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 for detecting a rotational blockage of a rotor of said motor, said detection step comprising a step for determining a signal (200), said transformed signal, representing an amplitude of the supply currents (Iph) of said motor, and a first step for comparing said transformed signal (200) with a first threshold (202), said comparison being intended to provide information on an occurrence of said blockage if said transformed signal (200) is less than said first threshold (202). Figure for the abstract: Figure 2

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 automotive heating, ventilation, and / or air conditioning systems, it is known to control electric motors used to drive the flow generators. More specifically, it is known to detect a rotational blockage of a rotor of said motor, also called motor stalling. Indeed, if such stalling is not detected, the motor continues to be supplied with current, which can generate mechanical and / or thermal stress effects as long as the motor rotor attempts to rotate while remaining blocked.

[0003] Currently, to detect engine stalling, it is known to use measurement strategies linked to variations in the engine's back electromotive force and / or speed detection. However, these require significant computing power. They also rely on expensive digital components.

[0004] The invention aims to overcome at least in part the previous drawbacks and proposes to this end a method for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator, said method comprising a step of detecting a rotational blockage of a rotor of said motor, said detection step comprising a step of determining a signal, said transformed, representing an amplitude of supply currents of said motor, and a first step of comparing said transformed signal and a first threshold, said comparison aiming to deliver information of an occurrence of said blockage if said transformed signal is lower than said first threshold.

[0005] The applicant observed that, at least at low speeds, the occurrence of rotor lock-up induced a current underconsumption that could be observed provided that a signal reflecting the amplitude of the motor supply currents was used, notably through filtering. Indeed, in this scenario, the sinusoidal signals relating to the motor supply currents do not, in themselves, allow differentiation between nominal operation and rotor lock-up due to the difficulty of using these physical quantities, which vary with Given the high frequency and measurement uncertainties that these variations imply, using a signal that is the image of the amplitude of these currents allows for reliable comparisons of this signal with a threshold and thus provides a relevant estimate of the occurrence of a blockage.

[0006] It is thus possible, according to the invention, to detect a motor blockage from the motor supply currents, which makes it possible to avoid having to use specific sensors or expensive processing units and / or those requiring significant computing power.

[0007] According to various additional features of the invention, which may be taken together or separately and which constitute so many embodiments of the invention:

[0008] - said step of determining the transformed signal includes a step of determination of a torque current Iq, obtained in relation to a Park and / or Clarke transformation applied to the supply currents of said motor,

[0009] - said first threshold is established from an experimental design for a set of engines with identical physical characteristics

[0010] - said step of determining the transformed signal occurs during a control in closed loop of said motor,

[0011] - said method includes a step of estimating the motor speed,

[0012] - said closed-loop control is a speed control,

[0013] - said first comparison step is carried out during a time interval, said test,

[0014] - said test interval begins during a switchover between a loop control open said motor and closed-loop control,

[0015] - said first comparison step delivers rotor blocking information if the torque current Iq remains below said first threshold for a time interval greater than or equal to said test interval,

[0016] - said blocking control step includes a second comparison step of the transformed signal and a second threshold designed to deliver an intervention signal for said blocking if the transformed signal is greater than said second threshold, said second threshold being greater than said first threshold,

[0017] - said second comparison step is carried out during said test interval,

[0018] - said second comparison step delivers intervention information said blocking occurs as soon as the transformed signal exceeds the second threshold.

[0019] - said first and second comparison steps are carried out in parallel.

[0020] 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 process described above.

[0021] 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 process described above, when said program is running on a computer.

[0022] 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 process described above.

[0023] 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:

[0024] [Fig. 1] illustrates, according to a functional diagram, an example of implementation of the method for controlling a motor according to the invention;

[0025] [Fig.2] represents graphs illustrating, in a first case, the evolution of a current used to control a motor according to a method according to the invention, as a function of time, this according to different control phases, a first graph 2a corresponding to a phase current in the case of no blocking of the motor, a second graph 2b corresponding to said phase current in the case of a blocking of said motor, a third graph 2c corresponding to a torque current in the case of no blocking of the motor, a second graph 2d corresponding to said torque current in the case of a blocking of said motor;

[0026] [Fig.3] represents 3a to 3d graphs similar to those of [Fig.2], in a second scenario.

