Motor torque minimization for wound rotor synchronous machine during battery thermal pre-conditioning

Abstract

The invention relates to a method for generating a heat loss in a power train (2) comprising 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 power train; a step of estimating the relative angle between the rotor and the stator; a step of controlling the rotor and the stator according to the acquired temperatures such that the rotor and the stator produce a heat loss and such that the rotor and the stator remain substantially stationary relative to each other, the rotor being controlled with a non-zero rotor current. The invention also relates to a drive train suitable for carrying out the method according to the invention and to a motor vehicle equipped with such a drive train.

Description

[0001] The present invention relates generally to electric machines, and more particularly to electric machines powered by batteries.

[0002] The invention more particularly relates to the conditioning or preheating of a battery associated with an electric machine.

[0003] The invention has particularly advantageous application in the field of motor vehicles. Background Art

[0004] Certain electric machines powered by batteries, especially those in motor vehicles, are sometimes subject to very low, even sub-zero temperatures, for example during winter.

[0005] However, the performance of the battery is somewhat inversely proportional to the temperature, so during motor starting, for example when the motor vehicle is ignited after being parked outdoors for a long time in cold weather, the battery performance may be somewhat unsatisfactory.

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

[0007] In these solutions, means for additional heating, known as PTC (Positive Temperature Coefficient) heating, are added specifically for preheating of the battery. However, this solution is costly.

[0008] Another solution consists in controlling the electric machine in such a way as to increase the heat losses generated by the powertrain and use this excess heat to heat the battery.

[0009] In order to preheat the battery when the vehicle is parked, the electric motor must be controlled in such a way that it does not generate motor torque in order to keep the vehicle stationary. This solution involves knowing the position of the rotor so precisely that the electromagnetic forces generated by the stator do not generate torque. However, the rotor position measured by the vehicle can be inaccurate by several degrees. This in turn results in motor torque, which can cause the vehicle to start moving.

[0010] French patent application published under number FR 3 080 239 proposes a method in which the control of the stator is servo-controlled as a function of the value of the measurement error of the rotor position. Summary of the invention

[0011] In order to provide an alternative to the prior art, the present invention proposes increasing the heat losses of the powertrain without generating a torque that would set the vehicle in motion and without servo-controlling the control of the stator according to the value of the measurement error of the rotor position.

[0012] More particularly, according to the invention, a method is proposed for generating heat losses in a powertrain comprising a synchronous machine having a stator and a wound rotor, the method comprising:

[0013] - a step of obtaining a temperature in or around the powertrain,

[0014] - a step of estimating the relative angle between the rotor and the stator,

[0015] - a step of controlling the rotor and the stator in accordance with the temperature acquired so that they generate heat losses and so that they remain substantially stationary relative to each other,

[0016] wherein the stator is controlled in a Park reference frame resulting from an estimate of the relative angle such that a first one of the stator currents is zero and a second one of the stator currents is non-zero, and

[0017] The rotor is controlled with a non-zero rotor current.

[0018] The estimation of the relative angle between the rotor and the stator may include an estimation of the relative angle between the rotor current and the stator current. In other words, the (estimated or measured) angle of the rotor is used and the Park transformation is applied to the three currents used to control the stator in order to obtain two stator currents in the Park reference frame. The relative angle between the stator current and the rotor in the Park reference frame is then directly contained in the first stator current and the second stator current, since the control of the stator can be expressed in polar coordinates in the Park reference frame by means of the magnitude of the stator current vector and the angle of the stator current vector relative to the q-axis of the Park reference frame.

[0019] By means of the invention, it is possible to generate heat losses while maintaining negligible or zero torque. In particular, the control of the rotor makes it possible to compensate in a simple manner for the torque that would be caused by a measurement error in the rotor position. Thus, it is omitted to determine a possible error from the measured position of the rotor and to servo-control the control of the stator according to the measurement error of the rotor position.

[0020] Further advantageous and non-limiting features of the electric machine according to the invention, considered individually or in any technically possible combination(s), are as follows:

[0021] - The second stator current and the rotor current are determined based on the acquired temperature.

[0022] 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, preferably plus or minus 45 degrees.

[0023] - Since the electric machine is powered by the traction battery, the temperature at the traction battery is measured.

[0024] - transferring at least some of these heat losses to the traction battery via a heat transfer circuit.

[0025] The control of the rotor and the control of the stator comprise the use of a look-up table making it possible to associate each temperature value with the value of a second of the stator currents and with the value of the rotor current.

