Method and device for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator

Abstract

A method for controlling a brushless DC electric motor, in particular a motor for driving an airflow generator, said method comprising a step (2) of starting said motor up to a target speed (Vc) which may take different values, said method further comprising a parallel step (6) of measuring and / or estimating the speed (V) of the motor, said starting step (2) comprising a step (8) of controlling the speed (V) of the motor in open loop up to a speed (Vb), referred to as the switching speed, and a step (10) of controlling the speed (V) of the motor in closed loop from said switching speed (Vb), said method comprising a step (12) of applying a switching rule according to which the switching speed (Vb) is variable at least below a fixed speed (Vr), referred to as the reference speed,so that said tipping speed (Vb) is equal to said target speed (Vc) or said reference speed (Vr). Figure for the abbreviation: Figure 1,

Description

Title of the invention: Method and device for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator

[0001] The invention relates to a method and device for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator. It also relates to a digital management system, a computer program product, and a data recording medium for implementing said method.

[0002] In the field of airflow generators for heating, ventilation and / or air conditioning systems of motor vehicles, it is known to control the speed of the electric motors used to drive the flow generators by starting, at startup, with open-loop control and then switching to closed-loop control from a speed of about 350 revolutions per minute.

[0003] However, it was found that the engine was the source of noise that was particularly noticeable during this start-up phase.

[0004] The invention aims to overcome, at least in part, the aforementioned drawbacks and to this end proposes a method for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator, said method comprising a step of starting said motor up to a target speed which may take different values, said method further comprising a parallel step of measuring and / or estimating the motor speed, said starting step comprising a step of controlling the motor speed in open loop up to a speed, referred to as the tipping speed, and a step of controlling the motor speed in closed loop from said tipping speed, said method comprising a step of applying a tipping rule according to which the tipping speed is variable at least below a fixed speed, referred to as the reference speed,so that said tipping speed is equal to said target speed or said reference speed.

[0005] Thanks to the switching occurring only above a minimum speed, namely the target speed or the reference speed, the motor is prevented from operating in closed loop at excessively low speeds, thereby limiting parasitic noise. Indeed, the applicant noted that with state-of-the-art control strategies, parasitic noise is observed in a speed range where the system is already in closed loop, while its speed remains too low to obtain a good estimation of the motor angle. The control loop thus presents problems with Stability generating high-frequency micro-variations in speed that could explain the observed parasitic noise. Thanks to the switching mechanism that occurs as soon as the target speed is reached, or even at a lower speed (namely the reference speed), the motor is also prevented from operating in open loop over too wide a speed range, while ensuring that it operates from a speed where the counter-electromagnetic force is detectable with sufficient accuracy.

[0006] According to various additional features of the invention, which may be taken together or separately and which constitute so many embodiments of the invention:

[0007] - said method includes a step of selecting and / or determining the speed target,

[0008] - said target speed is between 400 and 5,000 revolutions per minute,

[0009] - the tipping rule is as follows: said tipping speed is equal to the target speed if the target speed is between 400 revolutions per minute and said reference speed, and said tipping speed is equal to said reference speed if the target speed is greater than said reference speed.

[0010] - said reference speed is greater than 700 revolutions per minute,

[0011] - said reference speed is approximately 800 revolutions per minute,

[0012] - said open-loop control step starts at zero speed.

[0013] The invention also relates to a method for testing an electric motor comprising starting steps for said motor, said starting steps exploiting the control method as defined above, said target speed being lower than said reference speed.

[0014] In automotive applications, target engine speeds are standardized and generally higher than the ranges in which unwanted noise is likely to occur. However, car manufacturers require engine testing across all speed ranges, and the variation in the tipping speed proposed by the control method according to the invention is therefore of interest, even in these applications, at least for this testing phase.

[0015] The invention also relates to a digital management system intended to be embedded in a motor vehicle, said system comprising hardware and / or software elements implementing the steps of the control process described above.

[0016] The invention further relates to a computer program product comprising program code instructions recorded on a computer-readable medium to implement the steps of the control process described above, when said program is running on a computer.

[0017] The invention also relates to a computer-readable data recording medium on which is recorded a computer program comprising program code instructions for implementing the steps of the control process described above.

