A New Dynamic Eccentricity Diagnosis Method for Permanent Magnet Motors Considering Variable-Speed and Speed Fluctuation Conditions

Nowadays, dynamic eccentricity (DE) diagnosis methods for permanent magnet motors (PMMs) face difficulties in constructing diagnostic functions and extracting features under variable-speed and speed fluctuation conditions. Motivated by this, this article proposes a new DE diagnosis method based on normalized envelope mean (NEM) of open-circuit back electromotive force (EMF), which enables accurate diagnosis within the full range of DE ratios under variable-speed and speed fluctuation conditions. First, the phenomenon and generation mechanism of periodic fluctuations in envelopes of back EMF caused by DE are investigated based on the analytical model (AM). Then, a new DE diagnosis method is proposed. Based on the proposed AM, the DE diagnosis function is constructed within the entire range of DE ratios. The NEM extraction algorithm based on instantaneous frequency estimation and speed normalization is proposed to handle variable-speed and speed fluctuation conditions. Finally, the accuracies of AM and diagnosis method are verified by experimental results under different speed conditions and DE ratios. This article provides a new idea for the DE diagnosis of external rotor permanent magnet motors (ERPMMs), which can be applied not only to constant-speed conditions with speed fluctuations but also to variable-speed conditions.