Pole Count Research Articles

Declining Cogging Torque Technique of an Integral Slot Number for Permanent Magnet Machines

The existence of cogging torque in electric equipment has been considered undesirable. This kind of friction in the air-gap impacts the alignment of flux and the stator slots, resulting in the observed outcome. Consequently, the imposition of restrictions on the rotation of the rotor is employed to generate electrical energy. This research endeavor primarily aims to mitigate the cogging torque of electrical machinery. The current utilization involves employing a total of 3 permanent magnet synchronous machines, often known as inset PMMs, which possess a slot count of 24 and a pole count of 8. The employed technique involves the integration of an optimal pole arc method in conjunction with the implementation of slots cut into the magnet's edge. The machine model under investigation has two fundamental variants, namely Models 1 and 2. These models are equipped with 1one-step slotted (OSS) and 2two-step slotted (TSS) edges on each magnet, in addition to pole arc optimization. The simulation was conducted using the Finite Element Method Magnetics (FEMM) 4.2 software together with LUA scripts, with a focus on rotor rotation ranges of 1 degree. Model 2 exhibited a decrease in cogging torque of 0.01 Nm, whereas Model 1 demonstrated a reduction of 0.015 Nm, and the basic model had a decrease of 0.02 Nm. When implementing a dual-layered cutting edge on a magnet and attempting to optimize its pole arc, it is imperative to consider that the cogging torque's peak magnitude becomes substantially diminished or entirely eliminated.

Inverter Design Considerations for Variable-Pole Induction Machines in Electric Vehicles

This article proposes a generalized inverter design framework for a variable-pole induction machine (IM). It quantifies the advantages of pole changing and a high number of inverter legs on converter efficiency and size. The framework is used to design an 18-leg drive that reconfigures a six-pole IM to four- and two-pole while increasing torque capability at maximum speed by a factor of 2.2 compared to a conventional 3-leg fixed-pole design. The framework also shows that a three-leg drive must be oversized by a factor of 1.5 to reach the same torque capability using an identical-sized machine. The proposed 18-leg drive has 50% less losses and requires 62% less dc-link capacitance compared to a 3-leg converter. The framework is used to propose a loss minimization method for the combined machine and converter, with pole count as an operational degree of freedom at partial load and high speed. As a result, variable-pole operation reduces combined machine and drive losses by up to 45% compared to a conventional three-leg drive with the same IM. An 18-leg experimental GaN-based 890 VA inverter driving a toroidally wound IM was designed, built, tested, and compared to a 3-leg inverter to validate the proposed framework.

Electromagnetic Design Characterization of a Dual Rotor Axial Flux Motor for Electric Aircraft

This article presents and evaluates a dual rotor axial flux permanent magnet motor for electric aircraft applications. Several features, including grain-oriented electrical steel, Halbach arrays, and wires with rectangular cross sections, are used to improve torque density and efficiency. A novel winding arrangement is used to mitigate interturn short-circuit faults. Rather than simply optimizing the motor by itself, this article evaluates the tradeoffs between motor performance and its interfaces with the drive, thermal management system (TMS), and mechanical structure. This information can be used along with similar analyses of these subsystems to select the design with the system-level optimal performance. This article uses finite-element simulations to characterize tradeoffs among active mass, efficiency, fundamental frequency, power factor, axial forces on the rotors, and cooling surface area. Several designs exceed 95% efficiency at takeoff with less than 8 kg of active mass. While high pole counts, a large outer radius, and short stator teeth tend to optimize the magnetic performance at takeoff, this can reduce cruise efficiency, reduce the surface area through which the TMS can extract heat, increase the fundamental frequency the drive must supply, increase the structural mass required to support the rotors, and introduce complexity to the manufacturing process. Further analysis for a selected design reveals that the power factor can be significantly improved with a minimal torque penalty via field weakening due to significant saturation in the stator teeth.