[0018] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent in the course of the detailed explanatory description that follows, of at least one embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the accompanying schematic drawings, among which:

[0019] [Fig-1] illustrates, using a flowchart, an example of implementation of the process in accordance with the invention;

[0020] [Fig.2] illustrates, according to a functional diagram, an example of implementation of the process according to the invention.

[0021] As illustrated in [Fig. 1], the invention relates to a method for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator. Specifically, it relates to a drive motor for a blower in a heating, ventilation, and / or air conditioning system, for example, in the passenger compartment of a motor vehicle. A particular feature of such an application is that, preferably, the motor must be able to deliver increasing torque with increasing motor speed.

[0022] A brushless DC motor is understood to mean, in particular, an electrical machine comprising a rotor equipped with one or more permanent magnets. This machine further comprises stator windings and enables the commutation of current in said windings so as to create a rotating magnetic flux driving the rotor. It is configured for detecting an angular position of the rotor, preferably to allow orthogonality of a rotor magnetic flux with respect to the stator magnetic flux, as in DC motors, hence its name.

[0023] The method according to the invention includes a step 2 of starting said motor up to a target speed Vc which can take different values. Said target speed Vc is, for example, between 400 and 5,000 revolutions per minute.

[0024] The target speed value Vc is derived, for example, from a step 4 of selecting and / or determining said target speed Vc. In the case of application to an airflow generator of a heating, ventilation and / or air conditioning device, it is, for example, the result of a selection step using a selector device, in particular located on a vehicle control panel. Alternatively, in particular in the case of a regulated heating, ventilation and / or air conditioning device, it is the result of a determination step using of a digital control system for said heating, ventilation and / or air conditioning device, based in particular on input information characteristic of ambient temperature and / or humidity conditions as well as a desired temperature and / or a selected operating mode of said heating, ventilation and / or air conditioning device. In each case, the target speed value Vc is preferably chosen from a limited number of values, for example four to eight possible speeds, each corresponding to a given airflow generated by the airflow generator driven by the motor.

[0025] Said step 4 of selecting the target speed Vc is preferably concomitant with a start of step 2 of starting the engine. In the embodiments mentioned above, the target speed Vc corresponds, for example, to that associated with the position in which the selector member is located or to that determined by the digital control system of the heating, ventilation and air conditioning device at the time of engine start-up, in particular when said system is triggered, whether at the time of starting the vehicle or at the command of the driver or a passenger of the vehicle.

[0026] The method further comprises a step 6, parallel to said starting step 2, for measuring and / or estimating the motor speed V. This step 6 is preferably continued beyond the starting step 2, in particular to ensure that the target speed Vc is maintained and / or to ensure, if necessary, that a new target speed, chosen and / or determined during motor operation, is reached.

[0027] Said starting step 2 first comprises a motor speed control step 8 in open loop up to a speed Vb, referred to as the switching speed. Said open-loop control step 8 begins, for example, at zero motor speed from the start of the starting step.

[0028] Said starting step 2 further includes a closed-loop motor speed control step 10 from said switching speed Vb.

[0029] According to the invention, said method includes a step 12 of applying a tipping rule according to which the tipping speed Vb is variable at least below a fixed speed Vr, said reference speed, so that said tipping speed is equal to said target speed Vc or to said reference speed Vr.

[0030] Thanks to the switching mechanism that only occurs above a minimum speed, namely the target speed Vc or the reference speed Vr, the motor is prevented from operating in a closed loop at excessively low speeds, thus limiting parasitic noise related to inaccurate estimation of the motor's angular position at low speeds. Thanks to the switching mechanism that occurs as soon as the target speed Vc is reached, or even at a lower speed, namely the reference speed Vr, we also prevent the motor from operating in open loop over too large a speed range.

[0031] According to the illustrated embodiment, step 12 of applying the tipping rule is carried out using information on the target speed Vc from step 4 of selecting and / or determining said target speed Vc and information on the speed Vr. The latter is, for example, stored in a computer program comprising program code instructions for implementing the steps of the process according to the invention.

[0032] According to a first embodiment, the switching rule used is as follows: said switching speed Vb is equal to the target speed Vc if the target speed is between 400 revolutions per minute and said reference speed Vr and said switching speed is equal to said reference speed Vr if the target speed Vc is greater than said reference speed Vr.

