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Wireless power transfer (WPT) is emerging as the preeminent way to charge electric vehicles, but there appears to be no fair way to measure the power transfer. In this article, Faraday coil transfer-power measurement (FC-TPM) is presented. FC-TPM employs non-contact, open-circuited sense coils to measure the electromagnetic field from WPT and calculates the real power propagating through the air gap between the transmitter and receiver coils. What is measured is the real electromagnetic power, representing the pure dispensation of energy that unambiguously demarcates the losses on either side. FC-TPM was demonstrated to be 0.1% accurate in hardware over an Rx coil misalignment of up to 10 cm using a 1-kW WPT system. Fair metering incentivizes businesses and individuals to make choices that conserve energy and advance technology by providing more information and by properly assigning the financial loss. This article is accompanied by a video highlighting the essential contributions of this article.

Foreign objects near wireless power transfer (WPT) systems are fire hazards that must be detected. In this article, a new accurate method is presented for foreign object detection based on an electromagnetic model for WPT. Foreign objects are detected by quantifying the deviation from a normal model. This deviation is caused by the foreign object's additional electromagnetic coupling. Advantages of this new method include invariance to receiver coil misalignment, and power level, allowing low-power detection prior to startup. Electromagnetic model-based foreign object detection was demonstrated in hardware to detect a 2 cm diameter U.S. nickel coin, a small disposable lighter, and a saline proxy for a living animal in a kilowatt-level wireless power transfer system, using a prestartup power of only 7 W. Furthermore, foreign objects can be detected regardless of an Rx coil misalignment of up to 10 cm. This article is accompanied by an instructional video.

Accurate measurement is a hinge pin of a functioning society, engendering a sense of value, fairness, trust, and safety. A particularly salient example is wireless energy transfer to electric vehicles. A robust calibration method is needed for the fair and accurate measurement of the wireless power transferred to electric vehicles using the TPM (Transfer-Power Measurement)method. A prevalent obstacle to affordable, reliable, and accurate measurements in the field is lack of suitable transfer standards. This paper presents both a new transfer standard and a calibration path for TPM towards the standardization of power and energy metering in wireless power transfer.

Foreign objects near wireless power transfer (WPT) systems are fire hazards that must be detected. In this paper, a new robust method is presented for foreign object detection based on an electromagnetic model for WPT. Foreign objects are detected by quantifying the deviation from a normal model. This deviation is caused by the foreign object’s additional electromagnetic coupling. Advantages of this new method include invariance to power level allowing low-power tests prior to startup, receiver coil misalignment, and varying transmitting and receiver losses.

Transfer-power measurement (TPM) provides fair metering for wireless power transfer (WPT) in electric vehicles (EVs). TPM employs sense coils between the transmitter coils (Tx) and receiver coils (Rx) to estimate the transferred power from the magnetic field. Two sense coils are enough for power estimation when the transmitter and receiver positions are always fixed. However, misalignment of coils leads to errors which can be corrected by using more sense coils. In this paper, TPM under misalignment using multiple sense coils is introduced, which give implicit information about the misalignment. A quadratic approximation of coupling coefficients under misalignment is used to correct the errors. Numerical models from precise theory confirm the fidelity of the approximation and experimental results concur.

Wireless power transfer is emerging as the preeminent way to charge electric vehicles, but there appears to be no fair way to measure power transfer. In this paper, transferpower measurement (TPM) is introduced. TPM employs non-contact sensing elements to measure magnetic field from wireless power transfer and calculate the real power propagating through space. TPM provides fair metering because individual losses from the transmitter and receiver are disaggregated. Signal and data processing as well as a calibration method are discussed. Experimental results demonstrate a fair method of metering the real transfer power with low estimation error. Fair metering incentivizes businesses and individuals to make choices that conserve energy and advance technology by providing more information and by properly assigning the financial loss.

The lightning impulse breakdown characteristics of liquid nitrogen are necessarily considered for designing high voltage superconducting machines required high reliability. This paper investigates the dielectric capability of liquid nitrogen (LN 2 ) to withstand lightning impulse. To gain the dielectric capability of LN 2 cryogenic cooling system, lightning impulse was induced in sphere–plane electrode systems which have six different diameters of sphere electrode. The pressure is one of major condition to decide dielectric strength at LN 2 cryogenic cooling system. Thus, the gaseous nitrogen was injected to control pressure in the cryostat, ranging from 100 kPa to 200 kPa. Moreover, field utilization factor was calculated between sphere and plane electrode systems by a finite element method analysis. The electric field criterion of LN 2 as insulation media was calculated from correlation between the experimental results and the field utilization factor. In the future, these results can be applied as the design parameter of electrical insulation for developing high voltage superconducting machines.

