Electromagnetic performance analysis of synchronous reluctance machines having non-overlapping concentrated winding and AC sinusoidal bipolar with DC bias excitation

This paper describes the operation principle and electromagnetic performance of synchronous reluctance (SynR) machines having the structure of the switched reluctance (SR) machines but excited by AC sinusoidal current with DC bias, i.e. salient-pole SynR with non-overlapping concentrated windings and DC bias excitation. Under such excitation, the machine becomes very similar to the permanent magnet (PM) counterparts. The DC bias, which is equivalent to the PM excitation, produces back-emf in the AC coils as well as cogging torque. If the AC coils are injected by 3-phase sinusoidal currents, output torque will be generated on the machine shaft. The produced back-emf, cogging torque magnitude and period, and optimal AC current angle as well as optimal AC/DC current density ratio strongly depend on the way of winding connection. The maximum average torque can be achieved when the AC/DC current density ratio is 2 and symmetrical winding connection, which results in lower torque ripple, is employed. A prototype machine is built and tested to confirm the analyses and conclusions.