Analyzing the Effect of Choke Placement on Differential-Mode Supra-Harmonics in Variable Frequency Drives: New Standardization

Three-phase motor drive systems are the foundation
of modern industrial and commercial applications, providing an
efficient and dependable way to operate electric motors. In order
to meet electromagnetic compatibility requirements within the
frequency range of 0 to 2 kHz, magnetic chokes are frequently
utilized, being connected to either the DC or AC sections of drive
systems. Recently, worldwide standard committees adopted new
emission limitations for the 2±9 kHz frequency range to minimise
power quality problems caused by the increased penetration of
power electronics equipment. The influence of choke location
on differential-mode supra-harmonics in the 0±9kHz frequency
range is investigated in this work. Mathematical calculations are
employed to conduct a comparative analysis in choosing between
two DC-link inductors or three AC line inductors for mitigating
differential-mode noise at the grid. To that end, single-phase
equivalent circuits are used to calculate differential-mode noise
components. Following that, supra-harmonic contents of currents
are estimated based on the commutation of the front-end rectifier.
In consequence, through the derived mathematical equations,
conducted noise emissions entering to the grid are analytically
modeled. The findings of laboratory tests are utilised to verify
the theoretical concepts.