Reduction of AC Copper Loss in Slotless Motors by Embedding Magnetic Composite Materials into Windings

Slotless motors inherently produce AC copper losses due to their structural design. To mitigate this, finestranded wires such as Litz wires are employed. However, these wires disrupt the alignment of the wires and increase the number of insulation layers, thereby reducing the winding space factor and subsequently increasing DC copper losses. This creates a trade-off between AC and DC copper losses.This study proposes a slotless motor structure that diminish AC copper loss without elevating DC copper loss. By incorporating a material that acts as a magnetic flux path around the coil, the magnetic flux linking the coil is controlled, effectively reducing AC copper losses. The integration of magnetic composite materials with the coil simplifies the motor structure while ensuring compatibility with conventional manufacturing processes. Moreover, enhancing the torquecontributing magnetic flux reduces the current needed to generate torque, thereby limiting the rise in DC copper loss. The effectiveness of the proposed structure was validated through magnetic field analysis based on finite element method.