FR3012270A1 - METHOD AND SYSTEM FOR CONTROLLING AN ELECTRIC MACHINE OF A MOTOR VEHICLE - Google Patents

Abstract

A control system of an electric machine of a motor vehicle comprising means (3) for determining current settings relative to each of the phases of the electric machine in the Park mark as a function of the driver's torque request, a control means (4) for the currents in the phases of the electrical machine (2) able to determine the supply voltages of each of the phases of the electric machine according to the current instructions received at the input. The system comprises a first calculation means (5), able to detect that the saturation of the voltage commands determined by the regulating means (4) is imminent, and, if so, to block and then not to allow that evolutions of the current setpoints in the direction which leads to a decrease of the voltage commands, a second calculation means (6) connected downstream of the means for determining (3) current setpoints and upstream of the regulating means ( 4), able to modify the current setpoints emitted by the determining means (3) in order to take into account the known or imminent saturation by determining and emitting corrected current instructions to the control means (4).

Description

The invention relates to the technical field of controlling an electric motor, and more particularly to controlling the supply voltage of the stator of such an engine. In the development of electric vehicles, the torque provided by the electric motor must be controlled. The torque of a machine being directly related to the currents flowing in it, it must therefore be able to precisely control these currents. The electric motor to be controlled may in particular be a three-phase synchronous machine with wound rotor.

The currents in the three phases of the stator are sinusoidal and each phase shifted by 2n / 3 rad. These currents create a rotating magnetic field in the machine. The rotor is traversed by a direct current which creates a magnetic field which makes it equivalent to a magnet. To achieve the mechanical torque, the stator magnetic field is controlled in quadrature, that is to say in constant controlled phase shift of 90 ° with the rotor field. Thus, the rotation frequency of the rotor field is equal to the frequency of the stator currents, hence the name "synchronous". It is the amplitudes of the stator currents and the value of the rotor current that create the torque necessary for the rotation of the machine. To control these currents, it will therefore be necessary to apply sinusoidal voltages between the phases of the stator, each being also out of phase by 2n / 3 rad and to apply to the rotor a constant voltage. On the other hand, the Park transform is used to project the stator currents and voltages into a space where the sinusoidal signals become constants. The Park mark corresponds to a reference linked to the rotating field, thus linked to the rotor in the case of the synchronous machine. The use of the Park transform makes it possible to regulate constants, which is much easier to achieve than to regulate sinusoidal signals. The challenge is to regulate constant currents by controlling constant voltages. By performing the inverse transform, it is possible to reduce to the reference of the stator of the machine and therefore to know precisely the voltages to be applied to each phase of the electric machine. To achieve the requested torque, it is therefore necessary to develop current instructions that satisfy the production of magnetic fluxes achieving the requested torque, minimizing losses of the machine and the inverter, all depending on the battery voltage. available. To carry out these current