Machine Stator Research Articles

Investigation of a novel intensifying-flux hybrid excited permanent magnet machine for electric vehicles

PurposeTo address the issues of the insufficient output torque associated with the application of intensifying-flux permanent magnet (PM) machines in electric vehicles, this paper aims to propose an intensifying-flux hybrid excitation PM machine. It is possible to adjust the air gap magnetic field by adjusting the field current in the excitation winding, thereby increasing the torque output capability and speed range of the machine.Design/methodology/approachFirst, a novel intensifying-flux hybrid excited permanent magnet synchronous machine (IF-HEPMSM) is proposed on the basis of intensifying-flux permanent magnet synchronous machine (IF-PMSM) and an equivalent magnetic circuit model is established. Second, the tooth width and yoke thickness of the machine stator are optimized to ensure the overload capacity of the machine while effectively improving the wide flux regulation range. Furthermore, the electromagnetic characteristics of the IF-HEPMSM are investigated and compared with the IF-PMSM and conventional permanent magnet synchronous machine (PMSM) by using finite element simulations.FindingsThe id of IF-HEPMSM and IF-PMSM is greater than zero low-speed magnetizing current. And the flux-weakening current of the IF-HEPMSM is 18% and 3% smaller than of the conventional PMSM and IF-PMSM.Practical implicationsAiming at the problems of IF-PMSM applied to electric vehicles, this paper proposes an IF-HEPMSM. The air gap magnetic field is adjusted by controlling the current of the excitation winding to improve the reliability of the machine. Therefore, the IF-HEPMSM combines the advantages of high-power density and high efficiency of the PMSM and the controllable magnetic field of the electro-excitation machine, which is of great engineering value when applied in the field of electric vehicles.Originality/valueThe proposed IF-HEPMSM offers better flux regulation capability with electromagnetic characteristics analysis and maps of dq-axis current as compared to IF-PMSM and conventional PMSM. Moreover, the improvement of the torque can make up for the shortcomings of the insufficient torque output capability of the IF-PMSM.

A Hybrid Physics-Based and Data-Driven Approach for Monitoring of Inverter-Fed Machine Stator Insulation Degradations Using Switching Oscillations

A Hybrid Physics-Based and Data-Driven Approach for Monitoring of Inverter-Fed Machine Stator Insulation Degradations Using Switching Oscillations

Winding inductance predictions of a double stator machine

Winding inductance predictions of a double stator machine

Blade imbalance fault identification in doubly fed induction generator through current signature analysis using wavelet transform

Using wind turbines (WTs) equipped with doubly fed induction generators (DFIG) is a popular technology for generating renewable energy. To ensure safe operation, prompt maintenance, and better operational reliability, the induction generator used in wind energy must be monitored. In this paper, an analysis is carried out on stator currents of the DFIG machine in a wind farm to identify any blade imbalances in the wind farm. A fault characteristics extraction analysis is carried out on the machine stator currents to detect the fault in the system. Firstly, the mathematical equation of the DFIG blade unbalanced stator current is generated using the DFIG model. Secondly, Park's Transformation is used to modify the stator's 3-phase current. Further, by evaluating the feature frequency amplitude variation in the squared signal by doing a spectral analysis on the stator current vector's squared signal. Lastly, a Simulink model for the DFIG is developed. The suggested approach analyses the fault signal of the imbalanced blade fault at various wind velocities. The outcomes show that the suggested method for diagnosing impeller imbalance faults can successfully locate the fault.

Cogging Torque Reduction of Dual Stator Machine Using Hybrid Magnet Excitation

Cogging Torque Reduction of Dual Stator Machine Using Hybrid Magnet Excitation

TUNING OF PI SPEED CONTROLLER IN DIRECT TORQUE CONTROL OFDUAL STAR INDUCTION MOTOR BASED ON GENETIC ALGORITHMS AND NEURO-FUZZY SCHEMES

Thanks to the positive characteristics of the double stator machine (DSIM), its high reliability, and reduced rotor torque ripples, it has become among the most important multiphase machines included in industrial applications. This article aims to apply the two techniques of artificial intelligence represented by the adaptive neuro-fuzzy inference systems (ANFIS) and the genetic algorithm (GA) for direct torque control (DTC) of the DSIM to improve the performance of the machine. The ability to learn and the parallelism of operation characteristics made exploiting the GA to control the machine possible instead of using the proportional integral controller (PI). Fixed switching frequency obtained, given with the vector selection table and hysteresis, allowed the inclusion of the ANFIS technique in the DTC strategy. Two-level inverters are included to feed the DSIM. Several results prove that the two techniques applied, ANFIS and GA, improve the quality of the electromagnetic torque and flux and the dynamic responses of the DSIM.

