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Pulsed readout of Direct Current (DC) Superconducting Quantum Interference Device (SQUID) is crucial for experiments which need to be performed at millikelvin temperatures, such as the readout of superconducting and electron spin based qubits. Pulsed readout algorithms used in these experiments are usually specific to the experimental setup and require some optimization. We present a circuit that emulates the behavior of a DC-SQUID in order to allow the development and evaluation of pulsed readout algorithms at room temperature without the need of a running dilution refrigerator. This novel circuit also constitutes a low cost device which can be used to teach the principles of a DC-SQUID in courses aimed at training the next generation of quantum engineers. [ABSTRACT FROM AUTHOR]

Searching similarity between a pair of shapes or data is an important problem in data analysis and visualization. The problem of computing similarity measures using scalar topology has been studied extensively and proven useful in the shape and data matching. Even though multi-field or multivariate (consists of multiple scalar fields) topology reveals richer topological features, research on building tools for computing similarity measures using multi-field topology is still in its infancy. In the current article, we propose a novel similarity measure between two piecewise-linear multi-fields based on their multi-resolution Reeb spaces - a newly developed data-structure that captures the topology of a multi-field. Overall, our method consists of two steps: (i) building a multi-resolution Reeb space corresponding to each of the multi-fields and (ii) proposing a similarity measure between two multi-resolution Reeb spaces by computing a list of topologically consistent matching pairs (of nodes) and the similarity between them. We demonstrate the effectiveness of the proposed similarity measure in detecting topological features from real time-varying multi-field data in two application domains - one from computational physics and one from computational chemistry. [ABSTRACT FROM AUTHOR]

The introduction of information and communication technologies makes network environments increasingly open, leaving smart-grid control systems incredibly vulnerable to malicious attacks. False data injection (FDI) attacks stealthily tamper with measurement data, resulting in erroneous decisions made by the control center that greatly influence the normal operation of the power system. By taking advantage of real-time data acquisition with edge computing, in this article, we propose a scheme based on classification of predicted residuals (CPRs) for the FDI attack detection. The CPR scheme first predicts the acquired measurement data at the edge of the sensing network via developing an accurate prediction model. Followed the novel real-time classification method under the edge devices supporting, it classifies the predicted residuals independent of the false data to enhance the detection accuracy. Through these two steps, the detection rate of FDI attacks is greatly improved. The proposed scheme is validated in a real microgrid testbed. Experimental results show that the CPR scheme performs well in detecting FDI attacks and remains sensitive in injection attack probability and magnitude. The detection scheme even has effectiveness at low injection attack probability and magnitude (5% and 0.018 per thousand, respectively). Furthermore, it also proves that the proposed scheme has applicability in high real-time requirements at the edge of smart grids. [ABSTRACT FROM AUTHOR]

Expendable current profiler (XCP) is one of the most vital devices detecting ocean currents. Compared with other methods, the expendable feature makes trials with XCP much faster and more hidden, while the accuracy of XCP is considerably influenced by electromagnetic noise all around. Aiming at researching the influence and reducing the noise, this study carried out laboratory simulation experiments. The designed laboratory experiments mainly have a self-developed rotation gear, an XCP prototype, a plastic flume, and two copper plates as power. Firstly, these experiments analyzed the main sources of electromagnetic noise for XCP detection. Secondly, we built a noise simulation environment and conducted XCP detection experiments under different noise in the flume. The data obtained by XCP were transmitted to the computer to be stored and processed. The results show the internal noise impact on XCP is significantly less than the external. For an excitation power of 1 mV, the offset of theoretical and actual data brought by internal noise is 12 times smaller than external and can be corrected. [ABSTRACT FROM AUTHOR]

