FR3082686A1 - METHOD FOR THERMAL PROTECTION OF A ROTATING ELECTRIC MACHINE - Google Patents

Abstract

The invention relates mainly to a method for controlling a rotary electrical machine, in particular for a motor vehicle, characterized in that it comprises: - a step of determining a limit excitation voltage (Uexc_lim) of the rotor as a function a rotational speed (Wmel) of the rotor and an ambient temperature (Tamb) of the rotary electric machine, - a step of determining a difference (ε) between a value relative to an actual excitation voltage ( Uexc_r) of the rotor and a value relating to the limit excitation voltage (Uexc_lim) of the rotor, - a step of applying, on the deviation (ε) previously determined, a filter (F) representative of a constant of thermal time of the rotating electrical machine to obtain a filtered difference (ε '), - a step of determining a maximum duty cycle (DClim) from the filtered difference (ε'), and - a step of application to the rotor of a duty cycle equal to the minimum between a duty cycle (DC_reg) from a regulation loop and the maximum duty cycle (DClim) previously determined.

Description

The present invention relates to a method of thermal protection of a rotary electrical machine.

The invention finds a particularly advantageous, but not exclusive, application in the field of alternators for motor vehicles.

Such an alternator transforms mechanical energy into electrical energy and can be reversible. A reversible alternator, called an alternator-starter, makes it possible to transform electrical energy into mechanical energy in particular for starting the thermal engine of the vehicle. The invention can also be implemented with an electric motor.

In a manner known per se, an alternator or an alternator-starter comprises a casing and, inside thereof, a claw rotor, integral in rotation with a shaft, and a stator which surrounds the rotor with the presence of 'an air gap.

Furthermore, the stator comprises a body constituted by a stack of thin sheets forming a crown, the inner face of which is provided with notches open towards the inside to receive the winding. The winding passes through the notches and forms buns protruding on either side of the stator body. The phase windings are obtained for example from a continuous wire covered with enamel or from conductive elements in the form of pins connected together by welding. These windings are polyphase windings whose ends corresponding to phase outputs are connected to a control device. This control device comprises a rectifier bridge provided with rectifier elements, such as diodes or transistors, for example of the MOSFET type.

Such a machine can implement a regenerative braking function making it possible to supply electrical energy to the battery during a braking phase. When such a function is activated, the alternator is requested to its limits in order to deliver the maximum possible current.

This causes a rise in temperature which must be controlled so as not to degrade the reliability of the alternator. This problem of thermal control arises particularly for alternators operating in overspeed, also designated by the terms boosted alternator. This type of alternator is used in the context of range reduction operations (designated by the term downsizing in English) consisting in using, in a vehicle of a certain category, equipment of a vehicle of a category lower by boosting its characteristics.

The invention aims to effectively solve this temperature control problem by proposing a method for controlling a rotating electric machine, in particular for a motor vehicle, characterized in that said method comprises:

a step of determining a limit excitation voltage of the rotor as a function of a speed of rotation of the rotor and of an ambient temperature of the rotary electric machine,

a step of determining a difference between a value relating to an actual excitation voltage of the rotor and a value relating to the limit excitation voltage of the rotor,

a step of applying, on the previously determined difference, a filter representative of a thermal time constant of the rotary electric machine to obtain a filtered difference,

a step of determining a maximum duty cycle from the filtered deviation, and

a step of applying to the rotor a duty cycle equal to the minimum between a duty cycle originating from a regulation loop and the maximum duty cycle previously determined.

The invention thus makes it possible to manage the temperature of the alternator while making it possible to apply, transiently, a very high flow rate at the output of the rotary electric machine, in particular when the regenerative braking function is activated. The invention also has an economic character, insofar as it can be implemented in software in the existing control device of the rotary electric machine.

According to one implementation, to determine the limit excitation voltage of the rotor, said method comprises:

a step of determining an excitation voltage as a function of the speed of rotation of the rotor, and

- a step of shifting the excitation voltage as a function of the ambient temperature.

According to one implementation, said method includes a step of correcting the filtered deviation.

According to one implementation, the correction is of the proportional type. This implementation has the advantage of being simple and effective and is therefore preferably chosen.

According to one implementation, the correction is of the proportional integral type.

According to one implementation, the correction is of the proportional integral derivative type.

