Compensation of detent torques of synchronous motors

Abstract

In a method and a compensation arrangement for compensating detent torques of identically constructed synchronous motors, a no-load detent torque and a bad detent torque are measured on a reference motor as a function of a rotor position relative to a stator. A differential detent torque for the reference motor is determined by subtracting the measured no-load detent torque from each measured bad detent torque, and an operating-point-dependent spectral component of the differential detent torque is determined, A model function modeling the spectral component as a function of the operating point is then formed, and a first compensation current, which generates a compensation torque that compensates a detent torque at the instantaneous operating point with a value of the model function, is superimposed for each of the identically constructed synchronous motors on a setpoint current when operating at an instantaneous operating point in a predetermined first operating range.

Claims

1. A method for compensating detent torques of identically constructed synchronous motors, which each have a stator and a rotor, comprising: measuring on a reference motor of the identically constructed synchronous motors a no-load detent torque during no-load operation as a function of a rotor position of the rotor relative to the stator; measuring for various operating points of the reference motor a load detent torque as a function of the rotor position relative to the stator; subtracting for each measured load detent torque from the measured load detent torque the measured no-load detent torque to determine a differential detent torque for the reference motor; determining an operating-point-dependent spectral component of the differential detent torque; forming a model function of the spectral component, the model function modeling the spectral component as a function of the operating point; and superimposing for each synchronous motor of the identically constructed synchronous motors, during operation at an instantaneous operating point in a predetermined first operating range, on a setpoint current of the synchronous motor a first compensation current, which generates a compensation torque that compensates a detent torque at the instantaneous operating point with a value of the model function.

2. The method of claim 1, wherein the operating point of a synchronous motor is defined by an actual value of a load torque.

3. The method of claim 1, wherein the operating point of a synchronous motor is defined by an actual value of a load torque and at least one additional parameter.

4. The method of claim 1, wherein the model function models an amplitude of the spectral component of the differential detent torque by way of a polynomial function of a load torque.

5. The method of claim 1, wherein the model function models a phase of the spectral component of the differential detent torque by way of a piecewise linear function of a load torque.

6. The method of claim 1, further comprising: measuring for each synchronous motor the no-load detent torque in a no-load operation as a function of the rotor position relative to the stator, and superimposing, during operation of the synchronous motor in a predetermined second operating range, on the setpoint current of the synchronous motor a second compensation current which generates a compensation torque that compensates the no-load detent torque of the synchronous motor.

7. The method of claim 6, wherein the first operating range is contained within the second operating range.

8. The method of claim 6, wherein the first operating range and the second operating range are defined for a rotating synchronous motor by a rotational speed interval of a rotor rotational speed and for a linear synchronous motor by a velocity interval for rotor velocities.

9. The method of claim 6, wherein the spectral component of the differential detent torque is, for a rotating synchronous motor, a Fourier component of the differential detent torque as a function of a rotor angle of a rotation of the rotor relative to the stator and, for a linear synchronous motor, a Fourier component of the differential detent torque as a function of a rotor position of the rotor relative to the stator.

10. The method of claim 1, further comprising generating or changing a compensation current for compensating a detent torque, and changing the detent torque after a dead time after the generation or change of the compensation current has elapsed.

11. A compensation arrangement for compensating detent torques of identically constructed synchronous motors, which each have a stator and a rotor, comprising: a measuring device configured to acquire a no-load detent torque and a load detent torque of a reference motor as a function of a rotor position of the rotor relative to the stator, an evaluation unit configured to subtract for each measured load detent torque from the measured load detent torque the measured no-load detent torque to determine a differential detent torque for the reference motor, to determine an operating-point-dependent spectral component of the differential detent torque; and to form a model function of the spectral component, the model function modeling the spectral component as a function of the operating point; and a control unit associated with each of the identically constructed synchronous motors and configured to control a motor current of a synchronous motor and to superimpose, during operation of the synchronous motor at an instantaneous operating point in a first operating range, on a setpoint current of the synchronous motor a first compensation current, which generates a compensation torque that compensates a detent torque at the instantaneous operating point with a value of the model function.

