WO2015121049A2 - Method of controlling a permanent-magnet electric machine optimizing the joule losses - Google Patents

Abstract

The present invention relates to a method of control (CON) of a permanent-magnet synchronous electric machine, in which the settings (SETT) of current id, iq of the electric machine are determined by means of an estimation of the flux (FLU) of the machine and in such a way as to minimize the Joule losses of the electric machine without a temperature sensor, or any estimation of the temperature of the electric machine.

Description

 METHOD FOR CONTROLLING A PERMANENT MAGNET ELECTRIC MACHINE

 OPTIMIZING JOULE LOSSES

The present invention relates to the field of control of synchronous electrical machines, especially for motor vehicles.

 A synchronous machine consists of a rotating part, the rotor, and a fixed part, the stator. The rotor may consist of permanent magnets or consist of a DC-powered winding and a magnetic circuit, which is called an electromagnet. The stator comprises three phases, on each of which is connected at least one coil (also called windings), these three coils are supplied with current and voltage. An external force is used to rotate the rotor: a magnetic field induced by an alternating electric current in coils (windings) of the stator causes a rotation of the rotor. The speed of this rotating field is called "synchronism speed".

 In order to control such electrical machines, vector control means of the torque of the machine are conventionally used. We speak of vector control, because for the machine to produce the torque required by the application, it is necessary to keep the electric currents circulating in phase and synchronized with the position of the rotor. To achieve this, the control means of the electrical machine apply voltages to the motor terminals, these voltages being provided by the torque control algorithm.

 Conventionally, this control depends on the voltage and current measurements of the electric machine, as well as the position and speed of the rotor of the electric machine. The position and the speed of the rotor of the electric machine can be measured using sensors, or estimated from the voltage and current measurements in the phases of the electric machine.

 Current control methods determine a control of the electrical machine to achieve the torque required by the application. However, these methods do not make it possible to determine a control that optimizes the power supplied to the electric machine. Indeed, the current methods do not take into account power losses, including Joule losses that correspond to the energy dissipated in the form of heat in the electric machine. The heat dissipated by the Joule losses causes in particular a heating of the electric machine, which can lead to a degradation of the operation thereof.

 To optimize the power supplied to the electric machine, it can be envisaged to instrument the electric machine with temperature sensors and to control the electric machine according to the temperature measurements made, but this

FIRE I LLE OF REM PLACEM ENT (RULE 26) instrumentation is complex, cumbersome and expensive, and requires a suitable command.

 The present invention relates to a method for controlling a permanent magnet synchronous electric machine, in which the current instructions of the electric machine are determined by means of an estimation of the flow of the machine and in order to minimize Joule losses. the electric machine without temperature sensor, nor estimate the temperature of the electric machine. Thus, the invention makes it possible to analytically determine the current setpoints in real time, and thanks to the invention, the control of the electric machine is optimal in terms of power and keeps maximum the accessible performances of the machine.

The process according to the invention

The invention relates to a method for controlling a permanent magnet synchronous electric machine in which the currents i _m and the voltages u _m of the phases of said electric machine are measured. For this process, the following steps are carried out:

a) estimating the total magnetic flux flowing in said electric machine by means of said currents i _m and said voltages u _m measured;

b) current setpoints i _d , i _{q are determined} by means of said total magnetic flux Φ, said current setpoints i _d , i _q being determined to reach a torque setpoint C _SP and to minimize the Joule losses of said electric machine; and c) controlling said electric machine so as to apply said current setpoints i _d , i _q .

Advantageously, said current setpoints i _d , i _{q are determined} by taking into account the speed of rotation of the rotor of said electric machine.

According to the invention, said current setpoints i _d , i _{q are determined} by taking into account current and voltage constraints relating to the operating limits of said electric machine.

Advantageously, said current constraint is written by an inequation of the type: i _d + <Ii _im with l _Um the current limit of said electric machine.

In addition, said voltage stress is written by an inequation of the following type: v _d + v _q <V _t ² _im with v _d , v _q the voltage setpoints of the electrical machine, a function of said current setpoints i _d , i _q and V _lim the voltage limit of said electric machine.

According to one embodiment of the invention, said current setpoints i _d , i _{q are determined} by the following steps: i) a maximum achievable torque C _{max is determined} by said electric machine as a function of said total magnetic flux Φ and said voltage and current constraints;

ii) comparing said maximum achievable torque C _max with said torque setpoint

C _SP ; and

iii) the current setpoints i _d , i _{q are determined} according to said comparison as follows:

(1) if the maximum achievable torque C _max is greater than the torque setpoint C _SP , then the currents i _d , i _{q are determined which make it} possible to reach said torque record C _SP and which minimize Joule losses by a method of optimization;

(2) otherwise, the currents i _d , i _q are the currents i _d , i _q that achieve said maximum attainable torque C _max .

