Coupled Electromagnetic-Dynamic Modeling and Bearing Fault Characteristics of Induction Motors considering Unbalanced Magnetic Pull

Abstract

Induction motors are complex energy conversion systems across the domains of dynamics, electricity, and magnetism. Most existing models mainly consider unidirectional coupling, such as the effect of dynamics on electromagnetic properties, or the effect of unbalanced magnetic pull on dynamics, while in practice it should be a bidirectional coupling effect. The bidirectionally coupled electromagnetic-dynamics model is beneficial to the analysis of induction motor fault mechanisms and characteristics. This paper proposes a coupled electromagnetic-dynamic modeling method that introduces unbalanced magnetic pull. By using the rotor velocity, air gap length, and unbalanced magnetic pull as the coupling parameters, the coupled simulation of the dynamic and electromagnetic models can be effectively realized. Simulation results for bearing faults show that the introduction of magnetic pull induces a more complex dynamic behavior of the rotor, which in turn leads to modulation in the vibration spectrum. The fault characteristics can be found in the frequency domain of the vibration and current signals. Through the comparison between simulation and experimental results, the effectiveness of the coupled modeling approach and the frequency domain characteristics caused by the unbalanced magnetic pull are verified. The proposed model can help to obtain a variety of information that is difficult to measure in reality and can also serve as a technical basis for further research on nonlinear characteristics and chaos in induction motors.

The influence of the unbalanced magnetic pull on fault-induced rotor eccentricity in induction motors

“…A Magnetic Equivalent Circuit (MEC) motor model is combined with a dynamic bearing model. The motor model provides a detailed simulation, compared to previously used analytical air gap models (Guo and Bai 2022) and multiple coupled circuit models (Huang et al 2022). Unlike previous methods, the novel use of MEC includes the effects of rotor slot harmonics.…”

“…The UMP is a radial electromagnetic force caused by an unbalance in the magnetic field. When RE is present, the UMP will pull the rotor approximately in the direction of the smallest air gap, worsening the existing RE (Huang et al, 2022). Robinson (1943) defined the UMP and provided an early calculation method.…”

“…However, it assumes a simplified Magnetomotive Force (MMF), thereby neglecting the coupling between rotor displacement and current. Huang et al (2022) improved this by increasing the motor model complexity using Multiple Coupled Circuit (MCC) theory and Winding Function Approach (WFA). They examined the impact on bearing faults and observed the UMP to have a significant influence.…”