instructions, a current regulator controlling the power supply of the electric machine is used. Depending on the setpoints transmitted, the current controller can output voltage setpoints that are saturated. Saturation means a value of the voltage setpoint greater than the maximum achievable voltage. Indeed, to optimize the losses of the system, it will be advantageous to maximize the voltages so as to minimize the currents in the machine. The optimization of the losses of the system leads therefore to generate tensions close to saturation. It may happen that the optimized voltages are subjected to saturation due to the dynamics of the regulator, and the dispersion of the parameters of the electric machine, the inverter and measures to control the entire system. These saturations disturb the regulator, and can even make it unstable. To overcome these problems of saturation, the generation of the current instructions must have mechanisms preventing saturation, and / or mechanisms allowing desaturation. It is recalled that in the space of Park, the system to be controlled is the following: Vd = Rsid ± Ld id ± M f if - corLqIq Vq - RsIq + Lq Iq + cor (LdId + MfIf) (Eq 1) Vf = Rf If ± Lf If ± aMf Id With: Vd, Vq and Vf: the voltages applied on the direct axes, in quadrature of the Park plane of the machine and the excitation voltage of the rotor (in Volt) Id, Iq and If: the currents flowing in the machine on the three axes of the Park plane (in Ampere) Rs and Rf the stator and rotor resistances of the machine (in Ohm) Ld, Lq and Lf: the inductances on each axis of the machine ( in Henry) Mf: the mutual inductance between the stator and the rotor (in Henry): a constant term resulting from the Park transform (without unit) cor: the speed of rotation of the magnetic field of the machine (in rad / s ). It should be noted that, in the case of a synchronous machine, the speed of rotation cor of the magnetic field of the machine is equal to the speed of rotation of the rotor multiplied by the number of pairs of poles of the machine. The voltages Vd and Vq are created with an inverter, the voltage Vf is created with a chopper, these two systems being powered by a battery. The constraints to respect Vvd2 _L q <V beats and 3 Vbat Vf Vbat are then as follows: (Eq.2) (Eq.3) With Vbat: the voltage of the battery which supplies the inverter and the chopper. It can therefore be seen that, depending on the battery voltage, certain setpoints may not be reached, which generates a saturation of the control. There is therefore a need for a method ensuring both optimal voltage setpoints and preventing saturation of the voltage regulator. Another need is a method for solving a situation in which the voltage setpoints are already saturated. An object of the invention is a control method of an electric machine of a motor vehicle comprising a step during which current instructions are determined for each of the phases of the electric machine, in the Park mark according to a torque request from the driver. Voltage instructions of the electric machine are then determined from these current instructions. The method comprises the following steps: it is detected whether the saturation of the voltage setpoints is imminent, if this is the case, only the evolutions of the current setpoints leading to an increase in the difference between the current setpoints and a saturation value, then dynamically corrects the current setpoints so as to solve the saturation by dynamically correcting the load angle of the stator currents so as to reduce the amplitude of the control voltage, and then new voltages are determined supplying the phases of the electric machine according to the corrected current instructions.