[0027] It should first be noted that the terms "first", "second", "third", ... are used only to distinguish the components concerned from each other and do not imply any order or possible importance of said components.

[0028] As illustrated in [Fig. 1], the invention relates to a method for controlling an electric motor 100. Said electric motor 100 is a brushless DC motor, in particular a drive motor for an airflow generator. Specifically, it is 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, said motor must be able to deliver increasing torque with increasing motor speed.

[0029] 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.

[0030] Said method advantageously includes a step of controlling a rotational speed V of said motor 100.

[0031] Said control step preferentially exploits an intensity and voltage of a flux current Vd, Id and a torque current Vq, Iq, obtained in relation to a Park and / or Clarke transformation, applied to supply currents of said motor, in particular stator phase currents la, Ib, le of said motor. In other words, said motor 100 is preferably subjected to vector control, in particular for the purpose of controlling its speed.

[0032] Advantageously, said speed control stage comprises an open-loop speed control stage 01 and / or a closed-loop speed control stage Cl, the second possibly succeeding the first after switching from one to the other.

[0033] According to the invention, as will be developed below, said method includes a step of detecting a blockage in rotation of a rotor of said motor 100.

[0034] As illustrated, the invention also relates to a digital management system intended to be embedded in a motor vehicle. This system comprises hardware and / or software elements implementing the steps of the control process described above. The hardware and / or software element(s) include, 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.

[0035] The invention further relates to a speed control device V of the motor 100. Preferably, said control device includes said management system.

[0036] Said control device is advantageously configured to generate a supply current for said motor. It includes for this purpose an inverter 102. Said inverter 102 is configured to receive control currents from switches of said inverter 102. Said control currents have respective voltages Va, Vb, Vc and serve to obtain at the output of said inverter 102 a three-phase current, each phase of which corresponds to the stator phase currents Ia, Ib, Ie of said motor 100, from a direct current supplying said inverter 102. Direct current presents a voltage Vbat. Said three-phase current is configured to generate the rotating magnetic flux of said motor 100.

[0037] 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.

[0038] 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 the torque current, exhibiting voltage Vq, and from the flux current, exhibiting voltage Vd.

[0039] Said torque control unit 108 is configured to define the voltage Vq of the torque current from a difference between a control current Iqref and a measured current Iqm of said torque current, in particular using a proportional, integral and / or derivative regulator.

[0040] Said flow control unit 110 is configured to set the voltage Vd of the flow current from a difference between a control intensity Idrefet and a measured intensity Idm of said flow current, in particular using a proportional, integral and / or derivative regulator.

[0041] Said device is configured to operate in open loop and / or closed loop. For example, it is configured to operate in open loop during a motor start-up phase 100 and then switch to closed loop once a minimum speed is reached and / or depending on various parameters.

[0042] 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.

[0043] 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.

[0044] Said third transformation unit 112 is configured to convert the intensities Ia, Ib, Ie of the motor 100 supply currents into the intensities Ia and I3 of the intermediate currents. Said fourth transformation unit 114 is configured to obtain the intensities of the torque currents Iq and flux currents Id from the intensities la and I[> of the intermediate currents. Said unit 116 for estimating the speed and / or angular position of the rotor of the motor 100 is configured to operate from the voltages Va and V[3 as well as the intensities la and I[> of the intermediate currents.

[0045] 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 a target speed Vc and the information relating to a speed Vm delivered by said estimation unit 116.

[0046] 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 inverted 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.

[0047] Moreover, in the application in question, the intensity Idref of the flux current used for control is preferably zero.

