Contactor status detection in power inverters
A sensor-less technique is described for detecting the status of an AC contactor of a power inverter. In one embodiment, a method is provided of sensing an unexpected condition of an AC contactor used to couple to a power distribution system a power inverter having at least one power conductor. The method includes determining a voltage value for the conductor; determining a current value for the conductor; determining a phase difference using the voltage value and the current value; and monitoring successive values of the phase difference to produce a monitoring result. Depending on the monitoring result, a determination is made whether or not to issue an alert signal. Control routines embodying such technique may be stored on computer-readable media. A power inverter using such technique is described.
1. A method of sensing an unexpected condition of an AC contactor used to couple to a power distribution system a power inverter having at least one power conductor, comprising:
determining a voltage value for said at least one conductor;
determining a current value for said at least one conductor;
determining a phase difference using the voltage value and the current value;
monitoring a plurality of successive values of the phase difference to produce a monitoring result; and
depending on the monitoring result, determining whether or not to issue an alert signal or perform a remedial action.
2. The method of claim 1 , wherein monitoring comprises comparing values of the phase difference to a threshold value.
3. The method of claim 2 , comprising producing one monitoring result when at least a majority of N successive values of the phase difference are greater than the threshold value, and producing a different monitoring result otherwise.
4. The method of claim 3 , wherein the power inverter is a three phase power inverter, and wherein determining a voltage value comprises:
obtaining voltage values for voltages of each phase of the three phase power inverter; and
transforming the voltage values to an α-β frame to obtain a voltage value in the α-β frame.
5. The method of claim 4 , wherein determining a current value comprises:
obtaining current values for currents of at least two of the three phase power inverter; and
transforming the current values to an α-β frame to obtain a current value in the α-β frame.
6. The method of claim 5 , wherein determining a phase difference comprises determining a phase difference between the voltage value in the α-β frame and the current value in the α-β frame.
7. The method of claim 6 , wherein determining a phase difference comprises filtering the voltage value in the α-β frame and filtering the current value in the α-β frame.
8. A non-transitory computer readable medium including program instructions for sensing an unexpected condition of an AC contactor used to couple to a power distribution system a power inverter having at least one power conductor, said instructions, when executed by a controller, performing steps comprising:
determining a voltage value for said at least one conductor;
determining a current value for said at least one conductor;
determining a phase difference using the voltage value and the current value;
monitoring a plurality of successive values of the phase difference to produce a monitoring result; and
depending on the monitoring result, determining whether or not to issue an alert signal or perform a remedial action.
9. The computer readable medium of claim 8 , wherein monitoring comprises comparing values of the phase difference to a threshold value.
10. The computer readable medium of claim 9 , comprising producing one monitoring result when at least a majority of N successive values of the phase difference are greater than the threshold value, and producing a different monitoring result otherwise.
11. The computer readable medium of claim 10 , wherein the power inverter is a three phase power inverter, and wherein determining a voltage value comprises:
obtaining voltage values for voltages of each phase of the three phase power inverter; and
transforming the voltage values to an α-β frame to obtain a voltage value in the α-β frame.
12. The computer readable medium of claim 11 , wherein determining a current value comprises:
obtaining current values for currents of at least two of the three phase power inverter; and
transforming the current values to an α-β frame to obtain a current value in the α-β frame.
13. The computer readable medium of claim 12 , wherein determining a phase difference comprises determining a phase difference between the voltage value in the α-β frame and the current value in the α-β frame.
14. The computer readable medium of claim 13 , wherein determining a phase difference comprises filtering the voltage value in the α-β frame and filtering the current value in the α-β frame.
15. A power inverter comprising:
an arrangement of power switches;
at least one power conductor coupled to the arrangement of power switches;
a transformer coupled to the at least one power conductor and having a primary side coupled to an AC grid and a secondary side coupled to a DC source; and
an AC contactor coupled to the transformer and used to couple the power inverter to a power distribution system;
a measuring device coupled to the at least one power conductor;
an input on the primary side of the transformer; and
a controller coupled to the measuring device and the input, and coupled to the arrangement of power switches to control switching of the power switches, wherein the controller is configured to:
determine a current value and a voltage value from the measuring device and the input for the at least one conductor, and
use the current value and the voltage value to sense an unexpected condition of the AC contactor.
16. The apparatus of claim 15 , wherein the controller is configured to:
determine a phase difference using the voltage value and the current value;
monitor a plurality of successive values of the phase difference to produce a monitoring result; and
depending on the monitoring result, determine whether or not to issue an alert signal or perform a remedial action.
17. The apparatus of claim 16 , wherein the controller is configured to compare values of the phase difference to a threshold value.
18. The apparatus of claim 17 , wherein the controller is configured to produce one monitoring result when at least a majority of N successive values of the phase difference are greater than the threshold value, and to produce a different monitoring result otherwise.
19. The apparatus of claim 18 , wherein the power inverter is a three phase power inverter, and wherein the controller is configured to:
obtain voltage values for voltages of each phase of the three phase power inverter; and
transform the voltage values to an α-β frame to obtain a voltage value in the α-β frame.
20. The apparatus of claim 19 , wherein the controller is configured to:
obtain current values for currents of at least two of the three phase power inverter; and
transform the current values to an α-β frame to obtain a current value in the α-β frame.
21. The apparatus of claim 20 , wherein the controller is configured to determine a phase difference between the voltage value in the α-β frame and the current value in the α-β frame.
22. The apparatus of claim 21 , wherein the controller is configured to filter the voltage value in the α-β frame and filter the current value in the α-β frame.