Minimizing the motor torque of a wound-rotor synchronous machine during the thermal preconditioning of the battery

Abstract

The invention relates to a method for generating thermal losses in a powertrain (2) that comprises a synchronous electric machine (3) comprising a stator and a wound rotor, the method comprising: - a step of acquiring a temperature in or around the powertrain; - a step of estimating a relative angle between the rotor and the stator; - depending on the acquired temperature, a step of controlling the rotor and the stator so that they generate thermal losses and that they remain substantially stationary relative to one another, the rotor being controlled with a nonzero rotor current. The invention also relates to a powertrain suitable for implementing the method according to the invention, and to a motor vehicle equipped with such a powertrain.

Description

Description Title of the invention: minimization of the motor torque of a wound rotor synchronous machine during thermal preconditioning of the battery

[0001] The present invention relates generally to electrical machines, in particular to electrical machines powered by a battery.

[0002] It concerns more particularly the conditioning, or preheating, of the battery associated with an electric machine.

[0003] The invention finds a particularly advantageous application in the automotive field. State of the art

[0004] Some battery-powered electrical machines, particularly electrical machines in motor vehicles, are sometimes subjected to very low or even negative temperatures, for example in winter.

[0005] However, battery performance is, to a certain extent, inversely proportional to temperature. Thus, when starting the electric machine, for example when starting a motor vehicle after prolonged outdoor parking in cold weather, the battery performance may leave something to be desired.

[0006] Solutions exist for preheating the battery before using the motor vehicle, which aim to obtain optimal performance from the vehicle from the first moments of its use.

[0007] Among these solutions, there is the addition of an additional heating device, called PTC (Positive Temperature Coefficient) heating, dedicated to preheating the battery. However, this solution is expensive.

[0008] Another solution involves controlling the electric machine in such a way as to increase the thermal losses produced by the traction chain, and to use this excess heat to warm the battery.

[0009] In order to preheat the battery while the vehicle is parked, it is necessary that the control of the electric machine does not cause the appearance of an engine torque in order to keep the vehicle stationary. This solution requires knowing the position of the rotor precisely so that the electromagnetic force generated by the stator does not generate a torque. However, it happens that the position of the rotor measured by the vehicle is erroneous by a few degrees. This then results in the generation of an engine torque which can cause the vehicle to move.

[0010] The French patent application published under number FR 3 080 239 proposes such a process in which the stator control is controlled by the value of the rotor position measurement error. Presentation of the invention

[0011] In order to provide an alternative to the state of the art, the present invention proposes to increase the thermal losses of the powertrain without producing a torque which would set the vehicle in motion, nor controlling the stator control on the value of the rotor position measurement error.

[0012] More particularly, the invention proposes a method for generating thermal losses in a traction chain which comprises a synchronous electrical machine comprising a stator and a wound rotor, the method comprising: - a step of acquiring a temperature in or around the traction chain, - a step of estimating a relative angle between the rotor and the stator, - depending on the acquired temperature, a step of controlling the rotor and the stator so that they generate thermal losses and remain substantially immobile relative to each other, in which the stator is controlled, in a Park reference frame resulting from the estimation of the relative angle, so that a first of the stator currents is zero and a second of the stator currents is non-zero, and in that the rotor is controlled with a non-zero rotor current.

[0013] Estimating the relative angle between the rotor and the stator can include estimating the relative angle between the rotor and the stator currents. In other words, the rotor angle (estimated or measured) is used and a Park transformation is applied to the three stator control currents to obtain the two stator currents in the Park frame. The relative angle between the stator currents in the Park frame and the rotor is then directly contained in the first and second stator currents, since the stator control can be expressed, in the Park frame, in polar coordinates using the amplitude of the stator current vector and the angle of the stator current vector with respect to the q axis of the Park frame.

[0014] Thanks to the invention, it is possible to generate thermal losses while maintaining a zero or negligible torque. In particular, the rotor control makes it possible to simply compensate for a torque that would be due to a measurement error in the rotor position. This eliminates the need to determine a possible error in the measured position of the rotor, and the need to control the stator control based on the measurement error in the rotor position.

