Rotor Slot Research Articles

An Analysis of the Design of a Low Rotational Speed Permanent Magnet Generator That Uses Radial Flux

A radial flux permanent magnet generator can be effectively used in generating wind power at low speeds. This generator uses a combination of permanent magnets and a stator to produce electricity from the wind’s kinetic energy. The permanent magnets are arranged in a radial pattern, which reduces the amount of heat lost and therefore increases the generator’s efficiency. This design allows for a low rotational speed, which makes it suitable for applications such as wind turbines. The air gap between the rotor and the stator affects the output voltage and power due to the decrease in magnetic flux. This study aims to increase the generator’s output voltage and output power by fitting stator teeth widths to the stator teeth. The stator teeth width fitting design method adjusts the air gap between the stator and the rotor to a uniform size. This helps to reduce the pulsating torque and ensure that the output voltage and power are maximized. The three variables are the stator slot width, the rotor slot width, and the air gap width. By adjusting these variables, the stator teeth width fitting design method can adjust the air gap between the stator and rotor.

Vibration and Noise Optimization of Rotor Structure of Permanent Magnet Synchronous Motor for Vehicles

In order to improve the vibration and noise level of permanent magnet synchronous motor, based on the ANSYS workbench multi-physical field coupling platform, the motor structure is designed and simulated to optimize the vibration and noise of the motor. The spatial and temporal order of the vibration noise caused by the first order tooth harmonic is analysed, and the vibration noise caused by the first order tooth harmonic is reduced by slotting the rotor. By analysing the influence of rotor slots with different positions and different size parameters on the air gap magnetic flux density of the motor, the most suitable optimization method is found, and the optimization level of air gap magnetic flux density of rotor slots with different shapes under the same position and slot area is analysed and compared, so as to select the most suitable rotor slot shape. The simulation analysis shows that the air gap magnetic density and torque ripple of the optimized motor have been significantly improved, and the electromagnetic noise of 48-time order caused by 12 times the electromagnetic frequency of the motor in the 0 space order has been significantly reduced, which proves the reliability of the optimized scheme.

Model Order Reduction of Cage Induction Motor With Skewed Rotor Slots Using Multiport Cauer Ladder Network Method

A method for efficiently deriving a reduced-order model of a cage induction motor (IM) with skewed rotor slots is proposed based on the multiport Cauer ladder network (CLN) method. This paper presents several formulations of the multiport CLN method for the skewed rotor, in which the continuity of the bar currents and the space harmonics included in the air-gap flux density waveform are treated differently. The effectiveness of the developed methods was verified from the viewpoints of computational accuracy and cost through application to a practical cage IM with skewed rotor slots.

Efficiency Improvement of Induction Motors Based on Rotor Slot and Tooth Structures

Due to simple structure, easy maintenance and low cost, induction motors (IMs) are widely applied in various industries, accounting for 60-80% alternating current (AC) motors used in industry. However, the efficiency of IMs is very low, and even small improvement can result in significant energy saving. For instance, 1% efficiency increase saves billions of kilowatt hours. Therefore, this paper aimed to improve the efficiency of IMs, thus reducing energy consumption and greenhouse gas emissions. For an IM with 7.5kW rated power and IE3 energy efficiency, the efficiency is improved by making various changes. Sequential quadratic algorithm and fmincon function are proposed to change the rotor slot and teeth structures, realizing nearly 91% motor efficiency, which is a significant improvement over the original efficiency. It is worth noting that improving the efficiency of IMs saves a lot of energy, especially in cases where IMs account for a large proportion of AC motors.

Derived Functions for MATLAB Non-Linear Solvers: An optimal rotor slot and bar design stopgap

The most striking difference between the Squirrel cage induction motor (SCIM) and other electric motors lies invariably in the rotor. The major running performance characteristics, together with the entire acceleration performance range, are all influenced, in varying degrees, by the rotor slot and bar design. Therefore, proper dimensioning of the slots and bars is therefore critical to attaining a high performing machine. The preliminary stage of the SCIM design, if well done, facilitates the refinement and optimization stages; serving as a good take-off point for ultimately realizing that final state of the art design. This study therefore attempts to derive relevant design functions that could be fed into the algorithms of various non-linear solvers, one of which is the Genetic Algorithm (GA), to output the rotor slot initial main dimensions for the SCIM; from where proper design refinement/optimization could cheaply evolve. The SCIM design obtained from implementing the derived equations, when compared with the appropriate reference datasheets, showed only minor deviations from the expected performance indices – an outcome deemed satisfactory for a preliminary design attempt. The so obtained initial dimensions may in practice be subjected to the appropriate refinement, depending on the target performance requirement of the motor to be designed.