[0033] Said reference speed Vr is preferably established by a design of experiments, in particular motor by motor or type of motor by type of motor. It is, for example, greater than 700 revolutions per minute, in particular about 800 revolutions per minute.

[0034] Such an embodiment is illustrated in [Fig. 1], from which it can be seen that the process according to the invention comprises a test step 14 located between the open-loop control step 8 and the closed-loop control step 10. If the result of the test V < Vb is positive, the process loops back to the open-loop control step 8. If the result of the test V < Vb is negative, the process proceeds to the closed-loop control step 10. Thus, either the target speed Vc is less than the reference speed Vr, and the switch to closed loop occurs when the motor speed V reaches the target speed Vc because: Vb = Vc. Or the target speed Vc is greater than the reference speed Vr, and the switch to closed loop occurs when the motor speed V reaches the reference speed Vr because: Vb = Vr

[0035] The execution of test step 14 is carried out, for example, from the information relating to the value of the tipping speed Vb provided by step 12 of application of the tipping rule and the information relating to the value of the motor speed provided by step 6 of measurement and / or estimation of the motor speed V.

[0036] According to another embodiment of the invention, not illustrated, the tipping rule used is as follows: said tipping speed is equal to said target speed Vc regardless of said target speed VC. In such an embodiment, it is not necessary to record the reference speed Vr in the computer program used to implement the method according to the invention since the latter does not constitute a tipping threshold.

[0037] It should be noted that the control method described above will be advantageously used during motor testing phases that include starting steps to achieve target speeds Vc lower than the reference speed Vr. Once the motor is validated and in nominal operation, the target speeds Vc used are then advantageously all higher than the reference speed Vr. According to the illustrated embodiment, the switching speed is then systematically equal to Vr.

[0038] The invention also relates to a digital management system intended to be embedded in a motor vehicle. Said system comprises hardware and / or software elements implementing the steps of the control process described above. Said hardware and / or software element(s) comprise, for example, one or more control devices equipped with digital processing means, such as one or more microprocessors, optionally integrated into an assembled printed circuit board.

[0039] As illustrated in [Fig. 2], the invention further relates to a motor speed control device, designated 100 in that figure. Preferably, said control device comprises said management system.

[0040] The control device is advantageously configured to generate a supply current for the motor. It includes an inverter 102 for this purpose. The inverter 102 is configured to receive control currents from switches of the inverter 102. These control currents have voltages Va, Vb, and Vc respectively and are used to obtain, at the output of the inverter 102, a three-phase current, each phase of which has an intensity Ia, Ib, and Ie respectively, from a direct current supplying the inverter 102. The direct current has a voltage Vdc. The three-phase current is configured to generate the rotating magnetic flux of the motor 100.

[0041] Said device is further configured to perform vector control of said motor 100. It includes here for this purpose a first unit 104 configured to perform an inverted Clarke transformation and / or pulse width modulation, a second unit 106 configured to perform an inverted Park transformation, a torque control unit 108 and / or a flux control unit 110.

[0042] Said first transformation unit 104 is configured to convert intermediate current voltages Va and V[3] into each of the control current voltages Va, Vb, Vc. Said second transformation unit 106 is configured to obtain the intermediate current voltages Va and V[3] from a current, called torque, having a voltage Vq and a current, called flux, having a voltage Vd.

[0043] Said torque control unit 108 is configured to set the torque current voltage Vq from a difference between a control current Iqref and an intensity measured Iqmdudit torque current, in particular using a proportional, integral and / or derivative regulator.

[0044] Said flow control unit 110 is configured to set the voltage Vd of the flow current from a difference between a control current Idref and a measured current Idm of said flow current, in particular using a proportional, integral and / or derivative regulator.

[0045] To operate in open-loop speed control, the device is configured to receive control information, for example in the form of a square wave signal representing the intensity Iqref of the torque current to be applied. The value of the square wave is determined, for example, from the characteristics of the motor.

[0046] To operate in closed-loop speed control, said device further includes here a third unit 112 configured to perform a Clarke transformation, a fourth unit 114 configured to perform a Park transformation, a unit 116 for estimating the speed and / or angular position of the rotor of the motor 100 and / or a speed control unit 118.

