Method for controlling a synchronous electrical machine, corresponding system and motor vehicle comprising the system

Abstract

A method for controlling a permanent magnet synchronous electrical machine powered by a battery delivering a supply voltage to terminals of the battery, the method including: calculating an initial direct voltage component Vdc and an initial quadratic voltage component in a rotating reference; checking a saturation condition; calculating an angle α of a formula; generating voltages to be applied to the electrical machine if α varies negatively and Vdc is positive or if α varies positively and V dc is negative. The method for example can be applied in a control of synchronous electrical machines.

Claims

1. A method for controlling a synchronous electrical machine with a permanent magnet powered by a battery delivering a power supply voltage at its terminals, the method comprising: computing, via processing circuitry, an initial direct voltage component Vdc and an initial quadratic voltage component Vqc in a revolving reference frame having a plurality of axes; verifying, via the processing circuitry, a saturation condition by verifying, in an orthogonal reference frame having the direct voltage components for X-axis and the quadratic voltage components for Y-axis, that a point of coordinates Vdc and Vqc is outside of a range dependent on Vbat and delimited by a contour, Vbat denoting a power supply voltage at terminals of the battery; computing, when the saturation condition is verified and via the processing circuitry, an angle $\alpha =\arctan \left(\frac{\mathrm{Vqc}}{\mathrm{Vdc}}\right);$ generating, via the battery and when the saturation condition is verified and if α varies negatively and Vdc is positive or if α varies positively and Vdc is negative, a direct axis voltage and quadratic axis voltage by determining a point of intersection between the contour and a straight line passing through the origin of the orthogonal reference frame and the point of coordinates Vdc and Vqc, the direct axis voltage corresponding to the X-axis of the intersection and the quadratic axis voltage corresponding to the Y-axis of the intersection; and applying to the electrical machine, via the battery and based on the saturation condition, Vdc and α, one of Vdc and Vqc, direct axis voltage and quadratic axis voltage, and a preceding direct axis voltage and preceding quadratic axis voltage.

2. The method as claimed in claim 1, wherein the verification of a saturation condition includes a comparison between √{square root over (Vdc.sup.2+Vqc.sup.2)} and $\frac{\mathrm{Vbat}}{\sqrt{3}}.$

3. The method as claimed in claim 2, wherein the direct axis voltage to be applied is equal to $\frac{\mathrm{Vbat}}{\sqrt{3}}\cos \left(\alpha \right)$ and the quadratic axis voltage to be applied is equal to $\frac{\mathrm{Vbat}}{\sqrt{3}}\sin \left(\alpha \right)$ if α varies negatively and Vdc is positive or if α varies positively and Vdc is negative.

4. The method as claimed in claim 1, further comprising: applying, via the battery and when the saturation condition is not satisfied, the initial direct voltage component Vdc and the initial quadratic voltage component Vqc to the electrical machine; and applying, via the battery and if α varies negatively and Vdc is positive or if α varies positively and Vdc is negative, the direct axis voltage and quadratic axis voltage to the electrical machine, and if not, applying a preceding direct axis voltage and preceding quadratic axis voltage to the electrical machine.

5. A system for controlling a synchronous electrical machine with permanent magnet, the system comprising: processing circuitry configured to compute, at an instant, an initial direct voltage component Vdc and an initial quadratic voltage component Vqc in a revolving reference frame having a plurality of axes, configured to verify a saturation condition by verifying, in an orthogonal reference frame having the direct voltage components for X-axis and the quadratic voltage components for Y-axis, that a point of coordinates Vdc and Vqc is outside of a range dependent on Vbat and delimited by a contour, Vbat denoting a power supply voltage at terminals of the battery configured to compute an angle $\alpha =\arctan \left(\frac{\mathrm{Vqc}}{\mathrm{Vdc}}\right)$ if the saturation condition is verified, and a battery configured to power the permanent magnet of the electrical machine and configured to generate, when the saturation condition is verified and if α varies negatively and Vdc is positive or if α varies positively and Vdc is negative, a direct axis voltage and quadratic axis voltage to be applied to the electrical machine by determining a point of intersection between the contour and a straight line passing through the origin of the orthogonal reference frame and the point of coordinates Vdc and Vqc, the direct axis voltage corresponding to the X-axis of the intersection and the quadratic axis voltage corresponding to the Y-axis of the intersection, and apply to the electrical machine, based on the saturation condition, Vdc and α, one of Vdc and Vqc, direct axis voltage and quadratic axis voltage, and a preceding direct axis voltage and preceding quadratic axis voltage.

