Rotor Step Skewing Research Articles

Vibration Mitigation of Interior Permanent Magnet Synchronous Motor Using a Targeted Rotor-Step Skewing Method

Vibration Mitigation of Interior Permanent Magnet Synchronous Motor Using a Targeted Rotor-Step Skewing Method

Vibration characteristics of electric drive system considering rotor-step skewing

Electric vehicle has been gaining popularity in the worldwide market. The drive system for an electric vehicle usually consists of a permanent magnet synchronous motor (PMSM) and a two-stage gear system. The vibration characteristics of electric drive system is of great importance to the noise and durability performance. Recently, rotor-step skewing has drawn attention as a means to reduce the vibration response for the PMSM, since it can effectively reduce the torque ripple as shown in the previous studies. However, the coupling relationship between the torque ripple and the gear transmission system has not been studied thoroughly. To explore the influence of torque ripple on the motor-gear system when considering rotor-step skewing, this paper proposes a coupled electro-mechanical system model to study the vibration characteristics of electric drive system. The effect of rotor-step skewing on cogging torque and torque ripple of PMSM, dynamic transmission error (DTE) of gear transmission system, and vibration characteristics of electric drive system is studied. The simulation results show that the torque ripple has a significant effect on the DTE and the vibration responses of the electric drive system. The rotor-step skewing not only effectively suppress the torque ripple, but also optimize the DTE harmonics induced by the torque ripple.

Prediction and Diagnosis for Unsteady Electromagnetic Vibroacoustic of IPMSMs for Electric Vehicles Considering Rotor Step Skewing and Current Harmonics

Prediction and Diagnosis for Unsteady Electromagnetic Vibroacoustic of IPMSMs for Electric Vehicles Considering Rotor Step Skewing and Current Harmonics

Analysis and Reduction of Slot Frequency Vibration of PMSMs With the Force-Harmonic Coupling Model Considering Phase Angle Characteristic

This paper establishes the force-harmonic coupling model considering phase angle characteristic for the analysis and reduction of the slot frequency force harmonic of PMSMs. Compared with the traditional analytical model, the significant influence of the force phase angle on the coupling relationship among force components is considered in the model. Firstly, the force-harmonic coupling model considering phase angle characteristic is deduced based on the Maxwell stress tensor, and considering the influence of the force phase angle on the coupling relationship among force components contributing to the slot frequency force harmonic, these force components are divided in to a series of combinations of positive and negative components. Combined the finite element model, the coupling model is verified. Based on the coupling relationship, the principle of the rotor-step skewing is further explained as the mutual compensation effect of the positive and negative force components, and the slot frequency vibration is effectively offset through choosing the appropriate segment number and skewed angle. Finally, the optimized prototype is tested, and the measured results are in good agreement with the FEM results.

Modified Halbach design for torque profile improvement in a permanent magnet synchronous motor dedicated to an electric city bus

In this work, a permanent magnet synchronous motor is designed for an electric city bus. The unit winding factor is considered for torque capability enhancement and completely open slots are adopted for low-cost rectangular wire winding implementation. Accordingly, extremely large pulsating torques that are predictable should be mitigated through the rotor design possibilities. In this regard, a modified Halbach pole configuration, named axially segmented Halbach, that is capable of producing considerably smooth torque as well as retaining the large mean torque is proposed. First, an optimised conventional Halbach array is calculated as the initial design. Then, following a detailed introduction to the new design concept, the modified Halbach pole parameters are obtained through the proposed 2D model-based optimisation algorithm. A rotor step skewing scheme is also evaluated to make the final comparisons, which are carried out via 3D FE models. The results demonstrate the admirable performance of the proposed Halbach configuration as an effective solution for torque profile improvement.

Voltage Pulsation Induced in DC Field Winding of Different Hybrid Excitation Switched Flux Machines

Voltage pulsation induced in dc field winding of hybrid excitation machines can cause current ripple in dc field winding and may even lead to unstable field excitation. Moreover, it may also impair the torque performance and complicate the drive, especially at high speed. In this article, the voltage pulsation induced in the dc field winding of different hybrid excitation switched flux machines (HESFMs) under both open-circuit and on-load conditions are comparatively studied. It shows that the HESFM topologies significantly affect the dc field winding induced voltage pulsations. To further suppress the induced voltage in field winding, three suppression methods, i.e., rotor step skewing, rotor pole notching, and rotor pole shaping are proposed and compared. It reveals that rotor step skewing has the best suppression performance. Finally, a prototype HESFM with both nonskewed and 2-step skewed rotors are fabricated and tested to confirm the finite element analyses.

