is also desirable to provide a solution that allows for precise control of braking and regulation of speed.

[0012] Finally, it is desirable to provide a compact, quiet solution that dissipates little heat. Description of the invention

[0013] One object of the present invention is to provide a method for regulating the speed of a motor, the motor being a brushless DC motor comprising a stator and a rotor, the motor being intended to drive a load uphill and downhill. The method is implemented by a motor control unit and comprises, when a driving load phenomenon is detected, applying braking by applying an angular offset to the stator's magnetic field relative to an optimal stator magnetic field orientation corresponding to the current angular position of the rotor, the angular offset being applied in the opposite direction to the motor's direction of rotation.

[0014] Thus, it is possible to perform environmentally friendly motor braking or braking compatible with battery power for the motor. Furthermore, the braking is quiet, dissipates little heat, and is easily implemented in a compact hardware solution.

[0015] According to a particular embodiment, the method includes a deceleration mode that can be alternately activated and deactivated, the deceleration mode being activated as soon as a driving load phenomenon is detected. The method further includes, when the deceleration mode is deactivated, the steps of: determining the actual motor speed; determining whether the motor is in an acceleration phase or a regulation phase; detecting the driving load phenomenon if the ratio of the actual speed to a theoretical speed is greater than a first predetermined threshold when the motor is in an acceleration phase; and detecting the driving load phenomenon if the actual speed is greater than a setpoint speed and if the ratio of actual average supply voltage to theoretical average supply voltage is less than a second predetermined threshold when the motor is in a regulation phase.

[0016] Thus, it is possible to trigger a braking when the load intended to be driven by the motor becomes driving.

[0017] According to one embodiment, the applied angular offset is equal to a predetermined initial angular value at the time the safe idle mode is activated and the method further comprises, when the safe idle mode is activated, steps of: determining a speed deviation equal to the difference between a set speed and the actual speed; determining a correction value equal to the speed deviation divided by a predetermined coefficient if the absolute value of the speed deviation is greater than a predetermined speed threshold; and applying a new angular offset calculated by adding the correction value to the previous angular offset and limited in absolute value to a predetermined maximum angular value.

[0018] Thus, it is possible to precisely control the applied braking and regulate the engine speed during braking.

[0019] According to a particular embodiment, the actual speed is determined periodically with a predetermined period of time, and the method further comprises, when the deceleration mode is activated: recording, for each actual speed determined, a value of the applied angular offset; recording each value of applied angular offset in association with the n previously recorded values ​​of the applied angular offsets, n being a first predetermined number, so as to constitute a set of n+1 values; calculating, for each set of n+1 values, a variation of offset equal to the absolute value of the difference between the sum of the absolute values ​​of the m oldest angular offsets of the set of n+1 values ​​and the sum of the absolute values ​​of the m most recent angular offsets of the set of n+1 values, m being a second predetermined number such that m < n / 2;and stop the application of an angular offset and deactivate the deceleration mode when the offset variation is greater than a training end threshold.

[0020] Thus, braking is easily stopped when the load is no longer driving.

[0021] According to a particular embodiment, the end-of-training threshold Sfe is equal to: Sfe = (roundfU - Ui) + fi, where U is a nominal voltage value of the motor's power supply, Ui is a supply voltage value measured prior to the motor's start-up, and P is a predetermined angle.

[0022] According to a particular embodiment, the method further comprises stopping the application of the angular offset and deactivating the retarder mode if a stop command is received by the motor.

[0023] Thus, it is possible to easily switch from a braking method adapted to speed regulation when a load is driving to a motor stopping phase for which the setpoint speed is zero.

[0024] The invention also relates to a device for regulating the speed of a brushless DC motor, the motor comprising a stator and a rotor, the motor being intended to drive a load uphill and downhill. The device includes means for braking by applying an angular offset to the stator's magnetic field relative to an optimal stator magnetic field orientation corresponding to the rotor's angular position with a direction opposite to the motor's direction of rotation when a driving load phenomenon is detected.

