Modal-Oriented High-Frequency Common-Mode Switching Oscillation Suppression in Inverter-Fed Machines Using Parity-Time Symmetry

The suppression of high-frequency (HF) common-mode (CM) switching oscillations in inverter-fed machine systems is a critical yet challenging task, primarily due to the presence of self-resonance in CM propagation paths, such as parasitic parameters of the filter. This article presents a novel approach based on parity-time (PT) symmetry to mitigate HFCM switching oscillation by utilizing a magnetically coupled external resonator to efficiently transfer transient oscillation energy. First, the HFCM switching oscillation in an inverter-fed machine system, treated as an internal resonator, is analyzed along with its modal characteristics. Subsequently, an external resonator is designed to operate at the exceptional point (EP) of PT symmetry for the suppression of oscillation modes. Experimental results obtained from a 380 V/3 kW variable-frequency drive (VFD) test rig demonstrate that the specially designed external reactor can effectively reduce the HFCM oscillation mode at 3 MHz by approximately 45% and attenuate the resonance spike in the CM spectrum by up to 13 dB. This solution is characterized by noncontact safety, compact size, excellent attenuation, and configurable flexibility.