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

Abstract

Disclosed is a method for controlling a brushless DC electric motor, in particular a drive motor of an air flow generator, the method comprising a step (2) of starting the motor, the starting step (2) comprising an initial starting step (8), the initial starting step (8) being carried out by open-loop control of the motor until members controlling the power supply current to the motor reach or exceed a threshold temperature (Ts).

Description

[0001] Method and device for controlling a brushless DC electric motor, in particular a drive motor for an airflow generator

[0002] The invention relates to a method and device for controlling a brushless DC electric motor, in particular a motor for driving an airflow generator, especially in cold weather. It also relates to a digital management system, a computer program product, and a data storage medium for implementing said method.

[0003] In this field, it is known to control electric motors by applying a rotational speed setpoint and ensuring that this setpoint is reached in a minimum time.

[0004] In cold weather, with this strategy, the applicant observed that unwanted micro-shutdowns of the engines occur, lengthening the time to reach the desired operating speed. In the case of engines used to generate airflow, such as blowers used in heating, ventilation, and / or air conditioning (HVAC) systems, this can cause a delay in proper temperature regulation of a passenger compartment and discomfort for occupants.

[0005] The applicant hypothesized that such micro-stops originated at least in part from electronic motor control devices, including electrical capacitors used in these devices, the performance of these capacitors dropping in cold temperatures.

[0006] One possible solution to this problem would be to choose more robust electronic components for motor control. However, these are expensive, which limits their appeal.

[0007] The invention aims to overcome at least in part the previous drawbacks and proposes to this end a method of controlling a brushless DC electric motor, in particular a drive motor for an airflow generator, said method comprising a starting step of said motor, said starting step comprising an initial starting step, said initial starting step being carried out by open-loop control of said motor until a threshold temperature of control elements for the supply currents of said motor is reached or exceeded.

[0008] Using open-loop motor control generates higher currents and consequently faster heating of the motor control components, thus reducing the risk of micro-interruptions during startup. Furthermore, this result is achieved without using different electronic components than those used for operation at lower temperatures. It is therefore possible to retain the same printed circuit boards, or at the very least, to continue using electrolytic capacitors for motor control.

[0009] In other words, according to the invention, preferably, said method is implemented using a control element comprising a printed circuit board, assembled, and / or one or more electrolytic capacitors, optionally implanted on said board.

[0010] According to various additional features of the invention, which may be taken together or separately and which constitute so many embodiments of the invention:

[0011] - the said threshold temperature is approximately -30°C,

[0012] - said open-loop control is an open-loop speed control,

[0013] - said control devices are configured to operate in open loop based on current setpoints from said motor supply,

[0014] - said currents are flux currents Id and / or torque currents Iq, obtained in relation to a Park and / or Clarke transformation of stator phase currents of said motor,

[0015] - said control devices include a temperature sensor and said start-up step uses information from said sensor to determine whether said threshold temperature has been reached or exceeded,

[0016] - said process includes a preliminary step of checking the temperature of said control elements, said initial start-up step occurring if the temperature of the control elements is less than or equal to said threshold temperature,

[0017] - said initial start-up stage occurs for a maximum time,

[0018] - said initial start-up stage is intended to power said motor without exceeding maximum current and / or rotational speed values, - said start-up stage aims to achieve a target rotational speed for said motor,

[0019] - said start-up stage includes a final start-up stage aimed at achieving said target speed, said final start-up stage occurring after said initial start-up stage, said final start-up stage including a closed-loop speed control stage to achieve said target speed.

[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 from the following detailed explanatory description 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, using a flowchart, an example of implementation of the process according to the invention;

[0025] [Fig 2] illustrates, according to a functional diagram, an example of implementation of the process according to the invention.

[0026] It should first be noted that the terms "first," "second," "third," etc., are used solely to distinguish the components concerned and do not imply any order or importance of said components. As illustrated in Figure 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, said motor must be able to deliver increasing torque with increasing motor speed.

[0027] A brushless DC motor is defined as an electrical machine comprising a rotor equipped with one or more permanent magnets. This machine also includes stator windings and allows for the commutation of current in these windings to create a rotating magnetic flux that drives the rotor. It is configured to detect the angular position of the rotor, preferably to ensure that the rotor magnetic flux is orthogonal to the stator magnetic flux, as in DC motors, hence its name.

[0028] The method according to the invention includes a step 2 of starting said motor preferably 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.