A high speed electromagnetic suspension (EMS) maglev has emerged as the solution to speed limit problem that conventional high-speed railroad has. In the EMS maglev, small levitation gap needs uniform guide-way which leads to increase the construction cost. The large levitation gap can reduce the construction cost. However it is hard for normal conducting electromagnet to produce larger magneto-motive force (MMF) for generating levitation force as increased levitation gap. This is because normal conductors have limited rating current to their specific volume. Therefore, the superconducting electromagnet can be one of the solutions for producing both large levitation gap and sufficient MMF. The superconducting electromagnets have incomparably high allowable current density than what normal conductors have. In this paper, the prototype of high temperature superconducting (HTS) electromagnets were designed and manufactured applicable to hybrid electromagnetic suspension system (H-EMS). The H-EMS consists of control coils for levitation control and superconducting coils for producing MMF for levitation. The required MMF for generating given levitation force was calculated by both equations of ideal U-core magnet and magnetic field analysis using the finite element method (FEM). The HTS electromagnets were designed as double pancakes with Bi-2223/Ag tapes. Experiments to confirm its operating performance were performed in liquid nitrogen (LN2).

This paper deals with the design and fabrication of prototype superconducting hybrid electromagnet(SH-EM) for EMS (Electromagnetic suspension)-based Maglev. The design requirements are based on the normal conducting EM used in the German high-speed Maglev. From the MMF-Levitation force curves simulated by FEM analysis, the required MMF by superconducting coil is suggested. As an experimental test setup to demonstrate the SH-EM, the experimental SH-EM with HTS coil cooled in is fabricated. From the expected operating current of the HTS coil, the levitation performance of the SH-EM is estimated.

In order to limit fault current from an accident in power grid, many research groups have developed resistive superconducting fault current limiters (SFCLs) with a bifilar solenoid and a bifilar pancake types. Comparing with a bifilar solenoid type, a bifilar pancake type has the advantage of its volume, but it has problems such as recovery and insulation of SFCLs. To eliminate the drawback of these two types, in this paper, a new type of coil that is an oval-shaped SFCL, have proposed. This type consists of inner and outer layers which are connected in parallel. A small-scale sample coil was fabricated and experiments for both a short circuit test and recovery characteristic test were performed in liquid nitrogen. Experimental results were compared with two types of coils; the bifilar solenoid and bifilar pancake coil. Consequently, we confirmed the feasibility of an oval-shaped type.

To design a large scale superconducting fault current limiter (SFCL) for power grids, a single long-length YBCO coated conductor (CC) wire is preferred. However this single YBCO CC wire can cause a problem of unequal voltage distribution between the parts on the long wire at quench by the faults. Inhomogeneous critical current of the YBCO CCs in the SFCL is a possibility. Furthermore, sub-cooled liquid nitrogen (LN2) condition is usually used to increase current capacity of the SFCL. However, this sub-cooled condition can worsen the inhomogeneity between the YBCO CCs. Therefore, it is important to understand the relation between the unequal voltage distribution and the inhomogeneous critical currents in the single long length YBCO CC. In this paper, experiments with the same single YBCO CC wire were conducted in various temperature conditions, LN2 and sub-cooled LN2 . In both experiments, the critical currents and voltage distributions generated by faults at short-circuit tests were measured. It was observed that the inhomogeneous condition impacts on the unequal voltage distribution.

This study deals with a conceptual design for a high temperature superconductor (HTS) coil fabricated with YBCO wire in a prototype HTS-electromagnet (HTS-EM) model for the electromagnetic suspension (EMS)-based Maglev. Because the size of the HTS coil and the power it consumes during operation are very critical factors in designing the HTS-EM, we focused on the number of coil turns and the operating conditions needed to generate the required magneto-motive force (MMF) effectively. The winding geometry of the sample HTS coil with the largest Ic value was selected for use in this study. To determine the operating condition corresponding to the number of coil turns, we produced the operating profile for the load current of DC current source and the Ic value of HTS coil. From the profile, the optimal number of coil turns to minimize the operating power is determined to be in the range of 1200 to 1400 turns. And the HTS coil should be operated with the current of 37 to 43 A at the cooling temperature of 73 to 76 K.

A resistive superconducting fault current limiter (SFCL) has two drawbacks-relatively higher impedance and longer recovery time than the requirement of the electric power system. A parallel-connected bypass reactor (BPR) can be a solution to both problems. As a stage of proof-of-concept, an SFCL comprised of an YBCO S/N switch and a Bi2223-BPR had been presented in the former paper. Although the previous one has shorter recovery time, the generated impedance after a fault was too low to satisfy the requirement of the power system. To apply the SFCL into the power system, the SFCL has proper impedance during the fault. Therefore, we proposed bypass reactors to achieve higher impedance than the previous one in this paper. The SFCLs with a bypass reactor were fabricated and short-circuit test with the SFCLs were conducted. The test results were compared in point of current limiting characteristics and recovery. This research would be applied to a conceptual design of BPR.