6. The system as claimed in claim 5, wherein the processing circuitry is configured to verify the saturation condition by comparing √{square root over (Vdc.sup.2+Vqc.sup.2)} and $\frac{\mathrm{Vbat}}{\sqrt{3}}.$

7. The system as claimed in claim 6, wherein the direct axis voltage is equal to $\frac{\mathrm{Vbat}}{\sqrt{3}}\cos \left(\alpha \right)$ and the quadratic axis voltage is equal to $\frac{\mathrm{Vbat}}{\sqrt{3}}\sin \left(\alpha \right),$ if α varies negatively and Vdc is positive or if α varies positively and Vdc is negative.

8. A motor vehicle with electric or hybrid drive comprising: a synchronous machine with permanent magnet and the machine control system as claimed in claim 5.

Description

(1) Other aims, features and advantages of the invention will become apparent on reading the following description, given purely as a nonlimiting example, and with reference to the attached drawings in which:

(2) FIG. 1 illustrates different steps of a method according to the invention,

(3) FIG. 2 illustrates a system according to the invention, and

(4) FIG. 3 illustrates a graphic representation for determining if the machine is in saturation mode.

(5) FIG. 1 schematically shows steps of a method according to one aspect of the invention. In this example, the saturation condition corresponds to the verification that a point is in a circle of radius

(6) $\frac{\mathrm{Vbat}}{\sqrt{3}}.$

(7) This method makes it possible to control a synchronous electrical machine, for example a synchronous machine of a motor vehicle with electric or hybrid drive.

(8) The method comprises a step E01 of computation of an initial direct voltage component denoted Vdc and of an initial quadratic voltage component denoted Vqc in a revolving reference frame comprising a plurality of axes, for example the Park reference frame. The computation of Vdc and of Vqc can be implemented by any means, for example by using a proportional integral corrector or a proportional integral derivative corrector.

(9) The method then comprises a test step E02 in which √{square root over (Vdc.sup.2+Vqc.sup.2)} and

(10) $\frac{\mathrm{Vbat}}{\sqrt{3}}$
are compared, Vbat being the power supply voltage supplied by the battery which powers the electrical machine. If this condition is not verified, the step E02′ is implemented in which Vdc and Vqc are applied directly to the machine.

(11) If √{square root over (Vdc.sup.2+Vqc.sup.2)} is greater than

(12) $\frac{\mathrm{Vbat}}{\sqrt{3}},$
a step E03 is implemented to compute an angle denoted α, obtained by the following computation

(13) $\alpha =\arctan \left(\frac{\mathrm{Vqc}}{\mathrm{Vdc}}\right).$

(14) The computation of the angle α makes it possible to implement another test step E04 in which, at an instant t, it is verified how alpha varies relative to the preceding implementation of the method at the instant t−Δt, and the sign of Vdc is verified.

(15) If α varies negatively and Vdc is positive, or if α varies positively and Vdc is negative, then it is possible to implement the step E05 and apply a voltage to the direct axis equal to

(16) $\frac{\mathrm{Vbat}}{\sqrt{3}}\cos \left(\alpha \right)$
and a voltage to the quadratic axis equal to

(17) $\frac{\mathrm{Vbat}}{\sqrt{3}}\sin \left(\alpha \right).$

(18) If the test of the step E04 is not verified, then the step E06 is implemented, in which the voltages already applied in the preceding implementation of the method are applied.

(19) FIG. 2 schematically represents a system SYS for controlling a synchronous electrical machine with permanent magnet powered by a battery.

(20) The various computation means of the system SYS can be contained in a computation unit, for example an electronic control unit of a motor vehicle.

(21) The system SYS comprises computation means 1 configured to implement the step E01 and deliver an initial direct voltage component Vdc and an initial quadratic voltage component Vdc in a revolving reference frame comprising a plurality of axes, for example the Park reference frame. Vdc and Vqc are voltage setpoints computed in the step E01 that are desired to be applied.

