The present invention relates to a control method implemented in a power converter connected to a synchronous electric motor with permanent magnets and making it possible to identify parameters linked to the magnetic saturation of the electric motor. The method of the invention also makes it possible to employ said parameters in controlling the electric motor.
These days, in the power converters of variable speed drive type, the magnetic saturation is often not taken into account in the models of the electric motors employed to check or identify the parameters of the motor. In most of the current variable speed drives, there is, however, the possibility of setting a parameter with which to optimize the output torque in the case of magnetic saturation of the electric motor. This parameter corresponds to a default fixed angle correction applied in the execution of the control.
Document JP2010246318 describes a solution optimizing the torque in the case of magnetic saturation. This solution consists in correcting the flux current and the torque current by taking into account a curve of saturation as a function of the mutual inductance between the rotor and the stator. This document does not propose any solution with which to identify parameters linked to the magnetic saturation of the electric motor.
The publication entitled “Measurement and Adaptative Decoupling of Cross Saturation Effects and Secondary Saliencies in Sensorless-Controlled IPM Synchronous Machines” (David Reigosa et al.—XP031146253, ISBN :978-1-4244-1259-4) presents the effects of the magnetic saturation in synchronous machines. The method proposed in this document relies on neural networks. This method requires many computations and is therefore difficult to implement.
A method is known from the publication entitled “Improved Rotor Position Estimation by Signal Injection Brushless AC Motors, Accounting for Cross-Coupling Magnetic Saturation” (Li Y et al—XP031146247, ISBN : 978-1-4244-1259-4) with which to determine the influence of the mutual magnetic saturation (“cross-coupling”) between the rotor and the stator of the motor. This method is applied to a brushless motor and cannot be adapted to a synchronous electric motor with permanent magnets. In practice, to be able to control a permanent magnet synchronous electric motor, it is necessary to characterize all the magnetic saturation phenomena, that is to say the mutual magnetic saturation between the stator and the rotor but also the intrinsic magnetic saturations of the rotor and of the stator.
The aim of the invention is to propose a simple and reliable control method for identifying parameters linked to the magnetic saturation of a permanent magnet synchronous electric motor, in order to use them subsequently to optimize the torque in the case of magnetic saturation. The method of the invention makes it possible to identify the parameters linked to the mutual magnetic saturation but also linked to the intrinsic saturation of the rotor and of the stator.
This aim is achieved by a control method implemented in a power converter comprising an inverter connected to a permanent magnet synchronous electric motor (M), said electric motor being modeled in the power converter by a mathematical model of the currents of the electric motor expressing a flux current and a torque current as a function of magnetic saturation parameters. The control method comprises:
To deduce the magnetic saturation parameters, the method implemented in the invention proves particularly simple because it requires only a basic computation. It is performed with the motor stopped and without using any position sensor. The voltages injected do not result in any rotation of the motor.
According to a particular feature, the step of determination of the magnetic saturation parameters comprises a step of extraction of the amplitude of the oscillation of the current obtained.
According to another particular feature, the step of determination of the magnetic saturation parameters comprises a step of estimation of said magnetic saturation parameters as a function of the amplitude of the oscillation of the current obtained.
According to another particular feature, the voltage sequence comprises:
According to another particular feature, the mathematical model of the electric motor is of Hamilton-Lagrange type.
According to another particular feature, the method comprises a step of use of said saturation parameters to determine a correction to the angle error existing between the position of a control marker defined by the axis of flux and the axis of torque and a position of the rotor of the electric motor.
According to another particular feature, said correction is applied to the angle error. According to a variant embodiment, the correction is applied to a reference flux current and to a reference torque current determined as input for the control law.