Acoustic Noise Mitigation in High Pole Count Switched Reluctance Machines Utilizing Skewing Method on Stator and Rotor Poles

Multiphysics analysis and experimental validation of acoustic noise reduction in a high pole count, high power, switched reluctance machine (SRM), through skewing are explored in detail in this work. An iterative optimization strategy covering electromagnetic, structural, and thermal domains is proposed to investigate the effect of different skewing methods and angles on a 24-stator slot/16-rotor pole (24/16) SRM rated at 100 kW. The contributions of this work are twofold. First, electromagnetic impact, considering average torque, torque ripple, radial and tangential air gap forces, of symmetric and asymmetric skewing on stator and rotor is studied in this work. Second, the impact of skewing methods on acoustic noise and vibration performance is studied and presented in detail. The study reveals that skewing both the stator and rotor by the same amount has superior electromagnetic performance over other types of skewing. Multiphysics simulations conducted, predict a 10.5 dBA reduction in the acoustic noise, compared to a baseline design with no skew, for an optimized rotor-stator skewing angle of 13.75°. Finally, 100 kW prototypes of the baseline and the optimized skewed SRM were constructed and subjected to wide speed range testing. Simulation and test results closely follow each other and validate the effectiveness of the proposed skew design in mitigating acoustic noise and vibration in high pole count SRMs.

Sensorless Control of Separately Excited Synchronous Electrostatic Machines

This article presents the analysis and demonstration of sensorless position estimation methodologies for separately excited synchronous electrostatic machines (SEMs). The torque density of the SEM comes at the cost of a high pole count (p >50) along with other enhancements. The high pole count makes the use of high-resolution position sensors necessary, driving up the cost of the system. The sensorless estimation of rotor position is seen as a solution for alleviating the need for high-resolution and high-cost position sensors. Key features of electrostatic machines that make them suitable for sensorless operation are identified. Back MMF (current) based rotor position sensing for medium to high speeds is investigated. High-frequency injection-based position estimation is investigated for zero and low-speed operating regions. The proposed methods are experimentally demonstrated using a current-source inverter-based drive platform.

Lesser Prairie‐Chicken Survival in Varying Densities of Energy Development

ABSTRACTAnthropogenic features increasingly affect ecological processes with increasing human demand for natural resources. Such effects also have the potential to vary depending on the sex and age of an individual because of inherent behavioral and life experience differences. For the lesser prairie‐chicken (Tympanuchus pallidicinctus), studies on male survival are limited because most previous research has been focused on females. To better understand patterns of lesser prairie‐chicken survival in habitat with varying levels of anthropogenic infrastructure associated with oil and natural gas development, we monitored survival of 178 radio‐tagged male and female lesser prairie‐chickens in eastern New Mexico, USA, from 2013 to 2015. We examined the relationships of shrub cover, proximity to and density of anthropogenic features (i.e., utility poles), displacement of natural vegetation by anthropogenic features (i.e., area of roads and well pads), and individual demographics (i.e., sex, age) with lesser prairie‐chicken survival. Furthermore, we categorized the probable cause of mortality and examined its relationship with oil and gas development intensity (indexed by utility pole density) within 1,425 m of an individual's mortality site or final observed location. We predicted that survival would be lower for individuals exposed to greater levels of anthropogenic features, and that males and subadults would be more negatively affected than females and adults because of increased exposure to predators during the lekking season and naiveté. Relationships between survival and utility pole density, sex, and age were supported in our top‐ranked models, whereas models including other anthropogenic and natural features (i.e., roads, well pads, shrub cover) received little support. We predicted a substantial decrease in adult and subadult male survival with increasing densities of utility poles. The relationship between survival and utility pole density for females was weaker and not as clearly supported as for males. We did not find a detectable difference in utility pole counts among probable mortality causes. Our findings highlight the importance of including male lesser prairie‐chickens in research and conservation planning, and the negative effect that high densities of anthropogenic features can have on lesser prairie‐chicken survival. © 2021 The Wildlife Society.

Design Guidelines and Scaling Effects for Bearingless PM Synchronous Machines Accounting for Eddy Current Reaction Field

Apart from mechanical constraints, the maximum size and output power of high-speed bearingless PM synchronous machines is mainly limited by two effects with disturbing influence on the bearing force vector. One is the interference between the stator drive field and the suspension air gap field. The other one is the air gap field deformation by rotor eddy currents due to the asynchronously rotating stator field wave, which generates a non-moving bearing force vector. The eddy current reaction field lowers the bearing force amplitude and leads to a spatial error angle. Apart from material properties, these two effects are mainly influenced by the split ratio and the permanent magnet height. It is discussed how the machine's main dimensions and pole count shall be chosen in order to keep the influences of these effects small. It is also shown how the motor efficiency suffers from these effects and how the corresponding limitations vary with machine size and electromagnetic utilization.