Analysis and Reduction of DC Winding Induced Voltage Pulsation in Five-Phase Non-Overlapped Stator Wound Field Flux Switching Machine

DC winding induced voltage pulsation in Wound field flux switching (WFFS) machine is the main cause of the current ripples in DC winding. It may also deteriorates the DC power source and enhances the challenging issues to the control performances of the machine. Hence, reduction of this pulsation is very considerable parameter to analyze in WFFS machine's analysis. In this paper, DC winding induced voltage for five phase non overlapping stator WFFS machine is analyzed and reduced through various techniques. Three techniques i.e. rotor pole arc optimization, chamfering and rotor step skewing are analyzed and optimized to reduce the DC winding induced voltage. For optimization, krigging method based on genetic algorithm (GA) is performed due to compatibility with non-linear data and then results are verified by finite element (FE) analysis. By applying the chamfering and rotor pole arc optimization, 49.58% and 28.45% reduction in the peak to peak value of DC winding induced voltage pulsation is achieved and electromagnetic torque is maintained at 97.82% and 100% respectively while by applying the rotor skewing, 33.29% reduction in DC winding induced voltage pulsation is achieved and the torque is maintained at 98.37% for the five phase 10S-11P WFFS machine.

Investigation of DC Winding Induced Voltage in Hybrid-Excited Switched-Flux Permanent Magnet Machine

The dc winding induced voltage in hybrid-excited machines can lead to dc winding current ripple and hence, fluctuating field excitation. It may also challenge the dc power source and increase the difficulty of machine control, especially at high speed. The dc winding induced voltage in a hybrid-excited switched-flux permanent magnet (HESFPM) machine is investigated in this article. The phenomenon and mechanism of the dc winding induced voltages under both open-circuit and on-load conditions are analyzed, with particular emphasis on on-load operation which consists of open-circuit induced voltage and armature current induced voltage, respectively. Two techniques, i.e., rotor step skewing and unequal rotor teeth, are proposed and comparatively investigated by the finite-element (FE) method to suppress the dc winding induced voltage under on-load condition. FE results show that the peak-to-peak value of on-load dc winding induced voltage can be effectively suppressed by 96.15% or 89.05% by rotor step skewing or unequal rotor teeth, respectively, while the average on-load electromagnetic torque can be maintained at 89.4% or 87.8%. A prototype HESFPM machine is built and tested to verify the FE results.

Study on the effects of rotor‐step skewing on the vibration and noise of a PMSM for electric vehicles

Radial force F r is the main cause of electromagnetic vibration and noise in motors. In this study, the vibration and noise characteristics of a permanent magnet synchronous motor (PMSM) with consideration of rotor-step skewing are investigated. Firstly, the analytical model of F r considering rotor-step skewing is deduced based on the Maxwell stress tensor method. The influence of rotor-step skewing on F r of the PMSM is then analysed and summarised. Taking a 65 kW PMSM commonly used in electric vehicles as an example, combined with electromagnetic finite element analysis, F r is then evaluated. Secondly, an electromagnetic vibration and noise simulation analysis is conducted based on a multi-physical field joint simulation platform, from which the influence of rotor-step skewing on the vibration and noise is then summarised. Finally, a noise experiment is then carried out. The results obtained from the multi-physical analysis and the tests conducted are presented to validate the precision of the simulation models, and the accuracy of the analytical model of F r .

Analysis and evaluation of electromagnetic vibration and noise in permanent magnet synchronous motor with rotor step skewing

In this paper, a multi-physics simulation model capable of electromagnetic noise prediction is established, and the effectiveness of the established simulation model in predicting and evaluating electromagnetic noise is verified. Based on the verified motor model, a rotor step skewing model which can affect electromagnetic noise is proposed, and the influence of the skewing angle on electromagnetic noise is investigated in detail. By studying the spectral characteristics of the low-order radial magnetic force which has a great influence on electromagnetic noise, the distribution of electromagnetic noise characteristics of the permanent magnet synchronous motor (PMSM) with or without the rotor step skewing is compared and analyzed. Therefore, it lays a technological foundation for predicting and suppressing the electromagnetic vibration noise of electric vehicle (EV) driving motor in the electromagnetic design.

Modified Rotor Material for Minimization of Torque Ripple for Interior Permanent Magnet BLDC motor

This paper presents a method to minimize the torque ripple of an interior permanent magnet BLDC motor by adopting modified rotor. The analysis method for torque ripple are established using two- dimensional (2 –D) finite-element method (FEM). A cost-effective modified rotor technique is proposed to minimize the torque ripple of the BLDC motor. This proposed method for low torque ripple has an advantage over rotor step skewing method from a manufacturing point of view. The proposed model is compared with the modified rotor method and non-modified rotor method by calculating torque characteristics to determine the effective method to minimize torque ripple distortion. Finally, the finite-element method results have revealed that the rotor angle vs torque. It shows the lower torque ripple but show a maximization of the average torque.