[0048] According to the illustrated embodiment, the concepts 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 control when there is no feedback on the speed, or even on the angular position of the rotor. This does not, however, preclude a feedback loop using the values ​​of the current intensity Iqm and Idm of the measured and / or estimated torque and flux currents. Conversely, the system is in closed-loop speed control when it operates with feedback on the speed, or even on the angular position of the rotor.

[0049] For switching from one control mode to another, said device here comprises a first and a second rocker unit 120, 122.

[0050] The first flip-flop unit 120 is configured to allow the device to take into account the value of the torque current intensity Iqref during open-loop operation, according to the position marked 01 on the [Fig.1], and to take into account the value of the torque current intensity Iqref coming from the speed control unit 118 during closed-loop operation, according to the position marked Cl on the figure.

[0051] 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 during open-loop operation, according to the position marked 01 on the [Fig.1], and to take into account this value during closed-loop operation, according to the position marked Cl on the figure.

[0052] 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.

[0053] As illustrated in figures 2a to 2d, according to the invention, said step of detecting the blockage of the motor 100 comprises a step of determining a signal 200, said transformed, image of an amplitude of the supply currents la, Ib, le of said motor, and a first step of comparing said transformed signal and a first threshold 202, said comparison aiming to deliver an information of an occurrence of said blockage if said transformed signal 200 is less than said first threshold 202.

[0054] More specifically, Figures 2a and 2b show the evolution of one of the stator currents of motor 100, here called Iph, which corresponds to any one of the supply currents Ia, Ib, of said motor 100. This current Iph is substantially sinusoidal with a relatively high frequency. It is understandable that, given its large variations, detecting the difference between a normal operating mode, as in Figure 2a, and an operating mode with motor stall, as in Figure 2b, directly from differences in the evolution of the current Iph presents difficulties or at the very least a high risk of error due to the uncertainties generated by these large variations.

[0055] According to a first embodiment of the invention, illustrated in Figures 2c and 2d, said step of determining the transformed signal includes a step of determining the torque current Iq, whether in relation to the embodiment of the invention illustrated in [Fig. 1] or any other embodiment allowing the determination of said torque current Iq. Indeed, such a torque current Iq is a reflection of the amplitude of the supply currents Iph or Ib of the motor 100.

[0056] Figures 2c and 2d show that such a torque current Iq is constant, at least over certain intervals. It is therefore simpler to compare it to said first threshold 202.

[0057] Said first threshold 202 is, for example, a current threshold. Said current Iq and / or said first threshold are expressed, for example, in Amperes.

[0058] According to a second embodiment of the invention, said step of determining the transformed signal consists of detecting signal peaks in the current Iph and using them to determine an amplitude of said current Iph.

[0059] In general, using values ​​of the motor supply currents and even more so values ​​of an image of the amplitude of these currents to detect a motor blockage makes it possible, according to the invention, to avoid having to use specific sensors and / or complex components.

[0060] Preferably, the strategy mentioned above makes it possible to detect an engine blockage at low speed, in particular when the blockage occurs while the engine was running at speeds below 800 rpm, or even below 400 rpm.

[0061] For this purpose, as mentioned in the context of the embodiment of [Fig.1] but without being limited to such an embodiment, said method includes a step of estimating the speed of the motor.

[0062] Said first threshold 202 is established, for example, from an experimental design for a set of motors having identical physical characteristics. As already indicated, it is, for example, a current threshold, possibly expressed in Amperes.

[0063] As illustrated in Figures 3a to 3d, said blockage control step here includes a second step of comparing the transformed signal 200 and a second threshold 204 aimed at providing an intervention signal for said blockage if the transformed signal 200 is greater than said second threshold 204. Said second threshold 204 is greater than said first threshold 202. Such an implementation of the method according to the invention preferentially allows detection of the blockage of the motor 100 in the event of high speed, in particular greater than 800 rpm.

[0064] Said second threshold 204 is, for example, a current threshold, possibly expressed in Amperes

[0065] Here again, we can see from figures 3a and 3b that it is difficult to draw any lessons from the sinusoidal supply currents of the motor, whereas exploiting the transformed signal 200 is easier given its small variations.

