Optimal flux weakening in surface PM machines using concentrated windings

A design approach is presented for achieving optimal flux weakening operation in surface PM synchronous machines by properly designing the machine´s stator windings using concentrated, fractional-slot stator windings. This technique makes it possible to significantly increase the machine inductance in order to achieve the critical condition for providing wide speed ranges of constant-power operation. The conditions for optimal flux weakening can be achieved while simultaneously delivering sinusoidal back-emf waveforms and low cogging torque. A closed-form analytical model is described that can be used to design SPM machines to achieve optimal flux weakening conditions. This technique is applied to design a 6 kW SPM machine that achieves constant-power operation over a wide speed range. Performance characteristics of this machine are compared using both closed-form and finite element analysis.