Effect of Neutral Grounding Resistance on Grid-Tie Active Front End Power Converter Systems Under Normal and Abnormal Conditions

Multiple grid-tie AFE converter systems requiring continuity of service under abnormal single line-ground fault conditions implies utilization of a floating or High Resistance Grounded (HRG) utility source. This paper shows floating or low amperage HRG units may generate high transient voltages at various system locations under this condition causing component or insulation damage. The paper describes three methods to mitigate transient fault voltages. It is not intuitively obvious that lowering source neutral ground resistance (R
NG
) has a major effect on reducing transient system voltages and is the 1
^st
significant factor analyzed. Method #2 involves grid-tie AFE software synchronization. Method #3 is a hybrid hardware solution comprised of input, output and DC bus filter conditioners.