Variable Reluctance Research Articles

AC/DC current ratio in a current superimposition variable flux reluctance machine

Abstract We have proposed a current superimposition variable flux reluctance machine for traction motors. The torque-speed characteristics of this machine can be controlled by increasing or decreasing the DC current. In this paper, we discuss an AC/DC current ratio in the current superimposition variable flux reluctance machine. The structure and control method are described, and the characteristics are computed using FEA in several AC/DC ratios.

The V-Shaped Distal Triceps Tendon Repair: A Comparative Biomechanical Analysis

Background: Restoring footprint anatomy, minimizing gap formation, and maximizing the strength of distal triceps tendon repairs are essential factors for a successful healing process and return to sport. Hypothesis: The novel V-shaped distal triceps tendon repair technique with unicortical button fixation closely restores footprint anatomy, provides minimal gap formation and high ultimate failure load, and minimizes iatrogenic fracture risk in acute/subacute distal triceps tendon tears. Study Design: Controlled laboratory study. Methods: Twenty-four cadaveric elbows (mean ± SD age, 66 ± 5 years) were randomly assigned to 1 of 3 repair groups: the transosseous cruciate repair technique (gold standard), the knotless suture-bridge repair technique, and the V-shaped distal triceps tendon repair technique. Anatomic measurements of the central triceps tendon footprint were obtained in all specimens with a 3-dimensional digitizer before and after the repair. Cyclic loading was performed for a total of 1500 cycles at a rate of 0.25 Hz, pulling in the direction of the triceps. Displacements were measured on the medial and lateral tendon sites with 2 differential variable reluctance transducers. Load to failure and construct failure mode were recorded. Results: The mean triceps bony insertion area was 399.05 ± 81.23 mm2. The transosseous cruciate repair technique restored 36.6% ± 16.8% of the native tendon insertion area, which was significantly different when compared with the knotless suture-bridge repair technique (85.2% ± 14.8%, P = .001) and the V-shaped distal triceps tendon repair technique (88.9% ± 14.8%, P = .002). Mean displacement showed no significant difference between the V-shaped distal triceps tendon repair technique (medial side, 0.75 ± 0.56 mm; lateral side, 0.99 ± 0.59 mm) and the knotless suture-bridge repair technique (1.61 ± 0.97 mm and 1.29 ± 0.8 mm) but significance between the V-shaped distal triceps tendon repair technique and the transosseous cruciate repair technique (4.91 ± 1.12 mm and 5.78 ± 0.9 mm, P < .001). Mean peak failure load of the V-shaped distal triceps tendon repair technique (732.1 ± 156.0 N) was significantly higher than that of the knotless suture-bridge repair technique (505.4 ± 173.9 N, P = .011) and the transosseous cruciate repair technique (281.1 ± 74.8 N, P < .001). Mechanism of failure differed among the 3 repairs, with the only olecranon fracture occurring in the knotless suture-bridge repair technique at the level of the lateral row suture anchors. Conclusion: At time zero, the V-shaped distal triceps tendon repair technique and the knotless suture-bridge repair technique both provided anatomic footprint coverage. Ultimate load to failure was highest for the V-shaped distal triceps tendon repair technique, while gap formation was different only in comparison with the transosseous cruciate repair technique. Clinical Relevance: The V-shaped distal triceps tendon repair technique provides an alternative procedure to other established repairs for acute/subacute distal triceps tendon ruptures. The reduced repair site motion of the V-shaped distal triceps tendon repair technique and the knotless suture-bridge repair technique at the time of surgery may allow a more aggressive rehabilitation program in the early postoperative period.

Design-Oriented Modelling of Axial-Flux Variable-Reluctance Resolver Based on Magnetic Equivalent Circuits and Schwarz–Christoffel Mapping

Axial flux variable reluctance (AFVR) resolvers have substantial benefits that make them suitable for motion control drives. However, they suffer from insufficient accuracy, especially in high-accuracy applications. Hence, optimizing the AFVR resolver structure is necessary for improving its commercial usage. However, its accurate modelling needs three-dimensional (3-D) time stepping finite element analysis (TSFEA) that is computationally expensive and unsuitable for co-usage with optimization algorithms. The aim of this paper is to establish an accurate, yet computationally fast, model suitable for optimal design of AFVR resolvers. The working of the proposed model is based on magnetic equivalent circuit (MEC) and conformal mapping, which are in turn based on Schwarz–Christoffel mapping. The model uses conformal mapping to calculate reluctances that are used in MEC for calculating magnetic fluxes linkages, inductances, and induced voltages. Then, the induced voltages are used for calculating angular position. The results of the proposed model are compared with those of 3-D TSFEA. Finally, the experimental prototype is used to evaluate the developed analytical model.

