Apparatus and method for controlling an electric machine

• US 20020041168A1
• Filed: 08/16/2001
• Published: 04/11/2002
• Est. Priority Date: 08/18/2000
• Status: Active Grant

• Current Assignee: Nidec S R Drives Ltd (Nidec Corporation)
• Original Assignee: Switched Reluctance Drives Limited (Nidec Corporation)
• Inventors: Mann, Raymond, Stephenson, John Michael, Hughes, Austin
• Granted Patent: US 6,498,447 B2
• Time in Patent Office: Days
• US Class Current: 318/254
• CPC Class Codes: H02P 25/098 Arrangements for reducing torque ripple

Abstract

A controller for an electronically commutated electrical machine receives a feedback signal indicative of a parameter which it is desired to minimize, e.g. torque ripple, current, voltage, vibration or acoustic noise. The controller computes the amplitude and phase of a set of harmonics in the parameter and sequentially injects harmonics of the correct amplitude and phase to minimize the parameter. An optimizing routine iterates through the set of harmonics to further reduce the parameter.

Claims

1. A method of counteracting a deviation in an output of an electrical machine, the method including:

deducing the magnitude and phase of at least two harmonics of the deviation in the output to produce signals indicative of the deduced harmonics;

deriving feedback signals from the deduced harmonics; and

sequentially injecting the feedback signals into an input of the electrical machine so as to reduce the magnitude of the deviation.

2. A method as claimed in claim 1 in which each feedback signal causes a harmonic substantially in antiphase to one of the deduced harmonics of the deviation in the output.

3. A method as claimed in claim 1 in which harmonic components in the output are reduced by adjusting the magnitude and phase of signals indicative of the deduced harmonics to derive the feedback signals and injecting the feedback signals into the input of the machine.

4. A method as claimed in claim 1 in which each of a predetermined number of harmonics of the deviation in the output are reduced in sequence.

5. A method as claimed in claim 4 in which the feedback signals are injected into the input in ascending order of frequency of the deduced harmonics.

6. A method as claimed in claim 4 in which the feedback signals are injected into the input in descending order of magnitude of the deduced harmonics.

7. A method as claimed in claim 1, including iteratively deducing the magnitude and phase of each harmonic and injecting the feedback signals into the input further to reduce the deviation.

8. A method as claimed in claim 1, in which the machine is operating as a motor and the output is torque, vibration or acoustic noise.

9. A method as claimed in claim 8, in which the machine is a rotary machine having a rotor revolving relative to a stator and having at least one energizable winding, and in which the input represents a current for energizing the winding, the method further comprising injecting the feedback signals according to the formula:

i(θ

)=Σ

_n=1^m1a_n sin(knθ

+φ

_n)

where;

i is a signal representative of the input current,

n is an integer,

m is the number of harmonics considered,

θ

is the mechanical angle of the rotor,

k is the basic number of pulses per rev, and

φ

is an angular offset.

10. A method as claimed in claim 1 in which the machine is operating as a generator and the output is current, voltage, vibration or acoustic noise.

11. A method as claimed in claim 10 in which the machine is a rotary machine having a rotor revolving relative to a stator and having at least one energizable winding, and in which the input represents a torque for driving the rotor, the method further comprising injecting the signals according to the formula:

T(θ

)=Σ

_n=1^ma_n sin(knθ

+φ

_n)

where T(θ

) is a signal representative of the input torque,

n is an integer,

m is the number of harmonics considered,

θ

is the mechanical angle of the rotor,

k is the basic number of pulses per rev, and

φ

is an angular offset.

13. A controller as claimed in claim 12 in which the means for controlling is operable to cause harmonics substantially in antiphase to at least one of the deduced harmonics of the deviation in the output.

14. A controller as claimed in claim 13 in which the means for controlling is operable to reduce the harmonic components in the output by adjusting the magnitude and phase of signals indicative of the deduced harmonics to derive the feedback signals and injecting the feedback signals into an input of the machine.

15. A controller as claimed in claim 12 in which the means for deducing is operable to deduce a predetermined number of harmonics of the deviation in sequence.

16. A controller as claimed in claim 15 in which the means for controlling is operable to inject the feedback signals into an input of the machine in ascending order of frequency of the harmonics.

17. A controller as claimed in claim 15 in which the means for controlling is operable to inject the feedback signals into an input of the machine in descending order of magnitude of the harmonics.