유도전동기의 슬롯 조합에 따른 진동/소음 특성 분석

The objective of this study is to examine the vibration and noise characteristics of a four-pole induction motor regarding the number of rotor slots. There are thirty six stator slots in the reference model, and its results are theoretically verified in case of a twenty-four-slot stator. Radial force density is obtained from two magnetic flux densities in the radial and tangential direction, and vibration performance is comparatively evaluated in terms of a rotor slot number by dividing radial force density into its temporal and spatial components through Fast Fourier Transform (FFT). Noise as the definition of sound pressure level is estimated in the units of decibels, and the noise of each motor is correlated with its vibration acceleration regarding temporal and/or spatial harmonic orders. In conclusion, the combination of stator and rotor slot numbers is critical since the 2nd orders lead to the deterioration of vibration and/or noise. As a result, the existence of the 2nd orders has to be carefully checked in advance by using several equations before the determination of physical dimensions in an induction motor in detail. In this paper, those equations have been given, and the comparison of vibration and noise in terms of a slot combination has been detailed in the step-by-step manner.

Investigation of the Influence of Skewed Slots and Degmagnetization Effects to Line Start Permanent Magnet Assistance Synchronous Reluctance Motors

A permanent magnet assistance synchronous reluctance motor can start directly with a net voltage or a power converter via a torque control method. However, this motor has usually a higher irreversible demagnetization level in comparison with interior permanent magnet motors, due to the fewer permanent magnets in rotor slots. In order to cope with this disadvantage, different arrangements of permanent magnets in the rotor of the line-start permanent magnet assistance synchronous reluctance motor are proposed in this paper. The V magnet shape taking skewed slots and demagnetization effect into account with the short circuit current are investigated by the finite element approach. The efficiency, torque, and output power of the proposed model have been also improved. Finally, the rotor with 3V layered magnets is prototyped to verify the efficiency of the proposed motor.

Development of a Comprehensive Analytical Model of Induction Motor Under Stator Interturn Faults Incorporating Rotor Slot Harmonics

The objective of this article isto developa comprehensive mathematical model of a three-phase induction motor to facilitate stator interturn (SIT) fault related study. A detailed analytical model that includes accurate inductance modeling considering rotor slot harmonics (RSH) under healthy as well as SIT faults is described. The proposed model is developed analytically in a step-by-step manner incorporating the features of RSH. A detailed but simplified analysis considering both magnetomotive force harmonics and air-gap flux harmonics has been presented. An asymmetric model is proposed, including SIT faults, in a single phase of the induction motor in the next stage of the modeling. The effect of saturation has also been considered in the model. The proposed model is validated by comparing the simulation results in transient, steady state, and frequency domain with the experimental results. Comparison shows a high degree of correlation with the results of the actual motor. The contributions of this work are justified by comparing the proposed model with the existing models. This article also shows that a frequency signature related to RSH present in the line current is capable of characterizing the SIT faults.

Prediction of Rotor Slot Size Variation Through Vibration Signal of Three Phase Induction Motor Using Machine Learning

Prediction of Rotor Slot Size Variation Through Vibration Signal of Three Phase Induction Motor Using Machine Learning

Design Optimization of a Synchronous Homopolar Motor with Ferrite Magnets for Subway Train

Brushless synchronous homopolar machines (SHM) have long been used as highly reliable motors and generators with an excitation winding on the stator. However, a significant disadvantage that limits their use in traction applications is the reduced specific torque due to the incomplete use of the rotor surface. One possible way to improve the torque density of SHMs is to add inexpensive ferrite magnets in the rotor slots. This paper presents the results of optimizing the performances of an SHM with ferrite magnets for a subway train, considering the timing diagram of train movement. A comparison of its characteristics with an SHM without permanent magnets is also presented. When using the SHM with ferrite magnets, a significant reduction in the dimensions and weight of the motor, as well as power loss, is shown.