Combined Variable Reluctance-Hall Effect Displacement Sensor

A new noncontact displacement sensor employing a combination of variable reluctance technique and Hall effect sensing is designed and developed. The magnetic part of the sensor consists of a sensor head that moves over two identical trapezoidal elements. It is also possible to fix the sensor head and move the trapezoidal parts over it. A permanent magnet (PM) provides magnetic excitation and a couple of Hall sensors sense the fluxes in the magnetic circuit. The direct digital output of the sensor, obtained with a signal conditioning circuit, is unaffected by variations in the strength of the PM as well as variations in the permeability of the magnetic parts. Since, the digital output is insensitive to variations in the actual value of the strength of the PM, any change in the magnetic strength of the magnet (either due to decay or misalignment) will not affect the performance of the proposed displacement sensor. Error analysis presented herein establishes the ground rules to be followed while designing the sensor. Results from simulation and that obtained from a prototype sensor built and tested establish the practicality of the proffered sensor.

A Superconducting Linear Variable Reluctance Machine for Urban Transportation Systems

This paper presents a new superconducting linear variable reluctance machine for urban transportation applications. The proposed linear machine has a doubly salient structure. Its armature adopts segmented configuration and houses both the copper armature winding and the high-temperature superconducting field winding, while the salient-pole rail consists of iron core only with no excitation sources. Performances of the proposed machine are analyzed and evaluated by the finite element method. By using segmented armature design, the force ripple can be suppressed to 5.5% that is very desirable for urban transportation systems.

Sex-Based Differences of Medial Collateral Ligament and Anterior Cruciate Ligament Strains With Cadaveric Impact Simulations.

Background:Female patients sustain noncontact knee ligament injuries at a greater rate compared with their male counterparts. The cause of these differences in the injury rate and the movements that load the ligaments until failure are still under dispute in the literature.Purpose/Hypotheses:This study was designed to determine differences in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) strains between male and female cadaveric specimens during a simulated athletic task. The primary hypothesis tested was that female limbs would demonstrate significantly greater ACL strain compared with male limbs under similar loading conditions. A secondary hypothesis was that MCL strain would not differ between sexes.Study Design:Controlled laboratory study.Methods:Motion analysis of 67 athletes performing a drop vertical jump was conducted. Kinetic data were used to categorize injury risk according to tertiles, and these values were input into a cadaveric impact simulator to assess ligamentous strain during a simulated landing task. Uniaxial and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect mechanical data for analysis. Conditions of external loads applied to the cadaveric limbs (knee abduction moment, anterior tibial shear, and internal tibial rotation) were varied and randomized. Data were analyzed using 1-way analysis of variance (ANOVA), 2-way repeated-measures ANOVA, and the Fisher exact test.Results:There were no significant differences (P = .184) in maximum ACL strain between male (13.2% ± 8.1%) and female (16.7% ± 8.3%) specimens. Two-way ANOVA demonstrated that across all controlled external load conditions, female specimens consistently attained at least 3.5% increased maximum ACL strain compared with male specimens (F 1,100 = 4.188, P = .043); however, when normalized to initial contact, no significant difference was found. There were no significant differences in MCL strain between sexes for similar parameters.Conclusion:When compared with baseline, female specimens exhibited greater values of ACL strain at maximum, initial contact, and after impact (33, 66, and 100 milliseconds, respectively) than male specimens during similar loading conditions, with a maximum strain difference of at least 3.5%. During these same loading conditions, there were no differences in MCL loading between sexes, and only a minimal increase of MCL loading occurred during the impact forces. Our results indicate that female patients are at an increased risk for ACL strain across all similar conditions compared with male patients.Clinical Relevance:These data demonstrate that female specimens, when loaded similarly to male specimens, experience additional strain on the ACL. As the mechanical environment was similar for both sexes with these simulations, the greater ACL strain of female specimens must be attributed to ligament biology, anatomic differences, or muscular stiffness.

