Difference in Reluctance Torque Utility between Concentrated and Distributed Windings

This paper formulates the difference in reluctance torque utility between concentrated and distributed windings, taking into account the gap modulation of concentrated-winding permanent magnet (PM) motors. It was found that distributed-winding PM motors, in principle, have larger q-axis inductance and smaller d-axis inductance than the concentrated-winding motors, which leads to the increase in the reluctance torque utility. It was also shown that the contribution of the above difference to output-torque improvement was so small that it could provide little impact on practical design. Applying the established formulae to a 2.2 kW concentrated-winding ferrite magnet motor, the maximum torque of the distributed motors was quantified with high accuracy, not relying on the finite element analysis (FEA). The validity of the proposed approach was demonstrated by the FEA and measurements for the designed concentrated-winding PM motors.