Synchronous Motor Operation in Voltage Imbalance Conditions

Voltage imbalance remains one of the secret killers of electric motors considering its multiplying effect on current magnitudes. Its impacts on conventional induction motors have been widely addressed, however considering the new technologies existing commercially as a result of the search for higher efficiencies, the evaluation in non-ideal conditions also becomes of significant interest to users. This paper presents an evaluation of the voltage imbalance impacts on a line-start permanent magnet motor (LSPMM). For the study, the motor was fed under different voltage imbalance conditions and varying the motor load percentage. The results revealed that for high levels of voltage imbalance in the motor phases, the current imbalance in combination with the permanent magnet's constant magnetic field produces negative single-phase power under low-load conditions. Power quality impacts are also addressed from current oscillography.