Apparatus and method for measuring ground impedance of a circuit
A ground continuity circuit is described. In one embodiment, a first voltage of a signal associated with an electrical line input to a circuit is measured with respect to a first resistance value of the circuit. A ground continuity test signal is asserted into the circuit that causes the resistance value of the circuit to change to a second resistance value. A second voltage of the signal is measured with respect to the second resistance value. A ground impedance value of the circuit is determined as a function of the first and second measured voltages and the first and second resistance values.
1. A method, comprising:
measuring, with respect to a first resistance value of a circuit, a first voltage of a signal associated with an electrical line input to the circuit, wherein a first set of one or more resistors provides the first resistance value of the circuit;
asserting a ground continuity test signal into the circuit that causes a switch to close to change the resistance value of the circuit to a second resistance value by causing a second set of one or more resistors to be connected in parallel with the first set of resistors, wherein the second resistance value is lower than the first resistance value;
measuring, with respect to the second resistance value, a second voltage of the signal associated with the electrical line input; and
determining a ground impedance value of the circuit as a function of the first and second measured voltages and the first and second resistance values.
2. The method of claim 1 , wherein the ground impedance value is determined by a ratio between the measured second voltage and the measured first voltage.
3. The method of claim 2 , wherein the ratio being below a predetermined threshold indicates a high impedance of the grounding path.
4. The method of claim 3 , further comprising:
wherein the circuit is part of an electric vehicle charging system; and
preventing charging circuitry of the electric vehicle charging system from being energized when the ratio indicates high impedance of the grounding path.
5. The method of claim 3 , further comprising:
wherein the circuit is part of an electric vehicle charging system; and
interrupting charging circuitry of the electric vehicle charging system when the ratio indicates high impedance of the grounding path during charging operation.
6. An apparatus, comprising:
a first set of one or more resistors providing resistance to a circuit;
a second set of one or more resistors connected in parallel with the first set of resistors by a switching mechanism, wherein the second set of resistors provides resistance to the circuit when the switching mechanism is closed and not when the switching mechanism is open; and
a processor operable to:
periodically assert a ground continuity test signal into the circuit for operating the switching mechanism, and
determine a ground impedance value of the circuit based on a ratio between a first voltage measurement of the circuit when the switching mechanism is closed and a second voltage measurement of the circuit when the switching mechanism is open.
7. The apparatus of claim 6 , wherein the ground impedance value is high impedance when the ratio is below a predetermined threshold.
8. The apparatus of claim 7 , further comprising:
charging circuitry connected to a load terminal for charging electric vehicles;
control circuitry for energizing and de-energizing the charging circuitry;
wherein the processor is further operable to prevent the charging circuitry from being energized when the ratio is below the predetermined threshold.
9. The apparatus of claim 7 , further comprising:
charging circuitry connected to a load terminal for charging electric vehicles;
control circuitry for energizing and de-energizing the charging circuitry;
wherein the processor is further operable to cause the control circuitry to de-energize the charging circuitry when the ratio is below the predetermined threshold.
10. The apparatus of claim 6 , wherein the switching mechanism includes a transistor.
11. An apparatus, comprising:
a means for measuring, with respect to a first resistance value of a circuit, a first voltage of a signal associated with an electrical line input to the circuit, wherein a first set of one or more resistors provides the first resistance value of the circuit;
a means for asserting a ground continuity test signal into the circuit that causes a switch to close to change the resistance value of the circuit to a second resistance value by causing a second set of one or more resistors to be connected in parallel with the first set of resistors, wherein the second resistance value is lower than the first resistance value;
a means for measuring, with respect to the second resistance value, a second voltage of the signal associated with the electrical line input; and
a means for determining a ground impedance value of the circuit as a function of the first and second measured voltages and the first and second resistance values.
12. The apparatus of claim 11 , wherein the ground impedance value is determined by a ratio between the measured second peak voltage and the measured first peak voltage.
13. The apparatus of claim 12 , wherein the ratio being below a predetermined threshold indicates a high impedance of the grounding path.
14. The apparatus of claim 13 , further comprising:
wherein the circuit is part of an electric vehicle charging system; and
a means for preventing charging circuitry of the electric vehicle charging system from being energized when the ratio indicates high impedance of the grounding path.
15. The apparatus of claim 13 , further comprising:
wherein the circuit is part of an electric vehicle charging system; and
a means for interrupting charging circuitry of the electric vehicle charging system when the ratio indicates high impedance of the grounding path during charging operation.