 Advantageously, said maximum achievable torque is determined by performing the following steps:

(3) a maximum torque is determined by means of said current constraint, and if the voltage stress is satisfied, then the maximum achievable torque C _max is said determined torque;

(4) otherwise, a maximum torque is determined by means of said voltage stress, and if the current constraint is verified then the maximum achievable torque C _max is said determined torque; and

(5) otherwise, the maximum achievable torque C _{max is determined} by means of said current and voltage constraints.

 According to an alternative embodiment of the invention, the Joule losses are minimized by solving the following equations:

with R the resistance of the windings of the electrical machine, ω _ε the electrical speed of rotation of the rotor, L _q and L _d the inductances of the electric machine, and p the number of pairs of poles of the electric machine.

According to another variant embodiment of the invention, Joule losses are minimized by means of said voltage constraint by solving an equation system of the type: f (, i _q ) = C {Ri _d - iu _e L _q i _q ) + io) _e L _d i _d + Ri _q + ω _β J-Φ

with R the resistance

windings of the electric machine, ω _ε the rotation speed of the rotor, L _q and L _d the inductances of the electric machine, and p the number of pairs of poles of the electric machine.

Alternatively, the Joule losses are minimized by determining the currents i _d , i _q guaranteeing said torque set point C _SP and minimizing the sum i _d + i _q .

 Preferably, said total magnetic flux circulating in the electric machine is estimated by means of a state observer of said electric machine.

In addition, the invention relates to a control system of a synchronous electric machine. The control system is adapted to apply the control method according to the invention.

The invention also relates to a vehicle, in particular a hybrid or electric motor vehicle, comprising at least one synchronous electric machine. The vehicle further comprises a control system as described above.

Brief presentation of the figures

 Other features and advantages of the method according to the invention will appear on reading the following description of nonlimiting examples of embodiments, with reference to the appended figures and described below.

 FIG. 1 illustrates the steps of the control method according to the invention.

 FIG. 2 illustrates the step of determining the current setpoints according to one embodiment of the invention.

FIG. 3 illustrates the iso-torque, current constraint, and several voltage stress curves in a reference frame (i _d , i _q ).

 FIG. 4 illustrates the comparative curves of control strategies according to the prior art and according to the invention for a portion of the Artemis cycle, without variation of the temperature.

 FIG. 5 illustrates the Joule loss gain of the method according to the invention for the portion of the Artemis cycle of FIG. 4.

FIG. 6 illustrates the evolution of the temperature imposed for an example of application. FIG. 7 illustrates the setpoint torque, the torque obtained by a control method according to the prior art, and the torque obtained by a control method according to the invention as a function of time with variation of the temperature as illustrated in FIG. figure 6. Detailed description of the invention

 The invention relates to a method for controlling a permanent magnet synchronous electric machine. For this, the electric machine is controlled so as to guarantee the torque required by the application of the electric machine. Ratings:

 During the description, the following notations will be used:

 u: voltages at the terminals of the phases of the electric machine.

 : currents flowing in the phases of the electric machine.

 Θ: angular position of the rotor of the electric machine relative to the stator, this position can be estimated or measured.

Q, _m : rotor speed, corresponding to the rotational speed of the rotor of the electric machine relative to the stator, this speed can be estimated or measured.

 p: number of pairs of poles of the electric machine.

(ù _e : electrical speed of the machine, with ω _β = pQ, _m The electric speed is proportional to the mechanical rotation speed.

Q, _m = mechanical rotation speed of the machine.

 Φ: intensity of the magnetic field created by the magnets of the machine.

C _SP : Torque setpoint, corresponding to the torque required for the application of the electric machine.

C _max: maximum torque achievable by the electric machine dependent operating limits of the electrical machine.

 Ium: current limit of the operation of the electrical machine, it is a known parameter (manufacturer data) or obtained experimentally.

V _Um : voltage limit of the operation of the electrical machine, it is a known parameter (manufacturer data) or obtained experimentally.

 R: resistance of the windings of the electric machine, it is a known parameter (manufacturer data) or obtained experimentally.

^ ^d : direct inductance of said electric machine, it is a parameter of the electric machine which is known (data manufacturer or obtained experimentally). L _q : inductance in quadrature of said electric machine, it is a parameter of the electric machine which is known (data manufacturer or obtained experimentally).

