High temperature superconducting flywheel energy storage system (HTS FESS) based on asynchronous axial magnetic coupler (AMC) is proposed in this paper, which has the following possible advantages: ...the generator/motor (G/M) can be installed outside of the vacuum chamber with the torque being transferred by the magnetic coupler, and the stator liquid cooling system is not needed; the idle loss of G/M during the stage of energy maintaining can be eliminated by disconnecting the coupler from the system by the magnetic field shielding device. Up to now, there has been little research on AMC for high-speed application. In this paper, the performance parameters of the torque, axial force, and magnetic flux density in the middle of airgap and at the mean radius are calculated based on finite-element model. The prototype used to update the 30 kJ/2 kW HTS FESS developed in 2014 is manufactured, and the test platform of transfer characteristics at high speed is established. The experiments at high speed are conducted and the measured results show a good agreement with the simulation results. Meanwhile, the correlations between the magnetic flux density, the axial force, and HTS FESS are analyzed. At last, the feasibility of AMC used for HTS FESS is validated by the charge and discharge experiment. The system efficiency and technical problems are analyzed.
This paper proposes an improved figure-of-eight coil for transcranial magnetic stimulation (TMS) by using the magnetic resonant coupling (MRC) effect, aiming to improve the treatment effect for ...psychiatric disorders. The proposed MRC-based figure-of-eight coil consists of two reverse-winding resonance coils, which embraces two series-connected source coils, respectively. Different from conventional figure-of-eight coils, the proposed topology can produce the resonant electromagnetic field to accumulate the stimulation energy. In such ways, the improved TMS system can effectively enhance the stimulation focality and depth while significantly reducing the requirement of the power supply, thus improving the safety as well as facilitating the miniaturization and portability. Last, this paper gives the simulated and experimental results to verify the theoretical analysis, which can further illustrate the feasibility of the proposed MRC-based figure-of-eight coil for TMS systems.
In this article, a new double-rotor multiwinding machine (DRMWM) that utilizes the flux modulation principle is proposed for propulsion system of hybrid electric aircrafts (HEAs). First, the ...operation principle of DRMWMs and the corresponding HEA propulsion configuration are introduced, where different operation modes of two rotors and three sets of windings of DRMWMs to cope with various flight tasks of HEAs are elucidated. Then, an improved subdomain method is utilized to solve the magnetic field distribution of DRMWMs with the consideration of saturation effect of soft-magnetic material (SMM). Finally, a prototype is manufactured to verify the effectiveness of the proposed improved subdomain method in predicting the electromagnetic performances of DRMWMs. The experiment shows that the DRMWM is a good candidate to be applied in HEA with different operation modes.
The current and loss of a transformer increase significantly under DC bias, which cause overheating and insulation aging. Depended on the Jiles-Atherton (JA) hysteresis theory, an estimation model of ...the core loss under DC bias is proposed in this paper. First, based on the iron loss separate theory, the origin JA model without DC bias is extended to JA dynamic hysteresis model considering the frequency-dependent eddy current loss and the anomalous loss. Second, a DC bias experiment is built by using Epstein frame, from which the hysteresis loss and the dynamic loss coefficients of the core are obtained. Finally, the relationship between DC bias and the dynamic loss coefficient is analyzed. The dynamic loss coefficient is normalized and fitted, and JA dynamic hysteresis model is revised by using the fitted results. The calculation results are compared with the measurement from the Epstein frame, which demonstrates the effectiveness of the method.
Aiming at the problem that the traditional water-lubricated bearing cannot carry the heavy load and adapt to the constantly changing operating conditions for the high-power Rim Driven Thruster (RDT), ...the principle structure of the Magnetic Water-double-suspension Elastic-support Thrust Bearing (MWETB) is designed and the optimal structure parameters of the bearing are selected using simulation. To demonstrate the reliability of the MWETB under the RDTs’ actual working conditions, performance tests, which include the magnetic flux density, magnetic force, and lubrication performance, are carried out. The simulation and experimental results indicate that the optimal offset ratios are in two intervals, and the magnetic alignment and sheath materials have a great effect on the load reduction. The load-carrying force has obvious zoning characteristics with the change in bearing clearance. Besides, compared with the water-lubricated thrust bearings, the MWETB has advantages in terms of minimum film thickness and friction coefficient.
The magnetic field produced in the air gap by any particular "short coil" at a fixed current is affected by a highly complex interaction between the coil and workpiece geometries, as well as changes ...in frequency. A frequency-modified semiempirical short-coil correction factor, based upon the formula published by Vaughan and Williamson in 1945, is presented and experimentally verified. This new equation is shown to predict the total system reactive power and the average magnetic flux at the surface of the workpiece with typical differences of less than 2% at 50 Hz ac and to accurately predict workpiece heating rates typically within 5% for aluminum billets at 50 Hz to 500 kHz ac. The workpiece real and reactive powers, as well as total system reactive power, are compared with both analytic and 2-D axial symmetric finite-element modeling (FEM) model solutions as a function of operating frequencies from 50 Hz to 500 kHz. The measured flux density is compared to FEM and analytical predictions at 50 Hz.
For bulk superconductor application, J C -B characteristics (J C : critical current density, B: magnetic flux density) are fundamental and important. We have studied the estimation methods of the J C ...-B characteristics: one is based on the inverse problem analysis of full magnetization, and the other is on small field magnetization after field cooing in background magnetic fields. The proposed small field cooling magnetization in background fields can estimate the critical current density for higher magnetic fields than the inverse problem analysis method.
This paper describes the effects of changing the magnet shape of permanent magnets (PMs) in a Halbach array applied in a slotless tubular actuator. More specifically, the square shaped magnets are ...replaced by trapezoidal shaped magnets. A semi-analytical magnetic field solution of regular square shaped magnets is presented and used to approximate the airgap field produced by the trapezoidal shaped PMs. The method is based on dividing the magnets into several radial layers and superposition of the fields to calculate the total magnetic field. The results are compared to finite element analysis (FEA) and show excellent agreement. Using this magnetic field solution, the effect of the shape of the magnets on the magnetic field waveform is analyzed by means of a parametric search.
This paper investigates strategies to improve the volume energy density of superconducting solenoidal energy storage coil. A multiple population genetic optimization algorithm combined with MATLAB ...and COMSOL is used to optimize the structural parameters of the solenoid coil with rectangular cross section. The maximal radial magnetic flux densities, critical currents, volume energy densities, and tapes utilizing rates of rectangular and other three different step-shaped cross-sectional solenoidal coils are analyzed and compared. The coil with inner and outer step-shaped cross section is proposed as the topology to improve the volume energy density. The current injection strategy that different step coils are supplied with different currents according to the magnetic flux density distribution is employed to further improve the volume energy density.
Magnetic resonance (MR) signals captured by RF array coils should be delivered to analogue-to-digital converter (ADC) channels through an independent receiver (Rx) circuitry for precise MRI process. ...Since different types of RF coils should be utilised by a fixed port configuration on a patient table with a limited number of ADC channels, a highly flexible Rx front-end design is necessary. In this Letter, a compact distributed switch matrix structure for multi-channel RF coil Rx is proposed for supporting different types of array coils with small circuit size and sufficient reconfigurability. The proposed structure is configured by a multiple number of unit matrix cells consisting of a single double pole double throw and two single pole double throw RF switches to control the pathways of received MR signals. The proposed structure was implemented and verified at 9.4-Tesla (9.4 T) MR frequency (400 MHz) by comparing different RF path losses.
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