[0026] -If the acquired temperature is lower than a predetermined first threshold value, the second stator current and the rotor current among these stator currents are equal to a predetermined first value; if the acquired temperature is between the first threshold value and the second threshold value, the second stator current and the rotor current among these stator currents are equal to a predetermined second value, for example, the second value of the second stator current and the second value of the rotor current, the absolute values ​​of the second value of the second stator current and the second value of the rotor current are respectively greater than the predetermined first value of the second rotor current and the absolute values ​​of the predetermined second value of the rotor current; if the acquired temperature is greater than the second threshold value, the second stator current and the rotor current among these stator currents are equal to a third value, for example, the predetermined third value of the second stator current and the predetermined third value of the rotor current, the absolute values ​​of the predetermined third value of the second stator current and the predetermined third value of the rotor current are respectively greater than the predetermined second value of the second stator current and the predetermined second value of the rotor current.

[0027] - The rotor is controlled with a rotor current capable of producing a torque less than or equal to 2 N.m.

[0028] According to another aspect of the invention, a drive train is proposed, which comprises a synchronous machine having a rotor and a wound stator and is equipped with a module for controlling the rotor and the stator, which module is configured to implement the method according to the invention.

[0029] Further advantageous and non-limiting features of the powertrain according to the invention, considered individually or in any technically possible combination(s), are as follows:

[0030] The powertrain comprises a traction battery and a heat transfer circuit, the heat transfer circuit being common to the electric machine and the traction battery, the heat transfer circuit being suitable for cooling the electric machine and the traction battery.

[0031] The heat transfer circuit has a first section associated with the traction battery and a second section associated with the stator, in a first configuration of the heat transfer circuit the first section and the second section being thermally coupled and in a second configuration of the heat transfer circuit the first section and the second section being thermally isolated.

[0032] The heat transfer circuit has at least one valve configured to thermally couple the first section and the second section in a first configuration of the heat transfer circuit and to thermally isolate the first section from the second section in a second configuration.

[0033] According to another aspect of the invention, a motor vehicle is proposed which is equipped with a drive train according to the invention.

[0034] Of course, the various features, variants and embodiments of the present invention can be combined with one another in various combinations, as long as they are not mutually incompatible or mutually exclusive. DETAILED DESCRIPTION

[0035] The following description, with reference to the accompanying drawings, given by way of non-limiting examples, will make it easier to understand what the invention is and how it can be implemented.

[0036] In the attached picture:

[0037] [ Figure 1 ] shows a motor vehicle equipped with a powertrain according to the invention and suitable for implementing the method according to the invention;

[0038] [ Figure 2 ] shows an implementation of the method according to the present invention;

[0039] [ Figure 3 ] shows another implementation of the method according to the present invention;

[0040] [ Figure 4 ] shows how the torque applied to the rotor of the motor varies with the uncertainty about the rotor position for different values ​​of the rotor current;

[0041] [ Figure 5 ] shows the relationship between motor torque and rotor current for different stator current values;

[0042] [ Figure 6 ] shows how the losses produced by the motor of a vehicle vary with the rotor current for different values ​​of stator current;

[0043] [ Figure 7 ] shows how the losses generated by the power electronics of a vehicle's powertrain vary with the rotor current for different values ​​of the stator current;

[0044] [ Figure 8 ] shows how the total losses incurred by a vehicle's powertrain vary with the rotor current for different values ​​of stator current.

[0045] Firstly, it should be noted that the same elements of the present invention shown in different drawings will be denoted by the same reference numerals as much as possible.

[0046] It should also be noted that in this description an example of a motor vehicle according to the invention will first be described, then an example of a method implemented by the vehicle and then how this method is parameterized.

[0047] [ Figure 1 ] shows a motor vehicle 1 equipped with a powertrain 2 comprising an electric machine 3, in this case a synchronous three-phase wound rotor electric machine, which is powered by a traction battery 4 providing a continuous current. The powertrain 2 further comprises various components (not shown), in particular power electronic components, such as to enable the current provided by the traction battery 4 to be adapted to control the electric machine. An inverter is an example of such a component.

[0048] In this case, the control module 5 is configured to control the electric machine 3 , in particular to control the control signals circulating in the rotor and the stator of the motor vehicle 1 .

[0049] In this case, the motor vehicle 1 is equipped with a heat transfer system 6 which is thermally coupled to the electric machine 3 and to the traction battery 4 .

[0050] In this case, heat transfer circuit 6 has a first section 7 coupled to electric machine 3 and a second section 8 coupled to traction battery 4. Each of these sections has one or more lines for circulating cooling liquid and a heat exchanger associated with electric machine 3 or traction battery 4.