This article presents the design methodology, simulation results, and experimental results of a novel variable reluctance differential solenoid transducer (VRDST). The new ironless-stator VRDST (ISVRDST) is designed to mitigate the practical challenges inherent in the VRDST while maintaining its beneficial features compared to other linear inductive differential position sensors. The ISVRDST uses an air stator to reduce cost and increase compactness. FEA and Simulink simulations are used to predict the performance of the ISVRDST and a proof-of-concept prototype is designed to experimentally validate the simulation results. Like the VRDST, the ISVRDST is designed to utilize a complementary filter to fuse a low-speed position measurement with a high-speed velocity measurement, resulting in a single wide-bandwidth position measurement. The experimental results of the prototype ISVRDST prove that it is capable of robustly performing and fusing the two measurements utilized by the VRDST. In addition, the analytically predicted error of the fused measurement is found to be less than 1% different than the actual error relative to a high-precision laser vibrometer. When compared to the VRDST, the ISVRDST prototype is found to have a stroke-to-length ratio that is nearly four times greater and a cost that is over 100 times lower. [ABSTRACT FROM AUTHOR]

Accurate optical fiber current transducer based on the Faraday magneto-optical effect is described for high voltage direct current (HVDC) transmission. The transducer may be used to measure DC and high-order harmonic currents in a ± 800 kV DC transmission field. The performance characteristics of sensitivity, non-linearity, temperature stability, and harmonic accuracy of the prototype were investigated. The results show that the scale factor error in the −40 °C to 70 °C range is below ±0.2%. The presented optical fiber current transducer has potential applications for HVDC detection fields, such as for a polarity bus and a converter valve bridge arm. [ABSTRACT FROM AUTHOR]

Direct current (dc) systems have an increasingly important role in electrical systems, especially photovoltaic (PV) solar power plants and battery storage systems as they are essential for the development of more sustainable, efficient, and reliable electrical systems. PV panels and batteries are generally composed of multiple series-parallel cells. This fact makes their fault diagnosis challenging, especially against ground faults as these systems are generally ungrounded. In this article, a ground fault location method for dc sources with multiple series-parallel cells is proposed. It estimates the faulty branch, the faulty cell location inside this branch and its fault resistance. The method is based on the output current measurement of each branch and on the voltage measurement on a grounding resistor, which is switched between three positions: the positive, the midpoint and the negative terminals of the protected dc system. To validate it, several computer simulations and experimental tests on a battery pack have been carried out. The results obtained proves an excellent performance for faulty cell location and fault resistance estimation, although further investigations are required to better discern the faulty branch. [ABSTRACT FROM AUTHOR]

Acquisition of the accurate phase currents is indispensable for the control and protection of switched reluctance motor (SRM) drives for electric transportation applications. Existing phase current reconstruction techniques for SRM are implemented under the current control techniques, which generate large torque pulsations. Therefore, the direct torque control (DTC) method can be adopted to minimize torque pulsations and to enhance transient performance in electrified vehicles. However, the existing current estimation methods cannot be applied to DTC strategies due to the simultaneous conduction of all phases at any switching instant. Furthermore, it offers a lower torque per ampere ($T/A$) ratio and draws a high source current. This article addresses the aforementioned concerns by proposing a cost-effective phase current reconstruction method with an improved DTC strategy for a 4-kW four-phase SRM drive. This method employs a 16-sector partition method with a new voltage vector selection by detecting zero-current regions of each phase. As a result, the long-tail currents can be avoided, thereby limiting the simultaneous conduction of all phases. The simulation and test results show that the proposed DTC has minimal torque pulsations, high $T/A$ ratio, low converter losses, and lower source current ripple in comparison to the existing DTC schemes under various operating conditions. Also, the proposed phase current estimation method effectively reconstructs the phase currents under both steady-state and transient operating conditions. [ABSTRACT FROM AUTHOR]

