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.