χ _α β: total magnetic flux seen by the windings.

II I2 ^'■ two calibration variables to manage the observer convergence rate.

These notations, indexed by the word _ _m , represent the measured values. The estimated values are indicated by a circumflex accent. Derivatives with respect to time are indicated by a point. Notations indexed by the mention _ _αβ mean that the quantities are expressed in the Concordia coordinate system. The indexing of the - _d indication indicates that these are direct ratings expressed in the Park benchmark and the indexing of the - _q indicates that they are quadrature logs expressed in the Park benchmark. .

The invention relates to a method for controlling a permanent magnet synchronous electric machine, the method according to the invention being also adapted to a synchronous electric machine with double excitation. Figure 1 illustrates the different steps of the process. Beforehand, the voltages u _m and the currents i _m are measured in the phases of the electric machine. Indeed, the synchronous electrical machine is controlled in torque by a control of the voltages and supply currents of the phases of the synchronous electric machine. In order to optimally control this motor, it is necessary to measure the voltages u _m at the terminals of the phases and the currents i _m circulating there. Then, the following steps are carried out:

 1. Magnetic flux estimation (FLU)

 2. Determination of current instructions (CONS)

 3. Control of the electric machine (COM).

Step 1) Magnetic flux estimation (FLU)

Prior to the estimation of the magnetic flux, it is possible to carry out a pretreatment of the measured electrical quantities. Indeed, the measurements of the electrical quantities generally comprise measurement noise, which generates inaccuracies for the estimation of the magnetic flux. To overcome this problem, a pretreatment step of the electrical quantities can be performed. This pretreatment makes it possible to filter the quantities measured and therefore improve the quality of the magnetic flux estimation whose variation depends on the variation of the internal temperature of the machine.

According to one embodiment of the invention, the pretreatment of an electrical quantity y (voltage or current) is performed by decomposing the measured electrical signal y _m into sum of cosine and sinus functions dependent on the measured position: ym '' ^es coefficients a _i , b _i being determined by identification.

In practice, it can be seen that N = 3 or N = 4 makes it possible to correctly process the measured data. Then, we retain only the preponderant term (N = 1): y _f = a _x cos ^^ + b _j sin (# _m ). The pretreated size is then used for reconstruction of the magnetic flux.

Using the measured information, it is possible to reconstruct the total magnetic flux. This is the magnetic flux seen by the electrical machine, namely the flux of the magnets plus the flux due to the magnetic armature reaction (that is to say due to the rotor) for an electric machine with salient poles. The reconstruction of the magnetic flux is allowed by the use of a state observer. In automatic and information theory, a state observer is an extension of a model represented as a state representation. When the state of a system is not measurable (as is the magnetic flux), we construct an observer that allows us to reconstruct the state from a model of the dynamic system and measurements of other quantities (i _m , _m ).

According to one embodiment of the invention, the magnetic flux observer is constructed by performing the following steps: i) determining the voltages u _ap = in the reference frame of

 Concordia by transformation of measured voltages and currents. It is recalled that the Concordia transform is a mathematical tool used in electrical engineering to model a three-phase system using a two-phase model.

ii) said magnetic flux Φ is determined by an equation of the type: χ _α β = -Ri _aj e + υ. _α β with R the resistance of the windings of said electric machine and χ _αβ is a vector of dimension two which represents the total magnetic flux seen by the windings of the motor and which is neither known nor measured, it can be put under the following form: _χ αβ = λ + Φ ^^) - 'λ ^are parameters dependent on direct and quadrature inductance L _d = L _q = L. iii) we then define a vector χ _αβ = whose components are functions of the magnetic flux χ _αβ and the current ί _αβ which satisfy the following relation h (x _a p) = xa + x) ² - Φ ² = 0 with the functions x _a and χ _β defined by the following relations: χ _α χ _αβ ) = (χ _α - λί _α ) and χ _β χ _αβ ) = (χ _β - λί _β ). The relation thus obtained constitutes a new output equation, or a measurement for the system, in that it links the variables of the system to a quantity known in this instance 0.

iv) an observer calculates in real time an estimate χ _αβ of the total flow χ _αβ and φ an estimate of the flow Φ as follows:

= - ^Ri aB + ^U aB ~ ϊΛ ^Χ αβ or

the observation function h defined and its partial derivative are evaluated in χαβ {χαβ) - Yi and γ ₂ are two calibration variables that make it possible to manage the speed of convergence of the observer. Step 2) Determination of the current setpoints (CONS)

