Harmonic analysis Pass Band - Line Filters 500Hz & 5KHz - Digital power analyzer

[Kiriakos GR]

I am stretching here my brain cells, so to earn understanding about Harmonic analysis Pass Band, and Line and Frequency filters which are over a Digital power analyzer.

I can not discover a complete article about this topic.
But I do find scattered fragments of information.

Over a modern digital power analyzer (AC power meter), they are two type of filters.
First one this is named as Frequency Filter.
The second on is named as Line Filter.

Line filter is a digital low pass filter with a high attenuation rate of ≥70dB.
When line filter is enabled, the measured value will not include high frequency content, such as the high frequency noise of a switching converter.
Filter options : OFF and or 500Hz and or 5.5 kHz cutoff frequency is compliant to IEC 61000-3-2 international standards. It is suggested to turn this filter on when measuring harmonics. 

Frequency Filter ....... (Total Harmonic Distortion Measurement For Energy Monitoring - Texas Instruments Incorporated)
Frequency Measurement:
Because noise spikes can also cause errors, the application uses a rate of change check to filter out the
possible erroneous signals and make sure that the two points are interpolated from genuine zero crossing
points.
For example, with two negative samples, a noise spike can make one of the samples positive,
thereby making the negative and positive pair appear as if there is a zero crossing.
The resultant cycle-to-cycle timing goes through a weak low-pass filter to further smooth out any cycle-to-
cycle variations.
This filtering results in a stable and accurate frequency measurement that is tolerant of noise.


IEC 61000-4-30 edition 3
Power quality Analyzer, Upper harmonics inspection Pass Band 2 kHz to 150 kHz range are considered in Annex C (informative).
Standard relative to inspection of power supply systems with a declared fundamental frequency of 50 Hz or 60 Hz, these deliver power to the grid. 

IEEE 519:2022 require harmonic measurements to the 50th harmonic.
This is for Total Harmonic Distortion (THD), Total Demand Distortion (TDD).
The 50th harmonic is 3kHz @ 60Hz and 2.5kHz @ 50Hz

Supraharmonics can propagate through power supply networks.
Pass Band 2 KHz ~ 9 KHz
Supra Harmonics are not a requirement for compliance with these standards.
As of this writing, any PQ instrument claiming Supra Harmonic measurements use proprietary methods developed by the manufacturer.

EV Charger with 50 kHz Chopper Frequency
Chopper frequencies varied between 8 kHz and 50 kHz
Harmonics appeared at Pass Band 10 KHz up to 150 KHz (instrument Pass Band 200 KHz). 

Solar Inverter switching at 16 kHz
IGBT switching frequencies are between 2 kHz and 16 kHz

To be continued...

[Kiriakos GR]

Digital filtering
The design of a digital filter that takes an analog input signal applied to the ADC, then processes incoming samples, and finally provides an analog output using a DAC.