Concentrated Windings Research Articles

Exact THD Calculations Applied to Minimize Space Harmonic Content of Winding and Rotor Magnetic Fields

As a metric for measuring the combined space harmonic content of electric machine winding magnetomotive force (MMF), the winding total harmonic distortion (THD) is defined with an infinite series. Without truncation, the exact THD can be evaluated via a “family grouping” facilitated by a “family sum” over the fewest possible winding factors. Uniformly applicable to distributed windings and fractional-slot concentrated windings (FSCWs), this procedure also explains the inherent difference in harmonic content between both winding categories. Furthermore, the minimal THD (mTHD) that can be achieved by optimizing a winding is revealed with a closed-form expression. While intended for windings, the mTHD concept also benefits the design of low harmonic content rotor magnetic fields. Examples of both winding and rotor mTHD designs are provided.

Saturation-Induced Variable-Flux Characteristics in a 12-Slot 10-Pole Concentrated Winding Permanent-Magnet Motor

This paper proposes a stator core design to achieve variable-flux characteristics enhanced by magnetic saturation in fractional-slot concentrated winding (FSCW) permanent-magnet (PM) motors without additional excitation systems, complicated structures, or active controls. Magnetic saturation induced at suitable locations can enhance variable-flux characteristics because the PM flux linkage is variable with the magnetic saturation in cores. In distributed winding configurations, magnetic saturation is induced symmetrically for each rotor pole by the fundamental that is dominant in the spatial distribution of the air-gap flux density. The magnetic saturation at each rotor pole can enhance variable-flux characteristics. In FSCW configurations, magnetic saturation is not induced symmetrically for each rotor pole because of several dominant space harmonics. The magnetic saturation at several rotor poles cannot enhance variable-flux characteristics. In the proposed design, the stator core has thin tooth tips for inducing magnetic saturation. The magnetic saturation in the stator core achieves the variable-flux characteristics that are effective for expanding the operating region or decreasing electromotive force and increasing torque. The efficacy of the proposed design is determined by estimating motor performance through a finite element method analysis and demonstrating the actual motor performance of a prototype.

Concentric-Coil Distributed Winding Design for Large Direct-Drive Fully Superconducting Machines

Fully superconducting generators (FSCGs) use superconducting wires for both the field and armature windings to reach a high torque density for wind turbine applications. The AC armature winding of an FSCG design mostly employed racetrack tooth-coils to form fractional-slot concentrated windings. This winding type has high leakage flux and excessive harmonics, especially when used in superconducting machines. Other attempts like applying full-pitch racetrack coils can only be with one slot per pole per phase which also has significant slotting harmonics. This paper proposes an innovative concept of double-layer concentric coils to enable distributed windings with a larger integral number of slots per pole per phase. The concept successfully breaks the limitation that racetrack coils cannot be built with such integral slots. This paper then assesses the performance of the proposed winding concept within a context 20 MW FSCG design. The assessment finds out that the proposed concept has balanced three phases but reduces inductance compared to single-layer windings. The force on each concentric coil can significantly be different, thereby complicating the mechanical design of these superconducting coils.

Lumped model for the calculation of harmonic eddy current losses in permanent magnets for homogeneous flux distributions considering eddy current reaction flux

This is the first of a series of papers on novel methods for the calculation of eddy current losses in permanent magnets (PMs) and the shortcomings of previously conducted analyses. Eddy current losses in PMs and their mitigation are significant factors when designing inverter-fed electric drives. Especially with the need for drives with high power density, a trend toward increased rotational speeds and, therefore, higher fundamental frequencies and inverter switching frequencies are observable. Higher harmonic frequency components of concentrated windings and fractional slot windings are widely taken into account when designing rare sintered earth magnets for permanent magnet synchronous machines (PMSMs). However, inverter-related losses are rarely simulated in Finite Element Method (FEM) co-simulations and can contribute as a major factor to the power losses in PMSMs. In the worst case, this neglection can lead to the thermal demagnetization of the permanent magnets. Segmentation provides an effective measure to limit eddy current losses. However, not every kind of segmentation proves effective in a drive application. Depending on the frequency behavior of the magnetic flux in a permanent magnet, segmentation can increase eddy current losses within the magnet compared to a non-segmented magnet. This behavior is due to the reaction to the flux caused by the eddy currents within the magnet. The reaction of the eddy currents is often neglected [1, 2], and, in other cases, the vicinity of ferromagnetic material is neglected in analytical calculations [3] but proves crucial for the exact calculation of higher frequency losses [4, 5]. In this paper, an analytical solution to calculate harmonic eddy current losses in permanent magnets, including the reaction flux with homogeneous excitation, is given.