[0025] According to a particular embodiment, the control device further comprises: means for alternately activating and deactivating a retarder mode, the retarder mode being activated as soon as a driving load phenomenon is detected; means for determining an actual engine speed; means for determining whether the engine is in an acceleration phase or in a regulation phase; means for detecting the driving load phenomenon, when the retarder mode is deactivated, if the ratio of the actual speed to a theoretical speed is greater than a first predetermined threshold when the engine is in an acceleration phase;and means for detecting the phenomenon of driving load, when the deceleration mode is deactivated, if the actual speed is greater than a set speed and if the ratio of an actual average supply voltage to a theoretical average supply voltage is less than a second predetermined threshold when the motor is in a regulation phase.

[0026] The invention also relates to a computer program, which can be stored on a medium and / or downloaded from a communication network, in order to be read by a processor. This computer program includes instructions for implementing the method mentioned above in any of its embodiments, when said program is executed by the processor. The invention also relates to an information storage medium storing such a computer program. Brief description of the drawings

[0027] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of at least one exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

[0028] [Fig-1] schematically illustrates a motorized shuttering device for a bay;

[0029] [Fig.2] schematically illustrates an example of the hardware architecture of a control unit for a brushless DC motor;

[0030] [Fig.3] schematically illustrates a method for regulating the engine speed in a standard mode; and

[0031] [Fig.4] schematically illustrates the method of regulating the engine speed in a decelerating mode.

[0032] DETAILED DESCRIPTION OF IMPROVEMENTS

[0033] Figure 1 shows a motorized shuttering device for a window 100, intended to be installed in a shutter box of a building above the window to be shuttered. The motorized shuttering device 100 comprises:

[0034] - a load such as a roller shutter or apron 106, and,

[0035] - drive means consisting of a motor tube 103 and a tube winding 104 and intended to drive the curtain or roller shutter 106 up and down.

[0036] The motor tube 103 is, for example, coaxial with the winding tube 104 and is located inside it. The curtain or roller shutter 106 is attached to the winding tube 104 using a flexible or rigid locking device. The winding tube 104 is rotated by the motor tube 103, causing the curtain or roller shutter 106 to rise or fall, depending on whether the direction of rotation of the winding tube 104 causes the curtain or roller shutter 106 to wind or unwind around the winding tube 104.

[0037] Generally, the roller shutter or apron 106 is made up of slats fixed to each other in such a way as to present a space between them.

[0038] The motor is powered by an electrical supply obtained from an electrical supply network of a building in which the motor is located or by a battery.

[0039] The nominal voltage delivered by the power supply is for example equal to 6, 12, 18 or 24 Volts.

[0040] The motor 103 comprises a stator including coils and a rotor including at least one permanent magnet. For example, the stator has three coils and the rotor has a series of magnets including six poles. The stator coils are energized sequentially so as to generate a rotating induced magnetic field. The rotor is then driven to rotate due to the coupling between the rotating induced magnetic field of the stator and the magnetic field generated by the rotor's permanent magnet. In a particular embodiment, the motor 103 is intended to drive the movement of a load such as the curtain 106, or roller shutter, and thus allows the curtain or roller shutter 106 to be opened and closed.

[0041] The motor 103 is controlled by a controller that allows the power supply to each coil to be electronically switched, taking into account, at every instant, the angular position of the rotor. Thus, the power supply to the coils can be carried out from The optimal method for achieving the desired rotor rotation is as follows. The controller can follow a trapezoidal control scheme comprising six coil energizing configurations executed sequentially. Each of the six configurations causes the motor to rotate through a predefined angular sector when executed successively. In one particular embodiment, executing the sequence of six energizing configurations results in a partial rotor rotation through an angular sector of 120°, and this sequence is repeated three times per motor revolution. Each energizing configuration is associated with a specific angular region of the rotor within each angular sector, this angular region being distinct from the angular regions associated with other energizing configurations within that sector.For example, for a motor with three angular sectors of 120°, each power configuration is associated with an angular domain of 20° in each of the angular sectors.

[0042] According to one embodiment, the motor 103 is powered by a battery generating a nominal supply voltage. Furthermore, the controller generates a pulse-width modulation (PWM) signal comprising a periodic alternation between a first discrete state having a maximum voltage value equal to the motor's DC supply voltage and a second discrete state having a minimum voltage value of zero. The frequency of the PWM signal is fixed, while the time ratio between the first and second discrete states varies and is called the duty cycle. When the duty cycle of the PWM signal is 0%, the average supply voltage of the motor is zero, and when the duty cycle of the PWM signal is 100%, the average supply voltage of the motor is equal to the nominal voltage at the motor input.The PWM signal thus allows the average supply voltage of the motor to be varied by modifying the duty cycle.

