Analysis of Electromagnetic Excitations in an Integrated Centrifugal Pump and Permanent Magnet Synchronous Motor

The effect of unbalanced magnetic pull (UMP) caused by air gap eccentricity
on the vibration of a permanent magnet synchronous machine (PMSM) is
investigated. The force model is established analytically by the Maxwell stress
method. For accurate consideration of the eccentricity condition, mixed
eccentricity, axial-varying eccentricity, and eccentricity caused by motor
frame vibration are modeled and combined. The model of the rotor–bearing system,
which includes the UMP model, is developed with two different methods. In the
first method, UMP is added as a linear negative spring to the rotor model, whereas
in the second method, UMP is included as an external force. The rotor system of
a centrifugal pump driven by an integrated PMSM is modeled using beam elements,
and the two distinct modeling approaches for UMP are applied. From the results,
the UMP effect on vibration and the difference between the two modeling methods
are investigated. To verify the results of the analysis, experimental work is done
with a pump test rig, and results of frequency spectra are obtained. Based on
the analyses and experimental work, the negative stiffness effect and
additional vibration excitations caused by UMP are examined.