Source quality monitoring system

• US 5,555,182 A
• Filed: 05/04/1995
• Issued: 09/10/1996
• Est. Priority Date: 05/04/1995
• Status: Expired due to Term

• Current Assignee: Thomas & Betts International LLC (ABB Limited)
• Original Assignee: Cyberex, Inc. (Danaher Corporation)
• Inventors: Galm, James M.
• Primary Examiner(s): Ramirez, Ellis B.
• Assistant Examiner(s): Wachsman, Hal D.
• Application Number:
  US08/433,690
• Time in Patent Office: 495 Days
• Field of Search: 324/102, 324/103 P, 324/76.77, 324/76.78, 324/602, 324/606, 363/45, 363/46, 363/39, 361/85, 361/86, 361/96, 361/97, 327/37, 307/87, 307/80, 364/487, 364/483, 364/481
• US Class Current: 702/69
• CPC Class Codes: G01R 25/00 Arrangements for measuring phase angle between a voltage and a current or between voltages or currents

Abstract

A digital signal processor implemented monitoring circuit for detecting phase and magnitude disruptions in multi-phase alternating current input signals. A phase lock loop receives multi-phase alternating current input signals and provides one set of alternating current output signals in phase with a time average of the multi-phase alternating current input signals and provides a second set of alternating current output signals phase shifted in relation to the first set of output signals. In a three phase system the phase lock loop provides six alternating current signals. A demodulation circuit multiplies the first set of output signals from the phase lock loop circuit with the multi-phase input signals to produce demodulated sets of signals. An output circuit coupled to the demodulation circuit sums the first set of demodulated signals to provide a first source quality signal. The second set of demodulated signals is also summed to provide a second source quality signal. By comparing the first and second source quality signals with predetermined quality thresholds the output circuit produces a source quality indication.

Claims

1. Monitoring apparatus for detecting phase and magnitude disruptions in an alternating voltage input signal comprising:

a) an input circuit for receiving an alternating voltage input signal and providing a first alternating output signal that follows a phase of the alternating voltage input signal and for providing a second alternating output signal phase shifted in relation to the first alternating output signal by a specified amount;

b) a demodulation circuit for combining the first output signal from the input circuit with the alternating voltage input signal to produce a first demodulated signal and for combining the second alternating output signal from the input circuit with the alternating voltage input signal to produce a second demodulated signal, said demodulation circuit including circuitry for removing a ripple signal resulting from the combining of signals applied to the demodulation circuit; and

c) an output circuit coupled to the demodulation circuit for assessing the quality of the alternating voltage input signal by comparing the first and second demodulated signals with predetermined quality thresholds to produce an output indication of the quality of the alternating voltage input signal.

2. The monitoring circuit of claim 1 wherein the input circuit comprises a phase lock loop circuit that has as an input the alternating voltage input signal and produces two alternating outputs, one in phase and one out of phase with the alternating voltage input signal.

3. The monitoring circuit of claim 2 wherein the phase lock loop circuit has a time constant that is longer than the slowest transient of interest in the alternating voltage input signal.

4. The monitoring circuit of claim 2 wherein the phase lock loop has a type two control loop.

5. The monitoring circuit of claim 1 wherein the circuitry for removing the ripple signal is a filter circuit that extracts certain frequencies from the first and second demodulated signals provided by the demodulation circuit.

6. The monitoring circuit of claim 1 wherein the input circuit receives multiple phase alternating voltage input signals and wherein the circuitry for removing the ripple signal is an adder circuit for combining demodulation signals from each phase of the multiple phase alternating voltage input signals.

7. Monitoring apparatus for detecting phase and magnitude disruptions in multi-phase alternating voltage input signals comprising:

a) a waveform circuit for receiving a number of multi-phase alternating voltage input signals and for providing a first set of alternating output signals that follow a phase of the multi-phase alternating voltage input signals and for providing a second set of alternating output signals phase shifted in relation to the first set of alternating current output signals by a specified amount;

b) a demodulation circuit for combining the first set of output signals from the waveform circuit with the alternating voltage input signals to produce a first set of demodulated signals having suppressed spurious mixer products and for combining the second set of alternating output signals from the waveform circuit with the alternating voltage input signals to produce a second set of demodulated signals having suppressed spurious mixer products; and

c) an output circuit coupled to the demodulation circuit for assessing the quality of the alternating voltage input signals by combining the first set of demodulated signals to provide a first source quality signal, by combining the second set of demodulated signals to provide a second source quality signal, and for comparing the first and second source quality signals with predetermined quality thresholds to produce a source quality indication signal.

8. The monitoring apparatus of claim 7 wherein the waveform circuit comprises a phase lock loop circuit having an input for one or more of the multi-phase alternating voltage input signals and multiple outputs for providing alternating output signals that are in phase and phase shifted by 90 degrees with respect to the multi-phase alternating voltage input signals.

