Control of an electric machine, in particular a permanent magnet synchronous machine, to reduce torque fluctuations

Abstract

Method for field-oriented control of an electrical machine (1), in particular a permanent magnet synchronous machine having a rotor, wherein a target current, in particular a q target current or a d target current, is provided and a harmonic compensation oscillation of order n is imposed on the target current to reduce harmonics of order n in a torque of the electrical machine (1), wherein an amplitude of the harmonic compensation oscillation is set as a function of an electrical angle of the rotor (3), characterized by the fact that the amplitude I qn the harmonic compensation oscillation is adjusted in such a way that this lqn = lq 0 Ψ dn Ψ d 0 1 + Ψ dn Ψ d 0 sin ( n ω t ) is, where the individual sizes represent: I q0 : provided q-target current, Ψ dn: Amplitude of the nth order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage, ωt: electric angle, and n: Order of harmonics to be reduced.

Description

[0001] The invention relates to a method for field-oriented control of an electrical machine, in particular a permanent-magnet synchronous machine having a rotor, wherein a target current, in particular a q-target current, is provided and a harmonic compensation oscillation of order n is impressed on the target current to reduce harmonics of order n in a torque of the electrical machine. Furthermore, the invention relates to a control device for field-oriented control of an electrical machine, in particular a permanent-magnet synchronous machine having a rotor, with a current controller to which a target current, in particular a q-target current, can be provided, and a compensation unit for reducing harmonics of order n in a torque of the electrical machine, which compensation unit is configured to impress a harmonic compensation oscillation of order n on the target current.

[0002] Conventional field-oriented control of electrical machines, particularly permanent-magnet synchronous motors (PMSMs), assumes that the distribution of the magnetic flux in the motor's air gap, or the induced voltage (EMF), is sinusoidal. Therefore, the aim is to make the motor currents as sinusoidal as possible to avoid torque fluctuations—so-called torque ripple. In practice, however, the flux distribution in the air gap can deviate significantly from the ideal sinusoidal curve. This particularly affects electrical machines designed as permanent-magnet synchronous machines. Higher-order harmonics can result in torque fluctuations, which cause both mechanical vibrations and significantly impair the acoustic behavior of the drive.

[0003] To reduce such torque fluctuations, it is known from the article "Torque Ripple Reduction of an Interior PM Synchronous Motor by Compensating Harmonic Currents Based on Flux Linkage Harmonics", Nam et al., Journal of Power Electronics, Vol. 17, No. 5, pp. 1223-1230, September 2017, that a harmonic compensation oscillation can be impressed on the target current supplied to the respective controller. The frequency of this compensation oscillation is chosen to correspond to the frequency to be compensated in the torque of the electric machine. For field-oriented control, this means that to reduce n-order harmonics in the torque, the q- or d-target current in the rotor-related dq system is superimposed with the n-order harmonic. The impressed current harmonic, in interaction with the fundamental wave of the flux, reduces the torque fluctuation of the electric machine, or at best compensates it.

[0004] The compensation method known from the state of the art has proven to be quite effective in reducing n-order harmonics in the torque. However, it has proven disadvantageous that, as a side effect of this compensation, harmonics of order 2n occur and that the DC component of the torque changes undesirably. This latter side effect, in particular, can impair control accuracy.

[0005] In SCHRAMM, Andreas; SWOROWSKl, Eugen; ROTH-STIELOW, Jörg: Compensation of torque ripples in permanent magnet synchronous machines up to the field weakening range. in: 2017 7th International Electric Drives Production Conference (EDPC), 5-6 December 2017, Würzburg, Germany. 2017, pp. 1-8. ISBN 978-1-5386-1070-1. DOI: 10.1109 / EDPC.2017.8328154, a method for the field-oriented control of an electrical machine, in particular a permanent magnet synchronous machine, is described. Harmonic compensation oscillations are impressed on a target current. Against this background, the task arises of providing a method for reducing torque fluctuations that avoids or at least reduces the side effect known in the prior art – the occurrence of unwanted harmonics of order 2n and a shift in the DC component.

