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

Abstract

The effect of unbalanced magnetic pull (UMP) caused 6 by air gap eccentricity on the vibration of a permanent magnet 7 synchronous motor (PMSM) is investigated. The force model is 8 established analytically by the Maxwell stress method. For accu-9 rate consideration of the eccentricity condition, mixed eccentricity, 10 axial-varying eccentricity, and eccentricity caused by motor frame 11 vibration are modeled and combined. The model of the rotor-12 bearing system, which includes the UMP model, is developed with 13 two different methods. In the first method, UMP is added as a 14 linear negative spring to the rotor model, whereas in the second 15 method, UMP is included as an external force. The rotor system of 16 a centrifugal pump driven by an integrated PMSM is modeled using 17 beam elements, and the two distinct modeling approaches for UMP 18 are applied. From the results, the UMP effect on vibration and the 19 difference between the two modeling methods are investigated. To 20 verify the results of the analysis, experimental work is done with a 21 pump test rig, and results of frequency spectra are obtained. Based 22 on the analyses and experimental work, the negative stiffness effect 23 and additional vibration excitations caused by UMP are examined. 24 Index Terms-Axial-varying eccentricity, Eccentricity by frame 25 vibration, Permanent magnet synchronous motor, Mixed eccentric-26 ity, Unbalanced magnetic pull. 27 I. INTRODUCTION 28 E LECTROMECHANICAL interaction in rotating electrical 29 machines is a significant factor in the generation of nonlin-30 ear dynamic behavior of a system. In machines with a small air 31 gap, such nonlinear dynamic behavior can be dangerous for the 32 rotor system, and therefore, many studies have been conducted 33 on unbalanced magnetic pull (UMP) caused by electromechan-34 ical interaction. 35 The topic of UMP has been addressed in numerous studies 36 covering various factors such as asymmetry of rotor and stator, 37 rotor eccentricity, and magnetic saturation. Ortega et al.

Rotordynamic Simulation Method of Induction Motors Including the Effects of Unbalanced Magnetic Pull

“…This study considers static eccentricity and dynamic eccentricity simultaneously. Therefore, a mixed eccentricity model is defined by using the method studied in the previous research [1]. In this model, the dynamic eccentricity has a time-dependent term because it is defined from actual rotor behavior; however, in each time step, it can be considered a static condition calculated from the instantaneous location of the rotor.…”

“…This study focuses on the induction motor, which is the most widely used electrical machine type in industrial applications owing to its simple structure and low manufacturing cost. However, the process of UMP calculation in an induction motor is more complicated than in other types of electrical machines, such as traditional permanent magnet synchronous machines [1] or permanent magnet bearingless machines [2]- [4]. This is because the induction motor has a secondary circuit, where the rotor magnetic flux must be calculated.…”

Static Eccentricity Fault Analysis of Surface-Mounted Permanent Magnet Electromotor with Skewed Slots Based on 2D FEA

“…H. Lee proposed an analytical method to calculate the characteristics of eccentric electromotor quickly according to the design variables [11]. H. Kim established an analytical model of the force by Maxwell stress method and studied the influence of unbalanced magnetic tension on the vibration of permanent magnet synchronous electromotor caused by airgap eccentricity [12]. H. Lasjerdi proposed a comprehensive method based on the winding function method, and a non-invasive index was used to identify the type or even percentage of mechanical eccentricity failures [13].…”

Unbalanced Magnetic Pull Effects on Rotordynamics of a High-Speed Induction Generator Supported by Active Magnetic Bearings – Analysis and Experimental Verification

“…The parameters in the model were estimated by using an impulse method based on FEA. Kim et al [5], [6] developed a rotordynamics simulation method based on a mixed rotor eccentricity model for time-step analysis in an induction motor. They proposed an optimal way to calculate the UMP force by using a simple analytical model and its update with FEA.…”

“…For instance, Pennacchi [10] evaluated the UMP effect by investigating the vibrational behavior of a steam turbogenerator and comparing the results between no-load and load conditions of the generator. Kim et al [5] produced the static eccentricity condition by installing a shim on one side between the motor frame and the bearing housing. Then, they measured the vibration of the motor frame in the conditions of different static eccentricities, and the effect of UMP was investigated.…”