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The 12-phase synchronous generator–rectifier system is widely used in mobile platforms that require high system security. In the system, the stator internal short circuit is a kind of common fault that may compromise the security of the generator. This paper gives detailed analysis on the internal phase-to-phase short-circuit faults, including the faults within the same group of Y-connected phases and those between different groups of Y-connected phases in the 12-phase system. A multiloop mathematical model is built to calculate all the voltages and currents when the faults occur in the system. In the model, the additional short-circuit loop between different phases, as well as the fault effects on both the air-gap magnetic field and the circuit topology of the system, are taken into account. Then a series of fault experiments are carried out on a 12-phase model machine. In view of the good agreement of experiment and simulation results, the effectiveness of the mathematical model and the simulation method is confirmed. Finally, the electric characteristics of the internal phase-to-phase short-circuit faults are summarized, and the fault mechanism is revealed. [ABSTRACT FROM AUTHOR]

The interturn short circuit of field windings in synchronous machines will cause the field current increasing, reactive power output decreasing as well as the aggravation of vibration. In this paper, by using the multiloop theory and analyzing the steady-state characteristics of stator and rotor fault currents, the steady-state expression of each loop current is obtained, and then differential equations in steady-state system are reduced into linear equations; according to the principal that components of the same frequency are equal, the steady-state solution of the ac and dc components of each loop current can be obtained and the steady-state calculation of the fault can be achieved rapidly. The field winding interturn short-circuit experiments have been carried out on a 12-kW synchronous machine with three pairs of poles, the results of which agree well with that of steady-state simulations. Based on the aforementioned characteristics analysis and simulation results, an online fault monitoring method in view of the unbalanced current effective value of stator branches is proposed, by which the fault characteristics can be extracted to the highest degree and short circuit with small turns in field winding can be sensitively reflected. [ABSTRACT FROM AUTHOR]

The common method to mitigate the slot-frequency vibration and noise of the permanent magnet (PM) motors is skewing the stator slot or skewing the PM. However, the limitation of this method in pole-frequency vibration reduction exists. In this article, one method by adopting the piecewise stagger PM pole with a continuous skew edge is proposed to reduce the pole-frequency and slot-frequency vibration for surface-mounted permanent magnet (SPM) synchronous machines. First, the analysis of the radial force acting on the stator teeth is conducted. Basing on this, the limitation of the skewing slot method in reducing the vibration is revealed. In order to solve this problem, a piecewise stagger PM pole with a continuous skew edge for pole-frequency and slot- frequency vibration reduction is proposed and its principle of vibration reduction is presented in detail. The finite element models of three 6-pole/36-slot SPM motors are built to simulate the radial force. Finally, two 6-pole/36-slot SPM motors are manufactured and the experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The analytical methods are widely used to predict the vibration and noise of the permanent magnet motors in industry applications. In the traditional analytical method, the influence of the teeth is ignored and a large error of vibration calculation will occur in the slotted motor. In this article, a high-precision analytical method is proposed for vibration calculation of motors based on tooth modeling. First, the electromagnetic forces on each tooth of stator of the motor under no load and load are calculated. Then, the transfer function from the force acting on the teeth to the vibration on the surface of the shell is derived and verified by finite-element method (FEM). Next, the superposition method is introduced and used to superimpose the vibration excited by the force of all teeth to calculate the total vibration acceleration of the motor surface. Finally, the FEM and experiments are conducted to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The magnetic field including tooth effect can be calculated by the tooth harmonic permeance. However, the mechanical pivot role of tooth is always neglected in vibration analysis and the slotted stator is considered as a simple cylinder. In this article, the mechanical pivot role that the tooth plays in vibration analysis is illustrated, where the transfer function of force is proposed to represent the process of force from the top of tooth to the yoke. First, the magnetic pivot role of tooth in magnetic field analysis is described by the tooth harmonic permeance. Then the force on the top of tooth is transferred to the yoke by the transfer function of force, after that the yoke can be considered as a cylinder. Based on the pivot role of tooth, the phenomenon that the high order force can cause the low mode vibration is explained and clarified straightforwardly. Not only the fractional slot permanent magnet synchronous motor (PMSM), but also the integer slot PMSM, are analyzed to demonstrate the universality of these methods. Finally, the finite element method simulation, and the experiments on one fractional slot PM motor and one integer slot PM motor, are applied to validate the theory. [ABSTRACT FROM AUTHOR]