The invention relates to a power converter comprising an inverter connected to a permanent magnet synchronous electric motor, said electric motor being modeled in the power converter by a mathematical model of the currents of the electric motor expressing a flux current and a torque current as a function of magnetic saturation parameters. The power converter comprises control meals arranged to apply to the electric motor a voltage sequence comprising a steady-state voltage signal and a high-frequency voltage signal along the axis of the flux and/or the axis of the torque of the motor, in order to cause an oscillation of the current on the axis of the flux and/or on the axis of the torque, means for measuring the oscillation of the current obtained on the axis of the flux and/or on the axis of the torque, means for determining the magnetic saturation parameters as a function of said oscillation of the current. This power converter is, for example, a variable speed drive.
Other features and advantages will appear in the following detailed description with reference to an embodiment given as an example and represented by the appended drawings in which:
The invention relates to a control method implemented in a power converter of variable speed drive type connected to a permanent magnet synchronous electric motor M (called “PMSM”).
As is known, a power converter of variable speed drive type is connected upstream to an electrical network and downstream to the electric motor. The variable speed drive comprises:
The inverter module INV is controlled by employing a determined control law executed by control means. The control law consists in computing the voltages to be applied to the electric motor as a function of a stator speed setpoint to be given to the electric motor.
To take account of the magnetic saturation in the control law, the invention consists in previously determining parameters αx,y linked to the magnetic saturation of the electric motor. These parameters αx,y are identified outside the normal operation of the variable speed drive, for example during a learning procedure.
According to the invention, some of these magnetic saturation parameters are employed to determine, during the normal operation of the motor, a correction of the angle error that exists between the position of the control marker (d and q axes) and the position of the rotor (that is to say, of the permanent magnet).
The invention consists first of all of a control method making it possible to determine the parameters αx,y linked to the magnetic saturation of the electric motor. For this, a mathematical model of the permanent magnet synchronous electric motor, including the magnetic saturation, is used. In a Hamilton-Lagrange approach, the mathematical model of the permanent magnet synchronous electric motor, including the magnetic saturation phenomenon, follows, for example, the following expression:
From this expression, the following is deduced:
in which:
ΨS: complex writing of the stator leakage flux ΨSd+j·ΨSq,
φm: permanent flux,
ΨSd: d-axis stator leakage flux,
ΨSq: q-axis stator leakage flux,
Ld: d-axis inductance,
Lq: q-axis inductance,
uS: stator voltage,
RS: stator resistance,
IS: stator current,
ω: rotor speed (corresponding to np×mechanical speed),
J: inertia,
np: number of pairs of poles,
τEM: electromagnetic torque,
τ: motor torque,
αx,y: magnetic saturation parameters.
The invention consists in identifying the magnetic saturation parameters referred to in the relationships written above. This mathematical model takes into account all the magnetic saturation types and effects of the electric motor, that is to say the mutual saturation between the stator and the rotor and the intrinsic saturation of the rotor and of the stator.
These parameters are therefore designated α3,0, α1,2, α4,0, α2,2, α0,4.To identify these parameters, the identification principle implemented by the control program of the invention consists in injecting two types of voltage signals on the axis of the flux (hereinbelow, d-axis) and/or on the axis of the torque (hereinbelow, q-axis). The first voltage signal is steady-state and the second voltage signal is at high frequency. The expression “steady-state signal” should be understood to mean a continuous signal over a certain duration, this steady-state signal being able to assume different levels over time.
A voltage us including a steady-state part and a high-frequency part is expressed as follows:
uS=uSd+j·uSq with uSd=ūSd+ũSd·f(Ω·t), uSd=ūSq+ũSq·f(Ω·t)
in which ūS represents its steady-state part (on the d-axis or on the q-axis), ũS represents its high-frequency part (on the d-axis or on the q-axis), f is a periodic function and F its centered primitive.
We thus obtain the expressions:
in which, ĪSd and ĪSq represent the steady-state components of the flux and torque currents and ĨSd and ĨSq represent the oscillations of the flux and torque currents.
We obtain at first order in Ω and α (that is to say by using the relationships ΨSd≈Ld·ISd and ΨSq≈Lq·ISq):
Since the current oscillations ĨSd and ĨSq can be extracted from the measurement of the currents ISd and ISq, we obtain, through (4), relationships that make it possible to calculate the saturation parameters.