[0015] Other advantageous and non-limiting characteristics of the electrical machine according to the invention, taken individually or in all technically possible combinations, are the following: - the second stator current and the rotor current are determined as a function of the acquired temperature. - the second stator current and the rotor current are such that the rotor remains stationary even if the estimated relative angle has an error of plus or minus 15 degrees, and preferably plus or minus 45°. - the electric machine being powered by a traction battery, the temperature is measured at the traction battery. - at least part of the heat losses is transmitted to the traction battery by a heat transfer circuit. - rotor control and stator control involve the use of a correspondence table which allows each temperature value to be associated with a value of the second of the stator currents and with a rotor current value. - if the acquired temperature is lower than a first predetermined threshold, then the second of the stator currents and the rotor current are equal to first predetermined values, if the acquired temperature is between the first threshold and a second threshold, then the second of the stator currents and the rotor current are equal to second predetermined values, for example a second value of second stator current and a second value of rotor current greater in absolute value respectively than the first predetermined value of second rotor current and the second predetermined value of rotor current, if the acquired temperature is higher than the second threshold, then the second of the stator currents and the rotor current are equal to third values,for example a third predetermined value of second stator current and a third predetermined value of rotor current greater in absolute value respectively than the second predetermined value of second stator current and the second predetermined value of rotor current., - the rotor is controlled with a rotor current capable of generating a torque less than or equal to 2 Nm

[0016] According to another aspect of the invention, there is provided a traction chain comprising a synchronous electrical machine comprising a rotor and a wound stator and equipped with a rotor and stator control module configured to implement the method according to the invention.

[0017] Other advantageous and non-limiting characteristics of the traction chain according to the invention, taken individually or in all technically possible combinations, are the following: - the traction chain comprises a traction battery and a heat transfer circuit common to the electric machine and the traction battery, the heat transfer circuit being adapted to cool the electric machine and the traction battery traction. - the heat transfer circuit comprises a first section associated with the traction battery and a second section associated with the stator, the first section and the second section being thermally coupled in a first configuration of the heat transfer circuit and thermally isolated in a second configuration of the heat transfer circuit - the heat transfer circuit comprises at least one valve configured to, in the first configuration of the heat transfer circuit, thermally couple the first section and the second section and, in the second configuration, thermally isolate the first section from the second section.

[0018] According to another aspect of the invention, a motor vehicle is provided equipped with a powertrain according to the invention.

[0019] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0020] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0021] On the attached drawings:

[0022] [Fig.l] illustrates a motor vehicle equipped with a powertrain according to the invention and adapted to the implementation of the method according to the invention;

[0023] [Fig.2] illustrates a mode of implementation of the method according to the invention;

[0024] [Fig.3] illustrates another mode of implementation of the method according to the invention;

[0025] [Fig.4] illustrates the evolution of the torque applied to the rotor of an electric machine as a function of the uncertainty in the position of the rotor, for different values ​​of rotor current;

[0026] [Fig.5] illustrates the evolution of the motor torque as a function of the rotor current, for different values ​​of stator current;

[0027] [Fig.6] illustrates the evolution of the losses generated by the vehicle's electrical machine as a function of the rotor current, for different values ​​of stator current,

[0028] [Fig.7] illustrates the evolution of the losses generated by the power electronics of the vehicle's traction chain as a function of the rotor current, for different values ​​of stator current,

[0029] [Fig.8] illustrates the evolution of the total losses generated by the vehicle's traction chain as a function of the rotor current, for different values ​​of stator current,

[0030] As a preliminary point, it will be noted that the identical elements of the invention represented in the different figures will, as far as possible, be referenced by the same reference signs.

[0031] It will also be noted that in this description, we will begin by describing an example of a motor vehicle in accordance with the invention, then an example of a method implemented by this vehicle, before describing how this method was configured.

[0032] [Fig.l] illustrates a motor vehicle 1 equipped with a traction chain 2 comprising an electric machine 3, here a three-phase synchronous electric machine with wound rotor, powered by a traction battery 4 providing a direct electric current. The traction chain 2 further comprises various components (not shown), in particular power electronic components, making it possible, for example, to adapt the current supplied by the traction battery 4 to the control of the electric machine. An inverter is an example of such a component.

[0033] A control module 5 is here configured to control the electrical machine 3, in particular to control the control signals circulating in the rotor and in the stator of the motor vehicle 1.

[0034] The motor vehicle 1 is here equipped with a heat transfer system 6 thermally coupled to the electric machine 3 and to the traction battery 4.

[0035] The heat transfer circuit 6 here comprises a first section 7 coupled to the electric machine 3, and a second section 8 coupled to the traction battery 4. Each of these sections comprises one or more coolant circulation pipes, and a heat exchanger associated with the electric machine 3 or the traction battery 4.

[0036] In this embodiment, the heat transfer circuit 6 comprises a system 9 of valves making it possible to connect the first section 7 and the second section 8 so that they form a single circuit, or to isolate the first section 7 from the second section 8 so that they form two separate circuits, i.e. thermally isolated. For example, the valve system is controlled by the control module 5. For example, the control means can control the valve system so that the sections 7, 8 are dissociated during the running of the vehicle 1, and so that they are coupled during the implementation of the method according to the invention.

