Single winding core-insensitive fluxgate current sensor
An open-loop fluxgate-type current sensor is described. The current sensor includes a single winding around a core that combines drive and sense that is used as both an excitation source and a feedback element to measure current through a primary winding. The current sensor further includes an H-bridge driver to impress voltage to the single winding to cause current to saturate the core, the voltage being impressed with opposing polarities repeatedly causing the core to saturate at opposing polarities. The current sensor further includes an analog transconductance integrator that continuously integrates the current to infer magnetizing force being driven into the core at the opposing polarities. The current sensor further includes a microcontroller unit (MCU) that calculates residual current based on the inferred magnetizing force being driven into the core at the opposing polarities and cause remedial action to be taken when the calculated residual current exceeds a threshold.
1. A method, comprising:
signaling an H-bridge driver to impress a first voltage of a first polarity onto a single winding that combines drive and sense that is used as both an excitation source and a feedback element to measure current through a primary winding, wherein the single winding is around a core, wherein impressing the first voltage of the first polarity onto the single winding causes first current to rise to saturate the core, and wherein the first current is continuously integrated by an analog transconductance integrator;
detecting that the first current through the single winding has risen above a threshold indicating saturation of the core, and responsive to this detecting:
signaling the H-bridge driver to stop impressing the first voltage of the first polarity onto the single winding, and
receiving a first current integral value from the analog transconductance integrator;
resetting the analog transconductance integrator;
signaling the H-bridge driver to impress a second voltage of a second polarity onto the single winding, wherein impressing the second voltage of the second polarity onto the single winding causes second current to rise to saturate the core, and wherein the second current is continuously integrated by the analog transconductance integrator;
detecting that the second current through the single winding has risen above the threshold indicating saturation of the core, and responsive to this detecting:
signaling the H-bridge driver to stop impressing the second voltage of the second polarity onto the single winding, and
receiving a second current integral value from the analog transconductance integrator; and
determining a residual current value through the core based on at least:
a time value from signaling the H-bridge driver to impress the second voltage onto the single winding to detecting that the second current through the single winding has risen above the threshold indicating saturation of the core,
the first current integral value, and
the second current integral value.
2. The method of claim 1 , wherein the core is a toroidal shape.
3. The method of claim 1 , wherein the core is a square Ferrite material.
4. The method of claim 1 , further comprising:
determining that the determined residual current value exceeds a threshold, and responsive to this determination, taking a remedial action.
5. The method of claim 4 , wherein the remedial action includes causing a set of one or more contactors to open to prevent current from flowing.
6. The method of claim 1 , wherein saturation of the core is at approximately a coercive force of the core.
7. The method of claim 1 , further comprising:
determining that the determined residual current value does not exceed a threshold, and responsive to this determination, resetting the analog transconductance integrator.
8. The method of claim 1 , wherein resetting the analog transconductance integrator includes configuring pins connected to an operational amplifier of a microcontroller as general-purpose input/output (GPIO) pins.
9. An open-loop fluxgate-type current sensor, comprising:
a single winding around a core that combines drive and sense that is used as both an excitation source and a feedback element to measure current through a primary winding;
an H-bridge driver to impress voltage to the single winding to cause current to saturate the core, the voltage being impressed with opposing polarities repeatedly causing the core to saturate at opposing polarities;
an analog transconductance integrator that continuously integrates the current to infer magnetizing force being driven into the core at the opposing polarities; and
a microcontroller unit (MCU) that calculates residual current based on the inferred magnetizing force being driven into the core at the opposing polarities and cause remedial action to be taken when the calculated residual current exceeds a threshold.
10. The open-loop fluxgate-type current sensor of claim 9 , wherein the core is a toroidal shape.
11. The open-loop fluxgate-type current sensor of claim 9 , wherein the core is a square Ferrite material.
12. The open-loop fluxgate-type current sensor of claim 9 , wherein the open-loop fluxgate-type current sensor is used as part of a residual direct current detecting device of an electric vehicle service equipment.
13. The open-loop fluxgate-type current sensor of claim 9 , wherein the MCU is to signal the H-bridge driver to impress the voltage to the single winding.
14. The open-loop fluxgate-type current sensor of claim 9 , wherein the analog transconductance integrator includes:
a sense shunt resistor that measures real-time current going through the single winding and provide a voltage to the MCU, and
an operational amplifier that integrates the voltage provided by the sense shunt resistor into a capacitor.
15. An electric vehicle supply equipment (EVSE), comprising:
a charging port that provides a connection to the EVSE for an electric vehicle;
a current control device that controls current flowing on a power line connected to the charging port; and
a residual direct current detecting device that includes an open-loop fluxgate-type current sensor, the open-loop fluxgate-type current sensor including:
a single winding around a core that combines drive and sense that is used as both an excitation source and a feedback element to measure current through a primary winding,
an H-bridge driver to impress voltage to the single winding to cause current to saturate the core, the voltage being impressed with opposing polarities repeatedly causing the core to saturate at opposing polarities,
an analog transconductance integrator that continuously integrates the current to infer magnetizing force being driven into the core at the opposing polarities, and
a microcontroller unit (MCU) that calculates residual current based on the inferred magnetizing force being driven into the core at the opposing polarities and cause remedial action to be taken when the calculated residual current exceeds a threshold.
16. The EVSE of claim 15 , wherein the core is a toroidal shape.
17. The EVSE of claim 15 , wherein the core is a square Ferrite material.
18. The EVSE of claim 15 , wherein the MCU is to signal the H-bridge driver to impress the voltage to the single winding.
19. The EVSE of claim 15 , wherein the analog transconductance integrator includes:
a sense shunt resistor that measures real-time current going through the single winding and provide a voltage to the MCU, and
an operational amplifier that integrates the voltage provided by the sense shunt resistor into a capacitor.