Estimating tree-related power outages for regional utility network using airborne LiDAR data and spatial statistics

Trees play an integral role in the “green” framework of an urban ecosystem. However, just as they are beneficial to the environment, they can pose a significant risk to utility infrastructure networks, particularly in severe weather events. The objectives of this research were to explore the effect of scale and spatial variation on the relationships between trees and utility assets for vegetation-related power outages through the incorporation of remote sensing and geographic information system (GIS) analysis. Tree location and structural metrics derived from airborne Light Detection and Ranging (LiDAR) data were combined with regional utility network GIS data to test the prediction analysis capabilities of global and local statistics at multiple scales. Pearson’s correlation was carried out to examine the relationships between tree structure and utility asset variables to vegetation-related power outages, including the effect of the resolution, or grid-cell size, on those relationships. To test the performance of global and local regression modeling on outage prediction, ordinary least square (OLS) and geographically weighted regression (GWR) models were evaluated using four explanatory variables (utility wire length, utility pole count, tree canopy area, maximum tree height) at four different grid cell scales (50 m, 500 m, 1 km, 2 km). In general, Pearson’s correlation demonstrated the strongest positive relationship between explanatory variables and power outages when only aggregating 50-m grid cells exhibiting co-location of trees and utility assets to 2-km grid cells. Local regression models performed better than global models at all scales, with GWR producing the highest adjusted R2 and lowest Akaike information criterion (AIC) values of 0.955 and 3213, respectively. Additionally, the performance of OLS and GWR models increased with scale as both models produced the highest adjusted R2 at 2-km grid-cell scale. GWR model outputs demonstrated unique spatial patterning across the study area. This research demonstrated the effect of scale and spatial variation on regression analysis for the estimation of tree-related power outages.

Optimization of Coaxial Magnetic Gear Design and Magnet Material Grade at Different Temperatures and Gear Ratios

Magnetic gears, like mechanical gears, transform power between different speeds and torques; however, magnetic gears' contactless nature provides inherent potential benefits over mechanical gears. A genetic algorithm was used to optimize magnetic gears at different temperatures across a range of gear ratios. Using different magnet material grades on the different rotors and for the tangentially and radially magnetized magnets can slightly increase the specific torque relative to designs with a single magnet material. The high pole count rotor requires a magnet material with higher coercivity than that of the low pole count rotor magnet material, especially for designs with a large gear ratio. While increasing the temperature produces an exponential decay in the achievable specific torque, with a compounding reduction of about 0.4% for each degree Celsius, the temperature does not significantly affect the optimal geometric parameters and primarily affects the optimal materials. The gear ratio significantly affects the optimal geometric parameters and can impact the optimal magnet materials. Additionally, the genetic algorithm was employed to characterize the impact of stack length using 3D finite element analysis. Designs with shorter stack lengths favored thinner magnets and higher pole counts and may be able to use magnet materials with lower coercivities.

Review and Analysis of Coaxial Magnetic Gear Pole Pair Count Selection Effects

Magnetic gears perform the same function as mechanical gears using magnetic fields instead of interlocking teeth. A review of the design processes used in the literature demonstrates that a critical design parameter, pole pair count, is often given inadequate consideration. In addition to reviewing the existing prototypes, this article uses a parametric simulation study to analyze the impacts of pole pair counts on gear performance and illustrate how the optimal pole counts vary with gear ratio and various design parameters. This article also introduces new ripple factors, which better correlate with torque ripple than the cogging factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{T}$ </tex-math></inline-formula> ) used in previous articles, and illustrates why designs with noninteger gear ratios tend to have much smaller torque ripples than designs with integer gear ratios. While selecting the pole counts to minimize symmetry can reduce torque ripple, designs without any symmetry are shown to experience unbalanced magnetic forces on each rotor. Thus, it is recommended to select pole counts that result in an even number of modulators but not an integer gear ratio. This article also reveals that for a fixed gear ratio, a nontrivial optimum pole count minimizes the electromagnetic losses.