During this step, the current setpoints i _d , i _q providing a torque set point C _SP required by the application of the electric machine are determined. In addition, the current setpoints i _d , i _q are determined so as to minimize Joule losses of the electric machine. This determination is carried out by means of observation of the flux carried out in the preceding step. Indeed, the equation of the couple in the Park landmark can be written in the form:

< I?_im. According to one embodiment of the invention, the determination of the current setpoints i _d , i _q also depends on the speed of rotation of the rotor of the electric machine. This determination may furthermore take into account current and voltage constraints relating to the operating limits of the electric machine. Indeed, the system is subject to material constraints, which will set the operating limits of the electric machine. The current constraint corresponds to the limit determined by the available power and the voltage stress corresponds to the limit created by the counter electromotive force of the machine, and the DC bus voltage. The current constraint can be written by an inequation of the type: i _d +

<I? _im .

 The stress of tension can be written by an inequation of the type:

va + ^v < ^v iim = ^V _DC> Which P ^was written in steady state in the following form:

(Ri _d - oi _e L _q i _q ) ² + < ^v

These constraints are illustrated in Figure 3. The current constraint is shown by the circle noted l _Um . The stress of tension is given for several speeds by the ellipses portions noted V _Um . The curve C _SP shows the pairs i _d , i _q , ensuring the same torque. This curve is called iso-couple. An arbitrary operating point is marked by the black cross. For example, this operating point is achievable for a zero speed, a speed of 3000 rev / min and a speed of 4000 rev / min. On the other hand, it is not reachable at high speed.

It is observed that an infinity of pairs i _d , i _q thus make it possible to generate a given pair. These pairs of currents i _d , i _q can be differentiated by determining those which verify the voltage and current constraints and those which generate Joule losses which contribute to warming the machine and consequently reduce the efficiency.

Thus, naturally, for parameters of a machine, and operating conditions, there exists a pair i _d , i _q making it possible to obtain a maximum torque, and a pair which, for a given torque, minimizes Joule losses. The method according to the invention makes it possible to find these particular pairs.

According to one embodiment of the invention, the Joule losses are minimized by determining the currents i _d , i _q which minimize the sum i _d + ί. Indeed, Joule losses of an electrical machine can be written R (i _d + i _q ).

According to one embodiment of the invention illustrated in FIG. 2, the determination of the current setpoints can be implemented by means of the following steps:

 a) Determination of the maximum achievable torque (MAX)

 b) Comparison of maximum torque and setpoint (DIF)

 c) Determination of the current setpoint (OPT) a) Determination of the maximum achievable torque (MAX)

During this step, a maximum torque C _max achievable by the electric machine is determined as a function of the total magnetic flux observed Φ and the current and voltage constraints. This is the maximum torque that the machine can provide depending on the flow magnetic and material limits of the electric machine. For this determination, one can write the problem in the form of Kuhn Tucker multipliers (KT), in a form:

+ μ ₂ I (Ri _d - WeLg iq) ² + ù) _e L _q i _q + Ri _q

According to an alternative embodiment of the invention, the maximum achievable torque C _{max is determined} by means of the following steps:

(1) a maximum torque is determined by means of the current constraint, and if the voltage stress is satisfied then the maximum torque C _max achievable is the determined torque. In this case, the resolution by Kuhn Tucker method gives the following analytical solutions:

This solution is a direct analytical solution from the system parameters, and returns the pairs (*; i _qma x) and {i _dmin i _qmin ) corresponding to the _extremes of the achievable torque when the current constraint is active. The geometric interpretation of this result is simple: the solutions correspond to the points for which the isocouple corresponding to the maximum torque tangents the current constraint. In general, the solution always corresponds to the point for which the isocouple corresponding to the maximum torque tangents the domain of (i _d , i _q ) feasible. The voltage stress is not a problem in low speed, this solution is the maximum torque delivered by the machine throughout the speed range. (2) otherwise (i.e., if the voltage stress is not satisfied in step (1)), a maximum torque is determined by means of the voltage stress, and if the current constraint is checked then the maximum attainable torque C _max is the determined couple. In this case, the pairs i _d , i _q can be parameterized in a form:

(¾ ⁼ G) ^C0S ^ ⁺ (¾ ^sin ^^ ⁺ © - ^{The coefficients a} ct < ^h d, b _q , c _d , c _q can be obtained directly from the coefficients of the stress of tension. the couple as follows:

The extrema of the torque for the voltage stress parameterized by Θ are given 2arctan (t,), where t, is a root of the polynomial:

(x ₂ ^- % i) t ⁴ + 2 (x ₃ - Χ) ί ³ - 6x ₂ t ² + 2χ ^ £ + x ₂ + x ₄ = 0

Xi = {b 2 b _{q d} - _q has _d a) (L _d - L _q)

