Method for controlling an electrical system including a motor

Abstract

The invention relates to a method for controlling an electrical system (1) including a motor, comprising: - an electric motor (2) configured to be supplied with power by multiple electrical phases (Iphase A, Iphase B and Iphase C), the electric motor in particular being a three-phase motor; - a control circuit (3) configured to control the supply of power from the electrical phases to the electric motor, this control circuit comprising switches, in particular transistor switches (5), these switches in particular being MOSFETs; - an electronic control unit (7) configured to supply PWM control signals to the switches of the control circuit in order to control them, the electronic control unit (7) furthermore being configured to generate an offset in the duty cycle of the PWM control signal for all of the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, this threshold value for example being equal to 20% or 25%, such that the PWM signal that is delivered increases, in particular continuously and proportionally, from a predetermined, non-zero starting value for any request for a PWM signal having a value lower than the predetermined threshold value.

Description

Method of controlling an electric 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, air or space 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 direct current battery (e.g. 12V), and an electronic control unit is configured to generate PWM signals of frequency 20Khz (Kilohertz) with a variable duty cycle in order to vary the voltage between 0 Volt and the maximum voltage of the battery (e.g. 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 proportionally between 0% and 100%, which corresponds to varying the voltage between 0V (0% duty cycle) and the maximum battery voltage (100% duty cycle).

[0005] It is known to use switches, especially formed by electronic components such as transistors, MOSFET, IGBT…etc., to inject PWM signals into the phase(s) of the electric motor, and in order to avoid a short circuit in the power switches, especially the High Side and Low Side cells of each phase, it is necessary to introduce a dead time. This dead time, also called "dead time" in English, is important to avoid simultaneous activation of the two MOSFETs, as this could lead to the creation of a low resistance path between a power supply and a ground, thus causing a risk of unwanted short circuit that could damage the battery.

[0006] Because of this effect, it is not possible to have the PWM signal between certain duty cycle percentages. For example, for a PWM signal with a frequency of 20 kHz, one period is 50 µs, and the dead time is typically between 0.3 µs and 1.5 µs (microseconds). Assuming that the dead time is 1 µs, there will be 2 µs of dead time per period (taking into account the rising and falling). Therefore, the percentage associated with the dead time is 4%. This means that it is not allowed to vary the PWM between 0% and 4%, nor between 96% and 100%. Typically, if the duty cycle required by the electrical system is less than 4%, the output duty cycle is considered to be 0%. The same applies to the requested duty cycle greater than 96% (the output duty cycle is then considered to be 100%). This is illustrated in the.

[0007] Due to the dead times between 0% and 4%, and between 96% and 100%, the control signal is degraded. For example, in the case of motors using three-phase sinusoidal controls, in order to generate sinusoidal voltages between two phases of the motor, Flat Bottom Space Vector Modulation is used. When there is a low speed, there is a low load and the PWM value is normally lower. The dead time between 0% and 4% can strongly distort the excitation signals (see figures 5 and 6) and create anomalies in the behavior of the electric motor such as noise, vibrations, undesirable EMC effects (EMC for "electromagnetic compatibility"). The shows the three phases affected by the dead times. The shows the voltage between two phases with anomalies due to these dead times, voltage obtained by two phases of the.

[0008] The present invention aims in particular to avoid or reduce these anomalies.

[0009] The subject of the invention is thus a method for controlling an electrical motor system comprising: an electric motor configured to be powered by one or more electrical phases, in particular the electric motor being of the three-phase type; a control circuit configured to control the power supply of the electrical phases to the electric motor, this control circuit comprising switches, in particular of the transistor type, these switches being in particular MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) or any other type of electronic components operating as a switch (open or closed);an electronic control unit configured to provide PWM control signals (Pulse Width Modulation in English, or MLI for "Modulation de Largeur d'Impulse" in French) to the switches of the control circuit to control them, the electronic control unit being further configured to generate an offset of the duty cycle of the PWM control signal for all the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal increases, in particular proportionally, from a predetermined, non-zero starting value, for any request for a PWM signal of a value less than the predetermined threshold value.;

[0010] By means of the invention, the delivered PWM signal and the requested PWM signal can have a proportional dependence over the entire operating range, namely from 0% to 100% in terms of duty cycle. In particular, the invention makes it possible to prevent the voltage delivered to the phases of the motor from being discontinuous (for example clamped to ground) over certain requested duty cycle values, in particular values ​​which are lower than the predetermined threshold, thus causing the generation of undesirable harmonics.

[0011] Preferably, the PWM signals delivered by the electronic control unit are configured to generate Flat Bottom Space Vector Modulation (or Flat Bottom SVM) type phases so as to generate sinusoidal voltages between two phases of the motor.

[0012] According to one aspect of the invention, the PWM signals delivered by the electronic control unit are configured to obtain a voltage between phases of the motor which is substantially sinusoidal, namely as sinusoidal as possible.

[0013] According to one aspect of the invention, the shift in the duty cycle of the PWM control signal is between 2% and 50%, in particular between 4% and 10%, being for example equal to 4%.