Optimal Coil Design for Coreless Linear Motors Based on the Extended Stream-Function Method

This paper concerns a coil design technique for coreless linear motors that is based on the stream-function methodology. This method allows for the synthesis of the optimal conductor shape on a source surface based on constraints and objectives in an optimization problem. The method is extended to allow for motion and multi-phase commutation and is applied to the design of coils for coreless linear motors with concentrated and distributed winding configurations. A manufacturable conductor is extracted for a motor with a concentrated coil configuration. The resulting coil is compared to a traditional concentrated coil-set by a simulation of a coreless linear motor, in which the windings are produced using printed circuit board technology. It shows an increase in force production for the geometry with the conductor designed using the stream-function method, whereas the average temperatures in the coils of both geometries are identical.

Investigation on Stator Shifting Technique for Permanent Magnet Vernier Machines With Two-Slot Pitch Winding

This paper investigates the stator shifting technique (SST) for permanent magnet vernier (PMV) machines equipped with two-slot pitch winding (TSPW). By employing SST, TSPWs can be generated from the combination of two sets of fractional-slot concentrated windings (FSCWs), with various shift angles. The effects of various shift angles on armature magnetomotive force (MMF) harmonic contents are explored. It shows that proper shift angles can be selected to preserve the working component while eliminating loss-producing harmonics. Besides, the implementation of various shift angles leads to uneven stator teeth structure, which affects field modulation. Therefore, the output torque capability, phase inductance, power factor, core losses, and fault-tolerance are affected by different shift angles. This paper aims to exploit the full potential of TSPW-PMV machines by SST, considering the synthetic effects on harmonic reduction and field modulation. Through the exemplification of 24- slot, 19-rotor pole pair, and 5-armature pole pair PMV machines, it indicates SST is a more general and flexible design method that can provide new design opportunities and improve various performance metrics by introducing shift angle as an additional design variable. Finally, a prototype of the double-layer TSPW-PMV machine with optimal shift angle is fabricated for concept validations.

Electromagnetic design and performance analysis of large-scale offshore wind generators with modular fractional-slot concentrated winding

Future offshore wind engineering raises demands on higher reliability, better power generating performance, as well as lower manufacturing and transportation cost. This paper presents a direct-driven permanent magnet generator (DDPMG) with modular fractional-slot concentrated winding (MFSCW), to meet the large-scale, low-cost and high-reliability requirements of offshore wind power applications. The corresponding pole–slot combination method and electromagnetic characteristics analysis for this novel generator are proposed and performed in detail, including the winding coefficient analysis, magnetomotive force (MMF) harmonic analysis, cogging torque analysis, finite element simulations and generator parameter optimization. After finite element simulations, a 3.3 MW prototype MFSCW-DDPMG is developed to validate the proposed scheme. The results provide a complete and feasible scheme of pole–slot​ combination and electromagnetic design for future MFSCW-DDPMG engineering applications.

Ice core chemistry database: an Antarctic compilation of sodium and sulfate records spanning the past 2000 years

Abstract. Changes in sea ice conditions and atmospheric circulation over the Southern Ocean play an important role in modulating Antarctic climate. However, observations of both sea ice and wind conditions are limited in Antarctica and the Southern Ocean, both temporally and spatially, prior to the satellite era (1970 onwards). Ice core chemistry data can be used to reconstruct changes over annual, decadal, and millennial timescales. To facilitate sea ice and wind reconstructions, the CLIVASH2k (CLimate Variability in Antarctica and the Southern Hemisphere over the past 2000 years) working group has compiled a database of two species, sodium [Na+] and sulfate [SO42-], commonly measured ionic species. The database (https://doi.org/10.5285/9E0ED16E-F2AB-4372-8DF3-FDE7E388C9A7; Thomas et al., 2022) comprises records from 105 Antarctic ice cores, containing records with a maximum age duration of 2000 years. An initial filter has been applied, based on evaluation against sea ice concentration, geopotential height (500 hPa), and surface wind fields to identify sites suitable for reconstructing past sea ice conditions, wind strength, or atmospheric circulation.

12/4 SynRel machine design with concentrated windings and novel polynomial fitting model-based continuous MTPA control method

12/4 SynRel machine design with concentrated windings and novel polynomial fitting model-based continuous MTPA control method

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.

Design of Limited-Angle Wound Rotor Resolvers for High Accuracy and Easy Manufacturability

The limited-angle resolver is commonly employed instead of an optical encoder as a position sensor in medical, special industrial, custom robotics, transportation and military applications owing to their reliability, low cost, and ability to work steadily in harsh and contaminated environments. In the design and optimization of resolvers, achieving high precision while maintaining a simple manufacturing process for mass production is a big challenge. This study proposes a systematic method for the determination of slot and pole number combinations of limited-angle wound rotor resolvers (LAWRRs) for high accuracy and easy manufacturability. A set of stator and rotor slot numbers ranging from 8–64 for 2 and 4 poles, which are suitable for concentric winding (CW) topology, have been considered. For high accuracy, number of turns distribution waveforms and their total harmonic distortion (THD) percentages are investigated. In addition, for easy manufacturability, low slot number combinations providing high accuracy are determined and the feasibility of employing solid core instead of laminated core is examined. Analytical calculation results of the proposed configurations are validated utilizing a two-dimensional time-stepping finite-element analysis (2D-FEA). Finally, in order to experimentally validate the methodology and analyses, two prototypes with low and high slot numbers are manufactured and tested.

A novel tubular High-Power-Factor Transverse-Flux linear machine with Concentrated-Flux teeth

Due to principle constraints of the conventional transverse flux permanent magnet linear machine, its PM utilization is less than half. Besides, the complex structure and the serious magnetic leakage also lead to the limited thrust increase and the sharp decline of power factor. Therefore, the high-power-factor transverse-flux permanent-magnet linear machine (HPF-TFPMLM) using the concentrated-flux teeth is proposed in this paper. First, the topology and operation principle of the circumferentially distributed HPF-TFPMLM are investigated. The concentrated-flux teeth and multi-unit concentrated windings are introduced to improve power factor of the HPF-TFPMLM. To further study the proposed HPF-TFPMLM, its counterpart of the axial distributed topology is proposed for comparative analysis. Then, the key electromagnetic performance of power factor, thrust and thrust density of the HPF-TFPMLM are analyzed. Its performances including no-load EMF, magnetic field distribution and overload capacity are evaluated and compared with its counterpart. Finally, the feasibility and correctness of the investigated HPF-TFPMLM are verified.

Design of multi‐phase permanent magnet synchronous motor with fractional‐slot windings for electromagnetic vibration reduction considering stator teeth modulation

AbstractA multi‐phase permanent magnet synchronous motor (PMSM) with fractional‐slot windings is proposed to reduce electromagnetic vibration and improve torque performance. Firstly, the analytical expression of electromagnetic force is derived, and the stator teeth modulation effect of electromagnetic force is introduced. The spatial order of the electromagnetic force and the stator teeth modulation are closely related to the slot‐pole combination of the PMSM. Then, three PMSMs with different slot‐pole combinations are presented, and they represent fractional‐slot concentrated winding, integral‐slot distributed winding and fractional‐slot distributed winding, respectively. Their torque performance and electromagnetic vibration performance are studied and compared considering stator teeth modulation. In addition, the multi‐phase winding technology is adopted to further improve the torque performance of the proposed PMSM. Finally, a 90s20p PMSM is manufactured, and the finite element method and experimental method are used to verify the proposed low vibration design method.

Impedance Modeling Oriented Toward the Early Prediction of High-Frequency Response for Permanent Magnet Synchronous Machines

This paper presents and validates a method for early estimation of the high-frequency impedance response for a real Permanent Magnet Synchronous Machine (PMSM). The main contribution of this work lays on the simplicity of the data required to tackle the prediction, which do not require any experimental tuning or 3D simulations. The required inputs for the method are the 2D cross-section of the machine and the material characteristics of the conductors, insulation and iron laminations. An approach using the Finite Element Method (FEM) coupled with a circuit simulator is utilized to obtain the machine common-mode and differential-mode impedances over a broad frequency range. Experimental measurements are performed up to the resonance band to validate the methodology. In addition, the influence of the machine rotor and housing on the impedance curves is experimentally assessed. A machine with concentrated winding is used as a case study machine to test the model.

Study of aerodynamic performance and wake effects for offshore wind farm cluster

The large-scale development of wind farms has led to an increase in the concentration of wind farms, due to factors such as concentrated wind resources, operational and maintenance costs. This has resulted in the formation of wind farm clusters, especially offshore wind farms. The wake and cluster effects of upstream wind farms have a significant impact on the power generation of downstream wind farms. In this study, the Large Eddy Simulation (LES) combined with actuator line model is used to simulate the flow field of a wind farm cluster under turbulence inflow conditions. The numerical methodology is first validated using data from the Nibe wind turbine. The wind farm cluster with NREL 5 MW wind turbine is then analyzed to examine the aerodynamic performance and wake effect for different wind farm cluster configurations. The results show that there is a clear wake and cluster effect for wind farm clusters, and that this effect reduces as the distance between wind farms increases, with 30D being a reasonable separation distance. The power of the wind farm still decreases when three wind farms are clustered, which is further reduced compared to two wind farms, indicating that the cluster effect becomes more severe as the number of wind farms increases. The study also found that staggering wind farms in a wind farm cluster can improve the overall power of the wind farm cluster.

Integration of high levels of electrolytic hydrogen production: Impact on power systems planning

The increasing interest in electrolytic hydrogen production using renewable electricity sources will require to adapt power systems to new electrical loads for hydrogen production and supply chains. Such high loads would impact the long-term planning and operation of power systems, as they need to balance the variability of renewable generation sources with electricity demand. This stresses the importance of characterizing the impact of incorporating hydrogen supply chains into power systems and planning accordingly. This study proposes a methodological framework to assess the integration and development of a national power system with electrolytic hydrogen production and supply chain. The framework is based on the well-known optimization tool for energy systems planning, Open Source Energy Modeling System (OSeMOSYS). For a detailed representation, a module was developed where demand side technologies – such as those associated to hydrogen supply chains – can provide operating reserves. As a case study, the integration of the Chilean power system with a hydrogen supply chain for exporting hydrogen between 2018 and 2050 was modeled. Among other findings, results indicate that an on-grid hydrogen supply chain would be more cost-effective than an off-grid one. However, the new electrical loads originated from such hydrogen supply chain would require additional generation capacity — primarily photovoltaic. Other generation capacities such as concentrated solar power, wind, and storage would experience significant variations in their investment requirements, compared to the off-grid hydrogen supply chain scenario. The study revealed that the coordinated operation of electrolyzers is crucial to the operational flexibility of the new electrical system.

Investigation of Air-Gap Field Modulation Effect in Spoke-Type PM Machines

In this article, the air-gap field modulation effects (AFMEs) in spoke-type permanent magnet (STPM) machines with concentrated winding are investigated and revealed by quantifying the torque contributions of the various air-gap flux density harmonics. Due to the relatively stronger flux concentrated effect, the STPM structure exhibits greater resulting air-gap field harmonics for torque generation. In order to provide an in-depth understanding of their torque generation mechanism, the contributed torque components of the various air-gap field working harmonics are quantified by employing the Maxwell stress tensor (MST) approach. It identifies a fact that the abundant air-gap flux density harmonics have participated in torque production in the STPM machine. As a consequence, the field-modulated harmonics contributed a nonnegligible torque component, and hence, a pronounced AFME can be obtained in the STPM machine. Besides, the influences of the key dimension parameters, including split ratio, stator slot opening ratio, rotor PM thickness, and length, on AFEM for torque performance of the STPM machines are evaluated by the finite-element (FE) method. Finally, the reliability and effectiveness of theoretical analysis and FE simulation are verified by experiments on an STPM machine prototype.

Comparative Study of Dual-Rotor Slotless Axial-Flux Permanent Magnet Machines With Equidirectional Toroidal and Conventional Concentrated Windings

Axial-flux permanent magnet (AFPM) machines are gaining popularity in low-speed and high torque applications due to their high torque density, high efficiency, and compact structure. In this article, a dual-rotor slotless AFPM (DRSAFPM) machine equipped with equidirectional toroidal winding (EDTW) is proposed and compared with that equipped with conventional single-layer and double-layer concentrated windings (CWs). First, the differences between the DRSAFPM machine with EDTW and that with conventional CWs in coil layout, electromotive force (EMF), and winding magnetomotive force are revealed. Considering the special coil layout of the EDTW, the coil factor and size equations of the DRSAFPM machines with EDTW and conventional CWs are presented. Second, the electromagnetic performance including air-gap field, back-EMF, torque, and efficiency of the DRSAFPM machines with EDTW and conventional CWs are analyzed based on the three-dimensional finite-element method. The simulation results validate the correctness of the coil factor and size equations and indicate the EDTW–DRSAFPM machine has superiority in back-EMF amplitude and torque density. Finally, a prototype of the EDTW–DRSAFPM machine is manufactured and tested, which validates the feasibility of the EDTW–DRSAFPM machine and the correctness of the analysis.

Multiagent Control in Modular Motor Drives by Means of Deterministic Consensus

A modular motor drive (MMD) is composed of multiple identical pole drive units (PDUs), which consist of a concentrated stator winding fed by a dedicated power electronic converter module. To exploit the full flexibility and reliability of these MMDs, they are equipped with multiple controllers, operating as synchronized peers, and each driving only a limited set of PDUs. An MMD can hence be considered as a multiagent system, in which all the agents cooperate to deliver a certain torque demand. The goal of this work is to distribute this torque demand among the agents of a modular drive in a completely decentralized way, in order to comply with the flexibility and reliability of the hardware, while still taking into account the present condition of each agent. A deterministic consensus algorithm is used for this purpose, in combination with decentralized proportional integral (PI) current controllers. Communication is only allowed between neighboring agents, to limit the communication load. It is shown in this article that the total torque demand is delivered, under healthy conditions as well as during agent malfunctions and with nonidentical agents. The concept is demonstrated on a modular axial-flux permanent magnet synchronous machine with 15 PDUs that are assigned to five agents.

Design of a High Torque Density Robot Joint and Analysis of Force Control Method Applied for a Light Exoskeleton

In many robotic applications, the joint is required to have a small volume, low weight and high torque output. In this paper, based on the finite element analysis (FEA), a 36-slot 40-pole outer rotor surface-mounted permanent magnet (OR-SPM) motor with concentrated winding is designed for the exoskeleton robot. The fractional slot concentrated winding (FSCW) is employed to reduce end winding height, leading better portability. Since the motor is relatively flat, the 3D end effect is critical to the electromagnetic performances. Special attention is paid to 3D end effect during the multi-objective optimization of the OR–SPM motor. In order to increase the ending torque output, the planetary reducer is located between OR–SPM motor and load, and then system level optimization covering motor and reducer is carried out to achieve best torque output. In addition, the force impendence control method with parameter self-adaptive capability is proposed to improve user experience of the exoskeleton robot, where the key parameters in the algorithm vary according to different actions of the exoskeleton. In addition, the inertia of load is calculated using the parameter identification based on least squares method. Finally, the prototype of the joint is fabricated and tested to validate the above FEA results and control method. The user experience of the exoskeleton robot is also covered.