Showing papers on "Electromagnetic coil published in 2021"

Low-Noise Magnetic Coil System for Recording 3-D Eye Movements

Abstract: Vestibular and oculomotor research often requires measurement of 3-D eye orientation and movement with high spatial and temporal precision and accuracy. We describe the design, implementation, validation, and use of a new magnetic coil system optimized for recording 3-D eye movements using small scleral coils in animals. Like older systems, the system design uses off-the-shelf components to drive three mutually orthogonal alternating magnetic fields at different frequencies. The scleral coil voltage induced by those fields is decomposed into three signals, each related to the coil’s orientation relative to the axis of one field component. Unlike older systems based on analog demodulation and filtering, this system uses a field-programmable gate array (FPGA) to oversample each induced scleral coil voltage (at 25 Msamples/s), demodulate in the digital domain, and average over 25 ksamples per data point to generate 1-ksamples/s output in real time. Noise floor is <0.036° peak-to-peak and linearity error is <0.1° during 345° rotations in all three dimensions. This FPGA-based design, which is both reprogrammable and freely available upon request, delivers sufficient performance to record eye movements at high spatial and temporal precision and accuracy using coils small enough for use with small animals.

Advanced Control of Switched Reluctance Motors (SRMs): A Review on Current Regulation, Torque Control and Vibration Suppression

Abstract: With the increasing environmental concerns, a paradigm shift towards electric and hybrid electric vehicles is expected. Switched Reluctance Motors (SRMs) have emerged as a viable competitor to other established electrical machines. SRMs are known for their simple construction, robustness, inherent fault tolerant structure and low production and maintenance costs. Moreover, the machine has gained interest due to the absence of permanent magnets or windings in the rotor structure, which significantly reduces production costs when compared to other electric motors. The SRM, however, present some known drawbacks, such as increased torque ripple and acoustic noise production, as well as a highly nonlinear behavior. Through the use of adequate control strategies, however, the main challenges of the machine can be overcome. Thus, this paper presents a state-of-the-art review of the advanced control of SRMs, encompassing current regulation strategies, torque control strategies and vibration suppression techniques. First, two categories of current controllers are reviewed: model-independent and model-based. Next, indirect and direct torque control methods are explored. Then, three approaches to vibration suppression are discussed, namely active cancellation, current profiling and direct instantaneous force control. Lastly, a summary of each topic is presented and suggestions of future research topics are listed.

A Field Enhancement Integration Design Featuring Misalignment Tolerance for Wireless EV Charging Using LCL Topology

Abstract: This article proposes a magnetic integration design for EV wireless power transfer (WPT) systems, where the compensation and transmitting coils overlap one on top of the other to share the ferrite layer without any decoupling consideration. The magnetic field generated by both the compensation and transmitting coils are exploited to transfer power. To this end, a compensation method is proposed to enable magnetic field enhancement without any reactive power flow between the compensation and the transmitting coils, and to achieve input zero phase angle and constant current output. In addition, an efficient finite element analysis-based coil optimization algorithm is proposed to improve the coil misalignment tolerance on the horizontal plane, in which a reversely connected inner coil is used to stabilize the system output under misalignment conditions. Analytical and simulation results confirm transmission flux density enhancement and reduced leakage field characteristics of the proposed coil design. Finally, a scaled-down WPT prototype is built and tested to verify the performance and effectiveness of the design. The proposed design achieves 91.17% efficiency and misalignment tolerance up to 200 mm in any XY-direction while maintaining the power transfer and its efficiency. The results of this work provide insights into magnetic integration design of high-order compensation topologies featuring higher compactness, less ferrite usage, magnetic field enhancement, and misalignment tolerance for WPT systems.