= (A b _{d q} - _q b _d a) (L _d - L _q)

 The coefficients a, b and c are defined as follows:

aq b _d C _d

 with

a + b +) ² + 4c ²

λ _{1 =} 7 (g - b

 2c

α + δ - + 4c ²

λ, = 7 (g - b) ²

2c ² + lcde)

From the solutions thus formulated, it is trivial to go back to Θ, then to the currents (i _d , i _q ) for which the torque is an extremum on the current constraint. It is then sufficient to select the relevant solutions by simple sorting, which allows to express the solution to the problem of maximum torque under stress of tension.

(3) otherwise (i.e., if the current constraint is not satisfied in step (2)), the maximum attainable torque C _{max is determined} by means of said current and voltage constraints. In this case, the resolution is simpler than in the previous cases: it is sufficient to look for the intersection of the current and voltage constraints, if it exists. The maximum torque will be on one of these points. This intersection is given by the following equation system:

~ Ilim ⁼ ®

(Ri _d - WeLgiq) ² + - ½L = ⁰

The resolution of this equation system makes it possible to propose candidate points for the extrema. The values of i _d corresponding to the candidate intersection points are roots of the following polynomial:

X ₄ id + X3 ^ d. + ^x 2 ^ d + ^x id + ^x 0 ⁼ 0

with x ₄ = ω (ΐ¾ - L ² ) ² + 4 ² R ² (L _d - L _q f

x ₃ = 4L _d ^ Φω (ί - L ² _q ) + 8 J ^ O <uf fl ² (i _d - L _q ) x ₂ = 2 ^ _e ² {L ² _d - L ² _q ) + ^ 4ί ² _ά ω _β ² Φ ² - 4a> _e ² R ² (L _d - L _q ) ² I ² _m + 4R ² a> _e ² → ²

_Xl = \ L _d o> _e Ρ ΦΨ - 8 If Φω | fl ² (L _d - L _q ) 2

lim χ ₀ = Ψ ² - 4β ² _ω ² - Φ ^2/2 _ίΐη

Ψ = ω ² ^ Φ ² - 7 ² _m + (R ² + ω ² ! ² ) L ² _m

The currents i _q corresponding can naturally be calculated from the solutions of the current i _d . There are therefore 8 potential pairs solutions. The sorting of these solutions is done by first checking if the couples are real, and then if they check the equalization constraints. These operations make it possible to extract from 2 to 4 solutions. Two solutions have id <0, and are the solutions corresponding to the minimum and maximum achievable under these two constraints. The geometric interpretation of this problem is once again relatively simple: the extreme pairs are located at the intersection of the two constraints.

 In the case where no solution is possible, the constraints are disjointed: the electric machine operates outside its operating zone. b) Comparison of maximum torque and setpoint (DIF)

During this step, the maximum torque achievable by the electric machine C _max is compared to the torque setpoint required by the electric machine C _SP . This comparison makes it possible to check whether the requested torque (the torque setpoint) can be obtained by the electric machine. c) Determination of the current setpoint (OPT)

During this step we look for an optimal operating point in terms of Joule losses. Naturally, the current setpoints (i _d ; i _q ) must satisfy the current and voltage constraints, and the torque demand C _SP must be less than the maximum torque C _{max that} the machine can deliver under the operating conditions under consideration. Joule loss minimization can be formulated as an optimization problem. In this case, the electric machine delivers a torque C _SP lower than the maximum torque under the conditions of use in question.

From the parameters and the torque demand, the method calculates current setpoints i _d , i _q , which makes it possible to deliver the maximum torque if the requested torque is not attainable. Otherwise, the current setpoints minimize Joule losses.

If the maximum attainable torque C _max is less than the torque setpoint C _SP , then the electric machine can not reach the required torque (torque setpoint C _SP ) the current setpoints i _d , i _q which determine to reach this maximum torque C _max : these are the currents determined in step a). If the maximum attainable torque C _MAX is greater than the torque set point C _SP , then the current setpoints i _d , i _q which minimize the Joule losses are determined. The optimization problem that can be considered in this part can be: given the parameters R, L _d , L _q , φ, V | _im , l | _im , p, ω _β , find the current setpoints i _d0 , i _q0 verifying the torque equation and the current and voltage constraints, such as for all values of the currents i _d , i _q verifying the torque equation and the current and voltage constraints, i _d0 + i _q0 ≤ +

