Inductance Measurement of Synchronous Motors with Solid Elements Using Quasi-Static Approach Considering Saturation Effects

This paper presents an innovative method for measuring inductance in line-start synchronous reluctance motors (LS-SynRM), addressing the challenges posed by electrically conducting elements in the rotor, such as the squirrel cage. Conducting elements induce eddy currents that interfere with traditional AC inductance measurement techniques. The proposed quasi-static measurement approach minimizes the effects of eddy currents, enabling accurate inductance profiling across different rotor positions. The method requires the adoption of a custom current profile with a low slope to minimize the effects of the induced eddy current. This allows to observe different current levels, evaluating also the saturation effect of the machine. Experimental results demonstrate the method's efficacy in evaluating the impact of magnetic saturation on motor performance, including average torque and torque ripple, which are obtained by analyzing inductance harmonics (over rotor position angle). In addition, it is also possible to compute the direct and quadrature axis inductance, which are critical data for motor control optimization. Because the method separates the excitation and sensing circuits, it is possible to measure the inductance matrix without the influence of phase resistance or temperature fluctuations. This makes it highly applicable to industrial motors requiring precise performance tuning.