12. The compensation arrangement of claim 11, wherein the control unit of the synchronous motor is configured to store a no-load detent torque of the synchronous motor as a function of the rotor position and to superimpose, during operation of the synchronous motor in a predetermined second operating range, on the setpoint current of the synchronous motor a second compensation current which generates a compensation torque which compensates the no-load detent torque of the synchronous motor which generates a compensation torque that compensates the no-load detent torque of the synchronous motor.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

(2) FIG. 1 shows schematically electric synchronous motors and a compensation arrangement for the compensation of detent torques of the synchronous motors,

(3) FIG. 2 shows amplitudes of spectral components of a detent torque of a synchronous motor as a function of a load torque,

(4) FIG. 3 shows an amplitude of a spectral component of a detent torque of a synchronous motor as a function of a load torque,

(5) FIG. 4 shows a phase of a spectral component of a detent torque of a synchronous motor as a function of a load torque,

(6) FIG. 5 shows an amplitude of a spectral component of a differential detent torque of a synchronous motor as a function of a load torque.

(7) FIG. 6 shows a phase of a spectral component of a differential detent torque of a synchronous motor as a function of a load torque,

(8) FIG. 7 shows amplitudes of a spectral component of a detent torque of a synchronous motor as a function of a rotational speed of the synchronous motor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(9) Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom ones, diagramrnatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

(10) Turning now to the drawing, and in particular to FIG. 1, there are shown two identically constructed synchronous motors 1 and a compensation arrangement 3 for the compensation of detent torques of the synchronous motors 1.

(11) The synchronous motors 1 are each constructed as a permanently excited rotating electric machine or as a permanently excited linear motor with a stator 5 and a rotor 7 which is movable relative to the stator 5. For example, the rotor 7 may have permanent magnets and the stator 5 may have a laminated core with slots, through which a stator winding is routed. Alternatively, the stator 5 may have permanent magnets and the rotor 7 may have a laminated core with slots, through which a rotor winding is routed.

(12) The compensation arrangement 3 has a measuring device 9, an evaluation unit 11 and for each synchronous motor 1 a control unit 13.

(13) The measuring device 9 is used to measure for a reference motor 2 of the synchronous motors 1 a no-load detent torque during no-load operation as a function of a rotor position of the rotor 7 relative to the stator 5 and to measure, at various operating points, a respective load detent torque as a function of the rotor position.

(14) In this context, an operating point of a synchronous motor 1 is defined by an actual value of a load torque M.sub.load of the synchronous motor 1. Alternatively, an operating point of a synchronous motor 1 may be defined by an actual value of the load torque M.sub.load and at least one additional parameter, for example a temperature.

(15) The evaluation unit 11 determines, for each measured load detent torque of the reference motor 2, a differential detent torque by subtracting from the load detent torque the measured no-load detent torque of the reference motor 2. Furthermore, the evaluation unit 11 determines an operating-point-dependent spectral component of the differential detent torque and forms a model function of the spectral component, which models the spectral component as a function of the operating point.

(16) The spectral component of the differential detent torque is, for rotating synchronous motors 1, a Fourier component of the differential detent torque as a function of a rotor angle of a rotation of the rotor 7 relative to the stator 5 and, for linear synchronous motors 1, a Fourier component of the differential detent torque as a function of a rotor position of the rotor 7 relative to the stator 5.

