What is Unbalanced Magnetic Pull (UMP) or Unbalanced Magnetic Force (UMF)?

Definition

Unbalanced Magnetic Pull (UMP) or Unbalanced Magnetic Force (UMF) is the net electromagnetic force acting along X or Y axis in the stator frame. Similarly to cogging torque, it is characterized by an average / DC value and a ripple / time harmonic component.

It magnitude corresponds the magnitude of the Maxwell stress harmonic component of wavenumber r=1. In magnetically-balanced electrical machines, this force is null.

Example of a harmonic force wave of wavenumber r=1 (unbalance magnetic pull)
Example of a harmonic force wave of wavenumber r=1 (unbalance magnetic pull)

Application to e-NVH

UMP can create a bending motion of an outer stator electrical machine (especially in clamped-free conditions), resulting in air-borne acoustic noise. UMP can also excite the inner rotor shaft bending mode, resulting in structure-borne acoustic noise.

Application to MANATEE

MANATEE software can calculate the effect of UMP on the outer structure vibration (stator or rotor) and the resulting acoustic noise. Noise mitigation actions such as notching can be easily implemented in MANATEE. The net magnetic forces in X and Y directions can be plot using plot_FxFy command of MANATEE:

Global magnetic forces
Global magnetic forces
plot_FxFy

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