Harmonic distortion reduction in inductive position sensors
In at least one aspect, an inductive position sensor comprising a target. The inductive position sensor can include a stator including an excitation coil being inductively coupled to the target, and a receiver coil including a first loop connected in series with a second loop, and inductively coupled with the target such that a receiver coil voltage is generated at the receiver coil. The second loop can be offset, on the stator and relative to the first loop, by a portion of a harmonic period corresponding with a harmonic for nullification in the receiver coil voltage. The inductive position sensor can include a control unit configured to receive a plurality of receiver coil voltages including the receiver coil voltage, the control unit configured to generate an angular position signal based on the plurality of receiver coil voltages.
1. An inductive position sensor comprising:
a target including:
a first target coil including a first outer lobe, and
a second target coil including a second outer lobe offset from the first outer lobe, the first target coil being electrically isolated from the second target coil;
a stator including:
an excitation coil configured to be inductively coupled to the target; and
a receiver coil including a first loop connected in series with a second loop, and configured to be inductively coupled with the target such that a receiver coil voltage is generated at the receiver coil,
the second loop being offset, on the stator and relative to the first loop, by a portion of a harmonic period corresponding with a harmonic for nullification in the receiver coil voltage; and
a control unit configured to receive a plurality of receiver coil voltages including the receiver coil voltage, the control unit configured to generate an angular position signal based on the plurality of receiver coil voltages.
2. The inductive position sensor of claim 1 , wherein:
the portion is one-half (½) of the harmonic period, and
the harmonic is a seventh (7 th ) order harmonic.
3. The inductive position sensor of claim 1 , wherein the receiver coil is a first receiver coil,
the inductive position sensor, further comprising:
a second receiver coil having a first loop connected in series with a second loop, and configured to be inductively coupled with the target,
the first loop of the second receiver coil being offset, on the stator and relative to the second loop of the second receiver coil, by the portion of the harmonic period,
the first receiver coil having a rotational symmetry on the stator, and
the second receiver coil being offset, on the stator, by one-quarter (¼) of the rotational symmetry.
4. The inductive position sensor of claim 3 , wherein the rotational symmetry is a ninety-degree (90°) mechanical symmetry.
5. The inductive position sensor of claim 4 , wherein the harmonic is a seventh (7 th ) order harmonic.
6. The inductive position sensor of claim 4 , wherein the harmonic period is a first harmonic period, and the harmonic is a first harmonic, the receiver coil is a first receiver coil,
the target further including:
the first target coil including the first outer lobe extending a first ratio of a second harmonic period of the first receiver coil, and a first inner lobe extending a second ratio of the second harmonic period, the second harmonic period corresponding with a second harmonic, the first ratio being different from the second ratio; and
the second target coil including the second outer lobe having a size based on the second ratio, and a second inner lobe having a size based on the first ratio,
the first target coil inducing a first waveform associated with the second harmonic into the receiver coil, and the second target coil inducing a second waveform associated with the second harmonic, and opposite the first waveform, into the receiver coil such that the second harmonic is nullified in the receiver coil voltage.
7. The inductive position sensor of claim 6 , wherein the second target coil is offset relative to the first target coil by a third ratio of a third harmonic period such that a third harmonic is nullified.
8. The inductive position sensor of claim 7 , wherein the third harmonic is at least an eleventh order (11 th ) harmonic for a three-phase system, and the third harmonic is at least a fifth order (5 th ) harmonic for a two-phase system.
9. The inductive position sensor of claim 6 , wherein the first ratio is 3/N and the second ratio is 2/N for a three-phase system where N=5 or the first ratio is 1/N and the second ratio is 2/N for a two-phase system where N=3.
10. The inductive position sensor of claim 1 , wherein the receiver coil is a first receiver coil,
the inductive position sensor, further comprising:
a second receiver coil having a first loop connected in series with a second loop, and configured to be inductively coupled with the target,
the first loop of the second receiver coil being offset, on the stator and relative to the second loop of the second receiver coil, by the portion of the harmonic period,
the first receiver coil having a rotational symmetry on the stator, and
the second receiver coil having the rotational symmetry and being offset, on the stator, one-third of a sensor period relative to the first receiver coil; and
a third receiver coil having the rotational symmetry and being offset, on the stator, one-third of the sensor period relative to the second receiver coil.
