Method of controlling an electric motor system

Abstract

Title: Method for controlling an electric motor system The subject of the invention is a method for controlling an electric motor system (1), the method comprising the following steps: measuring the rotational speed (V) of the electric motor (2); associating with this measured rotational speed of the electric motor (2) a maximum control signal value (PWMmax); controlling the rotational speed of the electric motor (2) by PWM signals whose value is lower than the maximum control signal value (PWMmax). Figure for abstract: Fig. 1

Description

Title of the invention: Method for controlling an electrical motor system

[0001] The present invention relates in particular to a method for controlling an electrical motor system, and such an electrical motor system, in particular for a vehicle. The vehicle may be a land, sea or air vehicle.

[0002] Patent application FR3098063 discloses an electrical assembly for a wiping device of a motor vehicle, comprising an electric motor and using pulse width modulation (PWM) control.

[0003] In a known manner, an electrical motor system can be configured to be powered by a 12V battery, and an electronic control unit is configured to deliver PWM signals of frequency 20Khz (Kilohertz) with a variable duty cycle in order to vary the voltage between 0 and 12V.

[0004] In an ideal case, the electronic control unit varies, depending on the load and / or speed requirements of the electric motor, the duty cycle of the signal linearly between 0% and 100%, which corresponds to varying the voltage between 0V (duty cycle at 0%) and 12V (duty cycle at 100%).

[0005] It is known to use switches, in particular formed by MOSFET transistors, to inject the phases into the electric motor.

[0006] Electronic type motors require a protection strategy to limit the electric current. This is required in order to protect the motor electronics, the motor itself and the mechanical part connected to the motor. Today, in electronic wiper motors, protection based on the motor current and the motor torque is used. However, this does not provide effective protection, because the current is read with a delay and, once the current / torque exceeds a certain threshold, the excessive current damages the electronic part or the excessive torque damages the mechanical part, in particular a linkage linked to the wiper arms.

[0007] The present invention aims in particular to avoid or reduce these anomalies.

[0008] The invention thus relates to a method for controlling an electrical motor system, this electrical motor system comprising: - an electric motor configured to be powered by several electrical phases (Iphase A, Iphase B and Iphase C), in particular the electric motor being of the three-phase type; - a control circuit configured to control the supply of electrical phases to the electric motor, this control circuit comprising switches, in particular of the transistor type, these switches being in particular MOSFETs; - an electronic control unit configured to provide PWM signals to the switches of the control circuit to control them; the process comprising the following steps: - measure the rotation speed of the electric motor; - associate with this measured rotation speed of the electric motor a maximum control signal value (PWMmax); - control the rotation speed of the electric motor by PWM signals whose value is lower than the maximum control signal value (PWMmax), in particular the duty cycle of the PWM is smaller than the duty cycle of the PWMmax.

[0009] The invention thus makes it possible to anticipate a risk of malfunction on the wiper blade. In addition, the invention is easily implemented and allows robust protection. This makes it possible to reduce the weight of the electrical connection and the size of the MOSFET transistors.

[0010] Thus the invention makes it possible to limit the excitation voltage (which is given by the value of the PWM signal) as a function of the speed of the electric motor.

[0011] According to one aspect of the invention, the maximum value PWMmax is determined by a look-up table as a function of the measured speed of the electric motor.

[0012] According to one aspect of the invention, the correspondence table is stored in a memory of the electrical system.

[0013] According to one aspect of the invention, the maximum value PWMmax is determined by several look-up tables (Look Up Tables) as a function of the measured speed of the electric motor, each table being associated for example with a type of weather (for example rain, sun, cold).

[0014] According to one aspect of the invention, the maximum value PWMmax is determined as a function of the measured rotational speed of the electric motor and another parameter of the motor, for example the temperature.

[0015] According to one aspect of the invention, the rotation speed is measured periodically, for example every 10 ms.

[0016] According to one aspect of the invention, the rotation speed is evaluated in the last time interval (10 ms).

[0017] According to one aspect of the invention, the method comprises the step of evaluating the speed variation in the following time slot (at +10 ms), taking into account the speed variation in the previous time slot.

[0018] According to one aspect of the invention, the maximum value of the control signal (PWMmax) is chosen to increase at least over a range of rotation speeds, when the rotation speed of the electric motor increases.

[0019] For example, the maximum control signal value (PWMmax) is chosen to be less than 80% (duty cycle) when the measured rotation speed of the electric motor is zero.