[0043] The motor 103 further includes a control unit UC used to detect a driving load phenomenon. Such a driving load phenomenon can occur, for example, when the motor's rotation, intended to drive the curtain or roller shutter 106 in a downward movement, is driven by the movement of the curtain or roller shutter 106 due to its weight and speed. In this case, the curtain or roller shutter 106 drives the motor and not the other way around. Figure 2 schematically illustrates an example of the hardware architecture of a control unit (CU) for engine 103. The CU comprises, connected by a communication bus 20: a processor or CPU (Central Processing Unit) 21; a random access memory (RAM) 22; a read-only memory (ROM) 23; a storage unit or storage media drive, such as a hard disk drive (HDD) 24; and a communication interface 25 for communication to communicate with other engine components such as a speed sensor, a coil power supply controller, or a device receiving external commands. In one embodiment, the RAM 22 and ROM 23 are implemented using high-speed flash memory.

[0044] The processor 21 is capable of executing instructions loaded into RAM 22 from ROM 23, external memory (not shown), a storage medium, or a communication network. When the control unit CU is powered on, the processor 21 is capable of reading instructions from RAM 22 and executing them. These instructions form a computer program causing the processor 21 to implement all or part of the algorithms and steps described herein in relation to the control unit.

[0045] Thus, all or part of the algorithms and steps described in relation to the motor control unit CU can be implemented in software form by executing a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor) or a microcontroller, or in hardware form by a dedicated machine or component, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit).

[0046] Figure 3 schematically illustrates a method for regulating the speed of the motor 103 in a standard mode. The regulation method is implemented by the motor's control unit UC.

[0047] In a first step 301, the motor control unit (CU) is in standard mode; that is, a retarder mode is deactivated. In standard mode, the stator windings are energized, taking into account the angular position of the rotor at every instant in order to optimize the orientation of the induced magnetic field to achieve rotor rotation. In other words, each energizing configuration is executed during rotor rotation when the rotor's angular position is precisely within an angular range associated with that energizing configuration.

[0048] Furthermore, the coils are supplied with an average supply voltage so that the rotor rotates at a target speed, referred to as the setpoint speed Vc. The motor is capable of determining its actual speed Vr at any given moment. The actual speed Vr of the motor can be measured using a logic sensor, such as an on / off logic sensor measuring the variations in a magnetic field generated by a magnet located at the end of the motor shaft and having two poles. This magnet causes a change of state detected by the logic sensor at each half-revolution of the motor. The actual speed Vr is regulated by a control system whose role is to increase, or decrease, the average supply voltage when The actual speed Vr is lower, or higher, than the setpoint speed Vc. The average supply voltage can be modified by varying the duty cycle of the PWM signal.

[0049] In standard mode, the motor control unit UC seeks to detect a driving load phenomenon.

[0050] In a subsequent step 302, the control unit determines whether the motor is in an acceleration phase. For example, the control unit determines that the motor is in an acceleration phase after a start command or a command to increase the set speed Vc is received by the motor, and as long as the acceleration phase has not ended. An acceleration phase ends when a regulation phase begins, that is, when the actual speed Vr reaches the set speed Vc, or when a stop command is received. If the motor is in an acceleration phase, a step 303 is performed. Otherwise, a step 304 is performed.

[0051] In step 303, the control unit determines whether the ratio of the actual motor speed Vr to the theoretical speed Vth is greater than a first predetermined threshold SI, such that SI = 1.2. To do this, the control unit determines the actual speed Vr at a present time t, for example, by sending a measurement command to a speed sensor. In one embodiment, the actual speed Vr is determined periodically. Each new value of the actual speed Vr is thus determined after a predetermined delay of a predetermined duration At has elapsed since a previous determination of the actual speed Vr. For example, the actual speed Vr is determined every 100 ms.

[0052] Furthermore, the theoretical speed Vth is calculated by considering a predefined progression of speed as a function of time between an initial instant t0 of the acceleration phase, at which the initial speed is defined, and a final instant tf of the acceleration phase at which the setpoint speed Vc is assumed to be reached. The control unit thus compares the actual speed Vr, measured at time t, to the theoretical speed Vth calculated at time t-t0.