Experimental study of a teeth flux sensor for detection, location and severity evaluation of induction machine stator faults

PurposeThis paper aims to investigate the efficacy of teeth flux sensors in detecting, locating and assessing the severity of short-circuit faults in the stator windings of induction machines.Design/methodology/approachThe experimental study involves inducing short-circuit winding turn variations on the induction machine’s stator and continuously measuring the RMS values across teeth flux sensors. Two crucial steps are taken for machine diagnosis: measurements under load operating conditions for fault detection and measurements under no-load conditions to determine fault location and severity.FindingsThe experimental results demonstrate that the proposed approach using teeth flux sensors is reliable and effective in detecting, locating and evaluating the severity of stator winding faults.Research limitations/implicationsWhile this study focuses on short-circuit faults, future research could explore other fault types and alternative sensor configurations to enhance the comprehensiveness of fault diagnosis.Practical implicationsThe methodology outlined in this paper holds the potential to significantly reduce maintenance time and costs for induction machines, leading to substantial savings for companies.Originality/valueThis research contributes to the field by presenting an innovative approach that uses teeth flux sensors for a comprehensive fault diagnosis in induction machines. The originality lies in the effectiveness of this approach in providing reliable fault detection, location and severity evaluation.

Comparative analysis of dual stator machines

Electromagnetic performance of three different types of double stator permanent magnet machine is analyzed and compared in this study. The analyzed machines in this study are Machine 1, Machine 2 and Machine 3. These machines are designated as: M 1, M 2 and M 3, respectively. The studies are implemented using two-dimensional and three-dimensional finite element analysis (2D-FEA and 3D-FEA) methods. The predicted performance indices are: total harmonic distortion of the voltage, torque ripple, cogging torque, winding inductances, output torque and unbalanced magnetic force (UMF). The studies show that the investigated machine types have negligible reluctance torque and thus, similar axes inductance values. Therefore, the machines’ bulk torque components are contributed mainly by the magnets while the armature excitation sources yield lesser torque components. Amongst the compared machines, M 3 type has an outstanding performance in almost all the performance metrics, compared to M 2 and M 1 types. Nevertheless, M 1 machine type has some good attributes, particularly, with respect to its high output torque per applied magnet volume, in addition to its widest operating speed range ability. Low-speed high-torque applications are most suitable for the investigated machines in practice.

Spectrum of Induction Machine Stator Currents, Affected By Clutch Wobbling and Mixed Eccentricity

Current spectrum of a four pole-pairs, 550 kW, induction machine were calculated for the cases of full symmetry, clutch wobbling, static and mixed (static + dynamic) eccentricity. The calculations involve integration of 93 electrical plus four mechanical ordinary differential equations. Electrical equations account for variable inductances affected by slotting and eccentricities. The calculations were followed by Fourier analysis of the stator currents in steady state operation. Zooms of the current spectrums, around the 50 Hz fundamental harmonic as well as of the main slot harmonic zone, of both calculated and measured currents are included.

Harmonics and inter-harmonics of voltage converter supplied induction machine stator currents

The paper contains waveforms of currents for the direct and voltage source inverter supplied induction machine, with account for harmonics and inter-harmonics. By direct supply the grid is assumed to be either purely sinusoidal or polluted by 3rd, 5th and 7th harmonics. The voltage inverter operates in a PWM mode. Special model of the machine accounts for true dependencies of stator and rotor inductances versus rotor angle, resulting from air gap magnetic flux distribution. Calculations of true derivatives of inductances, with respect to rotor angle, allowed for calculation of electromagnetic torque and, in consequence, the machine's dynamics, with allowance for speed fluctuation in steady state operation.

Innovations in Axial Flux Permanent Magnet Motor Thermal Management for High Power Density Applications

For aerospace applications, power density is a major driving force in the design of electrified powertrains. At the forefront is the challenging design of electric motors with high efficiencies, torque, and power capabilities. Due to its high performance, the Axial Flux Permanent Magnet (AFPM) Motor is expected to be one of the leading technologies to meet the demands of these industries. Finding the balance between the cooling system’s effectiveness and subsequent parasitic losses is key to utilizing these performance benefits. Single stator double rotor topologies achieve the best torque density and lower stator losses, however are more challenging to cool as the stator is in the center of the motor. Single stator single rotor and double stator machines are less challenging to cool but typically have lower power density. Rotor air cooling is discussed including the effectiveness of blades, meshes, and vents which can be optimized to prevent demagnetization. Stator cooling is critical as many machines maximize current density producing a large amount of heat. The chosen strategy depends on the machine topology and can be accomplished by several strategies, including jackets, fins, channels, immersion cooling, hollow coils, and heat pipes.

