Frequency-Selective Grounding for Permanent Magnet Synchronous Motor Frequency Drives

Variable frequency drives (VFDs), including permanent magnet synchronous motor (PMSM) VFDs, have to be grounded in order to improve their operation and protection. In PMSM-VFDs, an adequate grounding can help in reducing common-mode voltages (CMVs), improving personnel safety, and limiting ground fault currents. Several standards and industrial codes have addressed the adequate grounding systems for VFDs, including PMSM-VFDs. This paper presents the design and performance assessment of the new frequency-selective grounding (FSG), when utilized in a PMSM-VFD. The design of the FSG is based on a parallel $R-C$ circuit, which behaves as a very low impedance for high frequency voltages and a low-resistance for low frequency voltages. Such functions of the FSG can significantly reduce common-mode voltages (CMVs) in PMSMVFDs, thus minimizing their adverse impacts on the drive and its components. The performance of the proposed FSG in PMSMVFDs is experimentally tested using a $5 h p, 3 \phi$ PMSM-VFD for different operating conditions. Experimental test results discussed and presented in this paper demonstrate the significant reductions in CMVs, along with negligible sensitivity to the operating speed and/or loading level of the PMSM-VFD.