According to one embodiment of the invention, if the maximum achievable torque C _MAX is greater than the torque set point C _SP , then the resolution method can follow the same principles as the method used to solve the maximum torque search problem. . In this case, the torque constraint is always active, ie the requested torque must be delivered (equality constraint). If the requested torque is less than the maximum torque that can only be reached under current constraints, the current constraint is always valid and therefore inactive. In this case, the power should only be minimized in two cases:

 1. Case where the torque constraint is active, the current constraint inactive, the voltage stress inactive. This case consists in minimizing the isocouple power. The optimization problem considered is the following:

min [f {i _d , i _q ), h (ii) with

The solution i _d is a root of the following polynomial:

 - (^ - ^) ¾r = °

The corresponding values of i _q can be obtained thanks to the torque constraint:

p (^ ⁽ ^ + (. ^L d - L _q ) ⁱ dj

A simple sorting of the candidate solutions makes it possible to find the solution of the problem (i _d i _q ) minimizing the power for a given couple. 2. Case where the torque constraint is active, the current constraint inactive, the active voltage stress. In the second case, the isocouple is always considered knowing that the stress of tension is active in this case. The intersection between the iso-torque curve and the stress of tension are sought. This intersection may in some cases be the optimal point to deliver torque while minimizing Joule losses. The following system must be resolved:

 2

f (i _d i _q ) = ( ^Ri _d - u _e L _q i _q ) ² + [ù) _e L _q i _q + Ri _q - ù) _e φ] - V? _im = 0h ( ⁱ d> ⁱ q) + (L _d - L _q ) i _d i _q ) = 0

It is possible to show that the i _q candidates for the solution are the real roots of the following polynomial:

x ₄ i _q + X ₂ lq + X i _q + X ₀ = 0 with

(^ff2 + <» _q)

x ₄ = p ² (L _d - L _(? ) ² (? ² + _ii j _e ² L ² x ₂ = (2RpC _SP ù ⁾ _e - V? _imV ² ) L _d - L _q ) ² +

( ^ff2 + <" _q )

The corresponding currents i _d can be easily calculated from the iso-torque constraint. The sorting of the roots and their analysis quickly makes it possible to find the optimal solution.

 The solutions presented above can be efficiently calculated by a simple matrix inversion. If the requested torque is less than the maximum torque, it is possible to test the feasibility of the solution without stress with respect to the stress of tension. If this constraint is feasible, it is of course the best solution, if it is not feasible, then the best solution is given by Case # 2. Thus, these solutions make it possible to maximize the yield for a given operating point.

This embodiment is therefore based on analytical solutions, equipped with computational tools that are efficient in terms of algorithmic complexity, which guarantees the execution of calculations in real time. Step 3) Control of the electric machine (COM)

During this step, the permanent magnet synchronous electric machine is controlled so as to apply the current setpoints i _d , i _q to the electric machine. For this, the electric machine is controlled by voltage u _d , u _q as a function of the current setpoints i _d , i _q .

 Thus, the electric machine is optimally controlled in real time to achieve the requested torque setpoint while minimizing Joule losses of the machine.

 Indeed, the minimization of Joule losses makes it possible to improve the efficiency of the electric machine.

In addition, the invention relates to a control system of a synchronous electric machine adapted to apply the method as described above. Such an electrical machine control system comprises means for controlling the electric machine constituted by means for determining the magnetic flux of the electric machine, means for determining the current setpoints i _d , i _q and means for controlling the torque. of the electric machine. The means for determining the magnetic flux determine the total magnetic flux of the electric machine from measurements of currents i _m and voltages u _m . These are the currents and voltages of each of the three phases of the electric machine. The means for determining the current setpoints calculate the current setpoints i _d , i _q by means of the magnetic flux. The torque control means apply voltages across the motor terminals as a function of the current setpoints i _d , i _{q in} order to ensure a torque setpoint for the electric machine and to minimize Joule losses.

 This control system can be used for a synchronous electrical machine on board a vehicle, especially in an electric or hybrid motor vehicle or a hovercraft. However, the described control system is not limited to this application and is suitable for all applications of synchronous electrical machines.

Application examples

In order to show the advantages of the method according to the invention, two examples of application are illustrated: a first example (FIGS. 4 and 5) compares the step of determining the current setpoints for a portion of an Artemis cycle determined according to the prior art and according to the invention, a second example (Figures 6 and 7) compares the method according to the invention to a method according to the prior art. For the first example of application, the step of determining the current setpoints for a permanent magnet synchronous electric machine on an Artemis cycle is tested in order to evaluate the gains made by the method according to the invention. The Artemis cycle is an automotive driving cycle designed to reproduce reproducibly the conditions encountered on the roads. It is mainly used for measuring the consumption and polluting emissions of vehicles.

