Magnetizing Curve Estimation of Induction Motors in Single-Phase Magnetization Mode Considering Differential Inductance Effect

To obtain an accurate magnetizing curve of induction motors at standstill, including both field-weakening region and saturated region, a novel method for estimation of mutual inductance L
_m
is proposed. At first, the reasons causing error of L
_m
identified by conventional ac-current-injection-based method, i.e., fluctuation of static L
_m
and differential inductance effect, are clarified in a theoretical view. To solve the problem, a continuous ac excitation of customized low frequency, with dc offset, is designed to excite the motor in single-phase mode. While dc offset with configurable amplitudes is used to fix the saturation level and restrain variation of static L
_m
, ac excitation maintains identifiability of the inductance. After the estimated L
_m
is retrieved from stator-side reactance, a direct numerical-integration method is proposed to effectively correct the differential inductance effect. The influence of injection frequency is rigorously investigated, which is also a key point for successful estimation. Both simulation and experiments have been implemented to demonstrate the feasibility and validity of the proposed method.