[0006] The object is achieved by a method for field-oriented control of an electrical machine, in particular a permanent magnet synchronous machine, which has a rotor, wherein a target current, in particular a q-target current or a d-target current, is provided and a harmonic compensation oscillation of order n is impressed on the target current to reduce harmonics of order n in a torque of the electrical machine, wherein an amplitude of the harmonic compensation oscillation is adjusted depending on an electrical angle of the rotor.

[0007] The method according to the invention controls an electrical machine according to the type of field-oriented control, which is also referred to as vector control. Within the scope of the method, a target current, in particular a q-target current or a d-target current, is provided. To reduce harmonics of order n, a harmonic compensation oscillation of order n is impressed on the target current. The invention is based on the finding that the occurrence of unwanted harmonics in the torque and the associated influences on the DC component of the torque can be reduced if the amplitude of the harmonic compensation oscillation is adjusted as a function of the electrical angle of the rotor.

[0008] This measure can be understood based on the following considerations.

[0009] For the sake of simplicity, it is assumed that the electric machine is in the base speed range or there is no field weakening, so that the d-set current I d = 0. The d-component of the flux of the permanent magnets Ψ d contains, in addition to the DC component Ψ d0 a harmonic of order n (n = 6,12,18, ...) with amplitude Ψ dn : Ψd=Ψd0+Ψdnsin nωt.

[0010] To compensate for the torque fluctuations, the constant I q0 -current with a harmonic I qn sin nωt of the same order n superimposed to Iq=Iq0+Iqnsin nωt.

[0011] The torque M is calculated as follows: M∝IqΨd=Iq0Ψd0+Ψd0Iqnsin(nωt)+ΨdnIq0sin(nωt)+ΨdnIqnsin2(nωt).

[0012] The unwanted vibrations can be completely suppressed if the following condition is met: Ψd0Iqnsin(nωt)+ΨdnIq0sin(nωt)+ΨdnIqnsin2(nωt)=0

[0013] Solving equation (3) for the amplitude I qn the harmonic compensation oscillation, we obtain: Iqn=−Iq0ΨdnΨd01+ΨdnΨd0sin(nωt) which means that the amplitude I qn the harmonic compensation oscillation I qn sin nωt is set as a function of the electrical angle ωt of the rotor. The minus sign in equation (4) simply means that the impressed current compensation oscillation is in antiphase with the flux oscillation. Therefore, according to an advantageous embodiment of the invention, the value I qn the amplitude of the harmonic compensation oscillation is adjusted in such a way that Iqn=Iq0ΨdnΨd01+ΨdnΨd0sin(nωt) where the individual sizes stand for: I q0 : provided q-target current, Ψ dn:Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ dn : DC component of the d-component of the magnetic flux linkage, ωt : electrical angle, and n: order of the harmonics to be reduced.

[0014] An alternative solution to the problem mentioned above consists in a method for field-oriented control of an electrical machine, in particular a permanent magnet synchronous machine, which has a rotor, wherein a target current, in particular a q-target current or a d-target current, is provided and a harmonic compensation oscillation of order n is impressed on the target current to reduce harmonics of order n in a torque of the electrical machine, whereby one or more harmonic compensation oscillations of an integer multiple of order n are additionally impressed on the target current.

[0015] The alternative field-oriented control method can achieve the same advantages as the field-oriented control method explained above. This is due to the following reasons: If you insert the formula (4) into the equation (1), you get for the q-set current Iq=Iq0(1−x1+x) with x=ΨdnΨd0sin nωt.

[0016] Considering that x « 1, the fraction can be approximated by Taylor polynomials up to the 3rd order as follows: x1+x≈x−x2+x3

[0017] By substituting x in formula (5) using equations (6), (7) we obtain Iq≈Iq0[(1+12(ΨdnΨd0)2)−ΨdnΨd0(1+34(ΨdnΨd0)2)sin (nωt)−12(ΨdnΨd0)2cos (2nωt)+14(ΨdnΨd0)3sin (3nωt)].

[0018] It can thus be seen that a reduction corresponding to the reduction of the torque ripple according to equation (4) can be achieved if one or more harmonic compensation oscillations of an integer multiple of the order n are additionally impressed on the target current, each of which has constant amplitudes.