Prediction of rotor slot width in induction motor using Dyadic wavelet transform and softmax regression

Abstract Predictive maintenance is required for Induction Motor (IM) to avoid sudden breakdown. In this paper, multimodal sensor data are used for prediction of the rotor slot width variation during runtime of IM. Moreover sensor data are visualized through visual image obtained using Scale Invariant Feature Transform (SIFT) and matching dictionary for various faults in motor such as overload, high speed, Broken Rotor bar (BRB), and unbalance magnetic pull. The multimodal sensor signals data acquired from different parts of three phase induction motor are analysed using various transforms such as Over Complete Rational Dilation Wavelet Transform (ORaDWT), Tuneable Q Wavelet Transform (TQWT), Polynomial Chirplet Transform (PCT) and Dyadic Wavelet Transform (Dyadic WT) for various fault conditions and rotor slot width mentioned during runtime condition of motor. The rotor slot width is predicted using Multiple Linear Regression (MLR), Polynomial Regression (PR), Logistic Regression (LR) and Soft-max Regression (SR) methods through the mean value and energy band of the acquired sensor signal. The Dyadic WT and SR perform better for rotor width prediction. The proposed method such as Dyadic WT and SR provides the prediction accuracy of about 95.2%. From experimental results the rotor slot width expansion more than 2% needs immediate attention to avoid breakdown of motor.

Optimal Stator and Rotor Slots Design of Induction Motors for Electric Vehicles Using Opposition-Based Jellyfish Search Optimization

This study presents a hybrid optimization technique to optimize stator and rotor slots of induction motor (IM) design for electric vehicle (EV) applications. The existing meta-heuristic optimization techniques for the IM design, such as genetic algorithm (GA) and particle swarm optimization (PSO), suffer premature convergence, exploration and exploitation imbalance, and computational burden. Therefore, this study proposes a new hybrid optimization technique called opposition-based jellyfish search optimization (OBJSO). This technique adopts opposition-based learning (OBL) into a jellyfish search optimization (JSO). Apart from that, a multi-objective formulation is derived to maximize the main performance indicators of EVs, including efficiency, breakdown torque, and power factor. The proposed OBJSO is used to solve the optimal design of stator and rotor slots based on the formulated multi-objective. The performance is compared with conventional optimization techniques, such as GA, PSO, and JSO. OBJSO outperforms three other optimization techniques in terms of average fitness by 2.2% (GA), 1.3% (PSO), and 0.17% (JSO). Furthermore, the convergence rate of OBJSO is improved tremendously, where up to 13.6% reduction in average can be achieved compared with JSO. In conclusion, the proposed technique can be used to help engineers in the automotive industry design a high-performance IM for EVs as an alternative to the existing motor.

Modeling of Fault-tolerant Flux-switching Permanent-magnet Machines for Predicting Magnetic and Armature Reaction Fields

The paper develops accurate analytical subdomain models for predicting the magnetic and armature reaction fields in fault-tolerant flux-switching permanent-magnet machines. The entire region is divided into five subdomains, followed by rotor slots, air-gap, stator slots, PM, and external air-gap imported to account for flux leakage. The coil turns and the remanence of magnets are adjusted by keeping the magnetic and electrical loading on the motor constant. The distance between the centers of two adjacent stator slots varies due to the introduction of fault-tolerant teeth. According to the variable separation method, the general solution expression of each region can be determined by solving the partial differential systems of equations. The magnetic field distributions of subdomains are obtained by applying the continuity conditions between adjacent regions. Some analytical field expressions are represented as new forms under armature reaction field condition compared to those under no-load condition. Based on the developed analytical models, the flux density distribution and the electromagnetic performance can be calculated under no-load or armature reaction field condition separately. The finite element analysis is carried out to verify the validity of the proposed analytical model.