According to one implementation, the determined difference is the difference between the actual excitation voltage of the rotor and the limit excitation voltage of the rotor.

According to one implementation, the determined difference is the difference between the square of the actual excitation voltage of the rotor and the square of the limit excitation voltage of the rotor.

According to one implementation, the ambient temperature is estimated.

According to one implementation, the ambient temperature is estimated from a temperature measurement carried out at a junction of an electronic circuit of a control device.

According to one implementation, the ambient temperature is estimated on the basis of a temperature measurement carried out on a control device, either on the rotating electric machine, or else on the basis of a temperature measurement supplied by an engine computer. .

According to one implementation, the ambient temperature is measured.

The invention also relates to a control device characterized in that it comprises a memory storing software instructions or a logic network programmed for the implementation of the method for controlling a rotary electric machine as defined above.

The invention further relates to a rotary electrical machine characterized in that it comprises a control device as defined above.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

FIG. 1 is a functional schematic representation of a rotary electrical machine implementing the method according to the present invention;

FIG. 2a is a diagram of the functional block making it possible to calculate the limit excitation voltage applicable to the rotor;

FIG. 2b shows graphical representations illustrating the adjustment of the limit excitation voltage of the rotor as a function of the ambient temperature;

FIG. 3 is a diagram of the functional block making it possible to calculate a maximum duty cycle applicable to the rotor from the limit excitation voltage;

FIG. 4 is a synthetic functional diagram of all the functions allowing the implementation of the method according to the invention;

FIG. 5 is a diagram of the temporal evolution of the signals of the functional blocks during the implementation of the method according to the invention making it possible to limit a temperature of the rotary electric machine;

Figure 6 is a graphical representation of the evolution of the excitation voltage and the temperature of the electric machine as a function of the load during the implementation of the method according to the invention.

Identical, similar, or analogous elements keep the same reference from one figure to another.

Figure 1 schematically shows a rotary electrical machine 10, in particular an alternator, implementing the method according to the invention. The alternator 10 is intended to be installed in a vehicle comprising an electrical network, also called an on-board network, connected to a Batt battery. The on-board network may have an operating voltage of 12V, 24V or 48V in particular.

The alternator 10 can operate in alternator mode also called generator mode, or in engine mode comprising a starter mode, known to those skilled in the art.

The alternator 10 notably comprises an electrotechnical part 11, a control device 122 and a rectifier bridge 13.

More specifically, the electrotechnical part 11 comprises an armature element 14, and an inductor element 15. In one example, the armature 14 is the stator, and the inductor 15 is a rotor comprising an excitation coil 16. The speed of the rotor 15 is calculated by the control device 122 from the measurement of the period of a phase connected to the control device. The stator 14 comprises a number N of phases. In the example considered, the stator 14 has three phases u, v and w. As a variant, the number N of phases may be equal to 5 for a five-phase machine, to 6 for a machine of the hexaphase or double three-phase type or to 7 for a heptaphase machine. The phases of the stator 14 can be coupled in a triangle or a star. A combination of triangle and star coupling is also possible.

The control device 122 comprises an excitation circuit 121 generating an excitation current which is intended to be injected into the excitation coil 16 of the rotor 15. This excitation circuit 121 is integrated into a control device 122 for slave the output voltage B + to a fixed value. To this end, the control device 122 includes a comparator to differentiate between the fixed value and the output voltage B + and to deduce therefrom a voltage error signal. In addition, a corrector determines the duty cycle as a function of the voltage error signal. The corrector may include proportional, integral, and derivative functions in order to improve the stability, the precision, and the speed of the voltage control loop.

The control device 122 comprises a rectifier bridge 13 provided with rectifier elements, such as diodes or transistors, for example of the MOSFET type. A control signal from the engine computer 20 is received via a communication means 21 of CAN ('' Controller Area Network in English), LIN (Local Interconnect Network in English) or other type.

The rectifier bridge 13 comprises a first switching element connecting a phase winding u, v, w to the supply voltage B + of the battery Batt when it is on, and a second switching element connecting this phase winding u, v , w to mass M when it is passing. The switching elements used are preferably MOSFET type power transistors, diodes, or else low loss diodes.

The control device 122 comprises a memory 124 storing software instructions or a logical network programmed for the implementation of the method according to the invention described below with reference to FIGS. 2 and 4.