Independent Electromagnetic Field Control for Practical Approach to Actively Locomotive Wireless Capsule Endoscope

Abstract: Toward wireless medical microrobot applications driven by an electromagnetic actuation (EMA) system, challenges associated with movability, the electromagnetic force, and the coil system size must be addressed. This paper presents an enhanced EMA system with a higher magnetic field via new coil configurations, an independent magnetic field control method, and application to the multi-degree-of-freedom (DOF) motion of an untethered capsule endoscope. The magnetically actuated capsule endoscope (MACE) system proposed herein consists of an endoscopic capsule with a permanent magnet in the body, eight air-cored stationary electromagnetic coils, and a control system. The coil system is designed to maximize the working space available within a limited equipment space. The MACE is designed to perform full 5-DOF motion, including 3-DOF translation and 2-DOF rotation. The independent magnetic field control method with the new coil configuration enables orientation-independent-driving (OID) control of the capsule endoscope that could not be accomplished by previous EMA systems. The developed system performance was verified by simulations and experiments. The MACE motion in the spatial domain was evaluated with a robotic endoscopic procedure and diagnostic performance by in-vitro and ex-vivo experiments.

Design, Challenges, and Trends of Inductive Power Transfer Couplers for Electric Vehicles: A Review

Abstract: The magnetic coupler is the heart of an inductive power transfer (IPT) system, which facilitates wireless power transfer through its air gap. The couplers are designed to maximize efficiency, power density, power transfer distance, and misalignment tolerance while minimizing leakage flux, weight, cost, and volume. The coupler design process becomes complex due to the nonlinear behavior of magnetics, sophisticated geometrical structures, and mandatory design limitations imposed by standards, such as SAE J2954/1, IEC 61980-1:2015, and ISO 19363:2020. Initially, this article reviews the advancements in coil design methodologies and their structures over the last few decades to identify the ongoing challenges and trends. The impacts of the power electronics system, industrial standards, material selection, numerical and analytical modeling methods, and thermal modeling on the coil design process are identified to formalize the design procedure. A coil design example based on finite element analysis (FEA) tools is presented to identify the drawbacks of the existing design and optimization process. A sensitivity analysis, 3-D-Pareto plots, and optimal design selection by considering misalignment variations are proposed to improve the multiobjective optimization process. A generalized guideline for coil design is proposed, which highlights the essential design stages of an IPT coupler. Current trends are identified, and future directions are proposed.

Locating Inter-Turn Faults in Transformer Windings Using Isometric Feature Mapping of Frequency Response Traces

Abstract: Power transformers usually confront various mechanical and electromagnetic stresses during an operation that may lead to defects in their windings. The short circuit in the windings is one of those severe defects. Early detection of short-circuits is necessary as extra heating in the shorted location can lead to progressive damage in windings insulation. Frequency response analysis (FRA) is a well-known method to diagnose short-circuits in transformers. Despite the accuracy of FRA, the interpretation of the obtained frequency response traces (FRTs) is still an intricate task. Due to the unknown impact of faults on FRTs, extracting efficient features from such traces is necessary for the interpretation of transformer's frequency response. In this article, an isometric feature mapping (Isomap) is used as a nonlinear dimensionality reduction technique to locate interturn faults in transformer windings due to its capability of capturing the nonlinear phenomena in FRT of power transformers. It is revealed that, after constructing the isometric mapping for a transformer, there is no need for any expertise to detect fault location even in nondirect (high impedance) short-circuits. In other words, it can be the first step for the automated interpretation of FRA of power transformers.

Unified Models for Coupled Inductors Applied to Multiphase PWM Converters

Abstract: Circuit models for multiphase coupled inductors are summarized, compared, and unified. Multiwinding magnetic structures are classified into parallel-coupled structures and series-coupled structures. For parallel-coupled structures used for multiphase inductors, the relationships between: 1) inductance-matrix models, 2) extended cantilever models, 3) magnetic-circuit models, 4) multiwinding transformer models, 5) gyrator-capacitor models, and 6) inductance-dual models are examined and discussed. These models represent identical physical relationships in the multiphase coupled inductors, but emphasize different physical aspects and offer distinct design insights. The circuit duality between the series-coupled structure and the parallel-coupled structure is explored. Design equations for interleaved multiphase buck converters based on these models are streamlined and summarized, and a simplified equation showing the relationships between current ripple with and without coupling is presented. The models and design equations are verified through theoretical derivation, SPICE simulation, and experimental measurements.