Fast design method of variable flux reluctance machines

In this paper, a fast design method is developed based on a combination of analytical and finite element (FE) methods for variable flux reluctance machines (VFRMs). Firstly, the feasibility of using analytical method in optimization under unsaturated condition is confirmed. Then, by applying the FE method, the influence of magnetic saturation is considered. Compared with the unsaturated case, the optimal split ratio for magnetically saturated case is increased by 1~1.2 times, the optimal rotor pole arc ratio varies within 0.33~0.44, and the stator pole arc ratio remains the same. Based on this, the optimal structural parameters can be initially set by analytical method and then refined by the FE method. Due to the fast speed of analytical method, less variable counts and narrowed variation ranges, the proposed method is significantly faster than the conventional pure FE based global optimization. Finally, the proposed method is used for optimizing the 6-stator-slots VFRMs having different numbers of rotor poles. The 6-stator-slot/7-rotor-pole (6s/7r) VFRM is found to have the highest torque density. It is prototyped and tested to verify the analyses.

Analytical Analysis of a Novel Flux Adjustable Permanent Magnet Eddy-Current Coupling With a Movable Stator Ring

This paper proposes a novel flux adjustable permanent magnet eddy-current coupling with a movable stator ring (MSR). The slip speed of the proposed coupling can be adjusted by shifting the MSR along the axial direction. The structural feature and operation principle of the coupling are illustrated. An analytical model based on magnetic equivalent circuit method is built to compute its electromagnetic characteristics efficiently. The dynamic process of the MSR movement is simulated by employing a variable air-gap reluctance model. The eddy-current field under asymmetric magnetic field is calculated by an improved analytical method. The electromagnetic characteristics of the coupling, such as air-gap magnetic field, eddy-current, and torque-slip speed characteristics, are analytically investigated. The analytical results are verified with the results obtained by the 3-D finite-element method.

Sex-Based Differences in Knee Kinetics With Anterior Cruciate Ligament Strain on Cadaveric Impact Simulations.

Background:Females are at an increased risk of sustaining noncontact knee ligament injuries as compared with their male counterparts. The kinetics that load the anterior cruciate ligament (ACL) are still under dispute in the literature.Purpose/Hypothesis:The purpose of this study was to determine whether there are differences in knee kinetics between the sexes that lead to greater ACL strain in females when similar external loads are applied during a simulated drop vertical jump landing task. It was hypothesized that female limbs would demonstrate significant differences in knee abduction moment that predispose females to ACL injury when compared with males.Study Design:Controlled laboratory study.Methods:Motion analysis data of 67 athletes who performed a drop vertical jump were collected. The kinematic and kinetic data were used to categorize tertiles of relative risk, and these values were input into a cadaveric impact simulator to assess ligamentous loads during the simulated landing task. Uni- and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect kinetic data and maximum ACL strain for analysis. Conditions of external loads applied to the cadaveric limbs were systematically varied and randomized. Data were analyzed with 2-way repeated-measures analysis of variance and the Fisher exact test.Results:Five kinetic parameters were evaluated. Of the 5 kinetic variables, only knee abduction moment (KAM) demonstrated significant differences in females as compared with males (F 1,136 = 4.398, P = .038). When normalized to height and weight, this difference between males and females increased in significance (F 1,136 = 7.155, P = .008). Compared with males, females exhibited a 10.3-N·m increased knee abduction torque at 66 milliseconds postimpact and a 22.3-N·m increased abduction torque at 100 milliseconds postimpact. For loading condition, the condition of “maximum ACL strain” demonstrated a maximum difference of 54.3-N·m increased abduction torque and 74.5-N·m increased abduction torque at 66 milliseconds postimpact.Conclusion:Under the tested conditions, increased external loads led to increased medial knee translation force, knee abduction moment, and external knee moment. Females exhibited greater forces and moments at the knee, especially at KAM, when loaded in similar conditions. As these KAM loads are associated with increased load and strain on the ACL, the sex-based differences observed in the present study may account for a portion of the underlying mechanics that predispose females to ACL injury as compared with males in a controlled simulated athletic task.Clinical Relevance:KAM increases strain to the ACL under clinically representative loading. Additionally, this work establishes the biomechanical characteristics of knee loading between sexes.

