A new concept for minimizing high-frequency common-mode EMI of three-phase PWM rectifier systems keeping high utilization of the output voltage

Three-phase PWM rectifier systems in principle show a common-mode voltage with switching frequency between the mains neutral point and the center point of the output voltage. Without any counter-measures this leads to a high common-mode noise emission of the system and possibly to disturbances of the control unit of the converter being fed by the rectifier. In this paper a detailed discussion of the formation of the common-mode voltage for the VIENNA Rectifier I is given and a modified circuit topology which significantly reduces the switching frequency component of the common-mode voltage is given. The proposed circuit modification is applicable also to other three-phase PWM rectifier topologies. The filtering concept is analyzed by digital simulation and guidelines for the dimensioning of the filter components are given. The reduction of the common-mode noise is verified by EMI measurements taken from a 10 kW laboratory unit of a VIENNA Rectifier I. Finally, the advantages and drawbacks of the proposed filtering concept are compiled in the form of an overview.