Impact of core losses on parameter identification of three-phase induction machines

Accurate knowledge about the machine parameters is of utmost importance for high performance speed control of induction machines. Out of all the various machine parameters, the stator and the rotor resistances are strongly dependent on the machine temperature, which is difficult to predict without any appropriate sensor mounted inside the machine. Online identification of these parameters requires correct knowledge about the machine magnetic parameters, which are the magnetising and leakage inductances. Moreover, estimation of the resistive parameters is affected by core loss in the machine. The magnetic parameters are almost unaffected by core losses and can be accurately calculated offline at different operating flux levels with known input variables and resistive parameters. A 'variable flux current limit test' is proposed to determine the parameters at various input frequencies and operating fluxes. The proposed identification method can be implemented with the same hardware available for normal operation of the drive. Various simulations and experiments performed on practical machines validate the proposed concept.