Due to ever-increasing power demand and high renewable energy penetration, the power system's harmonics and voltage unbalancing have become significant power quality issues. In this aspect, because of the multifunctioning ability of the power electronic converters, the grid-connected power electronic converter-based distributed generations are expected to provide desired compensation whenever required. Especially in a weak grid environment, the compensation draws more attention due to constricted coupling between the voltage and current at the point of common coupling as a consequence of high grid impedance. Therefore, this article presents a feedback-based flexible compensation strategy for a weak-grid-tied distributed generation (DG) to enhance the compensation of harmonics and voltage unbalance in the system. The main uniqueness of the proposed work is to seamlessly embed a flexible harmonic loop with a fundamental current control loop for achieving three control targets: voltage harmonic compensation, DG line current harmonic rejection, and voltage unbalance compensation. Achieving control targets require voltage feedback and no need to measure nonlinear load current. In order to execute flexible harmonic compensation (i.e., from voltage harmonic compensation to DG line current harmonic rejection) through the harmonic loop, the proposed strategy generates a harmonic reference from voltage feedback and inherent current feedback. The delay introduced by the harmonic compensators is accurately compensated distinctly to improve the performance of the harmonic loop. The voltage unbalance compensation is achieved through the fundamental current control loop by improving the fundamental positive sequence voltage and decreasing negative sequence components concurrently. To enhance the flexibility between two different targets (i.e., flexible harmonic compensation and voltage unbalance compensation), the harmonic and unbalanced compensations are executed on an individual target basis, subjected to the converter's maximum current and system voltage constraints. The proposed compensation strategy offers better harmonic suppression and voltage unbalance compensation than conventional methods. Because it exactly acts upon modulation signals and directly regulates sequence components and voltage harmonics. Furthermore, the proposed control's detailed design and stability analysis is presented, and its superiority is validated through simulations and real-time experimentations. [ABSTRACT FROM AUTHOR]

In this research work, a new harmonic responsibility measure is proposed to extract the amount of harmonic responsibility of each plant supplied from the point of common coupling (PCC). The proposed method uses a function of the correlation coefficients between the voltage and current signals measured synchronously at the PCC. After the verification of the method on synthetic data generated in simulation environment, field data measurements of voltage and current are used to test the practicability of the proposed method. Harmonic contributions of the iron and steel (I&S) plants obtained using the proposed method are compared with the results of one existing method in the literature and it has been shown that harmonic responsibilities of the plants can be obtained for each harmonic order. The harmonic currents absorbed by the shunt harmonic filters of the I&S plants from the rest of the system are also identified effectively with the proposed method to determine the actual source of the harmonics. The proposed method can serve the needs of the active power filters and other compensation systems to improve the effectiveness of those systems in reducing individual distorting effects of the I&S plants supplied from a PCC of the electricity transmission system. [ABSTRACT FROM AUTHOR]

The interaction mechanism between displacement damage and ionization damage in SiO2 layer has been researched on gate-controlled lateral p-n-p transistor (GLPNP). The sequential irradiation experiments of 400-keV O ions with high dose rate $\gamma $ -rays were carried out, and the degradation and defect evolution results of the device were analyzed by the reciprocal change of current gain change, gate sweep (GS) curve, and deep level transient spectrum (DLTS) results. The results show that there is a negative direct synergistic effect between 400-keV O ions and Co- $60~\gamma $ -rays in GLPNP. At the same time, combined with the GS curve and DLTS results, it can be concluded that the displacement defects of 400-keV O ions in SiO2 layer of GLPNP transistors will capture the holes generated by Co- $60~\gamma $ -rays, thus forming a large number of positive oxide charges ($N_{\mathrm {ot}}$). These $N_{\mathrm {ot}}$ are like “space charge wall,” hindering the movement of protons and holes to the Si/SiO2 interface, and thus inhibiting the generation of interface trap ($N_{\mathrm {it}}$). Due to the decrease of $N_{\mathrm {it}}$ and the increase of positive $N_{\mathrm {ot}}$ , the damage of transistor is weakened. The experimental results show the effects of displacement damage on the ionization effect in SiO2 layer and, more important, provide direct evidence for the space charge model. [ABSTRACT FROM AUTHOR]

For the International Thermonuclear Experimental Reactor magnets, a significant fraction of the Nb3Sn conductors will be operating at a low field (B < 4 T), such as the outer turns of the central solenoid modules and toroidal field winding packs, while so far, the Ic(B,T, Ɛ) parameterization has been derived from measurements carried out at higher fields (B ≥ 7 T). It may not be accurate enough to adopt this parameterization for the extrapolation of the conductors’ operating performance in terms of critical current (Ic) and current sharing (Tcs). The critical current characteristic can be effectively extended to the lower field region by means of a relation between the magnetization and critical current. The parameterization of the derived critical current scaling law Jc(B) is processed for the field range of the magnetization measurement (0 < B ≤ 9 T) and the critical current measurements (7 ≤ B < 12 T) in order to cover the full range up to 12 T. [ABSTRACT FROM AUTHOR]