(17) If an operating point is defined by an actual value of the load torque M.sub.load and the synchronous motors 1 are rotating electric machines, then an exemplary model function M.sub.detent(M.sub.load) for a spectral component of the differential detent torque as a function of the load torque M.sub.load is formed as follows:
M.sub.detent(M.sub.load)=amp(M.sub.load).Math.sin(n.sub.1.Math.+phase(M.sub.load)),
wherein is the rotor angle, amp(M.sub.load) model s an amplitude A.sub.diff of the spectral component of the differential detent torque as a function of the load torque M.sub.load, phase(M.sub.load) models a phase P.sub.diff of the spectral component of the differential detent torque as a function of the load torque M.sub.load and n.sub.1 is a multiplicity characterizing the spectral component. amp(M.sub.load) is, for example, a polynomial function, e.g. a quadratic function in accordance with
amp(M.sub.load)=k.sub.1.Math.M.sub.load.sup.2+k.sub.0.Math.|M.sub.load|,
wherein k.sub.1 and k.sub.0 are suitable constants to be specified. phase(M.sub.load) is, for example, a piecewise linear function, see FIG. 6 for this purpose.

(18) Instead of forming the model function as a function of the load torque M.sub.load, as described above, the model function may also be formed as a function of a torque-generating current of the synchronous motor 1, since a unique dependency exists between the torque-generating current and the load torque M.sub.load, which is frequently approximately linear.

(19) If the synchronous motors 1 are linear motors, then a model function M.sub.detent(M.sub.load) is formed accordingly for a spectral component of the differential detent torque, wherein instead of the rotor angle a position variable is used which indicates the position of the rotor 7 relative to the stator 5, and a wave number characterizing the spectral component is used instead of the multiplicity n.sub.1.

(20) A control unit 13 is used to control a motor current of a synchronous motor 1, In particular, each control unit 13 is configured to superimpose, during operation of the synchronous motor 1 at an instantaneous operating point in a predeterminable first operating range, on a setpoint current of the synchronous motor 1 a first compensation current, which generates a compensation torque which compensates at the instantaneous operating point a detent torque with the value of the model function.

(21) Furthermore, the control unit 13 superimposes, during operation of the respective synchronous motor 1 in a predeterminable second operating range, on the setpoint current of the synchronous motor 1 a second compensation current, which generates a compensation torque which compensates the no-load detent torque of the synchronous motor 1. To this end, the no-load detent torque of the synchronous motor 1 is measured as a function of the rotor position during no-load operation, and the acquired no-load detent torque is stored by the control unit 13.

(22) An operating range is defined for a rotating synchronous motor 1 by a rotational speed interval of rotor rotational speeds v and for linear synchronous motors 1 by a velocity interval for rotor velocities. For rotating synchronous motors 1, the first operating range is for example a first rotational speed interval having as a lower interval limit a rotational speed of zero and as an upper interval limit a predeterminable first rotational speed threshold value v.sub.S, and the second operating range is for example a second rotational speed interval having as a lower interval limit a rotational speed of zero and as an upper interval limit a predeterminable second rotational speed threshold value. Likewise, for linear synchronous motors 1, the first operating range is for example a first velocity interval having as a lower interval limit a velocity of zero and as an upper interval limit a predeterminable first velocity threshold value, and the second operating range is for example a second velocity interval having as a lower interval limit a velocity of zero and as an upper interval limit a predeterminable second velocity threshold value.

(23) Both when compensating a spectral component of the differential detent torque and when compensating the no-load detent torque of a synchronous motor 1, a dead time for controlling the synchronous motor 1 is taken into account, which is the elapsed time when the compensation current is changed and when the compensation torque changes due to the change of the compensation current. For this purpose, a respective compensation current for compensating the detent torque is generated that becomes effective at a point in time shifted by the dead time after the generation of the compensation current. For example, for compensating a detent torque of a rotating synchronous motor 1, by taking into consideration the instantaneous rotor rotational speed v, an instantaneous rotor angle is extrapolated to a value which the rotor angle assumes at a point in time shifted by the dead time. Likewise, for a linear motor 1, by taking into consideration the instantaneous rotor velocity, an instantaneous rotor position is extrapolated to a value which the rotor position assumes at a point in time shifted by the dead time.