[0051] In this embodiment, the heat transfer circuit 6 has a valve system 9 which makes 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 (i.e. thermally isolated) circuits. The valve system is controlled, for example, by the control module 5. For example, the control device can control the valve system so that during driving of the vehicle 1, the sections 7, 8 are separated, and during implementation of the method according to the invention, the two sections are connected.

[0052] The motor vehicle 1 is suitable for implementing the method according to the invention. In this case, the control module 5 is programmed to control the electric machine 3 in such a way that it generates heat losses independent of the motor torque, for example when the vehicle is at rest, as described in detail below.

[0053] [ Figure 2 ] shows a way of implementing the method by a control module of motor vehicle 1.

[0054] For the purpose of simplifying the explanation, the control of the stator is considered in this case in a Park reference frame with axis d and axis q. The Park transformation makes it possible to model the three-phase system of the motor 3 by a two-phase system in a rotating reference frame associated with the rotor, which is conventionally expressed in a fixed reference frame associated with the stator. Therefore, in this case, the control of the stator will not be expressed as a three-phase alternating current with a phase shift of 120°, but as a pair of direct currents Id and Iq (hereinafter referred to as the first stator current Iq and the second stator current Id). The first stator current Id corresponds to the stator current projected onto the direct axis of the rotor (conventionally referred to as the "d-axis"), which is parallel to the coil of the rotor. The second stator current Iq corresponds to the stator current projected onto the quadrature axis of the rotor (conventionally referred to as the "q-axis"), which is perpendicular to the coil of the rotor. The control of the stator can also be expressed in polar coordinates in the Park reference frame by means of the magnitude Is of the stator current vector and the angle of the current vector relative to the q-axis of the Park reference frame.

[0055] In this case, the control module 5 is configured to control the electric machine 3 so that the powertrain generates heat losses that are independent of the torque applied to the rotor. In particular, in this case, the control module is configured to generate heat losses without causing the vehicle 1 to move, i.e. while keeping the torque applied to the rotor below a predetermined threshold, for example below 5 N.m, even below 2 N.m, preferably equal to zero.

[0056] Preferably, the heat losses generated by the drive train are directed to one or more other elements of the drive train, in particular by means of the heat transfer circuit 6. Preferably, in this case, the heat losses are directed via the heat transfer circuit 6 to the traction battery 4 in order to heat this battery when its temperature is low.

[0057] In order to know the temperature of traction battery 4 and to infer therefrom the amount of heat losses to be generated, the method comprises a step E1 of acquiring the temperature in or around the drive train, for example at battery 4 , in particular by means of one or more dedicated temperature sensors.

[0058] The control module 5 then implements a step E2 of estimating the position of the rotor, for example by means of a module for measuring the relative angle between the rotor and the stator, allowing it to generate appropriate control of the stator in the Park reference frame corresponding to the estimated position.

[0059] As a function of the temperatures acquired, the control module 5 controls the electric machine 3 so that it generates heat losses and the rotor and the stator remain substantially stationary relative to each other (step E3). These heat losses may be generated, for example, as a function of the temperature measured for the traction battery 4 and of the target temperature to be reached.

[0060] In particular, the control module 5 controls the motor 3 so that, in a Park reference system determined based on the relative positions of the rotor and the stator, the first stator current Iq is zero and the second stator current Id has a non-zero value that depends on the acquired temperature; or, in polar coordinates, the amplitude Is of the current vector depends on the acquired temperature and the angle Psi is zero.

[0061] In order to compensate, inter alia, for any errors in the estimate of the rotor position, the control module 5 controls the rotor with a non-zero rotor current.

[0062] The method according to the invention can advantageously be used in the context of preconditioning or preheating the traction battery 4 before using the vehicle 1 , so that the traction battery 4 has optimal performance from the first moments when the vehicle is put into use, even in cold weather.

[0063] The method according to this embodiment may be programmed to be triggered at a precise time of day, for example one hour before the vehicle 1 is activated, or directly remotely, for example by means of a mobile communication system, in particular from a computer connected to the Internet.

[0064] In this approach, the control module is configured to operate in three different activity modes depending on the temperature of the battery 4. The idea is that the lower the temperature, the greater the losses emanating.

[0065] In a first operating mode associated with a temperature of the battery 4 below a predetermined first threshold value (in this case 0°C), the second stator current is equal to the first stator current value (in this case -176A) and the rotor current is equal to the first rotor current value (in this case 2.9A).

[0066] In a second operating mode associated with a temperature of the battery 4 between the first threshold and the second threshold (4° C. in this case), the second stator current Id is equal to the second stator current value (−115 A in this case) and the rotor current is equal to the second rotor current value (1.9 A in this case).