[0020] Again for example, the maximum value of the control signal (PWMmax) is chosen equal to 70% (duty cycle) when the measured rotation speed of the electric motor is zero.

[0021] The invention requires that, when the electric motor is rotating at reduced rotational speeds, the authorized rotational speed is capped.

[0022] In this range, the maximum control signal value (PWMmax) increases linearly with the rotation speed.

[0023] According to one aspect of the invention, the maximum value of the control signal (PWMmax) is chosen to be constant at least over a range of rotation speeds, when the rotation speed of the electric motor increases.

[0024] According to one aspect of the invention, the maximum value of the control signal (PWMmax) is chosen to be constant at least over a first range of rotation speeds, then increasing over a second range of rotation speeds, then constant over a third range of rotation speeds, when the rotation speed of the electric motor increases.

[0025] According to one aspect of the invention, the system comprises at least one sensor for measuring the rotation speed of the electric motor, and the information relating to the rotation speed of the electric motor is delivered by this sensor, in particular in real time.

[0026] According to one aspect of the invention, the system comprises at least one sensor for measuring the position of the output shaft of the motor, and the information relating to the rotation speed of the electric motor is obtained by derivation of the last two positions.

[0027] Other correspondence profiles between the maximum value of the control signal (PWMmax) and the rotation speed are of course possible.

[0028] According to one aspect of the invention, the maximum control signal value (PWMmax) is chosen to be dependent in stages on the rotation speed. The stages (each being of constant value) increase when the rotation speed increases.

[0029] According to one aspect of the invention, the electric motor may be of the direct current (or "DC" in English) or brushless (or "brushless DC" in English).

[0030] The invention also relates to an electrical motor system, in particular configured to actuate a wiper blade of a vehicle, in particular a motor vehicle, this electrical motor system comprising: - an electric motor configured to be powered by several electrical phases (Iphase A, Iphase B and Iphase C), in particular the electric motor being of the three-phase type; - a control circuit configured to control the supply of electrical phases to the electric motor, this control circuit comprising switches, in particular of the transistor type, these switches being in particular MOSFETs; - an electronic control unit configured to provide PWM signals to the switches of the control circuit to control them, the electronic control unit being configured to receive a measurement of the rotation speed of the electric motor and associate with this measured rotation speed of the electric motor a maximum control signal value (PWMmax), the electronic control unit being further configured to control the rotation speed of the electric motor by PWM signals whose value is lower than the maximum control signal value (PWMmax).

[0031] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and several examples of embodiment given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

[0032] [Fig.l] [Fig.l] is a simplified diagram of an electrical system for a motor vehicle according to an exemplary implementation of the invention;

[0033] [Fig.2] [Fig.2] shows the steps implemented by the motor-electric system of [Fig.l];

[0034] [Fig.3] [Fig.3] shows the variation curve of the maximum control signal value (PWMmax) as a function of the rotation speed for the system of [Fig.l];

[0035] [Fig.4] [Fig.4] shows two curves C1 and C2 with, on the abscissa, the time and, on the ordinate, the electric current, in the event of a sudden increase in the charge (following in particular a malfunction at the windshield, for example a STA blockage called "stall" in English), and curve C1 corresponds to a conventional system without limitation of the PWM, and curve C2 is obtained with system 1 according to the invention.

[0036] The features, variants and different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0037] [Fig. 1] shows a simplified diagram of an electrical system with a motor 1 for a motor vehicle in accordance with an example of implementation of the invention.

[0038] The electrical motor system 1 comprises a three-phase electric motor 2, configured to actuate one or more wiper blades of the motor vehicle. Of course, the electric motor 2 can be used for other applications, for example to operate a fan.

[0039] The electric motor 2, provided with a stator with electromagnetic excitation coils and a rotor with magnets, is of the brushless type.

[0040] The electrical motor system 1 further comprises a control circuit 3 configured to control the supply of the electrical phases Iphase A, Iphase B and Iphase C to the electric motor 2.

[0041] The control circuit 3 further comprises switches, here transistors 5 of the MOSFET type (or “Metal-Oxide-Semiconductor Field Effect Transistor”) which are six in number, with two transistors 5 for each phase Iphase A, Iphase B and Iphase C. The transistors 5 are arranged in an H-bridge configuration. These transistors 5 form an inverter.

[0042] In other words, the control circuit 3 comprises, for each phase, a MOSFET transistor on the low side (Low Side) and a MOSFET on the high side (High Side), i.e. two MOSFETs per phase Iphase A, Iphase B and Iphase C.