Design and Verification of In-Slot Oil-Cooled Tooth Coil Winding PM Machine for Traction Application

Abstract: Tooth coil windings, in particular when using a double layer structure, present opportunities for in-slot liquid cooling. Since the windings are not overlapping, access to the slot from the end section for coolant liquids is enabled. In this article, a solution for in-slot and in-stator direct oil cooling for a tooth coil winding machine is presented. The coils are prewound on bobbins and inserted on the stator teeth. The novelty of the design consists in the integration of the cooling, using a thermally conductive epoxy resin to create the channels within the slot as well as the positioning of the stator yoke cooling channels. A 50-kW machine for an automotive traction application is designed, manufactured, and tested. Conjugate heat transfer simulations are used in the design process in combination with finite-element analysis for the loss mapping. The thermal model is verified with measurements at 6-L/min oil flow and 17.5 A/mm $^2$ continuous and 35 A/mm $^2$ 30-s peak. The thermal model is then used to establish a continuous operating point at 25 A/mm $^2$ .

6.78-MHz Wireless Power Transfer With Self-Resonant Coils at 95% DC–DC Efficiency

Abstract: Megahertz-frequency inductive wireless power transfer holds the promise of compact and efficient wireless power transfer. Unfortunately, due to high-frequency losses in wide-bandgap semiconductors and low- $Q$ high-frequency coil designs, these systems are universally less efficient, on a dc–dc basis, than wireless power systems operating at conventional frequency regimes. This letter describes the design considerations for inductive wireless power transfer systems operating at 6.78 MHz. With a novel high-frequency resonant amplifier topology, a high- $Q$ self-resonant coil structure, and a better understanding of $C_{oss}$ losses in wide-bandgap power semiconductors, we demonstrate 6.78- MHz wireless power transfer systems that achieve 95% dc–dc efficiency at power levels up to and beyond 1 kW.

Multiobjective and Multiphysics Design Optimization of a Switched Reluctance Motor for Electric Vehicle Applications

Abstract: Switched reluctance motors (SRMs) have attracted much attention in industry due to the advantages of low cost, robust structure, high fault tolerance and high torque density. However, several disadvantages like high torque ripples and coil temperatures hinder their industrialization for some applications requiring high dynamic performance, like electric vehicles (EVs). In this paper, a multiobjective and multiphysics design optimization method considering both thermal and electromagnetic performance is presented for a 12/10 SRM. First, the topology of the SRM is introduced and the optimal parameters are defined. Then, the electromagnetic finite element model (FEM) is introduced and the improved transient lumped-parameter thermal model (TLPTM), considering both axial and radial heat transfer for the SRM, is proposed. Second, the objectives and constraints of the optimization are determined. To improve the optimization efficiency, the sequential subspace optimization strategy is employed to find the optimal solution of this high-dimensional design optimization problem. Finally, to validate the effectiveness of the proposed method, both simulation and experimental results are given and discussed. Compared with the initial design, the optimal solution exhibits lower temperature, higher torque, lower torque ripple and less loss.

Multiobjective Optimization of Inductive Power Transfer Double-D Pads for Electric Vehicles

Abstract: This article proposes a multiobjective optimization method of a primary double-D pad for inductive power transfer systems. First, a parametric sweep analysis is conducted to choose the crucial design parameters. Then, using the nondominated sorting genetic algorithm II, the structure of the double-D pad can be optimized based on two key objectives; ensuring a good coupling coefficient while minimizing the worst-case stray leakage magnetic fields. Several useful design guidelines are found from the optimization results, including how the dimensions of both the coil and layers affect the coupling coefficient and stray leakage magnetic fields around the pad. A practical coil suitable for wireless charging of electric vehicles at level 2, similar to that recommended in SAE J2954, is used as the reference and also as the starting point for the optimization. Two of the coil structures resulting from the optimization are chosen and investigated further to assess their performance with different secondary pad misalignments using finite element methods. Finally, an experimental setup is built to validate the optimal pad structures.

