Table 9 Summary of feature extraction techniques

Statistical features

Central tendency

 Summary of typical values in a specific time frame

 Low computational burden

Based only on quantitative, historical data

Not able to generalize the findings to a broader population of PQDs

[60, 62, 63, 65, 67, 68, 71,72,73,74,75,76,77, 80, 81, 83, 85, 87, 89, 91, 95,96,97, 100, 102, 105, 108,109,110, 112, 114, 117, 120, 123, 126, 128]

36

[132, 143, 149, 168]

7

[187, 196, 201]

12

Dispersion

 Summary of variability in a specific time frame

Based only on quantitative, historical data

High values might not be useful to describe the PQDs behavior

[34, 40, 41, 43, 48, 49, 52, 54,55,56,57, 60,61,62,63, 65, 67, 68, 70,71,72, 74,75,76, 79, 81, 83,84,85, 87,88,89, 91,92,93,94,95,96,97,98, 100, 102, 105,106,107,108,109,110, 112, 114, 115, 117, 118, 120, 123, 126, 128, 130]

58

[132, 143, 144, 148,149,150, 168, 169, 177, 178, 183, 184]

22

[187, 189, 191, 193, 196, 211]

24

Time series features

Sample-based

 Independent of sampling frequency

 Detailed information

Further processing might be required

[61, 64, 65, 67, 75, 77, 87, 91, 92, 96, 99, 115, 128]

13

[133, 145, 186]

5

[205,206,207,208,209, 211]

24

Cycle-based

 Suitable for steady-state disturbances

Limitations with sub-cycle disturbances (e.g., notches)

[33, 36,37,38,39, 42, 44,45,46, 52, 53, 56, 57, 59, 64,65,66, 69, 72, 79, 82,83,84, 88, 93, 96, 99, 101, 102, 106, 109, 110, 114, 118, 122, 123, 126, 128, 130]

61

[132, 135, 141, 146,147,148, 150, 155, 159, 167, 174, 175]

27

[189, 192, 194, 196, 199, 204, 208, 211]

32

Spectral features

 Non-evident periodicities might be reveled

Frequency-domain transformation is compulsory

Inaccurate for PQ events

[61, 62, 66, 70,71,72, 77, 82, 89, 97, 102, 110, 115, 118, 128]

15

[132, 149, 156, 161]

7

[188, 189, 197, 202, 211]

20

Image features

 Processing of 2-D signals

 Signal processing methods can be applied

Problems from "non-perfect" modulation (swing of main frequency)

[50, 111, 112, 130]

4

[140, 151,152,153, 157, 158, 163, 167, 169, 172, 181, 186]

22

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0