On-line measurement of induction machine stator and rotor winding parameters

An online parameter measurement technique which yields results similar to classical machine tests is used to determine the stator and rotor winding parameters for a cage induction machine. Low magnitude, high frequency voltage sets are injected into the machine´s supply so that the combined stator and rotor resistances and combined inductances may be determined. Variation of injected frequency results in impedance characteristics which account for variations due to skin and rotor bar thermal and frequency effects. A small DC offset is added to the supply for one phase and yields the stator winding resistance. The complete stator and rotor equivalent circuit at any instant during machine operation can be determined from these tests. The measurement system is implemented using a custom PWM generator and detection is carried out by means of a sampling circuit. Data analysis is by a software implemented fast Fourier transform algorithm