Torque characteristics in a large permanent magnet synchronous generator with stator radial ventilating air ducts

In this study, we investigated the torque characteristics of large low-speed direct-drive permanent magnet synchronous generators with stator radial ventilating air ducts for offshore wind power applications. Magnet shape optimization was used first to improve the torque characteristics using two-dimensional finite element analysis (FEA) in a permanent magnet synchronous generator with a common stator. The rotor step skewing technique was then employed to suppress the impacts of mechanical tolerances and defects, which further improved the torque quality of the machine. Comprehensive three-dimensional FEA was used to evaluate accurately the overall effects of stator radial ventilating air ducts and rotor step skewing on torque features. The influences of the radial ventilating ducts in the stator on torque characteristics, such as torque pulsation and average torque in the machine with and without rotor step skewing techniques, were comprehensively investigated using three-dimensional FEA. The results showed that stator radial ventilating air ducts could not only reduce the average torque but also increase the torque ripple in the machine. Furthermore, the torque ripple of the machine under certain load conditions may even be increased by rotor step skewing despite a reduction in cogging torque.

Torque Ripple Reduction of a Novel Modular Arc-Linear Flux-Switching Permanent-Magnet Motor with Rotor Step Skewing

A novel modular arc-linear flux-switching permanent-magnet motor (MAL-FSPM) used for scanning system instead of reduction gearboxes and kinematic mechanisms is proposed and researched in this paper by the finite element method (FEM). The MAL-FSPM combines characteristics of flux-switching permanent-magnet motor and linear motor and can realize the direct driving and limited angular movement. Structure and operation principle of the MAL-FSPM are analyzed. Cogging torque model of the MAL-FSPM is established. The characteristics of cogging torque and torque ripple are investigated for: (1) distance (dend) between left end of rotor and left end of stator is more than two rotor tooth pitch (τp); and (2) dend is less than two rotor tooth pitch. Cogging torque is an important component of torque ripple and the period ratio of the cogging torque to the back electromotive force (EMF) equals one for the MAL-FSPM before optimization. In order to reduce the torque ripple as much as possible and affect the back EMF as little as possible, influence of period ratio of cogging torque to back EMF on rotor step skewing is investigated. Rotor tooth width and stator slot open width are optimized to increase the period ratio of cogging torque to back EMF. After the optimization, torque ripple is decreased by 79.8% for dend > τp and torque ripple is decreased by 49.7% for dend < τp. Finally, 3D FEM model is established to verify the 2D results.

Comparison of Cogging Torque Reduction in Permanent Magnet Brushless Machines by Conventional and Herringbone Skewing Techniques

Cogging torque, as one of the main parasitic demerits of permanent magnet brushless machines, is of particular importance and primary concern during the machine design stage in many high-performance applications. Hence, numerous design techniques have been proposed and employed to effectively alleviate the cogging torque in permanent magnet brushless machines. The effects of rotor step skewing techniques including both conventional and herringbone styles on the cogging torque of permanent magnet brushless machine are comprehensively investigated and compared by synthesized 2-D and 3-D finite-element analysis in this paper. The results have revealed that both the conventional and herringbone rotor step skewing techniques can reduce the cogging torque significantly, but the latter is less effective than the former especially with small skewing step numbers. Moreover, the machine with herringbone rotor step skewing technique has rather peculiar and asymmetric cogging torque profiles, while the machine with conventional rotor step skewing technique exhibits normal and symmetric ones. The validity of the obtained results and findings is underpinned by the experiments on the prototype machine.

Torque Analysis of Permanent-Magnet Flux Switching Machines With Rotor Step Skewing

This paper investigates the torque characteristics of permanent-magnet flux switching (PMFS) machines with rotor step skewing. The cogging torque, torque ripple, and average output torque of a PMFS machine with a common stator and different rotor pole widths and rotor pole numbers are first established using two-dimensional (2-D) finite element analysis (FEA). A cost-effective rotor step skewing technique is then proposed to reduce the cogging torque and torque ripple of the machine with two different rotors. The results have revealed that the least step number and angle for optimal torque ripple mitigation of the PMFS machine are determined by the harmonic contents of the torque pulsation and the rotor pole number. The influences of load conditions on the machine torque characteristics are carried out by varying current excitations. The corresponding three-dimensional (3-D) FEA models are constructed and experimental prototypes are built for validations.