Approximation of Inductance Changes due to Saturation of Permanent Magnet Synchronous Machines to Increase the Accuracy of Observer Methods of Sensorless Control

Abstract:
In the course of this paper, an expansion of the dynamic fundamental wave model is presented that approximates the saturation behavior of the self- and mutualinductivities of a permanent magnet synchronous machine (PMSM), to increase the accuracy of model based rotor position observers. The saturation of the individual inductivities is dependent on all magnetization currents. For this purpose, the basic wave model of the machine is considered first. This already takes the mutualinductivities between orthogonal coordinate directions into account. For the analysis of saturation effects, a function for the field strength-dependent permeability of ferromagnetic materials is developed from the magnetization characteristic. The approximate replica of the permeability is carried out via a tangent hyperbolic function. The proportionality between the field strength and the magnetization current is determined by comparing the magnetization characteristic and the no-load characteristic of the PMSM. This leads to the current-dependent self- and mutualinductivities results. The current-dependent inductance matrix is then set up with consideration of the saturation and integrated into the basic wave model. Finally, the simulation results of the approximated saturation effect are presented.