For the evaluation on this cycle, it is considered that the torque loop is perfect, that the currents in the Park coordinate system are actually reached, and that the temperature is constant. Thus, at each instant, it corresponds to a pair (speed, torque) to which corresponds current orders i _d , i _q chosen by a given strategy. In this section, we evaluate the ability of three strategies to achieve this Artemis cycle, and the corresponding Joule losses. The three strategies considered are:

1. Strategy according to the art prior to i _d = 0

2. Strategy according to the prior art at i _d = -50A set so as to cover a wider range of potential use.

 3. Optimal method according to the invention (INV).

As a first step, the evaluation of the capacity of the three strategies to deliver the requested pair is carried out. Therefore, each strategy is required to provide the operating point providing that given torque. If the strategies are not able to deliver the requested torque, then they provide the maximum torque at the corresponding speed. Only the method according to the invention is able to provide the requested torque for all pairs (torque, speed). The strategy i _d = -50, which has been described as covering a satisfactory range of the potential of the machine, does not make it possible to provide extreme torques in all operating ranges, whether at high speed or at low speed. In addition, the strategy i _d = 0 shows its limits in both maximum torque and speed. The method according to the invention is particularly effective for electric machines highly defluxable (L _d ≠ L _q ).

In the case of the Artemis cycle, the strategy according to the invention makes it possible to provide the requested torque on 100% of the points, the strategy i _d = -50 makes it possible to provide the requested torque on 95% of the points. The strategy i _d = 0 only provides the required torque on 86% of the points. On the points where the three strategies are able to provide the requested torque, it is necessary to look at the Joule losses due to the internal resistance of the machine. These Joules losses induce heating of the machine. Figure 4 shows the Joule losses for a certain number of cycle points corresponding to the points where the torque demand is achievable with the three strategies presented, and for which the torque demand is greater than 1 Nm. The right part of the figure 4 illustrates the torque set point C _SP and the rotational speed ω _β for the portion of the cycle studied. These points make it possible to have an idea of the quality of Joule losses. This figure illustrates a number of issues related to a fixed choice of current i _d . For example, if the strategy i _d = - 50 is valid to deliver the pair as previously shown, this strategy defluxes the machine permanently. As a result, Joule losses are very high for very low torque values. In terms of Joule losses, the strategy i _d = - 50 is not acceptable, although it allows at any moment to satisfy the torque demand. The strategy i _d = 0 requires the choice of very strong currents for very strong torque values, while defluxing the machine makes it possible to greatly reduce Joule losses. On the other hand, one notices that whatever the point considered, the strategy according to the invention proposes an operating point for which the Joule losses are inferior to strategies fixing i _d . A strategy choosing i _d according to the speed is conceivable, with for example a linear dependence. These solutions would in any case not be as effective as the optimal method according to the invention. To close this study, the gain in Joule losses of the strategy according to the invention relative to the strategy i _d = 0 is presented in FIG. 5. The gain on Joule losses and therefore total warming for a given operating point can be raise up to 25%. This strategy can therefore have a significant influence on the warming of the machine.

 To illustrate the total energy gain spent on the cycle points for which the torque demand can be satisfied by the three strategies, Table 1 presents the energies expended by the three strategies compared:

Table 1 - Comparison of the control determination of the current setpoints on the Artemis cycle

Ce tableau permet d'illustrer le fait que, non seulement la méthode selon l'invention permet de satisfaire une palette plus large de demande de couple pour une même machine, mais qu'elle permet également de réduire les pertes Joules, et par conséquent réchauffement de la machine électrique. Les figures 6 et 7 illustrent l'intérêt de la méthode développée selon l'invention, qui utilise une estimation du flux puis calcule des points de commande optimaux. Pour cet exemple, l'évolution de la température est imposée telle qu'illustrée en figure 6 en variant de 0 à 30°C de 0 à 3 secondes, ce qui induit une variation du flux magnétique, le flux nominal étant défini pour une température de 0°C.

This table makes it possible to illustrate the fact that, not only the method according to the invention makes it possible to satisfy a wider range of torque demand for the same machine, but that it also makes it possible to reduce Joule losses, and consequently to warm up of the electric machine. Figures 6 and 7 illustrate the advantage of the method developed according to the invention, which uses an estimation of the flow then calculates optimal control points. For this example, the evolution of the temperature is imposed as illustrated in FIG. 0 to 30 ° C from 0 to 3 seconds, which induces a variation of the magnetic flux, the nominal flow being defined for a temperature of 0 ° C.