9. The monitoring circuit of claim 8 wherein the phase lock loop circuit has a time constant that is longer than the slowest transient of interest in the multi-phase alternating voltage input signals.

10. The monitoring circuit of claim 8 wherein the phase lock loop has a type two control loop.

11. The monitoring apparatus of claim 8 wherein the phase lock loop circuit comprises:

a) a voltage controlled oscillator for providing alternating output signals at the multiple outputs; and

b) a control transfer circuit for providing an input to the voltage controlled oscillator that varies in response to the phase and frequency of the multi-phase alternating voltage input signals.

12. The monitoring apparatus of claim 7 wherein the output circuit comprises one summing circuit for combining each of the signals that make up the first set of demodulated signals and a second summing circuit for combining each of the signals that make up the second set of demodulated signals.

13. The monitoring apparatus of claim 7 wherein the output circuit comprises first and second variable slope signal integrators to determine the suitability of the multi-phase alternating voltage input signals based on a magnitude and a duration of the first and second source quality signals.

14. Apparatus for assessing the quality of at least two alternating current sources to determine which of said at least two sources to couple to a load comprising:

a) switch sets having oppositely connected gate controlled switches for coupling signals from the alternating current sources to a junction coupled to a load;

c) monitoring circuits for monitoring a current state through the first and second switch sets;

d) gate control circuits for gating into conduction the switches of the switch sets; and

e) a controller coupled to the gate control circuits for activating switches in the switch sets by actuating the gate control circuits as said controller determines a quality of the alternating current signals from the alternating current sources coupled to the switch sets;

f) said controller comprising a phase lock loop circuit for each of said at least two alternating current sources that provides a slowly varying signal in synchronization with at least one alternating current signal of each source and a demodulation circuit for combining the slowly varying signal from the phase lock loop circuit with said at least one alternating current signal to provide a demodulation signal, comparing a demodulation signal with a threshold to provide a source quality signal for each source, and instructing the gate control circuits to activate a switch set based on the comparison between the demodulation signal and the threshold value.

15. Monitoring apparatus far detecting phase and magnitude disruptions in three phase alternating voltage source signals comprising:

a) a phase lock loop circuit for receiving an alternating voltage input signal and providing a first set of alternating current output signals that follow a phase of three phase alternating voltage source signals wherein one of said three phase alternating voltage source signals corresponds to the alternating voltage input signal and providing a second set of alternating current output signals phase shifted in relation to the first set of alternating output signals;

b) a detector circuit for combining the first set of output signals from the phase lock loop circuit with corresponding ones of the three phase alternating voltage source signals to produce a first set of demodulated signals and for combining the second set of alternating output signals from the phase lock loop circuit with corresponding ones of the three phase alternating voltage source signals to produce a second set of demodulated signals; and

c) an output circuit coupled to the detector circuit for assessing the quality of the input alternating voltage source signals by combining the first set of demodulated signals to provide a first source quality signal, combining the second set of demodulated signals to provide a second source quality signal, and for comparing the first and second source quality signals with predetermined quality thresholds to produce a source quality indication signal.

16. A method for detecting phase and magnitude disruptions in an alternating voltage source signal comprising the steps of:

a) receiving an alternating voltage source signal and providing a first alternating output signal that follows a phase of the alternating current source signal and providing a second alternating output signal phase shifted in relation to the first alternating output signal;

b) combining the first alternating output signal with the alternating voltage source signal to produce a first demodulated signal and combining the second alternating output signal with the alternating voltage source signal to produce a second demodulated signal; and

c) assessing the quality of the alternating voltage source signal by removing a mixer frequency component from the first and second demodulated signals to provide first and second source quality signals, and comparing the first and second source quality signals with predetermined quality thresholds to produce a resultant source quality indication signal.

17. The method of claim 16 wherein the alternating voltage source signal comprises three phase alternating voltage source signals and the step of providing in phase and phase shifted output signals is performed for each of the three phase alternating voltage source signals to provide a set of three in phase and a set of three phase shifted output signals which are combined with corresponding ones of said three phase alternating voltage source signals to produce first and second sets of demodulated signals which are added together to remove the mixer frequency component.

18. The method of claim 16 wherein in addition to comparing the first and second source quality signals to the thresholds, deviations of said source quality signals beyond the predetermined quality threshholds are monitored for the time durations they exceed said thresholds in producing the resultant source quality indication signal.

19. The method of claim 18 wherein the step of comparing the first and second source quality signals is performed by coupling said source quality signals to comparators that define boundaries of said signals in a complex two dimensional plane and wherein outputs from the comparators define constant magnitude signals that are integrated to provide linearly increasing functions with respect to time that are used to monitor the time durations the quality signals exceed the thresholds.

20. The method of claim 16 wherein the step of providing a second alternating output signal is conducted by phase shifting the second alternating output signal by 90 degrees with respect to the first alternating output signal.