Distributed Winding Machines Research Articles

Advanced Fault Tolerant 3×3-Phase PM Drive With Concentric Winding for EV Application

Fault tolerant machine drive is essential for EV application to ensure uninterrupted operation during fault event. Among various fault modes, inter-turn fault is the most challenging failure for the PM drive which requires special measures to suppress the excessive fault current. In this paper, a novel concentric winding (CW) is analyzed for a 3×3-phase PM drive to restrict the turn fault current. Compared with the conventional distributed winding (DW), the two sub-coils of each phase occupy the same space angle and both align with the phase axis, and the winding factor of each coil is 0.96 which is 4% lower than the DW. Owing to the two aspects, the coil flux linkages are more effectively nullified after applying winding terminal short circuit (TSC) which indicates lower fault current. The two machines’ healthy performance as well as various fault modes’ behaviors are investigated by detailed simulation and test investigation. The results prove the CW machine has the same healthy characteristics as the DW machine, and the maximum inter-turn fault current is up to 17% lower than the counterpart. In addition, the improved turn fault current suppression capability is achieved simply by re-arranging the coil layout without introducing any extra cost.

Electromagnetic Field Analysis of Distributed Winding Permanent Magnet Synchronous Motor Considering Axial Leakage Flux using Two-Dimensional Finite-Element Analysis

This paper proposes a method for the electromagnetic field analysis of permanent magnet synchronous motors (PMSMs) considering the axial leakage flux. To the axial leakage flux while employing two-dimensional (2D) finite-element analysis (FEA), the permeance of the axial leakage path is added into a slot region by increasing the permeability of elements in that region. The increased permeability is calculated based on the permeance relationship of the main magnetic and axial leakage paths, which are calculated using the equivalent magnetic circuit method. The effect of the proposed method is verified by comparing it with the 3-dimensional FEA results. The proposed coupling method uses finite element analysis and is developed from the lumped method proposed in our previous research. The developed method enables the analysis of distributed winding machines, which is not possible with the existing method.

Analysis of DC-Biased Vernier Reluctance Machines Having Distributed Windings

This article analyses the electromagnetic performance of dc-biased current vernier reluctance machines (DCB-VRMs) with distributed windings. Taking example of 12-stator slot machines, the coil connection and current configuration are illustrated. Moreover, the back electromotive force (EMF), torque capability, etc., are analyzed by finite-element analysis (FEA). In addition, the torque density of DCB-VRMs equipped with distributed and nonoverlapping windings are compared. The results show that some combinations of distributed winding machines present a higher torque capability thanks to the higher pole ratio.

ASYMMETRICAL STATOR GEOMETRY DESIGN FOR THREE-PHASE MACHINES WITH DISTRIBUTED WINDING

This work focuses in detail on the flux density distribution in three-phase distributed winding machines, showing how its asymmetries in the teeth and back iron can be evaluated, and eventually compensated for. In order to achieve uniform flux density distributions, an asymmetrical stator geometry is proposed. A new set of geometrical parameters has been defined to balance the flux densities in the stator, while maintaining the same slot geometry (i.e., current density and amount of copper) and iron volume. The comparison, between a classical geometry and the proposed asymmetrical one, is carried out with the results showing the differences on the stator flux densities and the resulting torque performance. The new concept of asymmetrical design is validated for a surface mounted permanent magnet (SPM) machine as a case study. The outcomes of this work highlight the potential benefits of the presented solution with respect to the core saturation.

A Nonlinear Model for the Rapid Prediction of the Magnetic Field in Eccentric Synchronous Reluctance Machines

This article introduces a novel numerical model for the fast characterization of concentric and eccentric synchronous reluctance motors (SynRMs) used in electric vehicles (EVs) applications. Regarding the high impact of the air gap and permeance function on the modeling accuracy, a step variation function is used to consider the flux barriers' effect on the air gap. Then, different types of eccentricity, including static, dynamic, and mixed eccentricity, are modeled. Besides, this model considers the magnetic saturation and the stator slots effect. Numerical computation for the motor inductances is applied to avoid any approximation in the permeance function. The air-gap flux density, electromagnetic torque, and radial force on the rotor are then calculated. This model can be used for the preliminary design of SynRMs to analyze the motor performance in different conditions and accelerate the design procedure. The model is simply adjustable to different configurations. For instance, a four-pole single-layer distributed winding machine with 36-slot and three-flux barriers per pole is investigated. In order to verify the proposed model, the obtained results are compared with finite-element analysis (FEA) and experimental tests. The accuracy of the proposed model for eccentricities up to 30% is 98%, and for higher degrees, it is about 95%.

Investigation of influence the slot/pole combinations on the torque performance for synchronous reluctance machine with distributed and concentrated windings

This paper explores the electromagnetic performance comparison of three different types of synchronous reluctance machines. The investigated machines including, conventional full pitch distributed winding (24 slots/4 poles), an integer slot concentrated nonoverlapping winding (12 slots/4 poles), and fractional slot concentrated nonoverlapping winding (15 slots/8 poles). A finite element analysis JMAG Designer is used to validate the performance for all machines, and have been employed for the optimisation process to improve the torque density as well as to minimise torque ripple. Meanwhile, the current density, slot filling factor and specific dimensions, viz., stator outer diameter, stack length and air gap are designed to be constant. The result shows that for a DW-SynRM, a high value of average torque is achieved, and the torque ripple is lower. The result also demonstrates that the FSCW-SynRM can reach a low torque oscillation. Meanwhile, the ISCW-SynRM exhibit a high reluctance torque, but the torque ripple is a big challenge. On the whole, the distributed winding machine has the best performance compared to concentrated winding machines.