To detect if the saturation of the commands is imminent, one can calculate the difference between the current setpoints and a saturation value, and one compares the calculated difference with a value of threshold. In the case of motor mode operation, the correction may be an increase in the load angle of the stator currents.

In the case of operation in generator mode, the correction may be a decrease in the load angle of the stator currents. Another object of the invention is a control system of an electric machine of a motor vehicle comprising a means for determining current setpoints relative to each of the phases of the electric machine in the Park mark according to the request. driver torque, means for regulating the currents in the phases of the electrical machine able to determine supply voltages of each of the phases of the electric machine according to the current instructions received at the input. The system comprises a first calculation means, capable of detecting that the saturation of the voltage commands determined by the regulating means is imminent, and, if so, blocking and then allowing only changes in the instructions of the regulation. current in the direction that leads to a decrease in voltage commands. The system also comprises a second calculation means connected downstream of the current setpoint determining means and upstream of the regulating means, able to modify the current setpoints transmitted by the determination means in order to take into account the saturation that has been established or imminent by determining and issuing corrected current instructions to the regulating means.

Other objects, features and advantages will appear on reading the following description given solely as a non-limitative example and with reference to the appended drawings, in which: FIG. 1 illustrates the main elements of a control system according to the invention, and - Figure 2 illustrates the main steps of a control method according to the invention. The control system 1, illustrated in FIG. 1, of an electric machine 2 comprises means 3 for determining the current setpoints relative to each of the phases of the electrical machine in the reference (d, q, f) of Park in function of the torque request of the driver Cref. The control system 1 comprises means 4 for regulating the currents in the phases of the electric machine 2. The regulating means 4 determines the supply voltages Vd, Vq, Vf of each of the phases of the electrical machine 2 according to the instructions current received as input. The control system 1 comprises a first calculation means 5 cooperating with the current regulating means 4. The first calculation means 5 makes it possible to detect that the saturation of the commands is imminent. When such saturation is detected, a first desaturator is able to block the current setpoints so as to ensure the maintenance of control of these currents. The blocking then only allows changes to the instructions in the direction that leads to a decrease in voltage commands. This device has a simple design allowing a very fast action. However, by simply blocking the instructions, it does not by itself to overcome the saturation and ensure the stability of the system on a sufficient time scale. For this purpose, the control system comprises a second calculation means 6 connected downstream of the current-point determination means 3 and upstream of the regulation means 4. The second calculation means 6 also receives a copy of the voltage instructions issued. by the regulation means 4 to the electric machine 2 and a measurement of the battery voltage Vbat - The second calculation means 6 makes it possible to modify the current setpoints transmitted by the determination means 3 in order to take into account the saturation proved or imminent by determining and issuing corrected current instructions in this sense. The operation of the second calculation means 6 will be more fully described below.

The control method of an electric machine comprises a step 7 during which current instructions are determined for each of the phases of the electric machine, in the Park mark. From these current setpoints, voltage instructions of the electric machine are determined by means of proportional-integral control. However, as explained above, saturation of the current setpoints can occur. To avoid this, the method continues with a step 8 during which it is detected that the saturation of the commands is imminent. For this purpose, the difference between the current setpoints and a saturation value is calculated. According to the calculated difference, it is determined that the saturation is close. For example, it can be determined that the saturation is close when the setpoints are 10% below the saturation value. When it is determined that the saturation is near, the process continues in step 9, during which the current setpoints are blocked so as to ensure the maintenance of the control of these currents. For this, only changes in the instructions leading to an increase in the determined difference are allowed. This blocking step is simple and very fast, but by blocking the instructions, it does not allow it alone to get out of saturation and to guarantee stability over a sufficient time scale. For this reason, the control method comprises a desaturation of the controls of the regulator presented below. During steps 10 and 11, the current setpoints are dynamically corrected so as to resolve the saturation. In other words, the blocking of the setpoints prevents the complete saturation of the regulation, while the steps described below ensure the complete exit of the saturation and the resumption of the follow-up of the setpoints. To overcome the saturation, the following constraint must be respected: vs <bat and (Eq.4) Vs = liVd2 + Vq2 (Eq.5) With V,: the module of the control voltage applied to the phases of the stator.

The stator current setpoints are written as follows in a polar coordinate system: fId = Issin (y) Iscos (y) (Eq.6) With I, the amplitude of the phase currents, and yr: the load angle of these currents, also called phase. The desaturation steps provide a dynamic correction of the angle y so as to reduce the amplitude of the control voltage V. In other words, it increases the defluxing of the machine, which implies the decrease of the overall flow. In the case of motor mode operation, the correction consists of an increase of y. In the case of generator mode operation, the correction is a decrease of y.

To ensure this dynamic correction of the setpoints, the angle y is acted on to ensure that the module of the voltage V is servocontrolled to a setpoint V, * defined by a margin coefficient with respect to the saturation value: Vs * = K , T, e * Vbat (Eq. 7) With Kmarge: the margin coefficient. This slaving is asymmetrical because its action can only reduce the flow of the machine, in order to lower the modulus of the voltage V. This is achieved by correcting the angle y, while keeping a constant amplitude of I ,. The correction of y can only be done in one direction, thanks to the normalization of the command, and the saturation at 0 of this standardized command.

