Fault Tolerant Operation of Active Front End Converter with High Resistance Grounding System

Abstract

High resistance grounding (HRG) system grounds the neutral point of a three-phase power distribution system through high resistance. This grounding scheme limits the ground short circuit current allowing continued operation in case of a single phase to ground fault. Since 1970s, HRG has become prevalent in continuous-process industries where ground fault tolerant operation is desired. An Active front end (AFE) converter is an AC-to-DC converter, in which the diode bridge in a threephase rectifier is replaced by solid state switches, and a line filter is installed between the line and the solid state switches. An AFE allows bidirectional power flow and is typically controlled to maintain near unity power factor. Because of these features, AFEs are gaining popularity in applications where high power factor and high energy efficiency are desired. An AFE has different operating characteristics and phenomena than that of a diode front end (DFE) converter particularly when a ground fault is present in an HRG system. If the system is not carefully considered, the fault tolerant feature of an HRG system will be compromised. So far there is limited literature that analyzed an AFE converter operating in HRG systems, and no literature can be found that studied the impact of a ground fault on the fault tolerant operation for this case. In this manuscript, the phenomenon is presented, verified by simulation and experiment, and the potential solution is discussed in the end.