Influence of magnetic saturation of non-salient pole permanent magnets synchronous motors on performance of a servo drive

Challenges and proven solutions dedicated to the field oriented vector control (FOVC) of magnetically saturated permanent magnets synchronous motors (PMSM) are discussed in this paper. It has been noticed that in case a PMSM operating in magnetic saturation the feedback currents in the d- q-reference frame oscillate at six times the electrical frequency. The oscillation mechanism has been analyzed and explained based on mathematical modeling in Matlab-Simulink and on finite elements modeling (FEM). The oscillations are quite often identified with the zero crossing effect. This research work decoupled those two oscillations driving mechanisms by using an electric power drive with a minimum dead time of the switching IGBTs what is equivalent to negligible zero crossing effect. In terms of solutions a FOVC scheme combined with a predictive current observer and gain adaptation of a current compensator is proposed. Practical guidelines for the observer gain selection and the adaptive scheme settings are given. Experimental results with the original FOVC scheme and step by step modifications towards better performance are presented in this paper. The future work recommendations and conclusions are also included. Proposed solution is important from practical point of view. It can make an electric power drive running stable with a PMSM in a deep magnetic saturation.