[0029] The target speed value (Vc) is derived, for example, from a step 4 involving the selection and / or determination of said target speed (Vc). In the case of application to an airflow generator of a heating, ventilation, and / or air conditioning (HVAC) system, it is, for example, the result of a selection step using a selector device, particularly one located on a vehicle control panel. Alternatively, particularly in the case of a regulated HVAC system, it is the result of a determination step using a digital control system for said HVAC system, particularly based on input information characteristic of ambient temperature and / or humidity conditions, as well as a desired temperature and / or a selected operating mode for said HVAC system.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 motor-driven airflow generator.

[0030] The said step 4 of selecting the target speed Vc is preferably concomitant with the 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 element 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 activated, whether at the time of starting the vehicle or at the command of the driver or a passenger of the vehicle.

[0031] The method advantageously includes a step 6, parallel to the 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.

[0032] According to the invention, said starting step includes an initial starting step 8, said initial starting step 8 being carried out by open loop control of said motor until a threshold temperature Ts of control elements of supply currents of said motor is obtained or exceeded.

[0033] The use of open-loop motor control generates higher currents and consequently faster heating of the motor control components, which helps to limit the risk of micro-interruptions at start-up.

[0034] As will be detailed below in relation to Figure 2, the said open-loop control is here an open-loop speed control.

[0035] The said threshold temperature is approximately -30°C. In other words, as long as the control elements of the supply currents of said motor do not have a temperature exceeding -30°C, the motor control takes place in open loop, at least until certain limits are reached.

[0036] The control devices are advantageously configured to operate in open loop based on supply current setpoints for the motor. These currents are, for example, flux currents Id and / or torque currents Iq, obtained in relation to a Park and / or Clarke transformation of stator phase currents of the motor, particularly within the framework of vector control of the motor.

[0037] Preferably, said control devices include a temperature sensor and said start-up step 2 uses information from said sensor to determine whether said threshold temperature Ts has been reached or exceeded.

[0038] The process advantageously includes a preliminary step 10 for checking the temperature T of the control elements. The initial start-up step 8 then occurs if the temperature T of the control elements is less than or equal to the threshold temperature Ts.

[0039] One such embodiment is illustrated in Figure 1, from which it can be seen that the method according to the invention comprises a test step 12 located upstream of the initial start-up step 8. If the result of the test T < Ts is positive, said initial start-up step is activated. Otherwise, the start-up step comprises a start-up step 16 in a standard mode, for example, a start-up beginning with open-loop speed control followed by closed-loop speed control, the switch from one to the other occurring at a predetermined speed or according to other criteria.

[0040] For safety reasons, the initial start-up step 8 is advantageously performed for a maximum duration. Alternatively or cumulatively, this initial start-up step 8 is intended to supply the motor without exceeding predetermined maximum current and / or speed values. For speed, this could be, for example, 5,000 rpm.

[0041] Preferably, said start-up step 2 includes a final start-up step 18 aimed at reaching the target rotational speed. This final start-up step 18 occurs after said initial start-up step 8. This final start-up step 18 includes, or even consists of, a closed-loop speed control step to reach said target speed. In other words, according to this embodiment, the speed control switches from an open-loop mode to a closed-loop mode once the threshold temperature Ts is reached.

[0042] One such embodiment is illustrated in Figure 1, from which it can be seen that the process according to the invention comprises another test step 20 located between the open-loop control step 8 and the closed-loop control step 18. If the result of the test T < Ts is positive, the process loops back to the initial start-up step 8. If the result of the test T < Ts is negative, the process proceeds to the final start-up step 18.

[0043] The invention also relates to a digital management system intended to be embedded in a motor vehicle. This system comprises hardware and / or software components implementing the steps of the control process described above.

[0044] The hardware and / or software components include, for example, the control elements mentioned above. These control elements are advantageously equipped with digital processing means, such as one or more microprocessors, possibly integrated into a printed circuit board, and / or one or more electrolytic capacitors, possibly mounted on said board. The temperature sensor of the temperature element(s) used to measure the temperature T in question according to the invention is mounted, for example, on or near said board, or even in close proximity to the electrolytic capacitor(s).

[0045] As illustrated in Figure 2, the invention further relates to a motor speed control device, designated 100 in that figure. Preferably, said control device comprises said management system.

[0046] The control device is advantageously configured to generate the supply currents for the motor. It includes an inverter 102 for this purpose. The inverter 102 is configured to receive control currents from its switches. 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 for the motor 100.

