On the Proprieties of the Differential Cross-Saturation Inductance in Synchronous Machines

The cross-saturation inductance is a mutual inductance due to the saturation of portions of the magnetic circuit of one axis caused by the current of the other axis. In sensorless drives, the differential cross-saturation inductance causes an error in the estimation of the rotor position when it is performed by means of the high frequency signal injection methods. The knowledge of the properties of cross-saturation inductance is therefore essential to minimize any distortion effect on the position estimation. This paper aims to describe the properties of the cross-saturation inductance for different types of synchronous machine, such as reluctance, interior permanent-magnet, and surface-mounted permanent-magnet machines. Information is also given to predict the error in the estimated position for any stator currents, useful for implementing an error compensation technique or to detect the feasible operating regions using the high frequency voltage injection technique. The analysis is supported by finite element simulations and experimental measurements.