Difference in Differential and Common Mode Currents of Output and Input Cables in Three-Phase Variable Speed Drive System for Evaluating Radiated EMI

The issue of electromagnetic interference (EMI) holds significant importance in the design of variable speed drives (VSDs). Even if the VSD is the source of radiated EMI due to the high-speed switching devices, the power cables are the main emission parts for the radiated EMI as antennas. The common-mode (CM) current of an output power cable of the VSD has been investigated as a radiation part. However, considering the radiation EMI, it is crucial to examine the CM current not only in the output power cable but also in the input power cable. This paper investigates the differential-mode (DM) and CM currents of input and output power cables of a three-phase AC/DC/AC VSD system using simultaneous time domain measurements to estimate the radiated EMI. The result demonstrated that the input and output power cables act as antennas, and the radiated EMI can be evaluated by considering the integrated CM currents of the input and output power cables, especially the comprised of the 3-phase wire and earth wires’ CM current.