Minimizing the circulating currents of a slotless BLDC motor through winding reconfiguration

Commonly, reconfiguring the winding in order to modify the torque-speed characteristic can be achieved by changing the coils configuration from series to parallel. This may produce an unwanted voltage unbalance between parallel conductors and circulating currents may appear. These currents produce losses that are usually neglected but they become significant the more the motor rotates rapidly. In this paper, we propose an analytical study on the influence of the spatial distribution of two parallel windings in the motor in order to minimise the above mentioned currents. Two reorganizations of the winding are developed: tangentially grouped and radially grouped. Subdividing the winding and reorganising the connections into two coils placed in parallel results in reducing 110 times circulating currents. Measurements performed on a prototype validate the theoretical analysis.