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EP-4370939-B1 - ELECTRICAL SIGNAL ANALYSIS AND APPLIANCE MONITORING

EP4370939B1EP 4370939 B1EP4370939 B1EP 4370939B1EP-4370939-B1

Inventors

  • CAHILL, Niall

Dates

Publication Date
20260506
Application Date
20210712

Claims (15)

  1. A method of detecting states of an electrical load from an electrical signal, comprising: providing (310) a mathematical model for the electrical signal; using (322) a sliding window to estimate (320) parameters of the model, wherein a plurality of windows are determined for the electrical signal, a window function is applied for each of the windows, and parameters of the model are determined (324) by interpolation; reconstructing (330) the waveform from the determined parameters and subtracting the reconstructed waveform from the original signal to obtain (340) a residual signal; determining (350) a state transition where the residual exceeds a threshold; and detecting (360) a state as existing for the time period between successive state transitions.
  2. The method as claimed in claim 1, wherein the mathematical model is a sinusoidal model comprising a fundamental frequency and harmonics of the fundamental frequency.
  3. The method as claimed in claim 1 or claim 2, wherein the window function is a Rife-Vincent window function.
  4. The method of claim 3, wherein the Rife-Vincent window function is a Class 1 Rife-Vincent Window function.
  5. The method of claim 4, wherein the Class 1 Rife-Vincent Window function is of order 6 or greater.
  6. The method of any preceding claim, wherein the residual signal exceeding a threshold involves determining whether the root mean square value of the residual signal exceeds the threshold value.
  7. The method of any preceding claim, wherein the method further comprises sampling the electrical signal into a buffer, and applying the sliding window to the buffer.
  8. The method of claim 7, further comprising emptying the buffer when a state transition is detected.
  9. A method of monitoring an electrical system, comprising: detecting states of an electrical load from an electrical signal according to the method of any of claims 1 to 8; and comparing the states of the electrical load with expected states of the electrical load.
  10. The method of claim 9, wherein comparing the states of the electrical load with expected states of the electrical load comprises determining the presence or absence of states of the electrical load.
  11. The method of claim 9 or claim 10, wherein comprising the states of the electrical load with expected states of the electrical load comprises determining times at which one or more states of the electrical load are present.
  12. The method of any of claims 9 to 11, further comprising determination of a fault in the electrical system from comparing the states of the electrical load with expected states of the electrical load.
  13. An electrical device comprising a detection element for detecting values of an electrical signal passing through the electrical device, wherein the detection element is adapted to carry out the method of any of claims 1 to 12.
  14. The electrical device of claim 13, wherein the electrical device is an electrical appliance, and wherein detected states are states of the electrical appliance.
  15. The electrical device of claim 13, wherein the electrical device is a circuit breaker.

Description

TECHNICAL FIELD The disclosure relates to methods and apparatus for electrical signal analysis and appliance monitoring. BACKGROUND For an electrical load such as a complex appliance, a detected electrical signal relating to that electrical load - such as the current to the load or the voltage across it with respect to time as power is switched on - will itself have a complicated form. This form will be representative of internal state changes within the complex appliance or other electrical load. Prior art document US2020/0292608A1 performs state detection for electrical loads in power networks, involving building a waveform model from measured electrical signals associated with the load and using the residual difference between the model output and the signals themselves to identify load states and -state transitions. It would be desirable to use the form of such electrical signals to represent and analyse changes in internal state within such loads. A technique that proved effective to do this would have numerous uses, for example in appliance monitoring - a change in the form of the electrical signal may be used to determine whether a component within the complex appliance was failing, or if it was working outside its normal range of operation. SUMMARY OF DISCLOSURE In a first aspect, the disclosure provides a method of detecting states of an electrical load from an electrical signal, comprising: providing a mathematical model for the electrical signal; using a sliding window to estimate parameters of the model, wherein a plurality of windows are determined for the electrical signal, a window function is applied for each of the windows, and parameters of the model are determined by interpolation; reconstructing the waveform from the determined parameters and subtracting the reconstructed waveform from the original signal to obtain a residual signal; determining a state transition where the residual signal exceeds a threshold; and detecting a state as existing for the time period between successive state transitions. Using this approach, the electrical signal can be broken down logically and repeatedly into a sequence of states. Variation in this sequence of states - for example, absence of a particular state, or a variation in the time taken for specific states to appear or finish - can be used to monitor an electrical device or an electrical system for changes, and may even be used for fault diagnosis, particularly if specific states can be identified with specific real world states or criteria. This mathematical model may be a sinusoidal model comprising a fundamental frequency and harmonics of the fundamental frequency. This is a particularly suitable approach to take in respect of an AC electrical signal. In embodiments, the window function is a Rife-Vincent window function - this choice of window function is found to be particularly appropriate to this approach to analysis of the electrical signal. This may be a Class 1 Rife-Vincent Window function, and this Class 1 Rife-Vincent Window function is of order 6 or greater. In embodiments, wherein the residual signal exceeding a threshold may involve determining whether the root mean square value of the residual signal exceeds the threshold value. In embodiments, the method may further comprise sampling the electrical signal into a buffer, and applying the sliding window to the buffer. The buffer may then be emptied when a state transition is detected. In a second aspect, the disclosure provides a method of monitoring an electrical system, comprising: detecting states of an electrical load from an electrical signal according to the method of the first aspect above; and comparing the states of the electrical load with expected states of the electrical load. In embodiments, comparing the states of the electrical load with expected states of the electrical load may comprise determining the presence or absence of states of the electrical load. Comparing the states of the electrical load with expected states of the electrical load may also comprise determining times at which one or more states of the electrical load are present. In embodiments, this method may further comprise determination of a fault in the electrical system from comparing the states of the electrical load with expected states of the electrical load. In a third aspect, the disclosure provides an electrical device comprising a detection element for detecting values of an electrical signal passing through the electrical device, wherein the detection element is adapted for carrying out the method of either the first or the second aspect above. Such an electrical device may be an electrical appliance, and wherein detected states are states of the electrical appliance. Alternatively, the electrical device may be a circuit breaker. BRIEF DESCRIPTION OF FIGURES Embodiments of the disclosure will now be described, by way of example, with reference to the following figures, in which: Figure 1 shows