There is only slot frequency electromagnetic vibration and no pole frequency vibration in rotating armature permanent magnet motor (RAPMM), which is the advantage of this motor. The open of slot makes the air-gap magnetic field distorted and causes the harmonic of electromagnetic excitation force. In order to reduce the slot frequency vibration of the RAPMM, the method of placing magnetic slot wedge (MSW) at the slot opening is put forward accordingly. Through the finite-element simulation, it is finally shown that the MSW is capable of weakening the harmonic of the air-gap flux density, as well as decreasing the high-frequency component of the electromagnetic excitation force. Therefore, it is acknowledged that MSW can suppress the cogging torque and the vibration of corresponding frequency on the stator significantly. Finally, it is confirmed by the experiments that the built-in MSW is an effective measure for reducing the vibration of the RAPMM. [ABSTRACT FROM AUTHOR]

Because the root of pole-frequency vibration is the fundamental component of magnetic field, which is the basis of electromechanical energy conversion, by now no effective reduction method of pole-frequency vibration has been proposed, even few literatures has touched on this. In this article, one method by adding some permanent magnet (PM) interpoles to fill the force valley and then reduce the pole-frequency vibration for surface-mounted PM synchronous machines, is proposed and verified by experiments on prototype motors. First, a general expression of radial force density, including the amplitude, frequency, and spatial order, of a PM motor is investigated in detail. Based on this, the deep reason of pole-frequency vibration is ascribed as the valley of force density and the zero-crossing area of magnetic flux density. To fill the force valley and reduce the vibration, some PM interpoles are arranged between original main PM poles and its principle of vibration reduction is presented. A three-dimensional weak-coupling electromagnetic- mechanical finite-element model is built to simulate the radial force and the vibration of the PM motors. Finally, to validate the proposed method and finite-element method results, two 6 poles/36 slots PM motors are manufactured and the experiments are conducted. [ABSTRACT FROM AUTHOR]

The electromagnetic vibration of permanent magnet brush dc (PMBDC) motors has its distinct feature, where only slot-frequency related components exist. Skew slot technique is naturally recalled to mitigate the slot-frequency vibration. Unfortunately, the straight skew slot normally used is not as effective as the mitigation of tooth harmonic electromotive force (EMF) or cogging torque. First, in this paper, the principle of vibration mitigation by straight skew is discussed and compared with mitigation of tooth harmonic EMF and cogging torque. The reason for poor effect of straight skew slot is illustrated by a specifically-designed experiment and finite-element method (FEM) simulation. In order to solve this problem, the zigzag skew PM pole technique is proposed for PMBDC motors for the first time, which overcomes the disadvantage of straight skew slot. The pulsating radial force and bending moment, two main causes of electromagnetic vibration, are derived and analyzed analytically and by the three-dimensional FEM for zigzag skew PM poles. At last, the experiments on two PMBDC motors, one with straight skew slots and the other with zigzag skew PM poles, are conducted to verify the effectiveness of the zigzag pole technique. [ABSTRACT FROM AUTHOR]

The experimental modal test of the structure of the driving motor has always provided a major contribution to understand and control the vibration phenomena encountered in practice. The hammer test is a common experimental method to obtain a mathematical model of the structure and to validate the theoretical model and finite element method model. However, the hammer or the real vibration exciter will increase the test cost. In this article, an electromagnetic vibration exciter is proposed to achieve the frequency response functions and then the modal parameters can be extracted. Its principle of modal parameters estimation is presented and described in detail. The finite-element analysis and experiments of a 6p/36s permanent magnet motor have been conducted to verify the proposed method. [ABSTRACT FROM AUTHOR]

For the integer slot permanent-magnet (PM) driving synchronous motor, the zeroth-mode slot frequency vibration and noise play a significant vibroacoustic role in the low-frequency domain. For conventional analysis in literature, it is usually assumed that the zeroth-mode vibration is caused by the zeroth-order radial force harmonic. But in this paper, the genuine reason for zeroth-mode vibration is proposed and discussed in detail, which is different from the conventional analysis. The teeth chopping effect is proposed and demonstrates that the slot number order radial force is the root of the zeroth-mode vibration of the motor. After the analysis of the zeroth-mode vibration in existing research work is presented, the teeth chopping effect is introduced and described. The amplitudes of the zeroth-order and slot number order forces are compared with an analytical method, while their amplitudes and caused deformations of these forces are calculated with the finite-element method (FEM). Finally, to validate the analytical and FEM results, a 6-pole 36-slot PM driving motor is manufactured and tested, and the results are in good agreement with those of the FEM results. [ABSTRACT FROM AUTHOR]