A 50-kW Three-Channel Wireless Power Transfer System With Low Stray Magnetic Field

Abstract: Adopting high-power wireless charging systems, particularly for heavy-duty electric vehicles (EVs) and fast charging of regular EVs, becomes extremely imperative. The stringent requirements of safety guidelines, high efficiency, and high-power density would continue to impede the rapid penetrations of wireless power transfer (WPT) systems for EVs at high power. This article investigates the potentials of multichannel WPT systems to achieve high-power transmission under such requirements. A multichannel WPT system consists of multiple power-transfer paths such that adjusting the number of channels affords the system become adaptive to multiple power levels that could eventually present an opportunity for developing high power, which would be seriously challenging with the conventional single-channel systems. Moreover, different channels can cooperate to achieve superior performance, such as a low stray magnetic field. A three-channel WPT system is designed in this article, and its capability of significantly reducing the stray magnetic field is investigated. By properly determining the power-sharing proportion of the channels, the magnetic field reduction of 80% and 63% can be achieved compared with the rectangular-pad and double D (DD) pad systems (under similar total pads area), respectively. A three-channel 50-kW prototype is produced with a dc–dc efficiency of 95.2% across the 160 mm air gap. The measured results of the magnetic field agree well with the simulation ones.

Optimization Design of Resonance Coils with High Misalignment Tolerance for Drone Wireless Charging Based on Genetic Algorithm

Abstract: The misalignment between the transmitting (Tx) coil and the receiving (Rx) coil is an urgent problem in the drone charging system using wireless power transfer (WPT) technology. The coupling coefficient is so low when the resonance coils is not aligned, which degrades the drone wireless charging performance. In this paper, the optimization processes of the coupling mechanism are presented in detail. First, we illustrate the great superiority of unequally spaced Tx coil, compared with traditional uniformly-spaced one. Then, a genetic algorithm (GA) to optimize the side lengths of the Tx coils is highlighted by discussing the main design considerations and methods in a comprehensive manner. Furthermore, the Rx coil with varying radius size per turn is proposed in terms of the distribution of magnetic field generated by the optimized Tx coil. Experimental results show that the optimized coils have better coupling performance due to small mutual inductance change under the condition of misalignment. Power transfer efficiencies in different misalignment situations are measured and the best PTE improvement achieved by the proposed system can reach 56.23% in contrast with traditional coils. This drone charging system can transfer a maximum power of 100 W with the remarkable transfer efficiency of 92.41%.

Quench and self-protecting behaviour of an intra-layer no-insulation (LNI) REBCO coil at 31.4 T

Abstract: This paper presents experimental results on a quench of an intra-layer no-insulation (LNI) (RE: rare earth)Ba2Cu3O7−δ (REBCO) coil in a 31.4 T central magnetic field and simulated results on the quench. We have been designing a persistent-mode 1.3 GHz (30.5 T) nuclear magnetic resonance (NMR) magnet with a layer-wound REBCO inner coil. Protection of the REBCO coil from quench is a significant issue and the coil employs the LNI method to obtain self-protecting characteristics. We conducted high-field generation and quench experiments on an LNI-REBCO coil connected to an insulated Bi2Sr2Ca2Cu3O x (Bi-2223) coil under a background magnetic field of 17.2 T as a model of the 1.3 GHz NMR magnet. The coils successfully generated a central magnetic field of 31.4 T. Although the LNI-REBCO coil quenched at 31.4 T, this quench did not cause any degradation to the coil. A numerical simulation showed the current distribution during the quench was non-uniform and changed rapidly over time due to current bypassing through copper sheets between layers, resulting in faster quench propagation than in an insulated REBCO coil. During the quench propagation, the peak temperature (T peak) and the peak hoop stress BzJR (σθ, peak) were calculated to be 330 K and 718 MPa, respectively. These are below critical values that cause degradation. The simulation also showed that the high electrical contact resistivity (ρ ct) of 10 000 µΩ cm2, between REBCO conductors and copper sheets in the LNI-REBCO coil winding, played an important role in protection. When ρ ct was as low as 70 µΩ cm2, the quench propagation became too fast and large additional currents were induced, resulting in an extremely high σθ, peak of 1398 MPa, while the T peak was as low as 75 K. In short, the high ρ ct in the present coil caused a high T peak, but succeeded in suppressing σθ, peak and protecting the coil from the quench.