In
In
In
In
As represented in
In
For example:
take the system y=a·x2+b·x+c, where a, b, c are parameters to be estimated and x, y known signals.
The estimation of the parameters a, b, c by the least squares is obtained by the matrix formulation:
which supplies
where (yk,xk) are the measured data:
Once the magnetic saturation parameters αx,y have been determined, they can be used, during the normal operation of the motor, in the execution of the control law by the variable speed drive.
For that, the control law as represented in
The control law comprises a reference flux current ISdref and a reference torque current ISqref, from which are determined a reference flux voltage uSdref and a reference torque voltage uSqref. The reference flux voltage uSdref has applied to it a high-frequency voltage signal uSh making it possible to generate current oscillations on the flux axis d. From the reference flux voltage uSdref and from the reference torque voltage uSqref the control law generates the reference voltages u Uref, uVref, uWref for the three phases U, V, W connecting the inverter INV to the motor M. As a function of the reference voltages uUref, uVref, uWref. the inverter generates the corresponding voltages which create the currents ISU, ISV, ISW in the three phases U, V, W of the motor. These currents are measured and processed by the control law to convert them into flux and torque current, ISd, ISq which are reinjected as input for regulation. From the measured flux and torque currents ISd, ISq, the control law calculates an angle error ε (block 10) corresponding to the difference between the position of the control marker (d- and q-axes) and the position of the rotor (that is to say, of the permanent magnet). To this angle error ε, the control law adds a correction corresponding to the inclusion of the magnetic saturation. The duly corrected angle error then makes it possible to evaluate the stator speed by applying gains Kp and Ki.
From a detailed point of view, when we write the motor model in the rotor marker when stopped, we obtain:
with ε being the angle error between the control marker and the position of the rotor
To the first order in ε, the equations (6) become:
Let us define the voltage, with a voltage injection on the d-axis:
uS=ūSdq+ũSd·f(Ω·t)
where ūSdq is the voltage applied by a standard control.
It amounts to the basis of the relationship (5):
where
Now we reinject the value of the flux (8) into the relationships (7) to isolate the oscillation of the current to the first order. We then obtain:
In the case of magnetic saturation, without current injection on the flux axis d, the angle error ε can be expressed as a function of the oscillation of the current and of a correction making it possible to optimize the torque produced. We then obtain:
The relationship (10) can thus be rewritten as follows:
in which εOffset corresponds to the correction to the angle error to be taken into account in the case of magnetic saturation of the electric motor, this correction being a function of the magnetic saturation parameters α1,2 and α2,2. It is interesting to note that the knowledge only of these two parameters is sufficient to determine the correction to be applied. The principle of identification of the parameters described above could therefore be limited to just these parameters.
In
The torque obtained from the torque current and from the angle ε is τEM=np·ISq·φm·cos(ε). The current consumed to supply a given torque is minimal when the angle ε is zero.
Number | Date | Country | Kind |
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Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2012/053428 | 2/29/2012 | WO | 00 | 8/30/2013 |
Publishing Document | Publishing Date | Country | Kind |
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WO2012/123255 | 9/20/2012 | WO | A |
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Entry |
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Li, Y. et al., “Improved Rotor Position Estimation by Signal Injection in Brushless AC Motors, Accounting for Cross-Coupling Magnetic Saturation”, Industry Applications Conference, 2007.42nd IAS Annual Meeting. Conference Record of the 2007 IEEE, pp. 2357-2364, XP031146247, (Sep. 1, 2007). |
Reigosa, D. et al. “Measurement and Adaptive Decoupling of Cross-Saturation Effects and Secondary Saliencies in Sensorless-Controlled IPM Synchronous Machines”, Industry Applications Conference, 2007. 42nd IAS Annual Meeting. Conference Record of the 2007 IEEE, pp. 2399-2406, XP031146253, (Sep. 1, 2007). |
International Search Report Issued May 17, 2013 in PCT/EP12/053428 Filed Feb. 29, 2012. |
Number | Date | Country | |
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20130334992 A1 | Dec 2013 | US |