[0067] In a third operating mode associated with a temperature of the battery 4 that is greater than the second threshold and less than a third threshold (in this case 8° C.), the second stator current is then equal to the third stator current value (in this case −55 A), and the rotor current is equal to the third rotor current value (in this case 0.8 A).

[0068] When the temperature of the battery reaches a third threshold, the method ends (inactive mode).

[0069] For example, in an initial situation, the vehicle has been parked outdoors in cold weather, and the battery 4 has been inactive for a long time, with its temperature being substantially equal to the outdoor temperature, in this case -5 degrees.

[0070] like[ Figure 3 ], when the method is triggered, the control module 5 triggers the measurement M0 of the temperature of the battery. In this case, the measured temperature is lower than the first threshold, so the method is triggered according to the first mode M1, which in this case causes the powertrain to produce a thermal power of 1500W. The control module 5 maintains the corresponding current value so as to increase the temperature of the battery. If the measured temperature is already different, the method will be carried out according to a different operating mode, for example according to an operating mode that causes a lower thermal power to be produced (in this case, the second mode M2 ​​or the third mode M3).

[0071] When the temperature of the battery 4 reaches a first threshold, the method is implemented in a second mode M2, which in this case causes the powertrain to generate a thermal power of 900 W and the temperature of the battery 4 continues to rise. When the temperature reaches the second threshold, the method is implemented in a third mode M3, which in this case causes a thermal power of 450 W to be generated and the temperature of the battery continues to rise. When the temperature reaches the third threshold, the method stops (step F, corresponding to the inactive mode) and the motor vehicle can be enabled with the best performance of the battery.

[0072] In this case, the value for controlling the current of the motor 3 is selected from a pre-established lookup table. For example, the lookup table may be a pre-established computer program implementing a quasi-static energy model (in this case a model of the components including the inverter and the motor).

[0073] In order to clearly understand the principles on which this model is based and how these values ​​are chosen, the following equation should be considered which gives the value of the torque Ce applied to the rotor:

[0074] [Math.1]

[0075]

[0076] Where Ld and Lq are the stator inductances on the d-axis and q-axis of the Park reference frame (these inductances are not equal in motors with salient poles), Mf is the mutual inductance between the rotor and the stator, If is the rotor current, and p is the number of stator pole pairs.

[0077] In order to eliminate the value of the torque Ce, it is obviously necessary to eliminate the first value of the stator current Iq. Then, the second stator current Id will ensure the generation of heat losses.

[0078] However, the concepts of the first stator current Iq and the second stator current Id only make sense relative to the position of the rotor, since the Park reference frame is a reference frame related to the rotor. Therefore, in the case of an error in the measurement of the rotor position (e.g. an error of a few degrees), the determined values ​​of the stator currents Id and Iq correspond to an incorrect Park reference frame, which is slightly offset relative to its actual position (the position of the rotor). This leads to slightly different effective values ​​of the currents Id and Iq (in the non-offset Park reference frame) and therefore to a non-zero current Iq (or a non-zero angle psi). This then risks generating dangerous motor torques when the motor vehicle must remain stationary.

[0079] The inventors have been able to determine, by means of simulations and bench tests, how the electromagnetic torque produced by the motor varies with the rotor position error, which in this case is represented by a variation of the angle Psi around -90° by plus or minus 15° (i.e., within a range from -105° to -75°), for a fixed value of the second stator current Id equal to -250A. [ Figure 4 ] shows the simulation results when the value of stator current If ranges from 0A to 6A.

[0080] exist[ Figure 4 ], it was observed that the optimal value of the rotor current is equal to 4 A, since it makes it possible to ensure an almost zero torque on the rotor (“motor torque”) over the entire range of variations studied.

[0081] Therefore, a quasi-static energy model has been developed in order to generate a lookup table or value map that can be used in the method according to the invention. This model takes into account the electromagnetic equations for operating the motor and uses the motor parameters obtained by simulation. This model receives as input values: the polar coordinates of the stator current in the unshifted Park reference frame, the rotor current, the motor speed, and the rotor temperature and the stator temperature. The quasi-static energy model provides as output the corresponding torque applied to the rotor shaft and the total losses (i.e., in this case the losses generated by the inverter and the losses generated by the motor 3).