Enhanced Stray-Load Loss Measurements Through a Zigzag Variable Load Test Approach

This article proposes an enhanced procedure for executing the standard variable load test that allows obtaining high correlation factors for indirectly measured stray-load loss during efficiency tests of induction motors. This helps to achieve the minimum values required by the international standards to consider the variable load test well executed, avoiding unwelcome test repetitions and leading to significant amount of time saved. With the machine at steady-state temperature, the enhanced procedure consists of alternatively applying load levels higher and lower than the rated load, so that the stator winding temperature zigzags around the rated value. Hence, multiple readings can be performed for each load point, having the machine in isothermal conditions. This allows averaging many measurements of the same load point to mitigate the impact of instrumentation and reading errors. The article includes load tests conducted on different induction motor sizes and pole counts, applying both the standard variable load test procedure and the proposed approach. The experimental results show that the proposed technique allows achieving higher correlation factors on the stray-load losses than the standard procedure.

Loss Minimization and Maximum Torque-Per-Ampere Operation for Variable-Pole Induction Machines

High power density, high efficiency, inexpensive drivetrains operating over a wide torque/speed range are critical for traction applications. An induction machine (IM) offers a cost-effective, rugged, and reliable alternative to permanent magnet solutions. Varying the IM’s pole count on-the-fly overcomes the finite inverter voltage constraint and extends the machine’s speed range. To date, the operating pole count of variable-pole IMs has been determined based on the operating speed irrespective of the torque requirement, utilizing a high pole count at low speeds and a low pole count at high speeds. This article expands the pole-selection strategy of variable-pole IMs to both torque and speed. The pole count is used to improve the machine efficiency and minimize the stator current over the entire operating torque–speed range. An experimental 36-slot toroidally wound IM driven by an 18-leg inverter validates the proposed pole-selection method for variable-pole IMs. Stator current and machine losses are reduced at partial loading conditions by utilizing lower pole counts rather than selecting the pole with the highest rated torque capability. The average loss reduction by 1/3 and torque-per-ampere improvement of $2\times $ are experimentally achieved at partial loading by using the proposed pole-selection method compared to linking the pole count solely to the operating speed.

Cogging torque sensitivity considering imperfect magnet positioning for permanent magnet machines of different slot and pole count

This work is about analyzing surface mounted permanent magnet machines regarding their sensitiveness related to erroneous magnet positioning. A finite element analysis based approach is presented and different topologies in terms of slot and pole count are compared. The study further includes the analysis of multiple magnet widths and stator teeth widths. By contrast to most of previous studies, the work is based on evaluating the cumulative distribution function of the cogging torque in case of non-idealities. A Monte Carlo importance sampling based strategy is focused. This approach facilitates studying arbitrary tolerance distributions. Results reveal that topologies with particularly promising rated cogging torque behaviour exhibit the most significant performance degradation in presence of tolerances. A linear relationship is identified for cogging torque performance as function of the accuracy in magnet positioning. Results emphasize the necessity of tolerance analyses for electric machine design to not overrate their performance in the presence of manufacturing uncertainties.

Influence of Pole-Pair Combinations on the Characteristics of the Brushless Doubly Fed Induction Generator

The brushless doubly fed induction generator (BDFIG) is an alternative to the doubly fed induction generator (DFIG), widely used in wind turbines which avoids the need for brush gear and slip rings. The choice of pole numbers for the two stator windings present in the BDFIG sets the operating speed, typically in the medium speed range to eliminate a gearbox stage. This paper focuses on how both the total number of poles and the assignment of poles between the windings affect machine performance. Analytical expressions have been developed for parameters including pull-out torque, magnetizing current and back-iron depth. The results show that the pole count can be increased without unduly compromising pull-out torque and that in cases where more than one combination of pole number is acceptable only the back iron depth is significantly affected. In addition an output factor has been introduced to enable a direct comparison to be made with conventional DFIGs. The torque density of a brushless DFIG is compromised to a degree relative to a comparable DFIG as a consequence of the presence of two magnetic fields and finite element analysis is needed to achieve an optimized design. Finally, predictions of the performance of multi-MW machines are made based on data from an existing 250 kW machine which show that suitable efficiencies can be obtained and excessive control winding excitation can be avoided.