The implementation of the dynamic correction of the current setpoints is carried out through the following calculation steps: During a step 10, the saturated value of the voltage error c is calculated: (K marg E = sat VVd2 + V2 e * vbat (Eq 8) The saturation is applied so that a negative value of the term VVd2 + \ T, e * Vba, is replaced by a null value V3 In the same step, the normalized control of the second calculation means 6 as a function of the saturated value of the previously determined voltage error, for which a Proportional-Integral type control is chosen, the control of which is determined by the following equation: u-Kp * (* c (Eq.9) 1 1+ TI With Kp and Ti the adjustment parameters of the desaturation regulator,: the saturated value of the voltage error, u: the command, s: Laplace variable. During a step 11, the current instructions Is, v, are then determined in polar coordinates according to the current instructions Id, Iq in Park coordinates, by applying the following equations: IS = Vid2 + 1q2 arctan (Eq.10) During the same step, a corrected phase angle tV is then determined by applying the equation: (max 0, V-2 ((Eq. 11) 71 71 -K.0 * sign y-- 2 + - i i 2 With: K: conversion gain of the standard control. It will be noted that the gain K is a parameter for adjusting the desaturation.

This calculation ensures that the correction of yr is always performed in the direction of the defluxing. In the space in polar coordinates, this implies to bring the current vector I, of the axis d. Finally, corrected current setpoints q are determined as a function of the corrected phase angle t V by applying the following equations: (id = is sin (y) (Eq.12) 7q cos (yr). current setpoints corrected by regulating means 4 which determines the corresponding supply voltages of the phases of the electrical machine Alternatively, it is possible to reduce the flux by also acting by a correction of the rotor excitation current setpoint If or although by correcting the current setpoint Id rather than the angle y, the implementation in both cases is similar.

However, this alternative embodiment generates the appearance of other difficulties. The regulation of the amplitude of V, with the set If, is difficult to finalize and can destabilize the system because of the slow dynamics of the If regulation compared to that of Id and Ig.

The regulation of the amplitude of V by the setpoint Id raises the problem of the variation of the amplitude of the stator currents IS which must be controlled in coherence with the excitation current If. Thus, the correction of the phase angle γ of the stator currents is the only one which ensures the efficiency of the desaturation of the controls with the dynamic control of the currents of the stator, and which does not modify the coherence of the ratio between I, and If. The method and the control system can be applied to all synchronous electrical machines, including synchronous electric magnet machines.

Claims (5)

REVENDICATIONS1. A method of controlling an electric machine of a motor vehicle, comprising a step during which current orders are determined for each of the phases of the electric machine, in the Park mark according to a torque request of conductor, then voltage instructions of the electric machine are determined from these current setpoints, characterized in that it comprises the following steps: it is detected whether the saturation of the voltage setpoints is imminent, if this is the case only the changes in the current setpoints leading to an increase in the gap between the current setpoints and a saturation value are allowed, then the current setpoints are dynamically corrected so as to solve the saturation by dynamically correcting the loading angle of the stator currents so as to reduce the amplitude of the control voltage, and then new phase supply voltages are determined of the electric machine according to the corrected current instructions. 2. Method according to claim 1, wherein, in order to detect whether the saturation of the commands is imminent, the difference between the current setpoints and a saturation value is calculated, and the calculated difference is compared with a threshold value. A method as claimed in any one of the preceding claims, wherein, in the case of motor mode operation, the correction consists of an increase in the load angle of the stator currents. 4. Method according to any one of claims 1 or 2, wherein, in the case of operation in generator mode, the correction is a decrease in the load angle of the stator currents. 5. Control system of an electric machine of a motor vehicle comprising means (3) for determining current setpoints relative to each of the phases of the electric machine in the Park mark according to the torque request of the driver , means for regulating (4) the currents in the phases of the electric machine (2) able to determine the supply voltages of each of the phases of the electric machine as a function of the input current setpoints, characterized in that it comprises a first calculation means (5), able to detect that the saturation of the voltage commands determined by the regulating means (4) is imminent, and, if so, to block and then not to authorize that evolutions of the current setpoints in the direction which leads to a decrease in the voltage commands, a second calculation means (6) connected downstream of the means for determining (3) current setpoints and in amon t of the regulating means (4), able to modify the current setpoints transmitted by the determining means (3) in order to take into account the known or imminent saturation by determining and emitting corrected current instructions to the control means (4).