Method and apparatus for pre-charging power converters and diagnosing pre-charge faults
Power conversion systems and diagnostic techniques are presented for detecting suspected converter faults when a pre-charge circuit is engaged during system startup, in which known or estimated system characteristics are used to derive expected converter voltage values or rate of change values and the levels are measured during startup to ascertain whether the pre-charge circuit or other converter components are faulted.
1. A power converter, comprising:
an input to receive AC electrical input power;
an output to provide DC electrical output power;
a rectifier operatively coupled with the input and the output and operative to convert the input power to provide DC electrical power at the output;
a pre-charge circuit, comprising:
a resistor coupled between the rectifier and the output, and
a switching device coupled between the rectifier and the output and being operable in a first mode to allow current to flow from the rectifier to the output through the resistor and in a second mode to bypass the resistor;
a feedback system operative to measure a DC voltage associated with the output and to provide a feedback signal indicative of the measured DC voltage; and
a controller receiving the feedback signal from the feedback system and providing a pre-charge control signal to the switching device to selectively operate the pre-charge circuit in a pre-charge mode with the switching device operated in a first mode during startup of the converter; and
a pre-charge diagnosis system operatively coupled with the controller to selectively detect at least one converter fault based at least partially on the feedback signal during startup and to selectively discontinue application of power to the input and place the converter in a fault state based on detected faults.
2. The power converter of claim 1 , wherein the pre-charge diagnosis system provides a fault indicator to an interface associated with the converter to indicate a diagnosed fault type.
3. The power converter of claim 1 , wherein the rectifier is a passive rectifier including at least one diode.
4. The power converter of claim 1 , wherein the pre-charge diagnosis system performs a separate fault detection operation in each of a plurality of different time periods during startup.
5. The power converter of claim 1 , wherein the feedback system measures the DC voltage and provides the feedback signal to the controller in two or more different time periods during startup, and wherein the pre-charge diagnosis system computes a rate of change in the DC voltage in the two or more time periods and selectively detects the at least one converter fault based at least partially on the computed rates of change during startup.
6. The power converter of claim 1 , wherein the pre-charge diagnosis system is operative to measure an initial DC voltage before power is applied to the input, to again measure the DC voltage, to compute an expected range of DC voltages or DC voltage change rates over time during startup using the initial DC voltage and known or assumed values for output capacitance coupled to the output, and the resistor, and to selectively detect the at least one converter fault based at least partially on the feedback signal and the expected range of DC voltages or DC voltage change rates.
7. The power converter of claim 6 , wherein the pre-charge diagnosis system is operative to use an expected range of DC voltages or DC voltage change rates computed in a previous startup.
8. The power converter of claim 1 , wherein the at least one converter fault is a fault in the pre-charge circuit.
9. The power converter of claim 1 , wherein the at least one converter fault is a short circuit in a DC bus connected to the output.
10. The power converter of claim 1 , wherein the at least one converter fault is incorrect capacitance connected to the output.
11. A method for detecting power converter faults during startup, the method comprising;
activating a pre-charge circuit connected to an output of a rectifier;
measuring an initial converter DC voltage;
determining an expected range of DC voltages or DC voltage change rates based at least partially on the initial converter DC voltage;
applying AC electrical input power to the rectifier;
again measuring the converter DC voltage after application of the input power during startup of the converter; and
determining whether a fault is suspected in the converter during startup based at least partially on the measured DC voltage.
12. The method of claim 11 , further comprising, if a fault is suspected, selectively discontinuing application of input power to the rectifier and placing the converter in a fault state.
13. The method of claim 11 , further comprising indicating a diagnosed fault type via an interface associated with the converter.
14. The method of claim 11 , further comprising performing a separate fault detection operation in each of a plurality of different time periods during startup.
15. The method of claim 11 , further comprising computing a rate of change in the DC voltage in two or more different time periods during startup and determining whether a fault is suspected based at least partially on the computed rates of change.
16. The method of claim 11 , further comprising:
computing an expected range of DC voltages or DC voltage change rates over time during startup using the initial DC voltage and known or assumed values for an output capacitance coupled to the converter, and a resistance of the pre-charge circuit; and
determining whether a fault is suspected based at least partially on the measured DC voltage and the expected range of DC voltages or DC voltage change rates.
17. The method of claim 11 , further comprising determining whether a fault is suspected based at least partially on the measured DC voltage and an expected range of DC voltages or DC voltage change rates computed in a previous startup.
18. A computer readable medium having computer executable instructions for performing the steps of:
activating a pre-charge circuit connected to an output of a rectifier;
measuring an initial converter DC voltage;
determining an expected range of DC voltages or DC voltage change rates based at least partially on the initial converter DC voltage;
applying AC electrical input power to the rectifier;
again measuring the converter DC voltage after application of the input power during startup of the converter; and
determining whether a fault is suspected in the converter during startup based at least partially on the measured DC voltage.
19. The power converter of claim 8 , wherein the at least one converter fault is a switching device short circuit fault.
20. The power converter of claim 8 , wherein the at least one converter fault is a switching device open circuit fault.
21. The power converter of claim 8 , wherein the at least one converter fault is a resistor open circuit fault.
22. The power converter of claim 1 , wherein the at least one converter fault is a phase loss fault.