Impact of Rotor End Effects on FEM-Based Flux Mapping of Synchronous Reluctance Motors

The paper deals with the accurate flux map modeling of synchronous reluctance motors, using finite element analyses. Non-negligible discrepancies were initially observed by comparing two-dimensional (2-D) finite element method (FEM) simulation results with measured flux maps of real machines. Conversely, the three-dimensional (3-D) FEM-based flux mapping offers more accurate estimation of the aforementioned flux linkage characteristics and gives evidence of the 3-D end effects being also a function of the relative position between the magneto-motive force waveforms of the rotor and the stator. The paper investigates such 3-D end effects for different rotor geometries and winding structures, utilizing 2-D and 3-D FEM analysis in comparison to experimental data. The paper confirms that the 3-D effects are non-negligible both in concentrated and distributed winding machines. A simple mathematical approach is proposed for the concentrated winding machine, capable of off-line correction of the 2-D FEM flux maps. The proposed closed-form equation is validated through 3-D FEM and experiments.

On the Accuracy of Fault Detection and Separation in Permanent Magnet Synchronous Machines Using MCSA/MVSA and LDA

In this paper, the motor current/voltage signature analysis and linear discriminant analysis (LDA) are evaluated with respect to the accuracy to detect the status of permanent magnet synchronous machines (PMSMs) whether it is healthy or faulted, determine the type of that fault, and estimate the severity in the case of static eccentricity or turn-to-turn short-circuit fault. Three types of faults are discussed: static eccentricity, turn-to-turn short circuit, and partial demagnetization fault. Two-dimensional finite element analysis (FEA) is used to model and simulate the machine under healthy and faulted conditions. Fast Fourier transform is applied to the phase voltage or current signals to obtain the frequency spectrum. A combination of the amplitude of the harmonics of the stator voltage or current signals are used as detailed features for the classifier for fault detection. LDA is chosen as a classification method for both detecting the fault and estimating its severity. Two different winding types of PMSMs are tested: a concentrated and a distributed winding machine. To validate the simulation results, experiments at different operational points are carried out and the results are compared with the sFEA.

Analytical Determination of Slot Leakage Field and Inductances of Electric Machines With Double-Layer Windings and Semiclosed Slots

Slot leakage field and inductance computation are, in general, nontrivial tasks in the analysis of electric machines equipped with semiclosed slots, even under the hypothesis of neglecting magnetic saturation. This paper proposes an analytical method to evaluate the slot leakage field and inductances in dual-layer distributed winding machines, extending the results of a previous work where the single-layer winding design was addressed. A direct solution to Poisson's differential equation in the slot domain is found by suitably defining boundary conditions in the slot opening area. Boundary conditions are defined exploiting the analytical form taken by the magnetic field in the neighborhood of ferromagnetic corner-shaped regions. The presented approach is successfully validated against finite element simulations.

Analysis and Experimental Study of Permanent Magnet Machines With In-Situ Magnetization

This paper evaluates the performance of surface-mounted permanent-magnet (PM) machines with anisotropic rare-earth magnets magnetized using its own stator windings. The magnets in this process (often called in-situ magnetization) are magnetized after complete assembly. For manufacture of PM machines using this process, part of the magnet may suffer from weaker magnetization due to the magnetizing flux pattern, in particular on the two sides of the anisotropic magnets. The machine performance can thus be affected and needs to be evaluated. The current required to sufficiently magnetize the machine should be carefully studied. In this paper, both finite element analysis and experiments on prototype PM machines manufactured with in-situ magnetization are used. The concentrated and distributed winding machines are both considered. The results show that distributed winding machines can magnetize the rotors more easily than concentrated winding ones. Also, it is found that a magnetizing field of 2.5 times coercivity allows the machine back EMF magnitude to achieve the levels of pre-magnetized cases.

Winding Inductances of an Interior Permanent Magnet (IPM) Machine With Fractional Slot Concentrated Winding

This paper investigates inductance characteristics of a novel 14 pole/18 slot, fractional-slot concentrated-winding (FSCW) IPM machine. The variations of the self and mutual inductances were calculated analytically and also obtained from the finite element model. These results were compared with experimentally measured values of the self and mutual inductances of the prototype machine. Study of the inductance characteristics reveals that both self and mutual inductances vary with rotor positions nonsinusoidally. Presence of harmonics in the magnetomotive force (MMF) is responsible for this nonsinusoidal variation of inductances. The conventional distributed winding machine does not have these harmonics. This paper analyses the contribution of these harmonics in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ld</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Lq</i> parameters in a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -model of the prototype FSCW machine constructed. The self and mutual inductances were represented by a Fourier series in the inductance matrix of the machine for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -transformation. It was seen that the difference between <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis inductance is mainly contributed by the harmonic terms of the mutual inductance.

Bifurcation Analysis of Five-Phase Induction Motor Drives With Third Harmonic Injection

The interest in variable-speed multiphase induction- motor drives has substantially increased in recent years and novel proposals show good prospects for industrial implementation in high-power applications. The additional degrees of freedom existing in multiphase machines have allowed for new applications with high torque density by current harmonic injection in concentrated winding machines. This paper addresses, for the first time, the bifurcation analysis of a five-phase induction-motor drive when a third harmonic is injected for torque-enhancement purposes. The main focus of this paper is to present a mathematically based study of the nonlinear dynamics of the proposed drive with torque enhancement. The overall bifurcation analysis for both concentrated and distributed winding machines confirms that the harmonic injection provides not only torque enhancement but also more robust controllers. This further advantage offers improved performance of multiphase drives compared to their three-phase counterparts.