A Novel Helical Superconducting Fault Current Limiter for Electric Propulsion Aircraft

Abstract: It is crucial to achieve a high safety and reliability standard in future electric propulsion aircraft (EPA). Due to low short-circuit impedance and high rate of fault current rise in EPA systems, the superconducting fault current limiter (SFCL) plays a promising role, with advantages of lightweight, high efficiency, and compact size compared with conventional FCL. A novel helical bifilar coil is proposed, which is composed of two windings wound in opposite directions on the same bobbin; these are connected in series to achieve equal current sharing and a noninductive circuit. The 12-mm-wide stainless steel-reinforced superconducting tape from AMSC was used for the windings. To characterize the proposed helical bifilar coil connected in series (BCS), AC loss tests under three frequencies and quench tests under prospective fault current up to 2223 A were carried out. They were compared with the results measured from a conventional helical bifilar coil connected in parallel (BCP) that had an identical specification to the BCS. It was concluded that the AC losses measured in the BCP are dependent on the current and frequency. The fault current was suppressed effectively by the BCS at the first half peak from 2223 to 495 A, corresponding to 22.3% of the prospective fault current. The quench performance of BCP was also tested and discussed.

Flexible Combination and Switching Control for Robust Wireless Power Transfer System With Hexagonal Array Coil

Abstract: Multitransmitter structure can improve the misalignment tolerance of wireless power transfer (WPT) system, but some new problems such as a sharp drop in transmission efficiency will occur when the receiver moves to the boundary situation between transmitters. It is very crucial to solve this problem for an efficient and stable WPT system. In this article, a flexible combination multitransmitter coupling structure based on hexagonal array coil and auxiliary switch is proposed, and the coupling characteristics under misalignment conditions has been deeply analyzed with mutual inductance model. Unlike using coupling coefficient, a convenient switching control strategy is proposed based on the primary current to activate the optimal coil working mode, and the experimental results favorably verified the theoretical analysis. Compared with the circular array coil and the square array coil, the proposed coupling structure and control method can greatly improve the transmission efficiency of the WPT system at the coil boundary, and has stronger robustness under different misalignment conditions.

An On-Board Two-Stage Integrated Fast Battery Charger for EVs Based on a Five-Phase Hybrid-Excitation Flux-Switching Machine

Abstract: In this article, to solve the existing problems in general on-board integrated chargers, a novel three-phase on-board two-stage integrated charger is proposed by taking the unique advantages of a five-phase hybrid-excitation flux-switching (HEFS) motor. The general topologies and newly presented integrated chargers are reviewed first, and existing problems are concluded. Then, a two-stage integrated charger is proposed, and all winding selections are thoroughly investigated by theoretical analysis, finite-element analysis (FEA), and experiments. In the proposed topology, the existing problems are all solved by employing this multiphase system, reasonable winding selection, and reconfiguring the field winding. After that, a current balance control method for charge mode without a phase-locked loop circuit is presented. The simulation results verify the effectiveness of the proposed control methods. Finally, based on a 5-kW five-phase HEFS prototype machine and two sets of the three-phase generic motor controller, an experiment platform is built. The experiment results agree well with the simulation results. Therefore, the feasibility of a two-stage integrated on-board charger that can operate at any voltage level is confirmed, where only the hybrid-exciting machine and its driving system are used without any additional power devices.

Airgap Search Coil based Identification of PM Synchronous Motor Defects

Abstract: On-line detection of rotor and load faults in permanent magnet synchronous motors (PMSM) based on spectrum analysis of current or vibration is not capable of identifying the root cause of the fault, since all faults produce identical fault signatures. The sensitivity of fault detection also depends on the motor and controller design making fault detection unreliable. In addition, operation under variable frequency and load limits the effectiveness of spectrum analysis based methods. In this paper, airgap flux monitoring is investigated as an alternative for providing reliable identification of rotor and load faults in PMSMs. Based on the analysis of airgap flux under partial and uniform demagnetization, dynamic eccentricity and load unbalance, an airgap search coil voltage based method for detection and classification of the faults is proposed. The claims made in the paper are verified through experimental testing on an IPMSM under emulated fault conditions along with a comparison to vibration and current spectra-based detection. It is shown that the proposed method provides reliable on-line identification of the faults for cases where conventional spectrum analysis based methods fail.

