US 6,184,673 B2 · Active reset current sensor with measurement feedback

Abstract

In a method of measuring a current, the current is received at a winding and permitted to flow through the winding, which is wound about a core. The flow of the current through the winding induces a first magnetic flux that flows through the core and that tends to drive the core into saturation. The core is actively reset to prevent the core from being saturated at least during selected time intervals. The current is then measured during at least a plurality of the selected time intervals. In a particularly preferred embodiment, the winding is a primary winding and the resetting step includes applying a reset voltage to a secondary winding using a source that is coupled to the secondary winding. The reset voltage determines a rate at which a net magnetic flux that flows in the core changes in a direction away from saturation. Advantageously, the current sensing method has a tremendous dynamic range. The current sensing method is especially well suited to measuring currents that are of a low frequency and/or a high magnitude, including DC currents.

Claims23

Dependent claims

A method of measuring a current comprising:

(A) receiving the current at a primary winding and permitting the current to flow through the winding, the primary winding being magnetically coupled to a core, the flow of the current through the primary winding inducing a first magnetic flux that flows through the core and that tends to drive the core into saturation;
(B) actively resetting the core to prevent the core from being saturated at least during selected time intervals, the resetting step including coupling an energy source to a secondary winding that is magnetically coupled to the core to induce a reset magnetic flux that flows through the core and opposes the first magnetic flux, and controlling the energy source in accordance with the magnitude of the current;
and
(C) measuring the current during at least a plurality of the selected time intervals.

1 more element

A method of measuring a primary current using a current transformer having a transformer core, a primary winding and a secondary winding, the primary and secondary windings being magnetically coupled to the transformer core, the method comprising:

(A) receiving the primary current at the primary winding and permitting the primary current to flow through the primary winding, the flow of the primary current through the primary winding inducing a first magnetic flux (1) that flows through the transformer core, (2) that magnetically couples the primary and secondary windings, and (3) that tends to drive the transformer core into saturation;
(B) actively resetting the core to prevent the core from being saturated at least during selected time intervals, the resetting step including providing a pulse width modulated reset current, the pulse width of the reset current being modulated in accordance with a magnitude of the primary current, the reset current inducing a reset magnetic flux that flows through the transformer core and that opposes the first magnetic flux, the reset magnetic flux causing a net magnetic flux that flows in the transformer core to change in a direction away from saturation, the net magnetic flux being a sum of all magnetic fluxes that magnetically couple the primary and secondary windings;
(C) measuring the primary current during at least a plurality of the selected time intervals, including
(1) permitting a secondary current to flow in the secondary winding, the flow of the secondary current being induced by the flow of the first magnetic flux, and
(2) measuring the secondary current to obtain an indirect measurement of the primary current.

2 more elements

A circuit for measuring a first current, the circuit comprising:

(A) a core;
(B) a first winding, the first winding being magnetically coupled to the core, the first winding having the first current flowing therethrough, the flow of the first current inducing a first magnetic flux that flows through the core and that tends to drive the core into saturation;
(C) a second winding, the second winding being magnetically coupled to the core, and the second winding being magnetically coupled to the first winding by the first magnetic flux;
(D) a switch;
(E) a source;
and
(F) a pulse width modulator, the pulse width modulator being electrically coupled to the switch, the pulse width modulator providing a control signal to the switch that causes the switch to selectively couple the source to the second winding to provide a pulse width modulated reset current to the second winding, the pulse width of the reset current being modulated in accordance with a magnitude of the first current;
wherein the reset current induces a reset magnetic flux that flows through the core, the reset magnetic flux opposing the first magnetic flux and at least temporarily preventing the core from being saturated.

5 more elements

A method of measuring a primary current using a current transformer having a transformer core, a primary winding, and a secondary winding, the method comprising:

(A) driving the current transformer into saturation, including the step of causing the primary current to flow through the primary winding, the primary current inducing a first magnetic flux that flows through the transformer core and that magnetically couples the primary and secondary windings, the flow of the first magnetic flux through the transformer core inducing a secondary current that flows through the secondary winding, the flow of the secondary current through the secondary winding inducing a second magnetic flux that flows through the core and that magnetically couples the primary and secondary windings, the first magnetic flux and the second magnetic flux resulting in a net magnetic flux that drives the current transformer into saturation, and the net magnetic flux that flows through the transformer being at a maximum magnitude in saturation;
then
(B) driving the current transformer out of saturation, including the step of causing a reset current to flow through the secondary winding of the current transformer, the reset current inducing a reset magnetic flux that flows through the transformer core and that magnetically couples the primary and secondary windings, the reset magnetic flux (1) opposing the first magnetic flux, (2) driving the current transformer out of saturation, and (3) reducing the net magnetic flux being to a minimum magnitude, the minimum magnitude being determined by an instant at which the flow of the reset current through the secondary winding is terminated, the instant at which the flow of the reset current through the secondary winding is terminated being determined by monitoring a voltage across the secondary winding;
then
(C) measuring the secondary current while the current transformer is not in saturation and while the net magnetic flux is returning from the minimum magnitude to the maximum magnitude;
(D) repeating steps (A) through (C) a plurality of times so as to obtain a plurality of measurements of the primary current.

3 more elements

Dependencies are inferred from the claim text.

Active reset current sensor with measurement feedback

Life of this patent

Active reset current sensor with measurement feedback

Life of this patent

Abstract

Claims23