Preferential peroneal nerve injury after acetabular fracture and reconstruction

Background: Sciatic nerve dysfunction typically involving the peroneal division infamously plagues acetabular reconstruction through a posterior exposure. Competing explanations include mechanical compression from retractor placement at the hip versus overstretch. In an effort to improve the current care paradigm, we asked what underlying mechanisms of injury lead to preferential injury to the peroneal division of the sciatic nerve. Methods: A cadaver model was established to measure both sciatic nerve strain and intraneural pressure generated during simulated retraction performed during acetabular reconstruction. The tibial and peroneal divisions were studied independently using a micro differential variable reluctance transducer (DVRT) to quantify strain and an angiocatheter to measure intraneural pressure. Measurements were recorded at both the hip and knee. Results: Both divisions of the sciatic nerve experienced significantly more pressure at the hip than at the knee. Knee flexion reduced intraneural pressure of the peroneal division at the hip by approximately 30%. Intraneural pressure at the knee was significantly greater in the peroneal versus tibial nerve during knee extension, yet was reduced with knee flexion. Conclusions: Our results suggest that direct compression of the peroneal nerve during hip retraction has the most potential to cause iatrogenic sciatic nerve injury. Knee flexion was beneficial for decreasing nerve stretch and pressure. The peroneal division, however, is vulnerable to dysfunction because of the higher intraneural pressures experienced by the tethering effect of the fibular tunnel at the knee.

Effects of Seating Load Magnitude on Incremental Cyclic Fretting Corrosion in 5°40’ Mixed Alloy Modular Taper Junctions

BackgroundMechanically assisted crevice corrosion of modular tapers continues to be a concern in total joint arthroplasties. A surgical factor that may affect taper fretting corrosion during cyclic loading is seating load magnitude. In this study, modular head-neck taper junctions were seated, capturing load-displacement, over a range of axially oriented loads, and electrochemical and micromotion data were captured during short-term incremental cyclic fretting corrosion (ICFC) tests. The hypothesis is low seating loads result in greater motion and fretting corrosion in ICFC tests. The effect of assembly load on pull-off force post-ICFC testing was also evaluated. MethodsThe study employed custom-built test fixtures which measured head-neck micromotion and an electrochemical chamber to monitor electrochemical reactions. Head-neck motion measurements were captured using 2 noncontact differential variable reluctance transducers mounted to the head. Seating experiments ranged from 1000 to 8000 N. ResultsSignificant differences due to seating loads were reported in seating displacement, ICFC subsidence, and fretting current at 4000 N cyclic load. Seating load decreased but did not eliminate currents. Fretting onset load remained fixed (approximately 1200 N) for tapers seated above 2000 N. Fretting subsidence was negligible for seating loads of 4000 N or higher, and increased subsidence was observed below 4000 N. ConclusionThis short-term test method evaluated the acute performance of modular implants which were assembled under various loads and demonstrated the link between seating loads, fretting motions, and electrochemical reactions. While increased seating loads reduced fretting corrosion and taper subsidence, it did not prevent fretting corrosion even at 8 kN seating.

Design of Sliding Mode Speed Controller for Switched Reluctance Motor

Switched Reluctance motors (SRM) can be classified into a group of multi-speed electrical motors. The low cost, rugged constructions and simple are feature advantages for this motor. The simplicity is the result of their torque generation principle, which known as variable reluctance principle. The SRM has many more features that have made it to be common for applications in commercial and industrial markets. The main disadvantage of SRM is the nonlinearity that it appears in their dynamics because of the magnetic saturation. It is required for SRM speed controllers to have features such as fast dynamic responses, parameter insensitivity and quick recovery from load disturbances. In this paper, a design of a robust sliding mode speed controller based on a nonlinear mathematical model is proposed. Matlab/Simulink software is used to simulate switched reluctance motor drive system under control of SMC. 6/8 switched reluctance motor has been taken as case study. The performance of proposed sliding mode control is tested at different load and speed conditions, and comparisons with conventional PI control for switched reluctance motor are presented. The sliding mode controller exhibits a better performance than the PI controller for all the studied cases.

A Survey on Variable Reluctance Energy Harvesters in Low-Speed Rotating Applications

Energy harvesting converts ambient energy to electrical energy that can be used to power, for example, sensors and sensor systems. Variable reluctance (VR) energy harvesting is a suitable candidate for the conversion of rotary kinetic motion, an energy form commonly found in industrial applications. The implementation of a VR energy harvester (VREH), however, has a significant effect on its performance and is not well studied. In this paper, we therefore conduct a survey on different structures of VREHs. Six existing structures, previously used in VR sensors, are presented and analyzed according to their approaches for magnetic flux change improvement. Together with a newly proposed structure, these structures are evaluated based on a finite element analysis, and their results are compared. It is demonstrated that the choice of structure considerably affects the power output of the harvester and is dependent on the improvement approaches the structure utilizes. The newly proposed structure outperforms all existing structures with respect to power output and power density, which comes at a cost of higher parasitic torque generation. A 53-fold power improvement over the reference and an 1.2-fold power improvement over the next best structure is observed. As a result, applications of VR energy harvesting become viable even at low angular velocities.

