Air-Gap Flux Position Estimation of Inaccessible Neutral Induction Machines by Zero Sequence Voltage

This paper describes a new and straightforward approach to estimate the air-gap flux position in induction machines. The proposed scheme is based on the injection of a high-frequency oscillating stator voltage instead of a three-phase high-frequency voltage, thus allowing a reduction in audible noises and torque ripple. The main feature of the proposed approach is that a simple air-gap flux tracking algorithm is developed using the amplitude variation of the highfrequency component of the zero-sequence voltage. Moreover, the zero-sequence voltage is sensed at the output of the inverter rather than at motor terminals. The estimated position is not influenced by load and parameter variation and can be performed at any frequency, including low and zero frequency. An experimental prototype has been implemented showing the performance of the proposed approach.