FIG. 2a shows a functional block B1 making it possible to determine a limit excitation voltage Uexcjim of the rotor 15 as a function of a speed of rotation Wmel of the rotor 15 and of an ambient temperature Tamb of the alternator 10. This is a limit voltage not to be exceeded when the alternator 10 is stabilized in flow so as not to exceed its maximum operating temperature.

To this end, the module M1 determines an excitation voltage Uexc as a function of the speed of rotation Wmel of the rotor 15. The excitation voltage Uexc is offset by application, via the adder module M2, of a voltage value of Voff offset from the M3 module. This module M3 generates the offset voltage value Voff as a function of the ambient temperature Tamb of the alternator 10. Thus, as can be seen in FIG. 2b, with respect to the reference curve C0 obtained for an ambient temperature Tamb of reference, the curve C1 obtained for an ambient temperature Tamb lower than the ambient temperature Tamb of reference is shifted upwards, and the curve C2 obtained for an ambient temperature Tamb higher than the ambient temperature Tamb of reference is shifted downwards. The modules M1 and M3 can take the form of a map.

The ambient temperature Tamb may be estimated by means of the module M4 on the basis of a measurement Tmes carried out on a junction of an electronic circuit of the control device 122, or of a measurement carried out directly on a control device 122 or on the rotary electrical machine 10, or again from a temperature measurement supplied by an engine computer 20. Alternatively, the ambient temperature Tamb of the alternator 10 is estimated for example using a sensor placed on a bun of winding. As can be seen in FIG. 3, the block B2 makes it possible to generate a maximum duty cycle DCIim applicable to the rotor 15 from the limit excitation voltage Uexcjim of the rotor 15 previously determined and from the actual excitation voltage Uexc_r of the rotor 15, that is to say of the measured excitation voltage.

To this end, the module M5 squares the actual excitation voltage Uexc_r of the rotor 15 and the module M6 squares the limit excitation voltage Uexcjim of the rotor 15. Then the subtractor module M7 determines by a difference ε between these two values Uexcjim ² and Uexcj · ² However, it is not essential that the difference ε is calculated from the values Uexcjim and Uexc_r squared. It can be calculated directly from the Uexcjim and Uexc_r values. More generally, the difference ε is calculated from a value relating to the actual excitation voltage Uexc_r of the rotor and from a value relating to the limit excitation voltage Uexcjim of the rotor 15.

A filter F representative of a thermal time constant of the alternator 10 is applied to the deviation ε previously determined. Thus, at the output of the filter F, the signal evolves with the same dynamics as that of the alternator temperature. This filter F is advantageously a filter of order 1 having a time constant of between 80 and 120 seconds.

The filtered difference ε 'is corrected using the correction module M7 at the output from which a homogeneous value is obtained at a duty cycle, for example in% / Volt, which is added to 100% via the adder module M8. The correction applied by the M7 module is preferably proportional, with a value between 0.01% A / olt and 0.1% A / olt.

A M9 clipping module makes it possible to limit the maximum duty cycle DCIim calculated to 100% in the case where the actual excitation voltage Uexc_r is less than the limit excitation voltage Uexcjim. Indeed, the difference ε is then positive, so that the output of the adder module M8 can be greater than 100%. The M9 clipping module therefore limits the output of the M8 adding module to 100%.

On the other hand, in the case where the real excitation voltage Uexc_r is greater than the limit excitation voltage Uexcjim. The difference ε is then negative, so that the output of the adder module M8 is less than 100%.

As can be seen in FIG. 4, the module M10 selects the minimum between the maximum duty cycle DCIim and the duty cycle DC_reg coming from the regulation loop of the control device 122.

The selected duty cycle is then applied to the rotor 15 by the excitation module 121.

The signals observable during the implementation of the method according to the invention are described below with reference to FIG. 5.

At time t1, a large load Ch is applied to the terminals of the alternator 10. The difference ε between the calculated limit excitation voltage Uexcjim and the excitation voltage Uexc_r applied to the rotor 15 becomes negative. The value of the filtered difference ε 'decreases. The maximum authorized duty cycle value DCIim remains at 100%. The alternator 10 then delivers the maximum current.