18. A controller as claimed in claim 12 in which the means for deducing is operable to iteratively deduce the magnitude and phase of the harmonics to produce a modified feedback signal.

19. A controller as claimed in claim 18 in which the means for controlling is responsive to the feedback signal from each iteration to inject the signals into the machine further to reduce the deviation.

20. A controller as claimed in claim 12 in which the means for deducing is operable to deduce the magnitude and phase of the deviation of one of torque, current, voltage, vibration and acoustic noise of the machine as the output.

21. A controller as claimed in claim 12 in which the machine is a rotary machine, having a rotor revolving relative to a stator, and having an energizable winding, and in which the means for controlling is operable to inject the feedback signals into an input of the machine according to the formula:

i(θ

) or T(θ

)=Σ

_n=1^m a_n sin(knθ

=φ

_n)

where;

i(θ

) is a signal representative of input current,

T(θ

) is a signal representative of input torque,

n is an integer,

m is the number of harmonics considered,

θ

is the mechanical angle of the rotor,

k is the basic number of pulses per rev, and

φ

is an angular offset.

22. A controller as claimed in claim 12 in which the means for deducing comprises means for determining the magnitude of the deviation in the output and means for generating a sine wave corresponding to each of the deduced harmonics, the means for controlling being operable to create the feedback signal by combining a sinusoidal signal corresponding to each harmonic having a magnitude corresponding to the harmonic and to combine the feedback signal with reference input of the machine.

23. An electric machine system including a controller as claimed in claim 12.

24. A switched reluctance machine system including a controller as claimed in claim 12.

26. A controller as claimed in claim 25, in combination with a switched reluctance motor as the electrical machine.

27. A controller as claimed in claim 25, in combination with a switched reluctance generator as the electrical machine.

28. A controller as claimed in claim 25, in combination with a rotary machine as the electrical machine, the rotary machine having a rotor revolving relative to a stator and having an energizable winding, wherein the controller is operable to inject the feedback signals into an input of the machine according to the formula:

i(θ

) or T(θ

)=Σ

_n=1^m a_n sin(knθ

+φ

_n)

where;

i(θ

) is a signal representative of input current,

T(θ

) is a signal representative of input torque,

n is an integer,

m is the number of harmonics considered,

θ

is the mechanical angle of the rotor,

k is the basic number of pulses per rev, and

φ

is an angular offset.

12. A controller for an electrical machine, the controller comprising:

means for deducing sequentially the magnitude and phase of at least two harmonics of a deviation in an output of the machine to produce signals indicative of the deduced harmonics;

means for deriving feedback signals from the signals indicative of the deduced harmonics; and

means for controlling the machine in response to the feedback signals so as to reduce the magnitude of the deviation.

25. A controller for an electrical machine, the controller comprising:

a deducer constructed and arranged to sequentially deduce the magnitude and phase of at least two harmonics of a deviation in an output of the machine to produce signals indicative of the deduced harmonics;

a deriver constructed and arranged to derive feedback signals from the signals indicative of the deduced harmonics; and

a controller constructed and arranged to control the machine in response to the feedback signals so as to reduce the magnitude of the deviation.

29. A method of counteracting a deviation in an output of an electrical machine, the method including:

deducing the magnitude and phase of at least two harmonics of the deviation in the output to produce signals indicative of the deduced harmonics;

deriving feedback signals from the deduced harmonics; and

sequentially injecting the feedback signals into an input of the electrical machine so as to reduce the magnitude of the deviation;

wherein each feedback signal causes a harmonic substantially in antiphase to one of the deduced harmonics of the deviation in the output;

wherein harmonic components in the output are reduced by adjusting the magnitude and phase of signals indicative of the deduced harmonics to derive the feedback signals and injecting the feedback signals into the input of the machine;

wherein each of a predetermined number of harmonics of the deviation in the output are reduced in sequence; and

wherein the machine is a rotary machine having a rotor revolving relative to a stator and having at least one energizable winding, and in which the input represents a current for energizing the winding, the method further comprising injecting the feedback signals according to the formula;

i(θ

)=Σ

_n=1^m a_n sin(knθ

+φ

_n)

where;

i is a signal representative of the input current,

n is an integer,

m is the number of harmonics considered,

θ

is the mechanical angle of the rotor,

k is the basic number of pulses per rev, and

φ

is an angular offset.