(24) FIG. 2 shows, by way of example, amplitudes A of spectral components, characterized in each case by a multiplicity n of an acquired load detent torque of a rotating synchronous motor 1 as a function of the load torque M.sub.load. FIG. 2 shows a typical situation where load-dependent detent torque portions are concentrated at a spectral component with a specific multiplicity n.sub.1, while the other spectral components depend to a lesser degree on the load torque M.sub.load or the operating point of the reference motor 2 and/or have considerably smaller load-dependent detent torque portions. According to the invention, in such a case the corresponding spectral component of the differential detent torque (namely those with the multiplicity n.sub.1) are only determined and compensated for the spectral component with the multiplicity n.sub.1. Frequently, the spectral component with the multiplicity n.sub.1=6p of six times the number of pole pairs p of the synchronous motor 1 dominates the load dependency of the detent torque. If the spectrum of the detent torque has a plurality of relevant load-dependent spectral components, then the corresponding spectral component of the differential detent torque is determined, modeled and compensated for each of these spectral components.

(25) FIGS. 3 and 4 show the amplitude A and the phase P of a load-dependent spectral component of a detent torque of a synchronous motor 1 as a function of the load torque M.sub.load.

(26) FIGS. 5 and 6 show the amplitude A.sub.diff and the phase P.sub.diff of the spectral component of the differential detent torque, which corresponds to the spectral component having the amplitude A and phase P shown in FIGS. 3 and 4, in each case as a function of the load torque M.sub.load. FIG. 5 further shows the graph 15 of a quadratic function amp(M.sub.load), which models the amplitude A.sub.diff, and FIG. 6 shows the graph 16 of a piecewise linear function phase(M.sub.load) of which models the phase P.sub.diff. In the example shown in FIG. 6, the function phase(M.sub.load) is constant for both positive and negative values of the load torque M.sub.load wherein the values of the constants for positive and negative values of the load torque M.sub.load differ from one another and correspond to the respective value of the phase P.sub.diff of the spectral component of the differential detent torque for large magnitudes of the load torque M.sub.load. Although the function phase(M.sub.load) thus deviates from the actual value of the phase P.sub.diff for small magnitudes of the load torque M.sub.load, this deviation is generally acceptable, since the differential detent torque is small for small magnitudes of the load torque M.sub.load. If, for large magnitudes of the bad torque M.sub.load, the phase P.sub.diff is not a constant function, but rather is in each case approximately a linear function with a non-vanishing gradient for, for example, positive and negative values of the bad torque M.sub.load, then the function phase(M.sub.load) is defined, for example, for positive and negative values of the load torque by the respective linear function M.sub.load.

(27) FIG. 7 shows amplitudes A of a load-dependent spectral component of a detent torque of a rotating synchronous motor 1 as a function of a rotor rotational speed v of the synchronous motor 1 at a fixed operating point of the synchronous motor 1. A first graph 17 shows here the amplitude A without a compensation of the spectral component of the differential detent torque, and a second graph 18 shows the amplitude A with a compensation of the spectral component of the differential detent torque. FIG. 7 shows that compensating the spectral component of the differential detent torque above a first rotational speed threshold value v.sub.S leads to a greater amplitude A than operating the synchronous motor 1 without compensation of the spectral component of the differential detent torque. This reflects the fact that the synchronous motor 1 generates voltage harmonics, which affect the current regulation as interference variables and prevent the amplitude and phase of the torque-generating current from being set correctly as the rotor rotational speed v increases. The compensation of a spectral component of the differential detent torque is therefore preferably switched off at rotor rotational speeds v above the first rotational speed threshold value v.sub.S. The compensation of the no-load detent torque is switched off at rotor rotational speeds v above a second rotational speed threshold value. The second rotational speed threshold value is hereby generally greater than the first rotational speed threshold value v.sub.S, i.e. the compensation of the no-load detent torque is switched off later (at higher rotor rotational speeds v) than the compensation of the spectral component of the differential detent torque.

(28) While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

(29) What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: