Single-layer Concentrated Windings Research Articles

Analysis and Suppression of Phase Unbalance Induced Force Ripples in Permanent Magnet Linear Motors

Low force ripples from permanent magnet linear motors (PMLMs) are typically essential requirements in a wide range of demanding control applications with high motion quality. Apart from the sources present in rotary PM machines, phase unbalance due to the end effect is another major contributor of the thrust force ripples in the PMLMs. In this paper, the phase unbalance and induced force ripples are investigated in the case of a planar PMLM typically equipped with single-layer concentrated windings and quasi-Halbach magnets. It demonstrates that although the PMLM is quite carefully deigned to minimize the end effect, the phase unbalance still exists, including both the amplitude and phase position unbalances. And the phase unbalances give rise to even order force ripple harmonics, in which the 2^nd-order force ripple is particularly significant. In order to compensate the end effect and the unbalance between the three phases, a novel PMLM topology is presented, in which the width of the two end teeth (instead of the edge teeth) is adjusted to reduce the force ripple. And the impact of the end teeth width on the ripple force magnitude is further revealed. It is shown that by proper design of the end teeth width, the 2^nd-order force ripple of the PMLM can be minimized to quite a low extent. In comparison with the original design, the 2^nd-order force ripple factor of the novel topology has been suppressed from 0.4% to less than 0.03% in the case study. Such a technique has provided a new way of force ripple minimization, and is applicable to other types of linear motors or actuators with appropriate changes.

Switched Reluctance Motors and Drive Systems for Electric Vehicle Powertrains: State of the Art Analysis and Future Trends

This paper presents a detailed literature review on switched reluctance motor (SRM) and drive systems in electric vehicle (EV) powertrains. SRMs have received increasing attention for EV applications owing to their reliable structure, fault tolerance ability and magnet free design. The main drawbacks of the SRM are torque ripple, low power density, low power factor and small extended speed range. Recent research shows that multi-stack conventional switched reluctance motors (MSCSRM) and multi-stack switched reluctance motors with a segmental rotor (MSSRM-SR) are promising alternative solutions to reduce torque ripples, increase torque density and increase power factor. Different winding configurations such as single-layer concentrated winding (SLC), single layer mutually coupled winding (SLMC), double layer concentrated winding (DLC), double layer mutually coupled winding (DLMC) and fully-pitched winding (FP) are introduced in the literature in recent years to increase average torque and to decrease torque ripples. This research analyzes winding methods and structure of the SRMs, including conventional and segmental rotors. They have been compared and assessed in detail evaluation of torque ripple reduction, torque/power density increase, noise/vibration characteristics and mechanical structure. In addition, various drive systems are fully addressed for the SRMs, including conventional drives, soft-switching drives, drives with standard inverters and drives with an integrated battery charger. In this paper, the SRM control methods are also reviewed and classified. These control methods include strategies of torque ripple reduction, fault-diagnosis, fault-tolerance techniques and sensorless control. The key contributions of this paper provide a useful basis for detailed analysis of modeling and electromechanical design, drive systems, and control techniques of the SRMs for EV applications.

Power Converter Topologies and Control Strategies for DC-Biased Vernier Reluctance Machines

This paper investigates the two latest proposed drive system topologies for dc-biased vernier reluctance machines (VRMs), aims to find out the preferable drive system configuration, and explains the performance discrepancy between the two configurations. Different from the regular ac machines, the armature winding current waveforms of dc-biased VRMs are sinusoidal with dc bias. To provide the dc flow path, the two drive system topologies are associated with the machine, namely, an open winding converter with single-layer concentrated winding and a dual three-phase converter with double-layer concentrated winding. The two configurations are investigated and compared in terms of machine operation principle, power converter configuration, voltage utilization, system cost, and system efficiency. The theoretical analyses and experimental results validate that the two drive systems have their respective advantages.

Consequent Pole Permanent Magnet Vernier Machine With Asymmetric Air-Gap Field Distribution

In recent years, permanent magnet vernier (PMV) machines have been attracting more and more attention due to the inherently exhibited advantages such as high torque density and simple mechanical structure. In this paper, a consequent pole (CP) PMV machine with single-layer concentrated winding is proposed. The novelty is that the asymmetric air-gap field distribution is introduced to improve its working harmonics and to reduce the PM consumption. By employing a CP structure, the flux density amplitude can be enhanced. Moreover, due to uneven distribution of modulator poles on the armature teeth and fault tolerant teeth, the number of periods of modulator poles is only half of that of the stator teeth. Then, significant improvement in flux density working harmonics can be achieved. Furthermore, the superior electromagnetic decoupling capability can be achieved by introducing the fault-tolerant teeth. The relevant electromagnetic performance such as flux density, back electromotive forces, cogging torque and on-load torque have been calculated by using finite-element analyses, which have also been validated by experiments.

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Design guidelines for fractional slot multi‐phase modular permanent magnet machines

This study presents the design considerations for a fractional slot multi-phase modular permanent magnet (PM) machine with single-layer concentrated windings. The winding factors for various slot/pole number combinations are calculated to identify the optimal slot/pole number combinations for different phase numbers. In addition, the electromagnetic performance influenced by flux gaps (FGs), such as air-gap magneto-motive force, back-electro-motive force, cogging torque, on-load torque and torque ripple etc. are comprehensively investigated by using the two-dimensional finite element (FE) method. Several general rules with respect to the influence of FGs on multi-phase modular PM machines performance are established. The prototypes of modular PM machines are built and the FE results are validated with experiments.

A Nine-Phase Six-Terminal Concentrated Single-Layer Winding Layout for High-Power Medium-Voltage Induction Machines

This paper proposes a new winding layout for high-power medium-voltage nine-phase induction machines (IMs) based on a single-layer concentrated winding layout having a unity winding factor. The machine is fundamentally an asymmetrical nine-phase IM, where phases are connected in such a way as to provide six terminals that are fed from two three-phase inverters. Compared to a conventional asymmetrical six-phase IM with the same stator and copper volumes, it provides improved torque density, a higher torque/current ratio, and a simpler winding layout. Finite-element simulation is used to compare the proposed winding layout with a conventional split-phase six-phase IM to assess the claimed merits. A 1.5-hp prototype IM is also used for experimental verification. The experimental results are given under both healthy and fault conditions, where the faulty converter is completely disabled. The achievable derating factors under this case are then given and compared with those of conventional six-phase IMs.

Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator

Generally, PM machines are used as PMG pre-exciters in 3-stage brushless excitations systems. This paper presents the design, characterization, and prototyping of a rotating brushless PM exciter used in a proposed 2-stage excitation system for a synchronous generator. The proposed design reduces the number of components compared with conventional systems. A comparison with the state-of-the-art conventional excitation systems is given. The design of a fast-response, or high initial response, brushless exciter requires active rectification on the rotating frame, replacing the noncontrollable diode bridge. The objective was to construct an exciter with the capability of a 50 A output field current, as well as a high value of the available ceiling voltage and ceiling current. The final exciter was constructed to be fitted into an in-house synchronous generator test setup. A finite element model of the exciter was validated with experimental measurements. The exciter prototype is also compared with an alternative armature design with nonoverlapping single-layer concentrated windings, but with the same main dimensions. The paper includes a general design procedure suitable for optimization of PM brushless exciters that fulfill the requirements of their synchronous generators and the grid.

Design and Analysis of Five-Phase Fault-Tolerant Interior Permanent-Magnet Vernier Machine

A new five-phase fault-tolerant interior permanent-magnet (PM) vernier machine is proposed in this paper, which possesses both high reliability and high torque density at low speed. It adopts single-layer concentrated windings and fault-tolerant teeth to improve fault tolerance. Since the spoke-type PMs are designed, the air-gap flux density is greatly improved, even with less PM consumption, due to the flux focusing effect. In addition, some stator teeth parameters are optimized in the proposed machine, which in return further improves the torque density and decreases the torque ripple. The time-stepping finite-element method is used to investigate the performance of the proposed machine, as compared with an existing fault-tolerant surface PM vernier machine.

Comparative Study of Switched Reluctance Machines With Half-and Full-Teeth-Wound Windings

The half-teeth-wound switched reluctance machines (HT-SRMs) having single-layer concentrated windings, feature simpler structures since the coil number is half, and phase-to-phase insulations in slot are eliminated. To evaluate the effects of winding configurations, the electromagnetic performances of HT-SRMs and conventional full-teeth-wound SRMs (FT-SRMs), including air-gap flux density, coil and phase flux linkage, inductance, torque, volt-ampere, and radial magnetic force (RMF), are comprehensively compared. The results based on theoretical analysis and finite-element (FE) method reveal that HT-SRMs would exhibit higher torque per ampere when the magnetic saturations are not too severe, whereas require higher voltage supply and generate more significant RMF. Further, it is found that the fault-tolerant capabilities of HT-SRMs are superior to FT-SRMs. A pair of prototypes with identical laminations but different winding configurations are manufactured and the experimental results confirm the predictions.

Mitigation of Turn-to-Turn Faults in Fault Tolerant Permanent Magnet Synchronous Motors

This study presents a method to mitigate and alleviate the effects produced by a turn-to-turn short in a fault tolerant permanent magnet synchronous motor with single-layer concentrated windings. The rotor magnets are capable of inducing a high voltage across the fault contact point; this voltage has the potential to generate a high circulating current that promotes the rapid propagation of the fault due to the thermal stress created by the increased localized fault power losses. The scope of this study is for applications where postfault operation is desired, even if it means operating at reduced power capacity and lower speeds. Upon quick detection of a fault, the proposed technique can be used to decelerate the propagation of the fault and extend the machine's postfault life span. The technique consists of a magnetic field-weakening strategy at speeds below nominal, to reduce the voltage induced in the faulted portion. The concept is validated through finite element analysis, modeling, and experimental data. It is demonstrated that the proposed technique reduces the fault current magnitude and winding temperature.

Design and Analysis of the New High-Reliability Motors With Hybrid Permanent Magnet Material

This paper proposes a new type of motor with hybrid permanent magnet material (HPMM); termed HPMM motor. The key of the proposed HPMM motor is the excitations, which combined rare-earth PM (REPM) with ferrite PM (FPM). To investigate the HPMM motor extensively, the HPMM motors with parallel magnetic circuit (PMC) and serial magnetic circuit (SMC) are designed. Because of the property difference between the REPM and the FPM, both PMC-HPMM motor and SMC-HPMM motor can offer low total harmonic distortion at high winding factor. Besides, the PMC-HPMM motor needs low consumption of REPM and offers low cogging torque, while the SMC-HPMM motor needs the extraordinary consumption of FPM, but offers little lower cogging torque. In addition, the reliabilities of both PMC-HPMM motor and SMC-HPMM motor are improved because of the single-layer concentrated winding and fault-tolerant teeth. Finally, the demagnetization of two motors has been studied, which indicates that the partial demagnetization will occur in the FPM. All these theoretical analyses are evaluated by the time-stepping finite element method.

Different Novel Electric Machine Designs for Automotive Applications

This paper presents three-different high efficiency and low costs electric machines types for automotive applications. For the PM machines with the single-layer concentrated windings, a novel stator topology with magnetic flux barriers in the stator teeth is used to increase the power density and the efficiency of the machine. Using this technique the material amount for the considered PM machine is reduced about 20% compared with the conventional design. For the asynchronous machines, two alternative solutions are presented; a new winding type with low space harmonic contents and also an ASM rotor with series connection of rotor bars solve the problem with high harmonics. Further, during the design of a new self-excited synchronous machine with concentrated winding, the high MMF winding harmonics are used to excite the rotor field winding.

Saliency ratio derivation and optimisation for an interior permanent magnet machine with concentrated windings using finite-element analysis

The implementation of concentrated windings in interior permanent magnet (IPM) machines has numerous advantages over distributed windings, with a major disadvantage being the decrease in saliency ratio. Theoretically, this would result in a lower field weakening range which is undesirable for traction applications. Although it is revealed in some studies that concentrated winding results in lower saliency ratio, experimental techniques used for accurately acquiring the saliency ratio of IPM machines with concentrated windings are yet to be fully understood. This study presents a proposed finite-element (FE) method, which is derived from the experimental AC standstill test method. With this method, the d- and q-axis inductances (Ld and Lq) of the IPM machine with fractional-slot concentrated windings can be accurately determined. Limitations of this method are discussed. Subsequently, this method is used to determine Ld and Lq of various winding configurations and rotor designs. From repeated FE testing using Flux2D, the authors derive a set of general rules for optimising the saliency of an IPM machine with fractional-slot, single-layer concentrated winding.

Design of High-Performance Spindle Motors With Single-Layer Concentrated Windings and Unequal Tooth Widths

This paper provides a method for the design of a high-performance permanent magnet (PM) spindle motor with single-layer concentrated windings. In order to maximize the flux linkage and torque density, a configuration with unequal tooth width is also presented. A comparison of the performance of the double-layer, single-layer, and single-layer with unequal tooth width is made using finite-element analysis. It provides a useful reference to be considered in the motor design