[0043] The control circuit 3 also comprises an electronic control unit 7 formed by a microcontroller and a driver.

[0044] The electronic control unit 7 is configured to receive set rotation speeds for the electric motor 2 and / or data concerning the desired operating mode of the electric motor 2.

[0045] The electronic control unit 7 is configured to provide PWM (Pulse Width Modulation) or MLP (for Pulse Width Modulation) control signals to the switches 5 of the control circuit 3 to control them (the PWM signal passage lines are symbolized by the lines 17 in [Fig.l]). The electronic control unit 7 is thus configured to carry out the variation of the duty cycle of the PWM signals.

[0046] The electrical motor system 1 is configured to be powered by a 12V battery, and the electronic control unit 7 is configured to deliver PWM signals with a frequency of 20Khz (Kilohertz) with a variable duty cycle in order to vary the voltage between 0 and 12V.

[0047] A method for controlling the electrical motor system 1 will now be described, the method comprising the following steps: - measure the rotation speed V of the electric motor (step SI in [Fig.2]); - associate with this measured rotation speed V of the electric motor 2 a maximum control signal value called PWMmax (step S3); - controlling the rotation speed V of the electric motor 2 by PWM signals whose value is lower than the maximum value of the control signal PWMmax, in particular the duty cycle of the PWM is smaller than the duty cycle of the PWMmax (step S3).

[0048] Thus the invention makes it possible to limit the excitation voltage (which is given by the value of the PWM signal) as a function of the speed of the electric motor.

[0049] Normally, the motor operates under stable conditions, where the motor torque is equal to the load torque, which gives a constant speed and current. In the event of a sudden increase in the load (following in particular a malfunction at the windshield, for example a STA blockage called "stall" in English), the speed decreases, and the electric current and the output torque increase. The invention aims to anticipate and prevent this increase in current, by limiting the output PWM value as a function of the motor speed. In other words, the invention caps the requested rotation speed when the motor is rotating at relatively low speeds.

[0050] The maximum value PWMmax is determined by a look-up table (Look Up Table) as a function of the measured speed of the electric motor 2.

[0051] The correspondence table is stored in a memory of the motor electrical system 1.

[0052] The maximum value PWMmax is determined by several look-up tables (Look Up Tables) as a function of the measured speed of the electric motor 2, each table being associated for example with a type of weather (for example rain, sun, cold).

[0053] PWMmax_table denotes a value from the table.

[0054] The maximum value PWMmax is modulated with the battery voltage value. If the battery voltage is low, the maximum value is increased and, if the battery voltage is high, it is reduced.

[0055] Vbat_ref is the nominal value of the battery voltage, for example being equal to 13.5V.

[0056] Vbat_measured is the measured value of the battery voltage at the time of limitation.

[0057] We have: PWMmax = PWMmax_table * Vbat_ref / Vbat_measured

[0058] In an exemplary embodiment of the invention, the maximum value PWMmax is determined as a function of the measured rotational speed of the electric motor 2 and another parameter of the motor, for example the temperature.

[0059] The rotation speed V is measured periodically, for example every 10 ms.

[0060] The rotation speed V is evaluated in the last time interval (10 ms).

[0061] The method comprises the step of evaluating the speed variation in the slot next time slot (at +10 ms), taking into account the speed variation in the previous time slot.

[0062] The maximum value of the control signal (PWMmax) is chosen to be constant at least over a first range PI of rotation speeds, then increasing over a second range P2 of rotation speeds, then constant over a third range P3 of rotation speeds, when the rotation speed of the electric motor increases, as can be seen on the curve in [Fig.3].

[0063] Thus the maximum value of the control signal (PWMmax) is chosen to increase over the range P2 of rotation speeds, when the rotation speed of the electric motor 2 increases.

[0064] For example, the maximum value of the control signal (PWMmax) is chosen to be equal to 70% (duty cycle) when the measured rotation speed of the electric motor 2 is zero.

[0065] The invention requires that, when the electric motor 2 rotates at reduced rotation speeds, the authorized rotation speed is capped.

[0066] In this range P2, the maximum value of the control signal (PWMmax) increases linearly with the rotation speed, as can be seen in the graph of [Fig.3].