[0019] According to a preferred embodiment of the invention, it is provided that a DC component of the desired current is multiplied by a constant, wherein the constant is preferably (1+12(ΨdnΨd0)2) where the individual sizes stand for: Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0: DC component of the d-component of the magnetic flux linkage. By multiplying this constant, the fundamental current of the target current can be adjusted in such a way that an undesirable change in the DC component of the torque is reduced, or in particular, compensated.

[0020] According to a preferred embodiment of the invention, it is provided that the harmonic compensation oscillation of order n has an amplitude which is defined by the term ΨdnΨd0(1+34(ΨdnΨd0)2) is defined, where the individual sizes stand for: Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage.

[0021] According to a preferred embodiment of the invention, it is provided that a harmonic compensation oscillation of order 2n is impressed on the desired current, wherein the amplitude of the harmonic compensation oscillation of order 2n is determined by the term 12(ΨdnΨd0)2 is defined, where the individual sizes stand for: Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage.

[0022] According to a preferred embodiment of the invention, it is provided that a harmonic compensation oscillation of order 3n is impressed on the desired current, wherein the amplitude of the harmonic compensation oscillation of order 3n is determined by the term 14(ΨdnΨd0)3 is defined, where the individual sizes stand for: Ψ dn: Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage.

[0023] As explained above in connection with equation (7), the variable amplitude lqn=lq0ΨdnΨd01+ΨdnΨd0sin(nωt) Preferably, the current is approximated by Taylor polynomials up to the third order. An approximation by higher-order Taylor polynomials, particularly fourth, fifth, sixth, etc., is also conceivable. In such a case, a harmonic compensation oscillation of order 4n and / or 5n and / or 6n, etc., can be imposed on the target current.

[0024] A further subject of the invention is a control device for the field-oriented control of an electrical machine, in particular a permanent magnet synchronous machine, which has a rotor, with a current controller to which a target current, in particular a q-target current or a d-target current, can be provided, and a compensation unit for reducing harmonics of order n in a torque of the electrical machine, which compensation unit is designed to impose a harmonic compensation oscillation of order n on the target current, wherein the compensation unit is configured to adjust an amplitude of the harmonic compensation oscillation as a function of an electrical angle of the rotor.

[0025] By means of this control device, the same advantages and technical effects can be achieved which have already been explained in connection with the method according to the invention and its possible embodiments.

[0026] A preferred embodiment of the control device provides a sensor connected to the compensation unit for determining the electrical angle. The sensor can be used to measure the electrical angle.

[0027] A further subject of the invention is a control device for the field-oriented control of an electrical machine, in particular a permanent magnet synchronous machine, which has a rotor, with a current controller to which a target current, in particular a q-target current or a d-target current, can be provided, and a compensation unit for reducing harmonics of order n in a torque of the electrical machine, which compensation unit is designed to impose a harmonic compensation oscillation of order n on the target current, wherein the compensation unit is configured to additionally impose one or more harmonic compensation oscillations of an integer multiple of order n on the target current.

[0028] By means of this control device, the same advantages and technical effects can be achieved which have already been explained in connection with the method according to the invention and its possible embodiments.

[0029] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment illustrated in the drawings. Herein: Fig. 1 schematically shows a first embodiment of a control device according to the invention for field-oriented control of an electrical machine; Fig. 2 schematically shows a second embodiment of the control device according to the invention for field-oriented control of an electrical machine; and Fig. 3 Simulation results of the torque of the electric machine with field-oriented control using a control device according to Fig. 2 without compensation, with compensation according to the prior art and with compensation according to the invention.

[0030] In Fig. Figure 1 schematically shows a first exemplary embodiment of a control device 100 according to the invention for carrying out a method according to the invention for field-oriented control of an electrical machine 1. The electrical machine 1 is a permanent-magnet synchronous motor in this exemplary embodiment.

[0031] The control device 100 comprises a vector control device 10 known as such with a current controller 11, a modulation and control unit 12 for controlling a converter 13 and a converter 13 for providing the phase currents for the electrical machine 1. This converter 13 provides, here three, phase currents for the winding of the stator of the electrical machine 1. The vector control device 10 further comprises a current sensor (not shown) for measuring the phase currents i abc and a transformation unit 14 for transforming the measured phase currents into the rotor-related dq coordinate system. The transformed phase currents I dq are fed to the current controller 11 as actual values. The representation in Fig. Figure 1 is simplified in that the d- and q-components of the respective quantities are not shown separately. This means, for example, that the current controller 11 has two parallel paths, one for the d-component of the current I d and the q-component of the current I q These two currents are in Fig. 1 summarized as I dq designated.