Improving the Performance of a 1-MW Induction Machine by Optimally Shifting From a Three-Phase to a Six-Phase Machine Design by Rearranging the Coil Connections

Abstract: It is well known that multiphase machines exhibit the better performance (efficiency, torque density, fault tolerance, etc.) than three-phase machines. From the manufacturing point of view, it is interesting to have the possibility of improving a machine design by just conducting minor changes in the production process. In this regard, six-phase machines emerge as the natural choice to improve a design without modifying the active parts. This article presents an optimal procedure to shift from a three-phase to a six-phase induction motor design by just rearranging the coil connections. By starting from a three-phase winding design, different six-phase winding arrangements are analyzed. A methodology to define all the possible six-phase winding arrangements is presented. Discard criteria based on balanced radial forces and impedances are defined. Afterward, selected winding candidates are compared in terms of analytical calculations and later on, based on finite element (FE) simulations for a 690 V, 1-MW induction machine design. Different possible configurations are evaluated in terms of stator Joule losses, torque ripple, power factor, and electromagnetic efficiency both under healthy and faulted inverter conditions. Finally, a six-phase machine prototype is tested in order to verify the improvement in machine characteristics, thus validating the proposed method.

Numerical evaluation of the deformation of REBCO pancake coil, considering winding tension, thermal stress, and screening-current-induced stress

Abstract: In recent years, the applications of high-field REBa2CuOy (REBCO) coils have remarkably progressed towards NMR MRIs, accelerators, and other such devices. In a REBCO coil, the magnetic field due to the screening current is generated in the direction opposite to the field by the transport current, thus reducing the magnetic field, deteriorating the field homogeneity, and affecting the time stability of the magnetic field. Recently, the additional force and stress due to the screening current (referred to as screening-current-induced stress) has become a topic of concern. The screening current results in non-uniform current distributions in the REBCO tape. Therefore, the distribution of electromagnetic force in REBCO coils differs from that during the designing of the coil, assuming that the current flow in the tape is uniform. Thus, there is the possibility that the existence of screening current is a serious problem in the mechanical design of REBCO coils. In this study, we evaluate the electromagnetic force and stress due to the screening current by using the developed numerical simulation code for the electromagnetics and stress. We discuss the winding tension, thermal and electromagnetic stresses, and mechanical strength structure of the REBCO coil.

A Novel Long-Distance Wireless Power Transfer System With Constant Current Output Based on Domino-Resonator

Abstract: In this article, a novel long-distance wireless power transfer (WPT) system that achieves excellent constant current (CC) output based on a domino-resonator is proposed. A thorough mathematical model of the n-coil domino WPT system is established, and the methodology of calculating and choosing the operating frequency in the CC mode is put forward to achieve high efficiency and the best stability. The zero-phase-angle (ZPA) condition is proven to be realized, in the meantime, by theoretical derivation. The phenomenon that operating frequency slightly shifts away from the resonant frequency in the CC mode due to the magnetic coupling between nonadjacent coils is studied. The efficiency of the system is evaluated. Moreover, system efficiency can be further improved by optimizing the number of coils and layers when the transfer distance is fixed. An experimental setup with an output current of 0.6 A has been built to demonstrate the validity of the proposed system. The experimental results show that the maximum system efficiency of the experimental setup in the CC mode can achieve 70% at the transfer distance of 0.7 m when the number of the coils is 8 and the radius of the coil is 100 mm.

Insulation Design of Wireless Auxiliary Power Supply for Medium Voltage Converters

Abstract: Auxiliary power supply (APS) that provides reliable power and voltage for gate drivers, controllers, and sensors is a critical component in a medium voltage (MV) converter. Compared to being fed from the power-cell dc-link, APS fed from an external earthed system has its own benefits. However, with the power-cell number scaled up, the insulation design of the externally fed APS becomes a significant challenge. Partial discharge (PD) can cause accumulative irreversible damages of insulation which further lead to auxiliary power circuit fault and eventually cascaded failures of the whole converter system. Therefore, a PD-free APS system ensuring the reliability of the MV converter is required. Among different technologies for building APS, wireless power transfer (WPT) becomes an attractive method because of its mechanical design flexibility and inborn insulation capability. In this article, in order to design a PD-free WPT converter, the insulation design criterion and electric field distribution under different coil geometries are analyzed, compared, and tested. Subsequently, a comprehensive insulation design including the influence of the ferrite shielding layer is shown. Finally, an optimized WPT prototype with 120-W output power, 92.78% full-power efficiency, 2.76-pF isolation capacitance, and 27-kV insulation capability is validated experimentally.