High Speed Permanent Magnet Assisted Synchronous Reluctance Machines – Part II: Performance Boundaries

The insertion of permanent magnets (PMs) within the rotor slots of Synchronous Reluctance Machines (SyRM) is the most common design strategy used to increase significantly their performance. In this paper it is shown how a permanent magnet assisted synchronous reluctance machine (PMaSyRM) can be optimized to satisfy all the electromagnetic and structural constraints arising as the maximum operating speed increases. This is done considering a variety PMs material. This work, the second of two companion papers, briefly recalls the novel systematic design approach proposed in Part I, and then describes the characteristics of the optimal machines achieved considering a maximum speed ranging from 1 to 140 krpm with and without the assistance of ferrite and neodymium based PMs. The reasons behind the performance deterioration as the speed increases are all investigated along with the geometrical variations of the optimal designs. The selection of the design solution to be manufactured is justified as well as the final structural and electromagnetic refinement stages leading to the prototype. All the reported considerations are experimentally validated testing an 8.5 kW at 80 krpm PMaSyRM, comparing the measured and expected performance in terms of torque and internal power factor.

Investigation of the temporal and spatial flow features within the high‐shear mixer by modal decomposition techniques

AbstractAn insightful comprehension of hydrodynamics in the high‐shear mixer (HSM) is crucial for its design and optimization. Therefore, the energetical and dynamical dominant features of inline HSM's velocity fields are extracted by proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), of which the sampling spaces are generated through Large‐Eddy Simulation. POD results reveal that the significant flow structures located in the shear gap and the adjacent regions of rotor/stator slot inlets comprise various energy levels. The strip‐shaped structures at the rotor/stator leading edges, wake and large‐scale vortices within the outflow region, and circulation inside the rotor slot are also visualized. DMD results emphasize the importance of flow patterns oscillating lower than rotor teeth passage frequency and reveal that the coherent structures shift and expand as their frequencies decrease. The POD and DMD analyses provide an insightful perspective of the spatial and temporal behaviors of the flow in HSM.

Sensorless Control Analysis of Electric Motor Drives Based on High-Frequency Signal Injection and Its Simulation Verification

The subject of this research is the sensorless control method verification of an asynchronous motor by a simulation in the area of low speed (up to 5 Hz) via the high-frequency analog signal injection method. The implementation of the continuous signal injection method is simpler when compared with the discrete signal injection; however, the discrete signal injection method has more advantages in signal processing. The injected analog signal will be superimposed on the main stator voltage. The response to this signal will be manifested mainly based on the asymmetries of the asynchronous motor, which are given by the design of the motor. The influence of the stator inductance LS will be suppressed by a suitable elimination method since this asymmetry is undesirable for the rotor position detection. The asymmetry caused by the rotor slotting will be used to detect the rotor position. The less the rotor slots are inclined, the stronger the asymmetry. Therefore, to verify the given estimation method as realistically as possible, a mathematical model of an asynchronous motor, including asymmetries due to magnetic core saturation and asymmetries due to rotor slotting, has been designed in order to get as close as possible to the real condition. Thus, the chapter “Asymmetry Creation due to Rotor Slotting” describes the given phenomenon in more detail. Subsequently, the INFORM method the rotor position detection is implemented and defined in the chapter: “Rotor Position Estimation Based on HF Signal Injection.” Given the fact that the asymmetries caused by magnetic core saturation are undesirable, he estimation error reaches up to 10%; therefore, saturations are suppressed by a convenient method. After filtering out these asymmetries, the control accuracy is achieved with the maximum rotor position estimation error of 0.05 rad, representing 1%. The inaccuracy is directly proportional to the rotor rotation speed, and it is also caused by the computing power, the processing frequency, and the complexity of the computing algorithm. The present research paper serves essentially to verify the sensorless method based on a high-frequency signal injection and as a basis for effectiveness and efficiency compared with other control methods.