[0032] In order to reduce harmonics of order n in the torque generated by the electric machine 1, the current controller 11 of the vector control device 10 is given a current as a setpoint value, which is composed of a setpoint current I dq0 and one on the target current I dq0impressed harmonic compensation oscillation, which is provided by a compensation unit 20. The compensation unit 20 comprises a basic unit 21 and a modulation unit 22. The basic unit 21 provides—as already known in the prior art—a harmonic compensation oscillation of order n, which is to be reduced or compensated for in the torque. The modulation unit 21 additionally provided according to the present invention varies the amplitude of the compensation oscillation depending on the electrical angle ωt. The electrical angle ωt of the electrical machine 1 is detected by a sensor 9, which is a position sensor, and provided to the compensation unit 20.

[0033] The Fig. The control device 100 shown in Figure 1 thus has a compensation unit 20 configured to adjust the amplitude of the harmonic compensation oscillation as a function of the determined electrical angle ωt of the rotor. Regarding the q-path of the vector control, this means that the amplitude I qn the harmonic compensation oscillation in the embodiment is set in such a way that this lqn=lq0ΨdnΨd01+ΨdnΨd0sin(nωt) where the individual sizes stand for: I q0 : provided q-target current, Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage, ωt: electrical angle, and n: order of the harmonics to be reduced.

[0034] In Fig. Figure 2 schematically shows a second exemplary embodiment of a control device 100 according to the invention for implementing the method according to the invention for field-oriented control of an electrical machine 1. The electrical machine 1 and the vector control device 10 are identical to the electrical machine 1 and the vector control device 10 of the first exemplary embodiment, so that reference is made to the explanations for the first exemplary embodiment.

[0035] In contrast to the first embodiment, the compensation unit 20 is not configured to adjust the amplitude of the harmonic compensation oscillation as a function of an electrical angle of the rotor. Rather, the compensation unit 20 is configured such that a harmonic compensation oscillation of an integer multiple of order n is additionally impressed on the target current. In the embodiment, this is in addition to the harmonic compensation oscillation I dqn of order n also a harmonic compensation oscillation I dq2n of order 2n.

[0036] In addition, the DC component of the target current is multiplied by a constant k0. In the second embodiment, this constant is defined as (1+12(ΨdnΨd0)2) chosen.

[0037] The harmonic compensation oscillation of order n has an amplitude which is given by the term ΨdnΨd0(1+34(ΨdnΨd0)) and the harmonic compensation oscillation of order 2n has an amplitude defined by the term 12(ΨdnΨd0)2 is defined, where the individual sizes stand for: Ψ dn: Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage.

[0038] In the Fig. Figure 3 shows simulation results for the torque of the electric machine 1, which is controlled by a control device 100 according to the second exemplary embodiment. The solid line shows the torque curve without the application of a harmonic compensation oscillation, i.e., with the compensation unit 20 switched off. The dot-dash line shows the torque curve with the application of a harmonic compensation oscillation of the order known from the prior art. The dashed line shows the torque curve with harmonic compensation oscillation I dqn of order n, harmonic compensation oscillations I dq2n of order 2n and multiplication of the DC component by the factor k0 as in Fig. 2 is shown.

[0039] It can be seen that without imposing a harmonic compensation oscillation (solid line), a harmonic of order 6 is detectable in the torque. The amplitude of this harmonic is approximately 10% of the DC component.

[0040] When the harmonic compensation oscillation of order 6 is applied according to the state of the art (dash-dotted line), the harmonics of order 6 disappear. However, harmonics of order 12 occur and the DC component of the torque is reduced.