At time t2, the value of the filtered difference ε 'becomes negative. The maximum authorized duty cycle value DCIim decreases, so that the excitation voltage of the rotor Uexc_r also decreases. The output current from alternator 10 also decreases. Indeed, in this case, the cyclic ratio DCIim has priority over the cyclic ratio DC_reg from the regulation loop of the control device 122.

At time t3, the rotor excitation voltage Uexc_r is stabilized at the value of the limit excitation voltage Uexcjim, the alternator 10 delivers current while not exceeding its operating temperature limit.

At time t4, the load Ch applied to the alternator 10 decreases, the excitation voltage of the rotor llexc therefore also decreases. The value of the filtered deviation ε 'becomes positive again, and the maximum authorized duty cycle value DCIim returns to 100%.

FIG. 6 illustrates the evolution of the excitation voltage Uexc and of the temperature Temp of the electric machine as a function of the load Ch. The thermal management via the method according to the invention offers more uptime at low current when the load is lower (the alternator temperature rises slowly) than when the load is high (rapid rise in temperature).

Thus, it is observed that, for a low load (cf. curve C3.1), the duration during which the excitation voltage (cf. curve C3.2) is greater than the excitation voltage is greater than for a high load (see curves C4.1 and C4.2). In addition, the temperature rise of the electric machine 10 for a low charge is slower for a low charge (see curve C3.3) than for a heavy load (see curve C4.3).

Curves C5.1, C5.2, and C5.3 were obtained for an intermediate load.

Of course, the foregoing description has been given by way of example only and does not limit the scope of the invention from which one would not depart by replacing the various elements with any other equivalent.

Furthermore, the various features, variants, and / or embodiments of the present invention can be combined with one another in various combinations, insofar as they are not incompatible or mutually exclusive of one another.

Claims (11)

1. Method for controlling a rotary electrical machine (10), in particular for a motor vehicle, characterized in that it comprises: a step of determining a limit excitation voltage (Uexcjim) of the rotor (15) as a function of a rotation speed (Wmel) of the rotor (15) and of an ambient temperature (Tamb) of the electric machine rotating (10), a step of determining a difference (ε) between a value relating to an actual excitation voltage (Uexc_r) of the rotor (15) and a value relating to the limit excitation voltage (Uexcjim) of the rotor (15) , a step of application, on the previously determined difference (ε), of a filter (F) representative of a thermal time constant of the rotary electric machine (10) to obtain a filtered difference (ε ¹ ), a step of determining a maximum duty cycle (DCIim) from the filtered difference (ε ¹ ), and - A step of applying to the rotor (15) a duty cycle equal to the minimum between a duty cycle (DC_reg) from a regulation loop and the maximum duty cycle (DCIim) previously determined. 2. Method according to claim 1, characterized in that to determine the limit excitation voltage (Uexcjim) of the rotor (15), said method comprises: a step of determining an excitation voltage (Uexc) as a function of the speed of rotation (Wmel) of the rotor (15), and - a step of shifting the excitation voltage (Uexc) as a function of the ambient temperature (Tamb). 3. Method according to claim 1 or 2, characterized in that it comprises a step of correcting the filtered difference (ε ¹ ). 4. Method according to claim 3, characterized in that the correction is of proportional type. 5. Method according to any one of claims 1 to 4, characterized in that the difference (ε) determined is the difference between the square of the actual excitation voltage (Uexc_r) of the rotor (15) and the square of the limit excitation voltage (Uexcjim) of the rotor (15). 6. Method according to any one of claims 1 to 5, characterized in that the ambient temperature (Tamb) is estimated. 7. Method according to claim 6, characterized in that the ambient temperature (Tamb) is estimated from a temperature measurement carried out at a junction of an electronic circuit of a control device (122). 8. Method according to claim 6, characterized in that the ambient temperature (Tamb) is estimated from a temperature measurement carried out on a control device (122), or else on the rotary electric machine (10), or even more from a temperature measurement supplied by an engine computer (20). 9. Method according to any one of claims 1 to 5, characterized in that the ambient temperature (Tamb) is measured. 10. Control device (122) characterized in that it comprises a memory storing software instructions or a programmed logic network for the implementation of the process for controlling a rotary electric machine (10) as defined according to any of the preceding claims. 11. Rotating electric machine (10) characterized in that it comprises a control device (122) as defined according to the preceding claim.