Frequency-Selective Grounding for Induction Motor Variable Frequency Drives

Variable frequency drives (VFDs) are recommended to be grounded in order to support operation continuity, reduce common-mode voltages (CMVs), enhance safety, limit ground fault currents, and minimize transient over-voltages during ground faults. Various standards and industrial codes are developed to address the design and configuration of adequate grounding systems for VFDs. This paper aims to test the performance of a VFD, when featured with the frequency-selective grounding (FSG). The FSG is designed to appear as a very low ground impedance for high frequency ground voltages, and to appear as a low-resistance for low frequency ground voltages. These features of the FSG can offer significant reductions of common-mode voltages (CMVs) in VFDs, thus minimizing their adverse effects on the motor, power electronic converters, and dc-link capacitors. The ability of FSG to minimize CMVs in VFDs is experimentally tested using a $10 hp, 3\phi$ induction motor VFD for different operating conditions. Experimental test results detailed in this paper demonstrate the significant reductions in CMVs, along with negligible sensitivity to the control of the VFD.