Residual current detecting (RCD) and ground impedance monitoring transformer and control methods
Systems, devices, and methods for a transformer including: a first drive winding (206) wound on a first core; a second drive winding wound on a second core; a sense winding wound across the first and second cores; and a compensation winding wound across the first and second cores; where one or more utility lines are threaded through a middle of the first and second cores, a common mode current in the one or more utility lines causes one or more pulses to appear on the sense winding, a current on the compensation winding is adjusted until the one or more pulses on the sense winding are cancelled out, and the common mode current on the one or more utility lines is the adjusted current on the compensation winding multiplied by a turn ratio between the compensation winding and the sense winding.
1. A transformer comprising:
a first drive winding wound on a first core, wherein the first drive winding is driven with a first frequency current;
a second drive winding wound on a second core, wherein the second drive winding is driven with a second frequency current;
a sense winding wound across the first and second cores; and
a compensation winding wound across the first and second cores;
wherein one or more utility lines are disposed proximate to a middle of the first and second cores, wherein a common mode current in the one or more utility lines causes one or more pulses to appear on the sense winding, wherein a current on the compensation winding is adjusted until the one or more pulses on the sense winding are cancelled out.
2. The transformer of claim 1 , wherein a net flux through the sense winding is zero if no common mode current is present on the one or more utility lines.
3. The transformer of claim 1 , wherein a saturation flux density of the first core is substantially equal to the saturation flux density of the second core.
4. The transformer of claim 1 , wherein a saturation flux density of the first core is within 10% of the saturation flux density of the second core.
5. The transformer of claim 1 , wherein the first core has a lower saturation flux density than the second core, and wherein the first drive winding is driven with less current than the second drive winding such that the first core saturates at substantially the same time as the second core.
6. The transformer of claim 1 , wherein the first drive winding applies a high frequency signal to the one or more utility lines, wherein the second drive winding measures an amplitude of a current that results, and wherein the amplitude of the current that results is proportional to a reciprocal of a ground loop impedance.
7. The transformer of claim 1 , wherein the common mode current in the one or more utility lines is at least one of: an AC residual leakage current and a DC residual leakage current.
8. The transformer of claim 1 , wherein the first core is disposed substantially parallel to the second core.
9. A method comprising:
providing a first frequency current to a first drive winding wound on a first core;
providing a second frequency current to a second drive winding wound on a second core;
sensing one or more pulses on a sense winding wound about the first and second cores, wherein the one or more pulses are created by a common mode current on one or more utility lines disposed proximate to the first and second cores;
adjusting a current to a compensation winding wound about the first and second cores to cancel out the one or more pulses on the sense winding; and
determining the common mode current on the one or more utility lines.
10. The method of claim 9 , wherein a saturation flux density of the first core is substantially equal to the saturation flux density of the second core.
11. The method of claim 10 , wherein a saturation flux density of the first core is within 10% of the saturation flux density of the second core.
12. The method of claim 11 , wherein the first core has a lower saturation flux density than the second core, and wherein the first drive winding is provided with less current than the second drive winding such that the first core saturates at substantially the same time as the second core.
13. The method of claim 11 , further comprising:
measuring one or more peaks of a rising edge of the sensed one or more pulses by a first sample and hold circuit;
measuring one or more peaks of a falling edge of the sensed one or more pulses by a second sample and hold circuit;
determining a difference in magnitude between an average of the peaks of the rising edges and an average of the peaks of the falling edges; and
adjusting at least one of: a first high frequency square wave current and a second high frequency square wave current based on the determined difference in magnitude, wherein the adjusted current compensates for a difference in a saturation flux density between the first core and the second core.
14. The method of claim 9 , further comprising:
providing a high frequency signal to the one or more utility lines by the first drive winding; and
measuring an amplitude of a current that results by the second drive winding, wherein the amplitude of the current that results is proportional to a reciprocal of a ground loop impedance.
15. The method of claim 14 , wherein the high frequency signal driven by the first drive winding flows to a utility ground, to an electric vehicle service equipment (EVSE) through a ground wire, to ground filter capacitors of the EVSE and to ground filter capacitors of an electric vehicle (EV), to the second core, and to the first core.
16. The method of claim 15 , wherein no signal is measured by the second core if a resistance of the utility ground is too high or open.
17. The method of claim 9 , wherein the common mode current in the one or more utility lines is at least one of: an AC residual leakage current and a DC residual leakage current.
18. A system comprising:
a transformer comprising:
a first drive winding wound on a first core, wherein the first drive winding is driven with a first frequency current;
a second drive winding wound on a second core, wherein the second drive winding is driven with a second frequency current;
a sense winding wound across the first and second cores; and
a compensation winding wound across the first and second cores;
one or more utility lines, wherein the one or more utility lines are disposed proximate to a middle of the first and second cores, wherein a common mode current in the one or more utility lines causes one or more pulses to appear on the sense winding, wherein a current on the compensation winding is adjusted until the one or more pulses on the sense winding are cancelled out.
19. The system of claim 18 further comprising:
an electric vehicle supply equipment (EVSE), wherein the transformer and the one or more utility lines are part of the EVSE;
a relay, wherein the relay is part of the EVSE;
wherein the system determines if the common mode current exceeds a set threshold, wherein the system sends a signal to a relay to cut power between the EVSE and a utility when the determined set threshold is exceeded.
20. The system of claim 19 , wherein the first drive winding applies a high frequency signal to the one or more utility lines, wherein the second drive winding measures an amplitude of a current that results, wherein the amplitude of the current that results is proportional to a reciprocal of a ground loop impedance, wherein the high frequency signal driven by the first drive winding flows to a utility ground, to the EVSE through a ground wire, to ground filter capacitors of the EVSE and to ground filter capacitors of an electric vehicle (EV), to the second core, and to the first core.