[0066] Preferably, said blockage determination step occurs during closed loop control of said motor, whether at low and / or high speed, as illustrated by the time interval marked 206, 306 in figures 2a to 2d and 3a to 3d.

[0067] More specifically, here, the said first comparison step is carried out during a time interval, called the test interval, Tsr. The said test interval begins when switching between the open-loop control 01 of said motor 100 and the closed-loop control Cl. In figures 2a 2d and 3a to 3d, the open-loop control is illustrated by the time interval marked 208, 308.

[0068] Said first comparison step delivers rotor blocking information if the torque current Iq remains below said first threshold for a time interval greater than or equal to said test interval Tsr.

[0069] In Figures 2c and 2d, it can be seen that the torque current Iq is relatively constant once the motor control takes place in closed loop, which facilitates its comparison with said first threshold 202 during said test interval Tsr. In this case, in Figure 2c, it can be seen that said torque current Iq is greater audit first threshold 202 which allows us to conclude that there is no blockage of motor 100 whereas, in figure 2d, said cutting current Iq is less than said first threshold 202, moreover over the entire duration of the test interval Tsr, which allows us to conclude that there is blockage of said motor 100, even if the difference between the value of Iq and said first threshold 202 is minimal.

[0070] As can be seen in Figures 3c and 3d, said second comparison step is also carried out during said test interval Tsr.

[0071] Said second comparison step delivers an intervention information for said blocking as soon as said transformed signal exceeds said second threshold 204 during said test interval Tsr.

[0072] In Figure 3c, it can be seen that the torque current Iq is relatively constant and below said second threshold 204 over the entire test interval Tsr, which allows us to conclude that there is no blockage of the motor 100, whereas in Figure 3d, the torque current Iq is initially relatively constant over the time interval Tsr then begins to increase at a certain point to exceed said second threshold 204 at a point 310 located before the end of said test interval Tsr, which allows us to conclude that there is a blockage of the motor 100.

[0073] Said first and second comparison steps are preferably carried out in parallel and are active at least during the entirety of said test interval Tsr.

[0074] As illustrated in 2a to 2d and 3a to 3d, in the event of detection of a blockage of the motor 100, said closed loop control step is interrupted, for example to launch a new motor start sequence.

Claims

Demands

1. Method for controlling a brushless DC electric motor (100), in particular a drive motor for an airflow generator, said method comprising a step of detecting a rotational blockage of a rotor of said motor (100), said detection step comprising a step of determining a signal (200), said transformed, image of an amplitude of supply currents (Iph, la, Ib, le) of said motor (100), and a first step of comparing said transformed signal (200) and a first threshold (202), said comparison aimed at delivering information of an occurrence of said blockage if said transformed signal (200) is less than said first threshold (202).

2. Method according to claim 1 wherein said step of determining the transformed signal (200) comprises a step of determining a torque current (Iq), obtained in relation to a Park and / or Clarke transformation applied to the supply currents (Iph, la, Ib, le) of said motor (100).

3. Method according to the preceding claim wherein said first comparison step is carried out during a time interval, called test, (Tsr).

4. Method according to the preceding claim wherein said test interval begins during a switchover between open loop control and closed loop control of said motor (100).

5. A method according to any one of claims 3 or 4 wherein said first comparison step delivers rotor blockage information if the torque current (Iq) remains below said first threshold (202) for a time interval greater than or equal to said test interval (Tsr).

6. A method according to any one of the preceding claims in which said blocking control step comprises a second step of comparing the transformed signal (200) and a second threshold (204) aimed at delivering an intervention information for said blocking if the transformed signal (200) is greater than said second threshold (204), said second threshold (204) being greater than said first threshold (200).

7. A method according to the preceding claim in which said first and second comparison steps are carried out in parallel.

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 the preceding claims.

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 7, 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 process steps of the process according to any one of claims 1 to 7.

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