Full 5D characterisation of the Sagittarius stream with Gaia DR2 RR Lyrae

Context. The Sagittarius (Sgr) stream is one of the best tools that we currently have to estimate the mass and shape of our Galaxy. However, assigning membership and obtaining the phase-space distribution of the stars that form the tails of the stream is quite challenging. Aims. Our goal is to produce a catalogue of the RR Lyrae stars of Sgr and obtain an empiric measurement of the trends along the stream in sky position, distance, and tangential velocity. Methods. We generated two initial samples from the Gaia DR2 RR Lyrae catalogue: one selecting only the stars within ±20° of the orbital plane of Sagittarius (Strip), and the other resulting from application of the Pole Count Map (nGC3) algorithm. We then used the model-independent, deterministic method developed in this work to remove most of the contamination by detecting and isolating the stream in distance and proper motions. Results. The output is two empiric catalogues: the Strip sample (higher-completeness, lower-purity) which contains 11 677 stars, and the nGC3 sample (higher-purity, lower-completeness) with 6608 stars. We characterise the changes along the stream in all the available dimensions, namely the five astrometric dimensions plus the metallicity, covering more than 2π rad in the sky, and obtain new estimates for the apocentres and the mean [Fe/H] of the RR Lyrae population. Also, we show the first map of the two components of the tangential velocity thanks to the combination of distances and proper motions. Finally, we detect the bifurcation in the leading arm and report no significant difference between the two branches in terms of metallicity, kinematics, or distance. Conclusions. We provide the largest sample of RR Lyrae candidates of Sgr, which can be used as input for a spectroscopic follow-up or as a reference for the new generation of models of the stream through the interpolators in distance and velocity that we constructed.

Evaluation and Mitigation of AC Losses in a Fully Superconducting Machine for Wind Turbine Applications

A significant challenge in the design of fully superconducting (SC) machines is managing ac losses in the SC armature. Recent developments in MgB 2 superconducting conductors promise low ac loss conductors suitable for fully SC machines. This paper presents an optimized design targeting low losses and low weight for a 10-MW fully SC generator suitable for offshore wind turbine applications. An outer rotor air-core machine topology is investigated to optimize the design with low weight and low losses. An active shielding concept is used to minimize the pole count without adding excessive weight. This enables a reduction in the electrical frequency for a practical design by a factor of 4 to 5 over current designs, driving ac losses and active components weight lower by an order of magnitude. In this study, armature current is varied to control electrical and magnetic loading in order to minimize losses. A pole count study is conducted to identify the design space suitable for MW scale machines. A comparison is made between active shield, passive shield and a hybrid topology to address the benefits of an active shield for weight reduction. Results suggest that low-pole-count designs with MgB 2 conductors will enable machines with less than 1 kW of ac losses.

Systematically Exploring the Effects of Pole Count on the Performance and Cost Limits of UltraHigh Efficiency Fractional hp Axial Flux PM Machines

Optimizing the design of electric machines is a vital step in ensuring the economical use of active materials. The three-dimensional (3-D) flux paths in axial flux permanent magnet (AFPM) machines necessitate the use of computationally expensive 3-D electromagnetic analysis. Furthermore, a large number of design evaluations is required to find the optimum, causing the total computation time to be excessively long. In view of this, a two-level surrogate assisted algorithm capable of handling such expensive optimization problems is introduced, which substantially reduces the number of finite element analysis (FEA) evaluations to less than 200 while conventional algorithms require thousands of designs to be analyzed. The proposed algorithm is employed to optimally design an AFPM machine within a specified envelope, and to identify the limits of cost and efficiency. In order to obtain these limits, the variables' ranges are assigned to be as wide as possible, resulting in a vast design space, the study of which was enabled by the developed special algorithm. Additionally, optimized designs with different rotor polarities are systematically compared in order to form the basis for a set of generalized design rules.