[0082] [ Figure 5 ]to Figure 8 Some results are shown for a rotor position error of 15° (ie, Psi = -105°) as the rotor current varies. Figure 5 ] shows the variation of the torque applied to the rotor (“motor torque”), [ Figure 6 ] shows the variation of heat losses (“ME losses”) generated by the motor 3, [ Figure 7 ] shows the variation of heat losses (“EDP losses”) generated by the power electronics of the powertrain 2, and [ Figure 8] show the variation of the total losses of the power train 2, i.e. the heat losses generated by the power electronics and the heat losses generated by the electric machine 3. Each of these figures shows five curves corresponding to five separate values ​​of the magnitude Is of the current vector in the Park reference frame, in this case 55 A, 85 A, 115 A, 145 A and 176 A. The cross marks correspond to the zero torque value and therefore to the optimum values ​​of the rotor and stator currents.

[0083] It is observed here that the value of the rotor current depends to a large extent on the value of the stator current.

[0084] The quasi-static energy model thus makes it possible to obtain a match between the stator currents, the rotor currents, and the losses generated by the power train, so that the motor torque is substantially zero. These values ​​can be recorded in a look-up table used in the method according to the invention.

[0085] Each set of three values ​​can also be associated with a corresponding temperature range to implement the above combination Figure 2 and Figure 3 The method of the described embodiment.

[0086] The present invention is not limited to the above-described embodiments and implementations. Therefore, although the above has described a method for implementing three operating modes M1, M2 and M3 associated with three temperature thresholds, the method is applicable to any number of operating modes, each of which is associated with a separate temperature range. These temperature ranges may also have different amplitudes. As an example, a single operating mode may be provided when the temperature is below 8°C. Also as an example, more than four operating modes may be provided.

[0087] Furthermore, it has been described here that the motor 3 and the traction battery 4 are heat-exchanged to heat the traction battery. Of course, the present invention is not limited to such exchange, and preferably heat exchange is realized between multiple elements of the powertrain (e.g., inverter, motor and battery).

[0088] Finally, the invention is not limited to preheating a battery, but is also applicable to preheating other elements of the vehicle 1 , for example for heating or preheating elements outside the drive train 2 , typically inside the vehicle 1 .

[0089] Additionally, the temperature may be measured at another stage of the powertrain or at another stage of the vehicle and / or at a different location in the vehicle.

[0090] Finally, the method may be implemented to heat another component of the powertrain.

Claims

1. A method for generating heat losses in a powertrain (2), the powertrain comprising a synchronous machine (3) having a stator and a wound rotor, the method comprising: - a step of acquiring the temperature in or around the powertrain (2), - a step of estimating the relative angle between the rotor and the stator, - a step of controlling the rotor and the stator in accordance with the acquired temperature so that the rotor and the stator generate heat losses and so that the rotor and the stator remain substantially stationary relative to each other, characterised in that the stator is controlled in a Park reference frame resulting from the estimation of the relative angle such that a first stator current (Iq) of the stator currents is zero and a second stator current (Id) of the stator currents is non-zero, and The rotor is controlled with a non-zero rotor current (If).

2. The method of claim 1, wherein: The second stator current (Id) and the rotor current (If) are determined according to the acquired temperature.

3. The method according to claim 1 or 2, wherein: 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, preferably plus or minus 45 degrees.

4. The method according to any one of claims 1 to 3, wherein: Since the electric machine (3) is powered by the traction battery (4), the temperature at the traction battery (4) is measured.

5. The method of claim 4, wherein: At least some of these heat losses are transferred to the traction battery (4) via a heat transfer circuit.

6. The method according to any one of claims 1 to 5, wherein: The control of the rotor and the control of the stator comprise the use of a look-up table making it possible to associate each temperature value with the value of a second of the stator currents (Id) and with the value of the rotor current (If).

7. The method of claim 6, wherein: - if the acquired temperature is below a predetermined first threshold, a second of the stator currents (Id) and the rotor current (If) are equal to a predetermined first value, - if the acquired temperature is between the first threshold and the second threshold, a second of the stator currents (Id) and the rotor current (If) are equal to a second value, If the detected temperature is greater than the second threshold value, the second of the stator currents and the rotor current are equal to a third value.

8. The method according to any one of claims 1 to 7, wherein: The rotor is controlled with a rotor current (If) capable of producing a torque less than or equal to 2 N.m.

9. A power train comprising a synchronous machine (3) having a rotor and a wound stator and provided with a module (5) for controlling the rotor and the stator, the module being configured to implement the method as claimed in any one of claims 1 to 8.

10. A powertrain according to claim 9, comprising a traction battery (4) and a heat transfer circuit (6) common to the electric machine (3) and the traction battery (4), the heat transfer circuit (6) being suitable for cooling the electric machine (3) and the traction battery (4).

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

12. A motor vehicle equipped with a drive train (2) as claimed in any one of claims 9 to 11.

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