[0014] The invention, thanks to the shift (or "offset" in English) of the duty cycle of the PWM signal, allows in a way to make the flat bottoms (or "flat bottoms") of the phases touch so that the voltage between two phases of the motor is sinusoidal.

[0015] According to one aspect of the invention, the control circuit comprises six switches, in particular six MOSFETs.

[0016] According to one aspect of the invention, each phase is controlled by two switches, in particular of the MOSFET type.

[0017] The invention allows to avoid the deformation of the excitation voltage of the motor, to introduce a significant improvement of acoustic noise, vibrations and EMC (Electromagnetic Compatibility).

[0018] According to one aspect of the invention, the control circuit comprises, for each phase, a low-side MOSFET transistor connected between one of the phases and the battery ground (directly or indirectly) and a high-side MOSFET connected between one of the phases and the positive terminal of the battery (directly or indirectly).

[0019] The PWM generation strategy according to the invention makes it possible in particular to avoid saturation of the low side of the MOSFET.

[0020] The invention also relates to an electrical motor system comprising: an electric motor configured to be powered by one or more electrical phases, in particular the electric motor being of the three-phase type; a control circuit configured to control the power supply of the electrical phases to the electric motor, this control circuit comprising switches, in particular of the transistor type, these switches being in particular MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors);an electronic control unit configured to provide PWM (Pulse Width Modulation) type control signals to the switches of the control circuit to control them, the electronic control unit being further configured to generate an offset of the ratio of the PWM control signal for all the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal increases, in particular continuously and proportionally, from a predetermined, non-zero starting value, for any request for a duty cycle of a value less than the predetermined threshold value.;

[0021] According to one aspect of the invention, the electrical motor system comprises one or more wiper blades, in particular of a motor vehicle, which can be actuated by the motor.

[0022] According to one aspect of the invention, the electric motor is of the direct current type.

[0023] According to one aspect of the invention, the electric motor is of the brushless type.

[0024] According to one aspect of the invention, the electric motor is configured to actuate one or more wiper blades.

[0025] The invention also relates to an electronic control unit for an electrical motor system as mentioned above, and configured to supply PWM type control signals to switches of a control circuit to control them, the electronic control unit being further configured to generate an offset of the duty cycle of the PWM control signal for all the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal increases, in particular continuously and proportionally, from a predetermined, non-zero starting value, for any request for a PWM signal of a value less than the predetermined threshold value.

[0026] 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:

[0027] This is a simplified diagram of an electrical system for a motor vehicle according to an example of implementation of the invention;

[0028] Lamontre shows the three phases delivered in the motor electrical system of the;

[0029] La shows the sinusoidal voltage Vm between phases Iphase A and Iphase C obtained using the phases illustrated on the ;

[0030] Lamontre the linear evolution of the output PWM signal called PWMe with respect to the requested PWM signal called PWMr for the motor electrical system of the;

[0031] Shows the linear evolution of the output PWM signal called PWMe with respect to the requested PWM signal called PWMr affected by dead times;

[0032] Lamontre shows the three phases affected by timeouts;

[0033] Lamontre the voltage between two phases with anomalies due to these dead times, voltage obtained by two phases of the.

[0034] 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 conceived 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.

[0035] There is shown 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.

[0036] The electrical motor system 1 comprises a three-phase electric motor 2, configured to operate 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.

[0037] The electric motor 2, provided with a stator with electromagnetic excitation coils and a rotor with magnets, is of the brushless type.

[0038] 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.

[0039] The control circuit 3 also includes switches, here MOSFET (or “Metal-Oxide-Semiconductor Field Effect Transistor”) type transistors 5 of which there are six, 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.

[0040] 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.

[0041] The control circuit 3 also includes an electronic control unit 7 formed by a microcontroller and a system for controlling power components such as MOSFETS (also called “Bridge driver” in English).

[0042] The electronic control unit 7 is configured to receive rotation speed instructions for the electric motor 2 and / or data concerning the desired operating mode of this electric motor 2.

[0043] The electronic control unit 7 is configured to provide PWM (Pulse Width Modulation) or MLI (for “Modulation de Largeur d'Impulse” in French) type 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 on the). The electronic control unit 7 is thus configured to carry out the variation of the duty cycle of the PWM signals.

[0044] The motor electrical system 1 is configured to be powered by a direct current battery (for example 12V), and the electronic control unit 7 is configured to deliver PWM signals with a frequency of 20Khz (Kilohertz) or any other modulation frequency, with a variable duty cycle in order to vary the voltage between 0 and the maximum battery voltage.

[0045] The PWM signals delivered by the electronic control unit 7 are configured to generate phase currents Iphase A, Iphase B and Iphase C of the Flat Bottom Space Vector Modulation (or in English "Flat Bottom Space Vector Modulation" or "Flat Bottom SVM" type (see which shows the three phases) so as to generate sinusoidal voltages between two phases of the motor. For example, shows the sinusoidal voltage Vm between phases Iphase A and Iphase C obtained thanks to the phases illustrated in the, in the following manner:

[0046] Vm=Vbat*((PWMA+∆PWM) – (PWMC +∆PWM)) where Vbat is the battery voltage for example equal to 12V, PWMA is the value of the current amplitude of phase Iphase A, PWMC the value of the current amplitude of phase Iphase C and ∆PWM the offset of the PWM signal (which is described below).

