Impact of the magnetic cross-saturation in a sensorless Direct Torque controlled Synchronous Reluctance Machine based on test voltage signal injections

This paper presents the impact of the magnetic cross-saturation in a sensorless Direct Torque Control (DTC) scheme for Synchronous Reluctance Machines (SynRMs). Due to the rotor saliency of the SynRM, the angular position of its rotor can be estimated by using inductance variations due to geometrical effects. This technique can be used at low and zero speeds of operation. However, the influence of the cross-saturation leads to a persistent error on the estimated angular position of the rotor. This error deteriorates the performance of the drive when the estimated position is used instead of the measured one in the control scheme. The aim of this paper is to present the impact of the position error as a function of the working point and to introduce a technique to minimize this problem in order to obtain a stable operation of the SynRM with load at very low speeds. Theoretical analysis is validated by experimental results, which have been obtained by using a DSP and a field programmable gate array based digital controllers and a SynRM of the transverse-laminated rotor type.