[0037] The motor vehicle 1 is suitable for implementing the method according to the invention. The control module 5 is here programmed to control the electric machine 3 in such a way that it generates thermal losses independent of the engine torque, for example when the vehicle is stationary, as detailed below.

[0038] [Fig.2] illustrates a mode of implementation of the method by the control module of the motor vehicle 1.

[0039] For the purpose of simplifying the presentation, the stator control is considered here in a Park frame of axes d, q. The Park transform makes it possible to model the three-phase system of the electrical machine 3, conventionally presented in a fixed frame linked to the stator, by a two-phase system in a rotating frame linked to the rotor. Thus, the stator control will not be presented here as a triplet of alternating currents phase-shifted by 120°, but as a pair of direct currents Id and Iq (hereinafter first stator current Iq and second stator current Id). The first stator current Id corresponds to the stator current projected onto the direct axis of the rotor (conventionally called the “d axis”), which is parallel to the rotor coil. The second stator current Iq corresponds to the stator current projected onto the quadrature axis of the rotor (conventionally called the “q axis”) which is perpendicular to the rotor coil.The stator control can also be expressed, in the Park frame, in polar coordinates using the amplitude Is of the stator current vector and the angle of the current vector relative to the q axis of the Park frame.

[0040] The control module 5 is here configured to control the electric machine 3 so that the drive train generates thermal losses which are independent of the torque applied to the rotor. In particular here, the control module is configured to generate thermal losses without causing movement of the vehicle 1, that is to say by keeping the torque applied to the rotor below a predetermined threshold, for example below 5 Nm, or even below 2 Nm, and preferably equal to zero.

[0041] Preferably, the thermal losses generated by the traction chain are directed towards one or more other elements of the traction chain, in particular thanks to the thermal transfer circuit 6. Preferably here, the thermal losses are directed towards the traction battery 4 via the thermal transfer circuit 6 in order to heat this battery when its temperature is low.

[0042] In order to know the temperature of the traction battery 4 and to deduce therefrom the quantity of thermal losses to be generated, the method comprises a step E1 of acquiring a temperature in or around the traction chain, for example at the level of the battery 4, in particular by means of one or more dedicated temperature sensors.

[0043] The control module 5 then implements a step E2 of estimating the position of the rotor, for example using a module for measuring the relative angle between the rotor and the stator, which will enable it to generate the appropriate command of the stator in the Park reference frame corresponding to the estimated position.

[0044] Depending on the acquired temperature, the control module 5 controls the electrical machine 3 so that it generates thermal losses and so that the rotor and the stator remain substantially immobile relative to each other (step E3). The thermal losses can be generated, for example, depending on the temperature measured from traction battery 4 and a target temperature to be reached.

[0045] In particular, the control module 5 controls the electrical machine 3 so that, in the Park reference frame determined from the relative position of the rotor and the stator, the first stator current Iq is zero and the second stator current Id has a non-zero value which depends on the acquired temperature or, in polar coordinates, so that the amplitude Is of the current vector depends on the acquired temperature and so that the angle Psi is zero.

[0046] In particular, in order to compensate for a possible error in estimating the position of the rotor, the control module 5 controls the rotor with a non-zero rotor current.

[0047] The method according to the invention can advantageously be used in the context of preconditioning, or preheating, the traction battery 4, prior to the use of the vehicle 1, so that even in cold weather, the traction battery 4 exhibits optimal performance from the first moments of use of the vehicle.

[0048] The method according to this embodiment can be programmed so as to be triggered at a specific time of day, for example one hour before the use of the vehicle 1, or be triggered directly remotely, for example using a mobile communication system, in particular from a computer connected to the Internet.

[0049] In this method, the control module is configured to operate in three different active modes, depending on the temperature of the battery 4. The idea is that the losses emitted are all the greater as the temperature is low.

[0050] In a first operating mode associated with a temperature of the battery 4 below a first predetermined threshold, here 0°C, the second stator current is equal to a first stator current value, here -176 A, and the rotor current is equal to a first rotor current value, here 2.9 A.

[0051] In a second operating mode associated with a temperature of the battery 4 between the first threshold and a second threshold, here 4°C, the second stator current Id is equal to a second stator current value, here -115 A, and the rotor current is equal to a second rotor current value, here 1.9 A.

[0052] In a third operating mode associated with a temperature of the battery 4 greater than the second threshold and less than a third threshold, here 8°C, then the second stator current is equal to a third stator current value, here -55 A, and the rotor current is equal to a third rotor current value, here 0.8 A.