(22) The system SYS also comprises computation means 2 for implementing the step E02 and configured to compare √{square root over (Vdc.sup.2+Vqc.sup.2)} and

(23) $\frac{\mathrm{Vbat}}{\sqrt{3}}.$

(24) The system SYS also comprises computation means 3 configured to compute an angle

(25) 0$\alpha =\arctan \left(\frac{\mathrm{Vqc}}{\mathrm{Vdc}}\right)$
is √{square root over (Vdc.sup.2+Vqc.sup.2)} is greater than

(26) $\frac{\mathrm{Vbat}}{\sqrt{3}}$
(and implement the step E03).

(27) The system SYS also comprises means 4 for generating voltages to be applied to the machine, the means being configured to deliver, if √{square root over (Vdc.sup.2+Vqc.sup.2)} is greater than

(28) $\frac{\mathrm{Vbat}}{\sqrt{3}},$
a direct voltage component to be applied equal to

(29) $\frac{\mathrm{Vbat}}{\sqrt{3}}\cos \left(\alpha \right)$
and a quadratic voltage component to be applied equal to

(30) $\frac{\mathrm{Vbat}}{\sqrt{3}}\sin \left(\alpha \right)$
if α varies negatively and Vdc is positive or if α varies positively and Vdc is negative.

(31) It should be noted that, in the Park space, the equation system to be controlled for the synchronous machine is as follows:

(32) $\begin{array}{cc}\{\begin{array}{c}{V}_d=R_s{I}_d+L_d{\stackrel{•}{I}}_d-{\omega }_r{L}_q{I}_q\\ V_q=R_s{I}_q+L_q{\stackrel{•}{I}}_q-{\omega }_r\left(L_d{I}_d+{\varphi }_f\right)\end{array}& \left(1\right)\end{array}$

(33) With V.sub.d and V.sub.q being the voltages applied to the two axes, respectively direct and in quadrature, of the Park plane of the machine, I.sub.d and I.sub.q being the currents flowing in the machine on the two axes, respectively direct and in quadrature, of the Park plane, R.sub.s being the equivalent resistance of the stator of the machine, L.sub.d and L.sub.q being the inductances on each axis, respectively direct and in quadrature, of the Park plane of the machine, ω.sub.r being the rotation speed of the magnetic field of the machine (i.e. the rotation speed of the rotor multiplied by the number of pairs of poles of the machine), and Φ.sub.f being the flux generated by the magnets of the rotor.

(34) For a machine in which L.sub.d and L.sub.q are equal, the following electromagnetic torque value C.sub.em is obtained:
C.sub.em=pΦ.sub.fI.sub.q

(35) With p being the number of pairs of poles of the rotor of the machine.

(36) This is the torque that should be retained while avoiding the saturation.

(37) FIG. 3 is a graphic representation of voltage values, respectively direct and in quadrature (Vd on the X-axis and Vq on the Y-axis), of the Park plane of the machine.

(38) In this figure, the saturation limit has been represented by a circle drawn in a thick line. The operating points located within this circle correspond to non-saturated operating conditions.

(39) If, by calculation, the operating point A, corresponding to VdcA and VqcA, is obtained, it can be concluded that there is saturation. The angle α represented in FIG. 3 can then be determined.

(40) If it is concluded that the angle α has decreased relative to the last implementation of the method, and since VdcA is positive, then voltage components, direct and in quadrature, are applied by choosing a point corresponding to the intersection between the circle and the straight line starting from the origin with an angle α. This point has VdaA for X-axis and VqaA for Y-axis.

(41) If, however, the angle α has increased, then the same voltage values continue to be applied.

(42) If, by calculation, the operating point B, corresponding to VdcB (negative) and VqcB, is obtained, it can be concluded that there is saturation. The angle α′ represented in FIG. 3 can then be determined.

(43) If it is concluded that the angle α′ has increased relative to the last implementation of the method, and since VdcB is negative, then voltage components, direct and in quadrature, are applied by choosing a point corresponding to the intersection between the circle and the straight line starting from the origin with an angle α′. This point has VdaB for X-axis and VqaB for Y-axis.

(44) If, however, the angle α has decreased, then the same voltage values continue to be applied.

(45) By virtue of the invention, a saturation condition can be rapidly left, while retaining a good regulation of the voltages, in particular a zero current on the direct axis.