Rotor Loss and Temperature Field of Synchronous Condenser Under Single-Phase Short-Circuit Fault Affected by Different Materials of Rotor Slot Wedge

A synchronous condenser (SC) can provide the dynamic reactive power for the ultra-high-voltage direct current converter station during the system voltage drop caused by the single-phase short-circuit fault, which is one of the prevalent faults. However, the single-phase short-circuit fault can also result in the increase of the rotor loss and temperature and thus restrict the transient operating ability of the SC. A key factor that affects the rotor loss and temperature rise is the material of the rotor slot wedges. For a 300-MVar SC with the rotor slot wedges made of the aluminum, beryllium bronze, and stainless steel, the rotor loss and temperature distribution under the single-phase short-circuit are calculated by coupling the electromagnetic and temperature field models of the SC with the models of the power grid. The variations of the rotor losses along with the rotor slot wedge conductivity are revealed. The rotor regions, where the highest temperature rise appears, are obtained. According to the maximum permissible temperature of the rotor material, the transient operating ability of the SC withstanding the single-phase short-circuit fault is obtained. This article can provide the theoretic basis for improving the transient operating ability of the SC.

Influence of Rotor Slot Wedge Materials on Rotor Losses of Turbogenerator During Loss of Excitation

A short period of steady-state asynchronous operation after loss of excitation can improve the reliability of turbogenerator. The rotor damping structure of the turbogenerator can provide asynchronous torque and, thus, play an important role in improving the asynchronous operating ability. The rotor slot wedges as a part of rotor damping structure often made of aluminum, beryllium bronze, or stainless steel. The different materials of the rotor slot wedges can affect not only the asynchronous operating ability of the turbogenerator but also the rotor losses. The selection of material for the rotor slot wedges is therefore a key factor that should be carefully considered in the design of turbogenerator. In this article, the effect of the rotor slot wedges made of different materials on the asynchronous operating ability, rotor loss densities, and loss distributions of the turbogenerator after loss of excitation is investigated by time-stepping finite element model. The variations of the asynchronous operating ability and the rotor losses are revealed along with the rotor slot wedge conductivity. The rotor regions where the losses are significantly affected by the rotor slot wedge material are obtained. The results provide theoretic basis for improvement of the asynchronous operating ability and reduction of the rotor loss of turbogenerator.

A Novel Hybrid Excitation Doubly Salient Generator with Separated Windings by PM Inserted in Stator Slot for HEVs

Aiming to design a generator with high reliability, high efficiency, and especially a constant output voltage over a wide speed range for hybrid electric vehicles (HEVs), this paper proposes a novel topology of a hybrid excitation doubly salient generator with separate windings (HEDSGSW). The topology herein utilizes a hybrid excitation type of PMs and DC windings to generate parallel magnetic circuits. In addition, PMs are embedded in the magnetic bridge to insulate the excitation windings with armature windings. This design can achieve compactness, efficiency, and especially constant output capability over a wide speed range. The geometry and flux regulation principles, including magnetic flux circuits, are elaborated. After comparing three power generation modes, the most suitable mode, namely, the doubly salient generation 2 (DSG2) mode, is confirmed to ensure a stable voltage output performance. Then, considering the non-uniformity effect of the stator and rotor slots, the no-load back electromotive force (EMF) expressions are derived based on the EMF to air-gap relative permeance method. Furthermore, a 1 kW HEDSGSW FEA model, with an output voltage of 42 V and a rated speed of 6000 rpm, is built to demonstrate the effectiveness of the proposed method. Finally, the operating properties of the HEDSGSW, such as no-load characteristics and adjustment characteristics, are analyzed to further verify the rationality of its magnetic flux circuit and the flexibility of the excitation regulation capability.

Speed Estimation of Six-Phase Induction Motors, Using the Rotor Slot Harmonics.

Multiphase machines have recently been promoted as a viable alternative to traditional three-phase machines. Most experts are looking for strategies to estimate the rotation speed of such complex systems, since speed data are required for high-performance control purposes. Traditionally, electromechanical sensors were used to detect the rotor speed of electric motors. These devices are extremely accurate, but they are also delicate and costly to deploy. New speed estimating algorithms must be created for these situations. This paper looks at how to estimate rotor speed in symmetrical six-phase induction motors (IMs) using a novel strategy for rotor speed estimation based on the Short Time Fourier Transform (STFT) method. The technique is based on tracking the frequencies of the rotor slot harmonics (RSH) seen in most squirrel-cage IM stator currents, thus assuring a broad range of applications. To monitor the RSH, the STFT employs a sliding window to perform the discrete Fourier transform technique, making it more suitable for online use with noisy and nonstationary signals. Experimental tests demonstrate the effectiveness of the suggested approach.