Pole Number Effects on the Output of a Double Stator Machine Having Magnets on the Inner Stator

Pole Number Effects on the Output of a Double Stator Machine Having Magnets on the Inner Stator

A model to account for magnetic permeability changes resulting from edge damage caused by laser cutting in a high performance cobalt-iron alloy

Laser cutting is the mainstay of electrical machine stator core manufacture for prototyping and for high value, small and medium batch sizes. However, it can introduce localized damage into electrical steels, with reduction in magnetic permeability and increase in core loss in regions adjacent to the edge. These phenomena have been studied in Silicon-iron alloys, but there is little published data on Cobalt-iron. This paper presents experimental measurements on magnetic edge damage effect in Cobalt-iron alloys due to laser cutting. The paper then uses magnetic measurements for an increasing number of cuts in test samples to develop a model that represents the deterioration of magnetic permeability with distance from the cut edge, including cumulative damage effects from multiple cuts. The model is suitable for incorporation into finite-element models, either as a continuous function of position or to generate individual magnetization curves for discrete layers in finite-element mesh. The paper concludes by using the model to generate a series of magnetization curves which include the damage effect and in turn uses these to predict the net magnetic behavior of a series of rectangular strips. Good agreement is obtained between these predictions and measurements of samples from the same batch of Cobalt-iron.

Precise Electrical Machine Stator Winding Modeling for Thermal Analysis of Efficient Cooling Concepts

<div>The current development of electric and hybrid electric vehicles has drawn more attention toward the development of electrical machines with high power densities. Though highly efficient, these machines heat up significantly during operation. By design, state-of-the-art water jacket cooling concepts remove the heat mainly through high internal thermal resistances of the electrical machine. The resulting maximum temperatures in the end winding region limit the achievable machine power output. In this study, alternative cooling concepts are presented, which efficiently use the existing heat conduction paths of an electric machine. For this purpose, two modeling methods for the stator windings were developed: a high-resolution approach that considers each individual wire and an abstract approach that uses zones of constant anisotropic thermal conductivity to specify the heat flow in the windings. Both models were used in conjugate heat transfer simulations of a long-term thermal test of the electrical machine integrated in the BMW i3. For both models the validation showed a very good agreement of simulated and measured temperatures. An evaluation of both methods showed the abstract approach to be more efficient than other simulation methods used in the current R&D. Its application for alternative cooling concepts revealed the necessary heat transfer coefficients at different fluid temperatures for a sole convective cooling of the end windings. However, it could be found that a homogeneous temperature distribution in the stator of the machine can only be achieved if a combination of water jacket cooling and convective end winding cooling is used.</div>

Circulating and Eddy Current Losses in Coreless Axial Flux PM Machine Stators With PCB Windings

Printed circuit board (PCB) stators in coreless axial flux permanent magnet (AFPM) machines have been proposed, designed, and studied for use in multiple industries due to their design flexibility and reduction of manufacturing costs, volume, and weight compared to conventional stators. This paper investigates mechanisms and methods of approximating open circuit losses in PCB stators within example wave and spiral winding topologies for a dual rotor, single stator configuration using 3D FEA, analytical hybrid techniques and experiments. The effect of rotor magnet shape, end winding, and active conductor geometry on eddy currents is studied, and some mitigation techniques are proposed. Through stator equivalent circuit analysis, circulating current losses caused by mechanical abnormalities and magnetic circuit asymmetry are assessed. Possible strategies and schemes to minimize circulating current losses are also described. The trade-off between stator loss components and some practical design considerations are outlined in detail. The open circuit power losses of a prototype coreless AFPM motor were experimentally tested using multiple example PCB stators and emulated rotor asymmetries, with the findings being comparable to the FEA and hybrid analytical methods results.

