A method for the calibration of harmonic analysers using signals containing fluctuating harmonics in support of IEC61000-3-2

The motivation for the calibration of harmonic analysers under fluctuating harmonic conditions is considered. An overview of the prescribed design of IEC61000-4-7 harmonic analysers is given. A class of signal is presented that can be used to calibrate analysers at the ‘maximum’ and ‘average’ limits as defined in the international standard.The inherent variation in results identified as a result distribution due to variable phase (RDVP) is considered together with the consequences of the RDVP for the use and calibration of these harmonic analysers. A method to fit analyser results to the RDVP, based on multiple phase shifted harmonic modulators is presented, such that analyser performance can be assessed. Sample results are given, showing significant errors on commercial devices, despite their apparent correct performance under steady-state conditions.