Depending on this flow, the torque delivered by the machine changes. The graph of Figure 7 shows the torque delivered by two control process choices. The horizontal curve denoted INV shows the choice made with the method according to the invention, the decreasing curve noted AA shows the torque delivered with current setpoints (i _d , i _q ) defined with the constant nominal flow according to a prior art. In the case of the method according to the invention, the error with the torque set point C _SP is constant and is proportional to the torque estimation error. On the other hand, the error with the torque set point C _SP increases continuously when the choice of the operating point is made with the nominal flow. This error will be all the more critical as the flux evolves far from its nominal value, because of the demagnetization due to its aging, or the temperature. The method according to the invention thus allows a torque control robust to errors on the flow.

Claims

Claims 1) Method for controlling a permanent magnet synchronous electric machine in which the currents im and the voltages um of the phases of said electric machine are measured, characterized in that the following steps are carried out: a) the flux is estimated total magnetic Φ circulating in said electric machine by means of said currents im and said voltages um measured; b) current setpoints id, ia are determined by means of said total magnetic flux Φ, said current setpoints id, ia being determined to achieve a torque setpoint CSP and minimize the Joule losses of said electric machine; and c) said electrical machine is controlled so as to apply said current instructions id, ia. 2) Method according to claim 1, in which said current instructions id, ia are determined by taking into account the rotation speed of the rotor of said electric machine. 3) Method according to one of the preceding claims, in which said current instructions id, ia are determined by taking into account current and voltage constraints relating to the operating limits of said electrical machine. 4) Method according to claim 3, in which said current constraint is written by an inequality of the type: id2 + < l im with lUm the current limit of said electric machine. 5) Method according to one of claims 3 or 4, in which said voltage constraint is written by an inequality of the type: vd + v < Vt2im with vd, va the voltage instructions of the electrical machine, function of said instructions of current id, ia and Vlim the voltage limit of said electrical machine. 6) Method according to one of claims 3 to 5, in which said current instructions id, ia are determined by means of the following steps: i) a maximum torque achievable Cmax is determined by said electric machine as a function of said total magnetic flux Φ and said voltage and current constraints; ii) comparing said maximum achievable torque Cmax to said torque setpoint CSP; and iii) the current setpoints id, iq are determined as a function of said comparison in the following manner: (1) if the maximum achievable torque Cmax is greater than the torque setpoint CSP, then the currents id, iq are determined allowing 'achieve said set torque CSP and which minimize Joule losses by an optimization method; (2) otherwise, the current instructions id, iq are the currents id, iq which make it possible to reach said maximum achievable torque Cmax. 7) Method according to claim 6, in which said maximum achievable torque is determined by carrying out the following steps: (1) a maximum torque is determined by means of said current constraint, and if the voltage constraint is verified, then the maximum torque C _max achievable is said determined torque; (2) otherwise, a maximum torque is determined by means of said voltage constraint, and if the current constraint is verified then the maximum achievable torque C _max is said determined torque; And (3) otherwise, the maximum achievable torque C _max is determined by means of said current and voltage constraints. 8) Method according to one of claims 3 to 7, in which the Joule losses are minimized by solving the following equations:

with R the resistance of the windings of the electric machine, ω _ε the electric speed of rotation of the rotor, L _q and L _d the inductances of the electric machine, and p the number of pairs of poles of the electric machine. 9) Method according to one of claims 3 to 7, in which the Joule losses are minimized by means of said tension constraint by solving a system of equations of the type: / ^" (Ai, iq) = (Ria ^~ u _e L _q i _q ) ² + {ù _e L _d i _d + Ri _q + ω^ Φ^ - V? _im = 0 with R la h(i _d , i _q ) = f ^C - ^→i _q + (L _d - L _q ) )ii _d i _q | = 0 resistance of the windings of the electric machine, ω _ε the rotation speed of the rotor, L _q and L _d the inductances of the electric machine, and p the number of pole pairs of the electric machine. 10) Method according to one of claims 1 to 7, in which the Joule losses are minimized by determining the currents i _d , i _q guaranteeing said torque setpoint C _SP and minimizing the sum

+ iq. 1 1) Method according to one of the preceding claims, in which said total magnetic flux Φ circulating in the electric machine is estimated by means of a state observer of said electric machine. 12) Control system for a synchronous electric machine, characterized in that it is adapted to apply the control method according to one of the preceding claims. 13) Vehicle, in particular hybrid or electric motor vehicle, comprising at least one synchronous electric machine, characterized in that it further comprises a control system according to claim 1 2.