[0053] According to one embodiment, the theoretical speed Vth is increased, during the acceleration phase, by a predetermined speed step at each predefined time interval. For example, the speed is increased by 150 rpm every 50 ms. The predetermined speed step can be calculated by multiplying the motor's rated speed, defined for a rated supply voltage, for example, 12 V, by a predetermined factor. For example, for a rated speed of 3000 rpm at 12 V and a predetermined factor of 5% determined empirically through functional testing, the predetermined speed step is 150 rpm. If the ratio of the actual speed Vr to the theoretical speed Vth is greater than the first If a predetermined threshold is reached, the control unit considers that a driving load phenomenon is detected and performs step 400. Otherwise, the motor returns to step 302.

[0054] In step 304, the control unit determines whether the motor is in a regulating phase. For example, the control unit determines that a regulating phase begins when a previous acceleration phase ends, that is, when the actual speed Vr reaches the setpoint speed Vc after a start command has been received by the motor. The control unit further considers that a regulating phase remains active as long as no stop command or no command to change the setpoint speed is received. If this is the case, step 305 is performed. Otherwise, the motor returns to step 301.

[0055] In step 305, the control unit determines whether the actual speed Vr is greater than the setpoint speed Vc. To do this, the control unit determines the actual speed Vr at a current time t or after the elapsed predetermined time from a previous determination of the actual speed Vr. The control unit compares this actual speed Vr to the setpoint speed Vc. If the actual speed Vr is greater than the setpoint speed Vc, step 306 is performed. Otherwise, the motor returns to step 304.

[0056] In step 306, the control unit determines an actual average supply voltage Ur. The average supply voltage Ur is obtained, for example, by reading the actual duty cycle of the PWM signal. The control unit then compares the actual average supply voltage Ur to a calculated theoretical average supply voltage Uth. This theoretical average supply voltage Uth, corresponding, for example, to a theoretical duty cycle of the PWM signal, is calculated by taking the ratio of the setpoint speed Vc to the motor's rated speed, multiplied by a correction factor to account for fluctuations in the supply voltage generated by the motor's power supply and equal to the ratio of the rated voltage to the actual current voltage of the motor's power supply, and multiplied by the resolution of the PWM signal.

[0057] If the ratio between the actual average supply voltage Ur and the theoretical average supply voltage Uth is less than a second predetermined threshold S2, for example S2 = 0.9, the control unit considers that a driving load phenomenon is detected and step 400 is performed. In other words, if Ur ≤ Uth < S2, a driving load phenomenon is detected. Otherwise, the control unit returns to step 304.

[0058] At step 400, the control unit switches from standard mode to retarder mode. Step 400 is detailed below in [Fig. 4].

[0059] Fig. 4 thus schematically illustrates the method of regulating the speed of the motor 103 in retarder mode.

[0060] At step 400, the control unit considers that a driving load phenomenon has been detected and switches to deceleration mode. In other words, deceleration mode is activated. The control unit then adjusts the average supply voltage to a nominal supply voltage by, for example, setting the duty cycle of the PWM signal to 100%.

[0061] In addition, the control unit determines a drive end threshold Sfe. The drive end threshold Sfe detects when the driving load phenomenon has stopped. This occurs, for example, when a driven object, such as the curtain or roller shutter 106, reaches an extreme position and is fully lowered or closed, when the drive torque of the curtain or roller shutter 106 decreases due to a reduction in the winding diameter of the curtain or roller shutter 106 around the winding tube 104, or when friction increases and slows the movement of the curtain or roller shutter 106. The drive end threshold Sfe is a predetermined angle value.According to a particular embodiment, the end-of-drive threshold Sfe is equal to the rounded difference between a predetermined voltage value U, i.e., a nominal voltage value of the motor's power supply, and a measured supply voltage value Ui prior to the motor's start-up, i.e., the nominal no-load voltage generated by the motor's power supply, plus a predetermined angle [3]. In other words, Sfe = rounded(U - Ui) + fi. For example, U = 12V and P = 9°.

[0062] In a subsequent step 401, the control unit brakes the motor. To do this, the control unit applies an angular offset to the magnetic field of the motor stator relative to an optimal stator magnetic field orientation corresponding to the current angular position of the motor rotor and in a direction opposite to the direction of motor rotation. In other words, during rotor rotation, each stator winding supply configuration is executed with a delay equal to the angular offset relative to the position of an angular sector of the rotor associated with said configuration. Thus, applying the angular offset makes it possible to brake the motor and limit the driving load phenomenon while limiting current consumption.