[0067] [Fig.4] shows two curves C1 and C2 with, on the abscissa, the time and, on the ordinate, the electric current, in the event of a sudden increase in the load (following in particular a malfunction at the windshield, for example a STA blockage called "stall" in English). Curve C1 corresponds to a conventional system without limitation of the PWM, and curve C2 is obtained with system 1 according to the invention, with limitation of the PWM. We see that curve C2 allows a reduction of the current to 45 A instead of 65 A for curve CL. The comparison between curves C1 and C2 shows that we reduce the current by 20 A with the new protection thanks to system 1 according to the invention.

[0068] The system 1 may comprise at least one sensor for measuring the rotation speed of the electric motor, and the information relating to the rotation speed of the electric motor is delivered by this sensor, in particular in real time, or the system comprises at least one sensor for measuring the position of the output shaft of the motor, and the information relating to the rotation speed of the electric motor is obtained by derivation of two last positions.

[0069] Other correspondence profiles between the maximum value of the control signal (PWMmax) and the rotation speed are of course possible.

[0070] The maximum value of the control signal (PWMmax) is chosen to be dependent in stages on the rotational speed. The stages (each of constant value) increase when the rotational speed increases.

Claims

Claims

1. Method for controlling an electrical motor system (1), this electrical motor system (1) comprising: - an electric motor (2) configured to be powered by several electrical phases (Iphase A, Iphase B and Iphase C), in particular the electric motor (2) being of the three-phase type; - a control circuit (3) configured to control the supply of the electrical phases to the electric motor (2), this control circuit (3) comprising switches (5), in particular of the transistor type, these switches (5) being in particular MOSFETs; - an electronic control unit (7) configured to supply PWM signals to the switches (5) of the control circuit (3) to control them; the method comprising the following steps: - measuring the rotational speed (V) of the electric motor (2); - associating with this measured rotational speed of the electric motor (2) a maximum control signal value (PWMmax);- controlling the rotation speed of the electric motor (2) by PWM signals whose value is lower than the maximum control signal value (PWMmax), in particular the duty cycle of the PWM is smaller than the duty cycle of the PWMmax.;

2. Method according to the preceding claim, in which the maximum value (PWMmax) is determined by a correspondence table as a function of the measured speed of the electric motor (2), the correspondence table being in particular stored in a memory of the electrical system.

3. Method according to the preceding claim, in which the maximum value (PWMmax) is determined by several correspondence tables as a function of the measured speed of the electric motor (2), each table being associated for example with a type of weather.

4. Method according to one of the preceding claims, in which the maximum value (PWMmax) is determined as a function of the measured rotational speed of the electric motor (2) and another parameter of the motor, for example the temperature.

5. Method according to one of the preceding claims, in which the rotation speed (V) is measured periodically, for example every 10 ms, and in particular the rotation speed is evaluated in the last time interval (10 ms).

6. Method according to the preceding claim, in which the method comprises the step of evaluating the speed variation in the following time slot (at +10 ms), taking into account the speed variation in the previous time slot.

7. Method according to one of the preceding claims, in which the maximum control signal value (PWMmax) is chosen to increase at least over a range of rotational speeds, when the rotational speed of the electric motor (2) increases.

8. Method according to one of the preceding claims, in which the maximum value of the control signal (PWMmax) is chosen to be constant at least over a first range (PI) of rotation speeds, then increasing over a second range (P2) of rotation speeds, then constant over a third range (P3) of rotation speeds, when the rotation speed of the electric motor (2) increases.

9. Method according to one of the preceding claims, in which the system comprises at least one sensor for measuring the rotation speed of the electric motor (2), and the information relating to the rotation speed of the electric motor (2) is delivered by this sensor, in particular in real time, or a sensor for measuring the position of the output axis of the motor, and the information relating to the rotation speed of the electric motor (2) is obtained by derivation of two last positions.

10. Electrical motor system in particular configured to actuate a wiper blade of a vehicle, in particular a motor vehicle, this electrical motor system comprising: - an electric motor (2) configured to be powered by several electrical phases (Iphase A, Iphase B and Iphase C), in particular the electric motor (2) being of the three-phase type; a control circuit (3) configured to control the supply of electrical phases to the electric motor (2), this control circuit (3) comprising switches (5), in particular of the transistor type, these switches (5) being in particular MOSFETs; an electronic control unit (7) configured to provide PWM signals to the switches (5) of the control circuit (3) to control them, the electronic control unit (7) being configured to receive a measurement of the rotation speed of the electric motor (2) and to associate with this measured rotation speed of the electric motor (2) a maximum control signal value (PWMmax), the electronic control unit (7) being further configured to control the rotation speed of the electric motor (2) by PWM signals whose value is lower than the maximum control signal value (PWMmax).

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