A General Investigation of the Sensitiveness of Brushless Permanent Magnet Synchronous Machines Considering Magnet Tolerances

This article is about investigating the tolerance sensitiveness of electric machines regarding permanent magnet failures. The focus is on established permanent magnet synchronous machine designs in terms of slot and pole count. A finite-element-based approach is presented that allows analyzing single air-gap magnetomotive force (MMF) harmonics and the therefrom caused effects. Their corresponding magnitudes can be estimated based on a relatively fast analytical evaluation of multiple simultaneous magnet failures. Examples of evaluated magnet tolerances are misplaced permanent magnets or differences in the magnets' width, height, or magnetization strength, and direction. In contrast to investigating numerous different combinations of permanent magnet failures, general statements regarding the tolerance sensitiveness of the machines can be derived within reasonable time. A case study is defined, featuring six different topologies and the sensitivity on cogging torque and linked flux harmonics is evaluated. Low-order MMF harmonics are focused, as those typically feature the most significant impact on the machine's performance. Significant differences among the configurations regarding cogging torque increase and additional linked flux harmonics compared to the ideal structure are observed. The presented general technique can thus help engineers to rate the sensitivity of machine designs with regard to tolerance-induced MMF harmonics. The presented approach is thus useful at both the early design stage to select the most suitable machine configuration in terms of the number of slots, poles, and the winding arrangement, and during machine design optimization to compare different geometrical configurations.

Slotless Lightweight Motor for Aerial Applications

A slotless, lightweight permanent-magnet (PM) motor with high pole count is designed and analyzed for a drone system that requires four motors of 0.5 kW each for a 2-kW propulsion power to attain the required torque–speed profile. The design optimization was carried out using finite-element analysis that lead to a slotless stator with outer rotor Halbach PM configuration achieving high power density, zero cogging torque, low torque ripple, sinusoidal back electromotive force, and good system efficiency. The Halbach configuration is found to have superior power density and torque ripple over the conventional concepts for the aerial applications. The power density and efficiency of the slotless motor can be enhanced through the use of nonconventional thermoplastic material and Halbach segmentation. The resulting low inductance of the slotless machine introduces a controls challenge, but it can be overcome with today's enabling technology of wide bandgap devices. A comprehensive analysis and comparison of the slotless design with an equivalent slotted-radial version showed the superiority of the former. An optimum slotless design has been prototyped and test results along with analysis are presented.

Gaia kinematics reveal a complex lopsided and twisted Galactic disc warp

Context. There are few warp kinematic models of the Galaxy able to characterise both structure and kinematics, since these require high accuracy at large distances. These models are necessary to shed light on the lopsidedness of the warp and the twisting of the line-of-nodes of the stellar warp already seen in gas and dust. Aims. We use the vertical information coming from the Gaia Data Release 2 astrometric data up to G = 20 mag to characterise the structure of the Galactic warp, the related vertical motions, and the dependency of Galactic warp on age. Methods. We analyse two populations up to Galactocentric distances of 16 kpc: a young bright sample mainly formed by OB stars and an older one of red giant branch (RGB) stars. We use two methods (the pole count maps of great circle bands and Galactic longitude – proper motion in latitude lines) based on the Gaia observables, together with 2D projections of the positions and proper motions in the Galactic plane. Results. This work confirms the age dependency of the Galactic warp, both in position and kinematics, the height of the Galactic warp being of the order of 0.2 kpc for the OB sample and 1.0 kpc for the RGB at a Galactocentric distance of 14 kpc. Both methods find that the onset radius of the warp is 12 ∼ 13 kpc for the OB sample and 10 ∼ 11 kpc for the RGB. From the RGB sample, we find from Galactocentric distances larger than 10 kpc that the line-of-nodes twists away from the Sun-anticentre line towards Galactic azimuths ≈180−200° increasing with radius, though possibly influenced by extinction. Also, the RGB sample reveals a slightly lopsided stellar warp with ≈250 pc difference between the up and down sides. The line of maximum of proper motions in latitude is systematically offset from the line-of-nodes estimated from the spatial data, which our warp models predict as a kinematic signature of lopsidedness. We also show a prominent wave-like pattern of a bending mode different in the OB and RGB samples. Both positions and kinematics also reveal substructures that might not be related to the large-scale Galactic warp or to the bending mode. Conclusions. Gaia Data Release 2 data reveals a high degree of complexity in terms of both position and velocity that triggers the need for complex kinematic models flexible enough to combine both wave-like patterns and an S-shaped lopsided warp.