[0063] The initially applied angular offset, called the initial angular offset, is defined by a predetermined initial angular value, for example 15°, and by a sign opposite to the direction of rotation of the motor. For example, if the direction of rotation of the motor is positive, in other words, if the motor speed is considered positive, the angular offset is -15°. Conversely, if the direction of rotation of the motor is negative, in other words, if the motor speed is considered negative, the angular offset is +15°.

[0064] In a subsequent step 402, the control unit determines whether a stop order has been received by the engine. If so, step 410 is performed. Otherwise, step 403 is performed.

[0065] In step 403, the control unit determines the actual speed Vr by measurement at a given instant. According to one embodiment, the actual speed Vr is determined after the elapsed time predetermined from a previous determination of the actual speed Vr. The actual speed Vr is thus determined periodically, with a period of the predetermined duration At, for example every 100 ms.

[0066] In addition, the control unit calculates a speed deviation equal to the difference between the actual speed Vr and the setpoint speed Vc, i.e.: speed deviation = Vr - Vc.

[0067] In a subsequent step 404, the control unit determines whether the absolute value of the speed deviation is greater than a predetermined speed threshold, for example, a threshold of 20 rpm. If so, the control unit performs a step 405. Otherwise, the control unit directly performs a step 407.

[0068] In step 405, the control unit determines an angular correction, dimensionally equivalent to a unit angle and equal to the speed difference divided by a proportionality coefficient c. The control unit then determines a new angular offset by adding the angular correction to the previous angular offset. If the calculated sum of the previous angular offset and the angular correction is greater in absolute value than a predetermined maximum angular value, the new angular offset is then equal to said predetermined maximum angular value and opposite in sign to the direction of rotation of the motor. For example, for a predetermined maximum angular value of 30°, if the sum of the previous angular offset and the angular correction is -31°, then the new angular offset is limited and equal to -30°.

[0069] In a subsequent step 406, the control unit applies the new angular offset in place of the previous angular offset. The control unit then performs step 407.

[0070] At step 407, the control unit records the current value of the angular offset, in other words the value of the angular offset actually applied.

[0071] The current value of the angular offset is further recorded in association with the n values ​​of the previously recorded angular offsets, n being a predetermined number, for example n = 14. A current value of the angular offset is recorded each time the control unit performs step 407. In other words, each new determination of the actual speed Vr corresponds to a recorded current value of the angular offset. Thus, two successive recorded current values ​​of angular offsets are temporally separated by the predetermined period of time At. The current value of the angular offset corresponds to the value of the new angular offset determined in the preceding step 405 when the absolute value of the speed deviation is greater than the speed threshold predetermined in step 405. 404 and is identical to the previously recorded angular offset value otherwise.

[0072] A set of n+1 successive angular offset values ​​is thus constituted in step 407, for example using a fixed-size circular buffer containing n+1 elements.

[0073] In a subsequent step 408, the control unit determines a change in AD offset. The change in AD offset is equal to the absolute value of the difference between the sum of the m oldest absolute value angular offsets and the sum of the m most recent absolute value angular offsets of the set of n+1 values, where m is a second predetermined number such that m < n / 2. For example, for n = 14 and m = 5: * _ iy5 |_y15 i „ i ! with *2* being the | j । । L-ij- j ] KL I j ' values ​​of the angular shifts of the set of n+1 = 75 values, of increasing rank i in chronological order.

[0074] In a subsequent step 409, the control unit compares the change in offset AD to the training end threshold Sfe. If the change in offset AD is greater than the training threshold Sfe, step 410 is performed. Otherwise, the control unit returns to step 402.

[0075] At step 410, the control unit stops the application of the angular offset. The control unit then performs step 301.

[0076] At step 301 described previously in [Fig.1], the control unit considers that there is no longer a driving load phenomenon and switches to standard mode.

Claims

Demands

1. Method for regulating the speed of a motor (103), the motor (103) being a brushless DC motor comprising a stator and a rotor, the motor (103) being intended to drive a mechanical load (106) up and down, the method being implemented by a control unit (CU) of the motor (103) and characterized in that it comprises, when a driving load phenomenon is detected, performing braking by applying (401) an angular offset on the magnetic field of the stator with respect to an optimal orientation of the magnetic field of the stator corresponding to the current angular position of the rotor, the angular offset being applied in the opposite direction to the direction of rotation of the motor.