Estimation of Stator Vibration in DFIM Under Various Types of Rotor Excitation

Variable speed power generation using Doubly Fed Induction Machine requires an adjustable frequency supply at the rotor terminals which can be achieved using power converters. Ideally, a variable frequency sinusoidal voltage should be applied, but it is not possible without the help of power converters. For a typical 250 MW DFIM with a speed variation of -10.73% to +8.33%, excitation power of 25 MW at 3.3kV and 11600 Amps is required. With this much high rotor current at low fundamental rotor frequency (3.75 Hz) electromagnetic forces in the air gap contain harmonic force components. Also, any time harmonic of radial force density in the rotor will be induced in the stator as a distinct time harmonic, modified by the influence of space harmonics in DFIM with regular three phase integral slot winding on both stator and rotor and vice versa. So, if the frequency and order of electromagnetic force components conflicts with mode shape and natural frequencies of the machine stator strong magnification in vibration will occur or more severely develops mechanical resonance. The stator vibration of electrical machine is generated by the electromagnetic forces acting on the surface of the stator tooths. This paper analyzes stator vibration for 250 MW DFIM in multiphysics simulation with its rotor winding excited through pure sinusoidal excitation at fundamental rotor frequency of 3.75 Hz and with two-Level voltage source converter at 3.75 Hz fundamental rotor frequency. Hardware results with supported multiphysics simulation on a laboratory prototype of 2.2 kW rating DFIM.

Modeling Common-Mode Current Due to Asymmetric Aging of Machine Winding Insulation

Machine stator winding insulation degradation is one of the main results of machine aging. It is non-negligible once this degradation process becomes asymmetric between phases. The traditional way to determine the insulation state of health is a partial discharge test. However, this method requires the system offline, which causes production loss and extra administrative burden. This paper presents an idea for better characterizing the insulation machine's state of health using common-mode (CM) behavior in the machine-drive system. With the help of circuit decomposition methods and modeling tools, the CM quantities due to asymmetric aging show a unique characteristic that distinguishes itself from other differential-mode (DM) quantities in the equivalent circuit. It is shown effective to represent the asymmetric aging effect from the detection of system leakage current. This paper provides an analytical method to quantify this characteristic from mathematical approaches, and a proper approximation has been made on the CM equivalent model (CEM) such that the CM behavior is accurately characterized. The proposed method will serve the purpose of predicting machine abnormal behavior using the simple RLC circuit. Researchers can adapt this method to quantify and characterize the machine insulation state of health (SOH).

A Proposed Fault Diagnostics Technique for Induction Motor Stator Winding

Online monitoring is widely used for induction motor fault diagnostics. This article presents a fault diagnostics technique for a 3-phase induction machine. The proposed technique was developed with fuzzy logic applied to a simplified induction motor model affected by the stator winding short turns. Based on the 3-phase time-domain model, the machine winding with different fault conditions has been simulated to check the resulting speed, torque, and stator current spectrum in each case. The results indicate that the developed fault diagnostics scheme is efficient to specify the fault type of the induction machines stator.

Application of a wavelet neural network approach to detect stator winding short circuits in asynchronous machines

Introduction. Nowadays, fault diagnosis of induction machines plays an important role in industrial fields. In this paper, Artificial Neural Network (ANN) model has been proposed for automatic fault diagnosis of an induction machine. The aim of this research study is to design a neural network model that allows generating a large database. This database can cover maximum possible of the stator faults. The fault considered in this study take into account a short circuit with large variations in the machine load. Moreover, the objective is to automate the diagnosis algorithm by using ANN classifier. Method. The database used for the ANN is based on indicators which are obtained from wavelet analysis of the machine stator current of one phase. The developed neural model allows to taking in consideration imbalances which are generated by short circuits in the machine stator. The implemented mathematical model in the expert system is based on a three-phase model. The mathematical parameters considered in this model are calculated online. The characteristic vector of the ANN model is formed by decomposition of stator current signal using wavelet discrete technique. Obtained results show that this technique allows to ensure more detection with clear evaluation of turn number in short circuit. Also, the developed expert system for the taken configurations is characterized by high precision.

Loss performance of an additively manufactured axial flux machine stator with an eddy-current limiting structure

AC electrical machines have mostly been limited to 2D magnetic circuits due to the use of electrical-steel laminations, however, in recent years advances in non-traditional motor architectures such as axial flux show promise for increased torque and power densities. 3D magnetic circuits as required by axial flux motors are difficult to manufacture using laminations, and for other architectures impossible. Soft magnetic composites enable 3D flux pathways but at the expense of magnetic properties. In this study, an axial flux stator is fabricated from high-silicon electrical steel (Fe-6.5 wt%Si) using additive manufacturing with Hilbert cross-sectional geometry to limit eddy current losses and compared with electrical steel laminations of 0.127 mm and 0.35 mm. This shows comparable performance between the additively manufactured Hilbert stator and 0.35 mm laminations below 500 Hz. A torque loss of approximately 20% was observed due to 34% less magnetic material in the Hilbert stator than 0.127 mm laminations, but improved torque density for the stator by 13%. By designing for additive manufacturing, tooth area could be scaled up providing an electrical machine with 3D magnetic flux pathways with acceptable loss behaviour and good magnetic circuit properties, enabling further flexibility to electrical engineers in their pursuit of higher torque and power density.