The Impact of the Control Strategy in Flux Observer Based Sensorless Control of Synchronous Reluctance Motors

This paper compares different control strategies of the synchronous reluctance motor to outline their impact on the accuracy of flux-observer based sensorless operation. Maximum torque per ampere, maximum efficiency, and maximum power factor controls, usually referred to optimize the operating performance of synchronous reluctance motors are considered. Alternative solutions not usual in literature but specifically investigated for supporting the estimation are also considered, namely constant direct-axis-current and constant direct-axis-flux controls. The flux-observer detects the flux components in the two-phase stationary reference frame by a non-linear model achieved by finite-elements computations. An auxiliary mechanical observer who accounts for the finite-elements mapping of the torque is adjusted by the flux estimation error and provides the rotor position and speed needed for sensorless control. An extended set of experimental tests is presented where the different control methods are compared in terms of position and speed estimation errors and overall control quality. A four poles, three kW synchronous reluctance prototype designed for general industry application is used for testing.