[0053] When the battery temperature reaches the third threshold, the process ends (inactive mode).

[0054] For example, in an initial situation, the vehicle is parked outside by cold weather and battery 4, inactive for a sufficiently long time, has a temperature roughly equal to the outside temperature, here -5 degrees.

[0055] As illustrated in [Fig. 3], when the process is triggered, the control module 5 triggers a measurement MO of the battery temperature. Here, the measured temperature is lower than the first threshold and the process is therefore triggered according to the first mode M1, which here results in the generation of a thermal power of 1500 W by the traction chain. The control module 5 maintains the corresponding current values ​​so as to increase the battery temperature. If the measured temperature had been different, the process would have continued according to another operating mode, for example an operating mode resulting in the generation of a lower thermal power, here the second mode M2 ​​or the third mode M3.

[0056] When the temperature of the battery 4 reaches the first threshold, then the method is implemented according to the second mode M2, which here results in the generation of a thermal power of 900 W by the drive train, and the temperature of the battery 4 continues to increase. When it reaches the second threshold, then the method is implemented according to the third mode M3, which here results in the generation of a thermal power of 450 W, and the temperature of the battery continues to increase. When it reaches the third threshold, the method ceases (step F, corresponding to the inactive mode) and the motor vehicle is ready for use with optimal battery performance.

[0057] The values ​​of the control currents of the electrical machine 3 are here chosen from a pre-established correspondence table. For example, the correspondence table may have been established from a computer program implementing a quasi-static energy model, here a model of an assembly comprising the inverter and the electrical machine.

[0058] In order to understand the principle on which this model is based and how these values ​​were chosen, it is appropriate to consider the following equation giving the value of the torque Ce applied to the rotor:

[0059] [Math.l] Ce = ^{ dldlq - LqldJq + Mf J fdqj

[0060] With Ld and Lq the stator inductances on the d and q axes of the Park frame (not equal in a salient pole machine), Mf the mutual inductance between the rotor and the stator, If the rotor current and p the number of stator pole pairs.

[0061] In order to cancel the torque value Ce, the cancellation of the first stator current value Iq seems obvious. The production of thermal losses would then be ensured by the second stator current Id.

[0062] However, the concept of first stator current Iq and second stator current Id only makes sense in relation to the rotor position, since the Park frame is a frame linked to the rotor. Thus, in the event of an error in measuring the rotor position, for example an error of a few degrees, the determined stator current values ​​Id and Iq correspond to an erroneous Park frame which is slightly offset from its actual position (the rotor position). This results in slightly different actual values ​​(in the unoffset Park frame) of the currents Id and Iq, and therefore a non-zero current Iq (or a non-zero angle Psi). This then risks producing a dangerous engine torque when the motor vehicle must remain stationary.

[0063] The inventors were able to determine, using simulations and tests on test benches, the evolution of the electromagnetic torque produced by the electrical machine as a function of the error in the position of the rotor, translated here by a variation of the angle Psi of plus or minus 15° around -90° (i.e. over a range from -105° to -75°), for a fixed value of the second stator current Id equal to -250 A. [Fig.4] illustrates the results from the simulation, for stator current values ​​If ranging from 0 to 6 A.

[0064] In [Fig.4], we observe that an optimal value of the rotor current is equal to 4 A, since it guarantees a torque to the rotor (the “machine torque”) that is almost zero over the entire variation range studied.

[0065] The quasi-static energy model was therefore developed in order to produce a correspondence table, or value mapping, which can be used in the method according to the invention. This model takes into account the electromagnetic operating equations of the electric machine and uses parameters of the electric machine derived from simulations. Such a model receives, as input value, the polar coordinates of the stator current in the unshifted Park frame, the rotor current, the speed of the electric machine and the temperatures of the rotor and stator. The quasi-static energy model provides as output the corresponding torque applied to the rotor shaft as well as the total losses, i.e. here the losses generated by the inverter and the losses generated by the electric machine 3.

[0066] [Fig.5] to 8 illustrate part of the results obtained for a 15° error in the rotor position (i.e. Psi = -105°) as a function of the rotor current. [Fig.5] illustrates the evolution of the torque applied to the rotor (the “machine torque”), [Fig.6] illustrates the evolution of the thermal losses generated by the electric machine 3 (the “ME losses”), [Fig.7] illustrates the evolution of the thermal losses generated by the power electronics of the traction chain 2 (the “EDP losses”), and [Fig.8] illustrates the evolution of the total losses of the traction chain 2, i.e. the thermal losses generated by the power electronics and by the electric machine 3. Each of the figures represents five curves which correspond to five values distinct from the amplitude of the current vector Is in the Park frame, here 55 A, 85 A, 115 A, 145 A and 176 A. The crosses correspond to thousand torque values, and therefore to the optimal values ​​of the rotor and stator currents.