11. The inductive position sensor of claim 10 , wherein the harmonic period is a first harmonic period, and the harmonic is a first harmonic,
the target further including:
the first target coil including the first outer lobe having a size based on a first ratio of a second harmonic period of the first receiver coil, and a first inner lobe having a size based on a second ratio of the second harmonic period, the second harmonic period corresponding with a second harmonic, the first ratio being different from the second ratio; and
the second target coil including the second outer lobe having a size based on the second ratio, and a second inner lobe having a size based on the first ratio,
the first target coil inducing a first waveform associated with the second harmonic into the receiver coil, and the second target coil inducing a second waveform associated with the second harmonic, and opposite the first waveform, into the receiver coil such that the second harmonic is nullified in the receiver coil voltage.
12. The inductive position sensor of claim 11 , wherein the second target coil is offset relative to the first target coil by a third ratio of a third harmonic period such that a third harmonic is nullified.
13. An inductive position sensor comprising:
a target including:
a first target coil including a first outer lobe, and
a second target coil including a second outer lobe having a size different from a size of the first outer lobe, the second target coil being concentrically disposed within the first target coil;
a stator comprising:
an excitation coil;
a receiver coil configured to be inductively coupled to the target such that a receiver coil voltage is generated, the receiver coil including a first loop, a second loop, a third loop, and a fourth loop, the first loop and the second loop being a first pair, the third loop and the fourth loop being a second pair,
the second loop being offset, on the stator and relative to the first loop, a ratio of a first harmonic period, the ratio being one-half, the first harmonic period corresponding with a first harmonic for nullification in the receiver coil,
the fourth loop being offset, on the stator and relative to the third loop, by the ratio of the first harmonic period,
the second pair being offset from the first pair by a ratio of a second harmonic period, the second harmonic period corresponding with a second harmonic for nullification in the receiver coil; and
a control unit configured to receive a plurality of receiver coil voltages including the receiver coil voltage, the control unit configured to generate an angular position signal based on the plurality of receiver coil voltages.
14. The inductive position sensor of claim 13 , wherein the receiver coil is a first receiver coil,
the inductive position sensor, further comprising:
a second receiver coil having an identical configuration as the first receiver coil,
the first receiver coil having a rotational symmetry on the stator, and the second receiver coil is offset, on the stator, by one-quarter (¼) of the rotational symmetry.
15. The inductive position sensor of claim 13 , wherein the receiver coil is a first receiver coil, the first receiver coil has a rotational symmetry on the stator,
the inductive position sensor, further comprising:
a second receiver coil having the rotational symmetry and being offset, on the stator, one-third of a sensor period relative to the first receiver coil; and
a third receiver coil having the rotational symmetry and being offset, on the stator, one-third of a sensor period relative to the second receiver coil.
16. The inductive position sensor of claim 15 , wherein the target further including:
the first target coil including the first outer lobe having the size based on a first ratio of a second harmonic period of the first receiver coil, and a first inner lobe having a size based on a second ratio of the second harmonic period, the second harmonic period corresponding with a second harmonic, the first ratio being different from the second ratio; and
the second target coil including the second outer lobe having the size based on the second ratio, and a second inner lobe having a size based on the first ratio,
the first target coil inducing a first waveform associated with the second harmonic into the receiver coil, and the second target coil inducing a second waveform associated with the second harmonic, and opposite the first waveform, into the receiver coil such that the second harmonic is nullified in the receiver coil voltage.
17. The inductive position sensor of claim 16 , wherein the second target coil is offset relative to the first target coil by a third ratio of a third harmonic period such that a third harmonic is nullified.
18. An inductive position sensor comprising:
a target including a target coil being asymmetric within each sensor period;
a stator including:
an excitation coil configured to be inductively coupled to the target; and
a first receiver coil including a first loop connected in series with a second loop, and configured to be inductively coupled with the target such that a receiver coil voltage is generated at the first receiver coil,
the second loop being offset, on the stator and relative to the first loop, by a portion of a harmonic period corresponding with a harmonic for nullification in the receiver coil voltage,
a second receiver coil having a first loop connected in series with a second loop, and configured to be inductively coupled with the target,
the first loop of the second receiver coil is offset, on the stator and relative to the second loop of the second receiver coil, by the portion of the harmonic period; and
a control unit configured to receive a plurality of receiver coil voltages including the receiver coil voltage.
19. The inductive position sensor of claim 18 , wherein the control unit is configured to generate an angular position signal based on the plurality of receiver coil voltages.
20. The inductive position sensor of claim 18 , wherein:
the first receiver coil has a rotational symmetry on the stator, and
the second receiver coil is offset, on the stator, by one-quarter (¼) of the rotational symmetry.