Performance Analysis of Synchronous Reluctance Machines Having Nonoverlapping Concentrated Winding and Sinusoidal Bipolar With DC Bias Excitation

Abstract

This paper describes the operation principle and analyzes the electromagnetic performance of synchronous reluctance (SynR) machines having the structure of switched reluctance machines but excited by an ac sinusoidal current with dc bias, i.e., salient-pole SynR with nonoverlapping concentrated windings and a dc bias excitation. Under such excitation, these machines become similar to permanent magnet (PM) counterparts. The dc bias, which is equivalent to the PM excitation, produces back electromotive force (EMF) in the ac coils as well as cogging torque. Thus, injecting the ac coils by sinusoidal currents results in output torque on the machine shaft. The produced back EMF and cogging torque, and torque ripple magnitudes and periods, as well as the optimal ac current angle and the ac/dc current density ratio, strongly depend on the winding connection configuration. The maximum average torque can be achieved when the ac/dc current density ratio is 2 and the symmetrical winding connection, which results in a lower torque ripple, is employed. A prototype machine is built and tested to confirm the analyses and conclusions.