[0067] We observe here that the rotor current value is strongly dependent on the stator current value.

[0068] Thus, the quasi-static energy model makes it possible to obtain a correspondence between the stator current, the rotor current and the losses generated by the traction chain so that the motor torque is substantially zero. These values ​​can be recorded in the correspondence table used in the method according to the invention.

[0069] It is further possible to associate each triplet of values ​​with a corresponding temperature range, in order to implement the method according to the embodiment described previously in connection with figures 2 and 3.

[0070] The invention is not limited to the embodiments and implementations described above. Thus, although a method implementing three operating modes M1, M2 and M3 associated with three temperature threshold values ​​has been described above, the method is compatible with any other number of operating modes, each associated with a distinct temperature range. The temperature ranges may also be of different amplitudes. For example, a single operating mode could be provided when the temperature is below 8°C. Again, for example, more than four operating modes could be provided.

[0071] Furthermore, heat exchanges between the electric machine 3 and the traction battery 4 have been described here in order to heat the latter. The invention is of course not limited to this exchange and preferably, the heat exchanges are carried out between several elements of the traction chain, for example the inverter and the electric machine, and the battery.

[0072] Finally, the invention is not limited to preheating the battery, but is also applicable to preheating other elements of the vehicle 1, for example to heat or preheat elements external to the powertrain 2, typically the passenger compartment of the vehicle 1.

[0073] Furthermore, the temperature measurement can be carried out at another level of the powertrain or at another level of the vehicle, and / or be carried out at different locations of the vehicle.

[0074] Finally, the process can be implemented to heat another element of the powertrain.

Claims

Claims

1. Method for generating thermal losses in a traction chain (2) which comprises a synchronous electrical machine (3) comprising a stator and a wound rotor, the method comprising: - a step of acquiring a temperature in or around the traction chain (2), - a step of estimating a relative angle between the rotor and the stator, - depending on the acquired temperature, a step of controlling the rotor and the stator so that they generate thermal losses and remain substantially immobile relative to each other, characterized in that the stator is controlled, in a Park frame resulting from the estimation of the relative angle, so that a first of the stator currents (Iq) is zero and a second of the stator currents (Id) is non-zero, and in that the rotor is controlled with a non-zero rotor current (If).

2. Method according to claim 1, in which the second stator current (Id) and the rotor current (If) are determined as a function of the acquired temperature.

3. Method according to claim 1 or 2, in which the second stator current (Id) and the rotor current (If) are such that the rotor remains stationary even if the estimated relative angle has an error of plus or minus 15 degrees, and preferably of plus or minus 45°.

4. Method according to any one of claims 1 to 3, wherein the electric machine (3) being powered by a traction battery (4), the temperature is measured at the traction battery (4).

5. A method according to claim 4, wherein at least part of the heat losses is transmitted to the traction battery (4) by a heat transfer circuit.

6. A method according to any one of claims 1 to 5, wherein the rotor control and the stator control comprise the use of a correspondence table which makes it possible to associate each temperature value with a value of the second of the stator currents (Id) and with a rotor current value (If).

7. A method according to claim 6, wherein - if the acquired temperature is lower than a first predetermined threshold, then the second of the stator currents (Id) and the rotor current (If are equal to first predetermined values, - if the acquired temperature is between the first threshold and a second threshold, then the second (Id) of the stator currents and the rotor current (If) are equal to second values, - if the acquired temperature is higher than the second threshold, then the second of the stator currents and the rotor current are equal to third values.

8. Method according to any one of claims 1 to 7, in which the rotor is controlled with a rotor current (If capable of generating a torque less than or equal to 2 Nm

9. Traction chain comprising a synchronous electrical machine (3) comprising a rotor and a wound stator and equipped with a control module (5) for the rotor and the stator configured to implement the method according to any one of claims 1 to 8.

10. Traction chain according to claim 9, comprising a traction battery (4) and a heat transfer circuit (6) common to the electric machine (3) and to the traction battery (4), the heat transfer circuit (6) being adapted to cool the electric machine (3) and the traction battery (4)

11. A traction chain according to claim 10, wherein the heat transfer circuit (6) comprises a first section (7) associated with the traction battery (4) and a second section (8) associated with the stator, the first section (7) and the second section (8) being thermally coupled in a first configuration of the heat transfer circuit (6) and thermally isolated in a second configuration of the heat transfer circuit (6) by a valve system.

12. Motor vehicle equipped with a traction chain (2) according to any one of claims 9 to 11.

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