Optimal design of BLDC multi-phase reluctance machines (MRM) for variable speed drives

BLDC-MRM is a brushless salient rotor multiple phase (m) stator reluctance machine fed with bipolar two-level-flat-top electronic controlled phase currents where m(F) phases play as "field" phases and m(T)=m-m(F) phases play as "torque" phases, like in a dc brush machine with brushes off the neutral axis and without dc excitation. With all phases active at all times, an inherent around 900 power angle, moderate air-gap (in axis d) and high magnetic reluctance in axis q, BLDC-MRM is expected to produce competitive performance over a wide constant power speed range (CPSR) at lower overall machine + converter costs, due to inherent flux-weakening and better inverter input dc voltage utilization. This paper introduces a magnetic circuit model (MEC) based optimal design methodology, with embedded FEM validation, illustrated for a 160Nm, 3000rpm application with promising results (94.1% efficiency for 31.5kg of active materials and no PMs).