[0047] Said third transformation unit 112 is configured to convert the current intensities la, Ib, le of the supply current into the intermediate current intensities la and I[3. Said fourth transformation unit 114 is configured to obtain the torque current intensities Iq and flux current intensities Id from the intermediate current intensities la and I[3. Said unit 116 for estimating the speed and / or angular position of the motor rotor 100 is configured to operate from the voltages Va and V[3 as well as the intermediate current intensities la and I[3.

[0048] The speed control unit 118 is configured to deliver a torque current value Iq to be applied to the torque control unit 112 from a difference between the target speed Vc and the speed information Vm delivered by said estimation unit 116.

[0049] It should also be noted that the information relating to the rotor position is used at the level of said second and fourth transformation units 106, 112 of reverse Park and Park. The said intensities of the torque currents Iqm and flux Idm delivered by said fourth transformation unit 114 are thus described as measured and / or estimated.

[0050] Moreover, in the application in question, the intensity Idref of the flux current used for control is preferably zero.

[0051] According to the illustrated embodiment, the concept of open loop and closed loop should be understood in relation to the speed and / or angular position of the rotor. The system thus operates in open-loop speed control when it is without Feedback is provided on the speed, or even the angular position, of the rotor. However, this does not preclude a feedback loop using the measured and / or estimated torque and flux current values ​​(Iqm and Idm). The system operates in closed-loop speed control when it receives feedback on the speed or angular position of the rotor.

[0052] For switching from one control mode to another, said device here comprises a first and a second rocker unit 120, 122.

[0053] The first flip-flop unit 120 is configured to allow the device to take into account the value of the torque current intensity Iqref from the square wave signal when the open-loop motor control step 8 is active, according to the position marked 01 on the [Fig.2], and to take into account the value of the torque current intensity Iqref from the speed control unit 118 when the closed-loop motor control step 10 is active, according to the position marked Cl on the [Fig.2].

[0054] The second flip-flop unit 122 is configured not to return the value of the rotor position to said second and fourth transformation units 106, 112 when the open-loop motor control step 8 is active, according to the position marked 01 in the figures, and to take this value into account when the closed-loop motor control step 10 is active, according to the position marked Cl in [Fig.2],

[0055] Said first and second toggle units 120, 122 are configured to switch from one control mode to another according to the operating modes, according to the arrows marked 124, 126.

Claims

Demands

1. A method for controlling a brushless DC electric motor (100), in particular a motor for driving an airflow generator, said method comprising a step (2) of starting said motor (100) up to a target speed (Vc) which may take different values, said method further comprising a parallel step (6) of measuring and / or estimating the speed (V) of the motor (100), said starting step (2) comprising a step (8) of controlling the speed (V) of the motor (100) in open loop up to a speed (Vb), referred to as the switching speed, and a step (10) of controlling the speed (V) of the motor (100) in closed loop from said switching speed (Vb), said method comprising a step (12) of applying a switching rule according to which the switching speed (Vb) is variable at least below a fixed speed (Vr), referred to as the reference speed,so that said tipping speed (Vb) is equal to said target speed (Vc) or to said reference speed (Vr).

2. Method according to the preceding claim comprising a step (4) of selecting and / or determining the target speed.

3. A method according to any one of the preceding claims wherein the tipping rule is as follows: said tipping speed (Vb) is equal to the target speed (Vc) if the target speed (Vc) is between 400 revolutions per minute and said reference speed (Vr) and said tipping speed (Vb) is equal to said reference speed (Vr) if the target speed (Vc) is greater than said reference speed (Vr).

4. Method according to the preceding claim wherein said reference speed (Vr) is greater than 700 revolutions per minute.

5. Method according to the preceding claim wherein said reference speed (Vr) is about 800 revolutions per minute.

6. A method according to any one of the preceding claims wherein said open-loop control step (8) starts at zero speed.

7. A method for testing an electric motor comprising starting steps for said motor, said starting steps exploiting the testing method according to any one of the claims previous, the said target speed (Vc) being lower than the said reference speed (Vr).

8. A digital management system intended to be embedded in a motor vehicle, said system comprising hardware and / or software elements implementing the steps of the process according to any one of claims 1 to 6.

9. Product computer program comprising program code instructions recorded on a computer-readable medium to implement the steps of the process according to any one of claims 1 to 6, when said program is run on a computer.

10. A computer-readable data recording medium on which is recorded a computer program comprising program code instructions for implementing the steps of the process according to any one of claims 1 to 6.

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