This paper focuses on the electromagnetic vibration and its reduction in PM brush dc motors. First, the air gap flux density distribution and the radial force density distribution are derived in detail, and compared with the results of the finite element method. Next, two types of vibration sources, called pulsating force and bending moment, are analyzed. Then, two passive improvement methods, called varied PM pole width in axial direction and copper ring, are proposed to reduce the magnetic forces and their vibration, and their principles of the vibration reduction are described in detail. For further explanation, a rotor-skewed motor is used for comparison, and the radial force on the motor is discussed and the influence of four different thicknesses of copper ring on the motor vibration is analyzed. Finally, three 2p/24s sample motors are manufactured and the experimental vibration results confirm the analysis and the proposed improvement technique. [ABSTRACT FROM AUTHOR]

This paper presents a PM pole with varied width in the axial direction for vibration mitigation in permanent magnet brush dc motors, which is proposed to decrease the deformation caused by radial pulsating force and bending moment together. First, the air gap flux density distribution and radial force density distribution are derived in detail. After two types of vibration modes and their reasons as pulsating force and bending moment are analyzed, the difficulty in vibration mitigation is pointed out. By investigating the change rule of the pulsating force and bending moment with PM pole width, a type of PM pole with varied width in the axial direction is proposed. Its principle of deformation reduction is presented, and the optimized pole shape is derived. A three-dimensional finite-element method is used to calculate the magnetic field, Maxwell force, modal analysis, and deformation of motors. In order to verify the effectiveness of the proposed method, the vibration of the proposed motor is compared with the other three types of traditional motors, including skewing slot or skewing pole. Finally, experimental results of two types of motors are compared to validate the proposed technique. [ABSTRACT FROM AUTHOR]

This paper presents the detail analysis of the radial force and bending moment responsible for vibration in the stator permanent magnet synchronous motors (PMSMs). The vibration characteristics, especially vibration mode, of stator PMSM are studied. First, the air-gap flux density distribution and radial force density distribution are derived in detail. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated which are not analyzed and verified before. In addition, the relationships between these two vibration shapes and pole width, pole number, and slot number are analyzed. To confirm the analysis and theory, the multi-probe mode-included test method of vibration acceleration is used to obtain the vibration mode information of motors, and the experimental results on a 6-pole/36-slot stator PMSM match well with the simulation results. [ABSTRACT FROM AUTHOR]

This paper presents a new method by sticking a copper ring on the permanent magnet pole of the permanent magnet brush dc (PMBDC) motor to reduce the electromagnetic vibration. First, the air-gap flux density distribution and radial force density distribution are derived and the principle of the electromagnetic vibration reducing technique by the copper ring is analyzed in detail. Then, finite-element method is used to calculate the Maxwell force and the vibration spectrum of a 2-pole 24-slot PMBDC motor and a modified motor. Finally, experimental results are given to validate the proposed technique, by testing the vibration spectrum of the two prototype PMBDC motors. It is shown that the acceleration of the motor with copper ring can reduce the vibration effectively compared with the origin motor, and the reduced ratio can be up to 40%. [ABSTRACT FROM AUTHOR]

The vibration mode of electric machines is an important characteristic of vibration, which is useful for finding the vibration sources with different frequencies, but has always been neglected before. In this paper, the vibration characteristics, especially the vibration mode, of permanent magnet (PM) brush DC motors are studied. First, the air gap flux density distribution and radial force density distribution are derived in detail and compared with the results of the finite-element method. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated, which have not been analyzed and verified sufficiently before. In addition, the relationships between these two vibrations and pole width, pole number, and slot number are analyzed. The main modal shapes and their frequencies are acquired from the modal test. To confirm the analysis and theory, the multiprobe mode-included test method of vibration acceleration is proposed and emphasized to obtain the vibration mode information of motors, and the experimental results on a PM brush DC motor match well with the simulation results. [ABSTRACT FROM AUTHOR]