[0041] If the harmonic compensation oscillation of order 12 is additionally applied and multiplied by the factor k0 (dashed line), the remaining harmonics are negligibly small and the undesired shift of the DC component is eliminated. List of reference symbols 1 Electric machine 9 Sensor 10 Vector control device 11 Current regulator 12 Modulation and control unit 13 inverters 14 Transformation unit 20 compensation unit 21 basic unit 22 Modulation unit 100 control device

Claims

[1] Method for field-oriented control of an electrical machine (1), in particular a permanent magnet synchronous machine, which has a rotor, wherein a desired current, in particular a q-desired current or a d-desired current, is provided and a harmonic compensation oscillation of order n is impressed on the desired current in order to reduce harmonics of order n in a torque of the electrical machine (1), wherein an amplitude of the harmonic compensation oscillation is adjusted as a function of an electrical angle of the rotor (3), characterized by that the amplitude I qn the harmonic compensation oscillation is adjusted in such a way that lqn=lq0ΨdnΨd01+ΨdnΨd0sin(nωt) is, where the individual sizes stand for: I q0 : provided q-target current, Ψ dn: Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage, ωt: electrical angle, and n: order of the harmonics to be reduced. [2] Method for the field-oriented control of an electrical machine (1), in particular a permanent magnet synchronous machine, which has a rotor, wherein a desired current, in particular a q-desired current or a d-desired current, is provided and a harmonic compensation oscillation of order n is impressed on the desired current in order to reduce harmonics of order n in a torque of the electrical machine (1), where one or more harmonic compensation oscillations of an integer multiple of order n are additionally impressed on the target current, characterized bythat a DC component of the target current is multiplied by a constant, whereby the constant is preferred (1+12(ΨdnΨd0)2) where the individual sizes stand for: Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage. [3] Method according to claim 2, characterized by that the harmonic compensation oscillation of order n has an amplitude which is given by the term ΨdnΨd0(1+34(ΨdnΨd0)2) is defined, where the individual sizes stand for: Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage. [4] Method according to one of claims 2 or 3, characterized bythat a harmonic compensation oscillation of order 2n is impressed on the target current, where the amplitude of the harmonic compensation oscillation of order 2n is given by the term 12(ΨdnΨd0)2 is defined, where the individual sizes stand for: Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage. [5] Method according to one of claims 2 to 4, characterized by that a harmonic compensation oscillation of order 3n is impressed on the target current, where the amplitude of the harmonic compensation oscillation of order 3n is given by the term 14(ΨdnΨd0)3 is defined, where the individual sizes stand for: Ψ dn: Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0: DC component of the d-component of the magnetic flux linkage. [6] Control device (100) for field-oriented control of an electrical machine (1), in particular a permanent magnet synchronous machine, which has a rotor, with a current regulator (11) to which a target current, in particular a q-target current or a d-target current, can be provided, and a compensation unit (20) for reducing harmonics of order n in a torque of the electrical machine (1), which is designed to impose a harmonic compensation oscillation of order n on the target current, characterized by , that the compensation unit (20) is designed to generate an amplitude I qn the harmonic compensation oscillation as a function of an electrical angle of the rotor (3) in such a way that these lqn=lq0ΨdnΨd01+ΨdnΨd0sin(nωt) where the individual sizes stand for: I q0 : provided q-target current, Ψ dn : Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0 : DC component of the d-component of the magnetic flux linkage, ωt: electrical angle, and n: order of the harmonics to be reduced. [7] Control device (100) according to claim 6, characterized by a sensor (9) connected to the compensation unit (20) for determining the electrical angle. [8] Control device (100) for field-oriented control of an electrical machine (1), in particular a permanent magnet synchronous machine, which has a rotor, with a current regulator (11) to which a target current, in particular a q-target current or a d-target current, can be provided, and a compensation unit (20) for reducing harmonics of order n in a torque of the electrical machine (1), which is designed to impose a harmonic compensation oscillation of order n on the target current, characterized by , that the compensation unit (20) is designed to additionally impose one or more harmonic compensation oscillations of an integer multiple of order n on the target current, where a DC component of the target current is multiplied by a constant, where the constant is preferred (1+12(ΨdnΨd0)2) where the individual sizes stand for: Ψ dn: Amplitude of the n-th order harmonic in the d-component of the magnetic flux linkage, Ψ d0: DC component of the d-component of the magnetic flux linkage.

Images