Auto-calibration for coreless current sensors
Auto-calibrating current sensor integrated circuits (ICs) are configured for mounting at a position relative to a conductor. The auto-calibrating current sensor ICs can include a plurality of magnetic field sensing elements disposed at different locations within the integrated circuit, respectively, and can be configured to measure a magnetic field produced by a current carried by the conductor. The auto-calibrating sensors can include an electromagnetic model of the IC and the conductor. The model can be operative to determine a magnetic field at points in space due to a given current in the conductor at a known location of the conductor from the IC, and also the inverse situation of determining an unknown current and/or location of the conductor based on measurements of a magnetic field at known locations in space due to an unknown current in the conductor. Related auto-calibration methods are also described.
1. An auto-calibrating current sensor configured for calibration at a mounted position relative to a given conductor, the sensor comprising:
a. a plurality of magnetic field sensing elements disposed at different locations within an integrated circuit (IC), respectively, and configured to produce a plurality of linearly independent magnetic field measurements of a magnetic field produced by a current carried by the conductor;
b. memory comprising computer-executable instructions, wherein the computer-executable instructions include an electromagnetic model of the integrated circuit and the conductor, and wherein the model is operative to determine a magnetic field at points in space due to a given current in the conductor; and
c. a processor coupled to the memory and operative to execute the computer-executable instructions, wherein, in response to executing the computer-executable instructions, the processor is configured to:
receive the plurality of linearly independent magnetic field measurements from the plurality of magnetic field sensing elements;
from the electromagnetic model, determine a plurality of coupling factors between the plurality of magnetic field sensing elements at their respective locations and the conductor, wherein each coupling factor is indicative of a magnitude of magnetic field measured per unit of current in the conductor;
based on the plurality of coupling factors and plurality of linearly independent magnetic field measurements, calculate the current applied to the conductor; and
based on the plurality of coupling factors and plurality of linearly independent magnetic field measurements, calculate the position of the integrated circuit at the mounted position relative to the conductor;
wherein the current sensor is calibrated at the mounted position to determine current flowing in the conductor.
2. The current sensor of claim 1 , wherein the processor is configured to calculate the position of the integrated circuit as a distance across an airgap between the conductor and the integrated circuit.
3. The current sensor of claim 1 , wherein the model includes the position and orientation of the magnetic field sensing elements of the integrated circuit relative to each other.
4. The current sensor of claim 1 , wherein the model comprises a three-dimensional (3D) electromagnetic finite-element-method (FEM) model.
5. The current sensor of claim 1 , wherein the model comprises a lookup table having coupling factor values corresponding to a range of distances between the integrated circuit and the conductor.
6. The current sensor of claim 5 , wherein the coupling factor values comprise coupling factors for corresponding distances, respectively, for different linear combinations of the magnetic field sensing elements.
7. The current sensor of claim 6 , wherein a linear combination comprises a differential measurement between two magnetic field sensing elements.
8. The current sensor of claim 1 , wherein the model comprises a system of non-linear equations expressing a coupling factor based on one or more distances between the conductor and the integrated circuit.
9. The current sensor of claim 8 , wherein the processor is configured to determine the coupling factors by interpolation between the non-linear equations.
10. The current sensor of claim 8 , wherein the non-linear equations comprise polynomials.
11. The current sensor of claim 10 , wherein the polynomials each express a coupling factor between the conductor and one of the magnetic field sensing elements as a function of a distance between the integrated circuit and the conductor.
12. The current sensor of claim 1 , wherein each of the plurality of magnetic field sensing elements has an axis of maximum sensitivity.
13. The current sensor of claim 12 , wherein one or more of the magnetic field sensing elements is configured such that the axis of maximum sensitivity is perpendicular to a planar surface of the IC.
14. The current sensor of claim 12 , wherein one or more of magnetic field sensing elements is configured such that the axis of maximum sensitivity is parallel to a planar surface of the IC.
15. The current sensor of claim 1 , wherein the plurality of magnetic field sensing elements comprises one or more Hall effect elements.
16. The current sensor of claim 1 , wherein the plurality of magnetic field sensing elements comprises one or more magnetoresistance elements.
17. The current sensor of claim 1 , wherein the plurality of magnetic field sensing elements comprises one or more fluxgate elements.
18. The current sensor of claim 1 , wherein the processor is configured to realize linear combinations of the magnetic field measurements from the plurality of magnetic field sensing elements.
19. The current sensor of claim 1 , wherein the IC comprises a first IC, and further comprising a second IC separate from the first IC, wherein the second IC includes a second plurality of magnetic field sensing elements disposed at different positions, respectively, and configured to measure a magnetic field produced by a current carried in the conductor.