Identification of the magnetising curve during commissioning of a rotor flux oriented induction machine

Numerous operating regimes of a rotor flux oriented induction machine require variation of the rotor flux reference. Correct setting of the stator d-axis current reference for each value of the rotor flux reference is only possible if an approximation of the magnetising curve of the machine is incorporated in the control system. Consequently, the magnetising curve has to be identified during commissioning of the drive. An experimental method for identification of the magnetising curve is proposed, developed specifically for vector controlled drives. The method utilises the same vector controller and the same PWM inverter used in normal operation of the drive. The identification relies on the signals that are already present within the drive controller (stator currents only, or stator currents and the DC link voltage), so that additional measurements are not required. The identification function proposed ensures precise acquisition of the magnetising curve, robust against the stator resistance variation and the inverter lock-out time. The algorithm does not require any test signals. It is sufficient to perform the measurements during running of the unloaded motor at around 100 rpm. The developed procedure is verified by extensive experimentation and is believed to be well-suited for application during commissioning of the drive, provided that rotation is permitted.

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