Effect of Paralleling the Stator Coils in a Permanent-Magnet Machine

As low-voltage machines require smaller number of turns per phase compared to higher voltage machines, it is normal to connect the various stator phase coils in parallel to form the phase winding. The placement of various coil sides in the slot and the difference in the field produced by different poles of the rotor magnet can influence the induced voltage in various coils and the impedance of the coils. The difference in the induced voltages in the various parallel paths results in a circulating current in the winding and will cause increased losses in the machine. The unequal induced voltage and impedance will cause unequal distribution of stator current in the various parallel paths and will impact the torque-ripple contents. This paper will discuss the effects of these unbalanced parallel paths on the machine performance