[0047] The device is further configured to perform vector control of the motor 100. For this purpose, it comprises a first unit 104 configured to perform an inverted Clarke transform and / or pulse-width modulation, a second unit 106 configured to perform an inverted Park transform, a torque control unit 108, and / or a flux control unit 110. The first transformation unit 104 is configured to convert intermediate current voltages Va and V|3 into each of the control current voltages Va, Vb, and Vc. The second transformation unit 106 is configured to obtain the intermediate current voltages Va and V|3 from a torque current with a voltage Vq and a flux current with a voltage Vd.

[0048] The said torque control unit 108 is configured to define the torque current voltage Vq from the difference between a control current Iqref and a measured current lq m said torque current, in particular with the aid of a proportional, integral and / or derivative regulator.

[0049] The 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.

[0050] 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 Iqref intensity of the torque current to be applied. The value of the square wave is determined, for example, from the motor characteristics.

[0051] To operate in closed-loop speed control, said device further includes here a third unit 1 12 configured to perform a Clarke transformation, a fourth unit 1 14 configured to perform a Park transformation, a unit 1 16 for estimating the speed and / or angular position of the rotor of motor 100 and / or a speed control unit 1 18.

[0052] The third transformation unit 112 is configured to convert the supply currents α, β, and λ into the intermediate currents α and λ³. The fourth transformation unit 114 is configured to obtain the torque currents εq and flux currents δ from the intermediate currents α and δp. The unit 116 for estimating the speed and / or angular position of the motor rotor 100 is configured to operate using the voltages ΔV and ΔV and the intermediate currents α and λ³.

[0053] The speed control unit 1 18 is configured to deliver a torque current value Iq to be applied to the torque control unit 1 12 from a difference between the target speed Vc and the speed information Vm delivered by said estimation unit 1 16.

[0054] It should also be noted that the rotor position information is used at the level of the second and fourth transformation units 106, 1 12 of inverted Park and Park. The said torque current intensities lq m and Idm fluxes delivered by said fourth transformation unit 1 14 are thus qualified as measured and / or estimated.

[0055] Furthermore, in the application in question, the intensity Idref of the flux current used for control is preferably zero.

[0056] According to the illustrated embodiment, the concepts of open and closed loops 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 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 lq.m and Idm of the measured and / or estimated torque and flux currents. The system, however, is in closed-loop speed control when it operates with feedback on the speed or even the angular position of the rotor.

[0057] For switching from one control mode to another, the said device here includes a first and a second toggle unit 120, 122.

[0058] The first 120 flip-flop unit is configured to allow the device to take into account the value of the torque current intensity lq re f from the square wave signal when open loop motor control step 8 is active, according to the position marked Ol in Figure 2, and to take into account the value of the torque current intensity lqref from the speed control unit 1 18 when closed loop motor control step 10 is active, according to the position marked Cl in Figure 2.

[0059] The second toggle unit 122 is configured not to return the rotor position value to the second and fourth transformation units 106, 112 when open-loop motor control stage 8 is active, according to the position marked Ol in Figure 2, and to take this value into account when closed-loop motor control stage 10 is active, according to the position marked Cl in Figure 2. The first and second toggle units 120, 122 are configured to switch from one control mode to the other according to the operating modes, according to the arrows marked 124, 126.

Claims

DEMANDS 1. Method of controlling a brushless DC electric motor, in particular a drive motor for an airflow generator, said method comprising a starting step (2) of said motor, said starting step (2) comprising an initial starting step (8), said initial starting step (8) being carried out by open-loop control of said motor until a threshold temperature (Ts) of control elements for the supply currents of said motor is reached or exceeded.

2. Method according to claim 1 wherein said threshold temperature (Ts) is about -30°C.

3. A method according to any one of the preceding claims wherein said open-loop control is an open-loop speed control.

4. A method according to any one of the preceding claims wherein said control elements comprise a printed circuit board, assembled, and / or one or more electrolytic capacitors.

5. A method according to any one of the preceding claims wherein said control elements comprise a temperature sensor and said start-up step uses information from said sensor to determine whether said threshold temperature (Ts) has been reached or exceeded.

6. A method according to any one of the preceding claims comprising a preliminary step (12) of checking a temperature of said control elements, said initial start-up step (8) occurring if the temperature (T) of the control elements is less than or equal to said threshold temperature (Ts).

7. A method according to any one of the preceding claims, wherein said starting step (2) is aimed at achieving a target rotational speed (Vc) for said motor, said starting step (2) comprising a final step (18) of start-up aimed at achieving said target speed (Vc), said final start-up step (18) occurring after said initial start-up step (8), said final start-up step (18) comprising a closed-loop speed control step to achieve said target speed (Vc).

8. 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. 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 7.

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