Design and control of a linear switched reluctance actuator of motorization a left ventricular assist device

We proposed a new concept of left ventricular mechanical circulatory assist device (LVAD) positioned on the descending aorta, called Pulsamag. In order to avoid the occurrence of thrombosis, this pulsatile pump incorporates the pump and valve function. A demonstrator has been designed and is based on a linear tubular actuator with variable reluctance. The inside of the tubular translator is equipped with a 20 mm diameter aortic valve allowing the circulation of blood. The dynamic response of the actuator is determined from coupling of the electrical and mechanical models, which is characterized by a constraining oscillating coport. Internal model control is applied to reduce oscillations and increase the performance of the LVAD system.

Current superimposition variable flux reluctance motor with 8 salient poles

Abstract We propose a current superimposition variable flux reluctance motor for a traction motor of electric vehicles and hybrid electric vehicles, which consists of 10 salient poles in the rotor and 12 slots in the stator. However, iron losses of this motor in high rotation speed ranges is large because the number of salient poles is large. In this paper, we propose a current superimposition variable flux reluctance motor that consists of 8 salient poles and 12 slots. The characteristics of the 10-pole-12-slot and 8-pole-12-slot current superimposition variable flux reluctance motors are compared using finite element analysis under vector control.

Analysis of Torque Production in Variable Flux Reluctance Machines

In this paper, the torque production mechanism of variable flux reluctance machines (VFRMs) is investigated. Initially, based on an analytical instantaneous torque model developed from the Lorentz force law and airgap field harmonic analysis, the magnetic gearing effect is revealed in the torque production of VFRMs. Then, by using a 6-stator-pole/4-rotor pole (6s/4r) VFRM as an example, all its torque components, including synchronous torque, reluctance torque, and cogging torque, are analyzed separately under linear condition. Their average torque and torque ripple characteristics are comprehensively illustrated. Finally, the influence of saturation effect is also accounted for with the help of finite element and frozen permeability methods. The analysis results are verified experimentally.

Analysis of fractional order inductive transducers

Inductive sensors have been widely used for precise measurement of position, displacement, temperature and pressure as they are extremely reliable in the harsh industrial atmosphere. In this paper, fractional order models of inductive transducers namely fractional order variable reluctance inductive transducer and fractional order resonant inductive transducer are developed and its characteristics are analysed. The impact of fractional order parameter on the characteristics like sensitivity and nonlinearity of the fractional order transducer are studied. The results are enriched when a fractional order inductor is connected in parallel to the fractional order resonant inductive transducer.

Torque Ripple Reduction for 12-Stator/10-Rotor-Pole Variable Flux Reluctance Machines by Rotor Skewing or Rotor Teeth Non-Uniformity

Variable flux reluctance machines (VFRMs) are interesting candidates to substitute permanent-magnet synchronous machines in many applications. However, they suffer from large torque ripple. In this paper two methods, stepped rotor skewing and rotor teeth non-uniformity, are researched to reduce the torque ripple of 12/10 (stator/rotor-pole ratio) VFRMs. Based on semi-analytic results and finite-element simulations, the effectiveness of these two methods is validated in both non-saturated and saturated machines.

Electromagnetic Torque Performance Analysis of a Parallel Hybrid Excitation Machine With Axial Paralleling of Permanent Magnet Part and Variable Reluctance Part

In this paper, the electromagnetic torque (EM) performance analysis of a parallel hybrid excitation machine (PHEM) is investigated. It is composed of a permanent magnet (PM) part and variable reluctance part. The flux paths of the two parts are independent and the armature windings are connected in series. PHEM is an axial parallel coupling of two different types of brushless machine. The mechanisms of EM torque for the two parts are quite different and many problems of torque coupling still remain unsolved. A 2-D EM-circuit coupling simulation model is built to analyze the torque characteristics and coupling relationships. The simulation results indicate that the PM part plays a main role in the output torque of PHEM. The large inductance ripple of variable reluctance part would cause large torque ripple in PHEM. The target machine is experimentally tested to verify the output torque characteristics. Furthermore, the torque-angle characteristics are studied with different field current and it shows that the best load angle could be around 110° to get maximum output torque and relatively smaller torque ripple.

FEM Study of the Effects of Geometric Changes on the Variable Reluctance Shaded-Pole Motors Performance

FEM Study of the Effects of Geometric Changes on the Variable Reluctance Shaded-Pole Motors Performance