[0047] In the example in Figures 2 and 3, the ∆PWM offset is 4%.

[0048] The electronic control unit 7 is configured to generate a shift in the PWM signal duty cycle for all phases Iphase A, Iphase B and Iphase when the amplitude of the phase voltage applied to a phase is less than a predetermined threshold value TR, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal is continuous and proportional, from a predetermined, non-zero starting value, for any request for a phase voltage amplitude of value less than the predetermined threshold value TR.

[0049] This is an example showing the linear evolution of the output PWM signal called PWMe with respect to the requested PWM signal called PWMr. As can be seen in the, for a PWM signal request that starts at a PS value lower than the predetermined threshold value TR, the linear evolution starts from the starting PS value.

[0050] For a PWM signal request that starts at PS=0%, the linear evolution starts from the value PS=0% (see curve C1).

[0051] For a PWM signal request that starts at PS>0%, the linear evolution starts from the PS value (see curve C2).

[0052] The linear evolution starts at a point above zero (either curve C1 or curve C2), with the offset ∆PWM. In other words, the invention adds an offset to all three phases to use only the linear region.

[0053] By adding this offset, the phase-to-phase voltage of the motor becomes sinusoidal, which avoids distortion of the motor excitation voltage, introducing a significant improvement in acoustic noise, vibrations and EMC (Electromagnetic Compatibility).

[0054] The motor electrical system 1 further includes circuits 15 for current detection on phases Iphase A, Iphase B and Iphase C and a temperature measurement circuit 16, for more precise control of the three-phase motor.

Claims

Method for controlling an electrical motor system (1) comprising: an electric motor (2) configured to be powered by one or more electrical phases (Iphase A, Iphase B and Iphase C), in particular the electric motor being of the three-phase type; a control circuit (3) configured to control the power supply of the electrical phases to the electric motor, this control circuit comprising switches, in particular of the transistor type (5), these switches being in particular MOSFETs;an electronic control unit (7) configured to provide PWM control signals to the switches of the control circuit to control them, the electronic control unit (7) being further configured to generate an offset of the duty cycle of the PWM control signal for all the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal increases, in particular continuously and proportionally, from a predetermined, non-zero starting value, for any request for a PWM signal of a value less than the predetermined threshold value.; Method according to the preceding claim, in which the PWM signals delivered by the electronic control unit (7) are configured to obtain a voltage between phases of the motor which is substantially sinusoidal. Method according to one of the preceding claims, in which the PWM signals delivered by the electronic control unit (7) are configured to generate phases of the “Flat Bottom Space Vector Modulation” type so as to generate sinusoidal voltages between two phases of the motor. Method according to one of the preceding claims, in which the shift in the duty cycle of the PWM control signal is between 2% and 50%, in particular between 4% and 10%, being for example equal to 4%. Method according to one of the preceding claims, in which the control circuit (3) comprises six switches (5), in particular six MOSFETs, and in particular each phase is controlled by two switches, in particular of the MOSFET type. Method according to one of the preceding claims, in which the control circuit comprises, for each phase, a low side MOSFET transistor connected between one of the phases and the ground of the battery and a high side MOSFET connected between one of the phases and the positive terminal of the battery. Electrical motor system (1) comprising: an electric motor (2) configured to be powered by one or more electrical phases, in particular the electric motor being of the three-phase type; a control circuit (3) configured to control the power supply of the electrical phases to the electric motor, this control circuit comprising switches, in particular of the transistor type, these switches being in particular MOSFETs (5);an electronic control unit configured to provide PWM control signals to the switches of the control circuit to control them, the electronic control unit being further configured to generate an offset of the duty cycle of the PWM control signal for all the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal increases, in particular proportionally, from a predetermined, non-zero starting value, for any request for a duty cycle of value less than the predetermined threshold value.; Electrical motor system (1) according to the preceding claim, wherein the electrical motor system (1) comprises one or more wiper blades, in particular of a motor vehicle, which can be actuated by the motor (2). Electric motor system (1) according to claim 7 or 8, wherein the electric motor is of the direct current type, in particular of the brushless type. Electronic control unit for an electrical motor system (1) according to one of claims 7 to 9, and configured to supply PWM control signals to switches (5) of a control circuit (3) to control them, the electronic control unit being further configured to generate an offset of the duty cycle of the PWM control signal for all the phases when the amplitude of the voltage of the phases resulting from the applied duty cycle is less than a predetermined threshold value, for example this threshold value being equal to 20% or 25%, so that the delivered PWM signal increases, in particular continuously and proportionally, from a predetermined, non-zero starting value, for any request for a PWM signal of a value less than the predetermined threshold value.

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