2. A method according to claim 1, characterized in that it comprises a retarder mode that can be alternately activated and deactivated, the retarder mode being activated (400) as soon as a driving load phenomenon is detected, and in that it comprises, when the retarder mode is deactivated (301), the steps of: - Determining an actual motor speed, - Determining whether the motor is in an acceleration phase (302) or in a regulation phase (304), - Detecting the driving load phenomenon if the ratio of the actual speed to a theoretical speed is greater than a first predetermined threshold (303) when the motor is in an acceleration phase,- Detect the phenomenon of driving load if the actual speed is greater than a setpoint speed (305) and if the ratio of an actual average supply voltage to a theoretical average supply voltage is less than a second predetermined threshold (306) when the motor is in a regulation phase.

3. A method according to claim 1 or 2, characterized in that the applied angular offset is equal to a predetermined initial angular value at the time the deceleration mode is activated, the method further comprising, when the deceleration mode is activated (400), the steps of: Determine (403) a speed difference equal to the difference between a set speed and the actual speed, - Determine a correction value equal to the speed difference divided by a predetermined coefficient if the absolute value of the speed difference is greater than a predetermined speed threshold (404), - Apply (406) a new angular offset calculated by adding the correction value to the previous angular offset and limited in absolute value to a predetermined maximum angular value.

4. A method according to claim 3, characterized in that the actual speed is determined periodically with a predetermined period of time and in that the method further comprises, when the retarder mode is activated: - Recording (407), for each actual speed determined, a value of the applied angular offset, - Recording each value of the applied angular offset in association with the n previously recorded values ​​of the applied angular offsets, n being a first predetermined number, so as to constitute a set of n+1 values, - Calculating (408), for each set of n+1 values, a change in offset equal to the absolute value of the difference between the sum of the absolute values ​​of the m oldest angular offsets in the set of n+1 values ​​and the sum of the absolute values ​​of the m most recent angular offsets in the set of n+1 values,where m is a second predetermined number such that m < n / 2, - Stop (410) the application of an angular offset and deactivate the deceleration mode when the offset variation is greater than a training end threshold.

5. A method according to the preceding claim, characterized in that the end-of-drive threshold Sfe is equal to: Sfe = (rounded U - Ui) + f, where U is a nominal voltage value of the motor's power supply, Ui is a pre-measured supply voltage value. lablement at engine start-up, and is a predetermined angle.

6. A method according to any one of claims 1 to 5, characterized in that the method further comprises stopping (410) the application of the angular offset and deactivating the retarder mode if a stop command (402) is received by the motor.

7. Speed ​​control device for a brushless DC motor, the motor (103) comprising a stator and a rotor, the motor being intended to drive a mechanical load up and down, the device being characterized in that it comprises: - means for performing braking by applying (401) an angular offset on the magnetic field of the stator with respect to an optimal orientation of the magnetic field of the stator corresponding to the angular position of the rotor with a direction opposite to the direction of rotation of the motor when a driving load phenomenon is detected.

8. A control device according to the preceding claim, characterized in that it further comprises: - Means for alternately activating (400) and deactivating (301) a retarder mode, the retarder mode being activated as soon as a dragging load phenomenon is detected, - Means for determining an actual engine speed, - Means for determining whether the engine is in an acceleration phase (302) or in a regulation phase (304), - Means for detecting the dragging load phenomenon, when the retarder mode is deactivated, if the ratio of the actual speed to a theoretical speed is greater than a first predetermined threshold (303) when the engine is in an acceleration phase, - Means for detecting the dragging load phenomenon, when the retarder mode is deactivated.if the actual speed is greater than a setpoint speed (305) and if the ratio of an actual average supply voltage to a theoretical average supply voltage is less than a second predetermined threshold (306) when the motor is in a regulating phase.

9. A computer program that can be stored on a medium and / or downloaded from a communication network, in order to be read by a processor, and characterized in that it includes instructions for implementing the method according to any one of claims 1 to 6, when said program is executed by the processor.

10. Information storage medium storing a computer program according to the preceding claim.

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