Piezoelectric resonance impedance spectroscopy is a standardized measurement technique for determining the electromechanical, elastic, and dielectric parameters of piezoceramics. However, commercial measurement setups are designed for small-signal measurements and encounter difficulties when constant driving voltages/currents are required at resonances, higher fields, or combined AC and DC loading. The latter is particularly important to evaluate the DC bias-hardening effect of piezoelectrics. Here, we propose a novel measurement system for piezoelectric resonance impedance spectroscopy under combined AC and high-voltage DC loading that complies with established standards. The system is based on two separate output amplifier stages and includes voltage/current probes, a laser vibrometer, custom protection components, and control software with optimization algorithm. In its current form, the measurement setup allows the application of AC frequencies up to 500 kHz and DC signals up to ±10 kV on samples with impedance between 10−1 and $10^{6} \Omega $. The operation of the proposed setup was benchmarked against commercial impedance analyzers in the small-signal range and reference equivalent circuits. Test measurements under combined AC and DC loading were performed on a soft Pb(Zr,Ti)O3 piezoceramic. The results revealed that a DC bias voltage applied along the polarization direction ferroelectrically hardens the material, while the material softens and eventually depolarizes when the DC bias voltage is applied in the opposite direction. The results confirm the suitability of the designed measurement system and open new exciting possibilities for tuning the piezoelectric properties by DC bias fields. [ABSTRACT FROM AUTHOR]

Aiming at the misdiagnosis problem of the interturn short-circuit (ITSC) fault detection method caused by the inverter nonlinearity and the current measurement errors, a d-axis residual voltage-based fault diagnostic strategy is proposed for sensorless control of the surface permanent magnet synchronous motor (SPMSM). The model of the three-phase wye-connected SPMSM with ITSC fault is established, and the expression of the d-axis residual voltage caused by the ITSC fault, the inverter nonlinearity, the current measurement errors and the motor parameter errors is derived. The proposed fault diagnostic strategy can eliminate the current relative gain coefficient error and locate the ITSC fault by using the eighth and second harmonics of the estimated d-axis residual voltage, respectively. The experimental results verify the effectiveness of the proposed fault diagnostic strategy. [ABSTRACT FROM AUTHOR]

In this article, a sensorless control method based on signal injection and a high-pass filter (HPF) circuit is presented to control the unsymmetrical bistable multimagnetic circuit permanent magnetic actuator. In this method, a high-frequency sinusoidal signal was indirectly injected into the idle phase via a HPF circuit, and the peak of the high-frequency capacitance current was measured, which was used to calculate the idle phase inductance. Thereafter, the mover position was calculated by the one-to-one relationship between the idle phase inductance and the mover position. Combined with the HPF circuit and the proposed average current peak algorithm, the influences of back-EMF and coil resistance were eliminated. The magnetic saturation effects can also be ignored in the proposed strategy. The estimated noise, caused by measurement noise and signal distortion, was filtered using a simple mathematical filter. The flexibility and accuracy of the presented strategy were verified by simulation and experimental investigation. [ABSTRACT FROM AUTHOR]

The wide bandwidth impedance of grid and inverter are the critical parameters for small-signal stability analysis and control optimization of grid-tied inverter systems. The impedance measurement is an effective way to obtain the grid and inverter impedance by injecting a series of perturbations into the measured system. However, previous studies fail to fully consider the adverse grid voltage conditions; including harmonics, unbalance, frequency deviation, voltage sag, and phase jump; which may bring errors to the measured impedance. In this article, a cascaded delayed signal cancellation (CDSC)-based method is proposed to accurately obtain the impedance of the measured system under adverse grid voltage conditions. The proposed CDSC-based method is mainly composed of the perturbation extraction module (PEM) and frequency adaptive module (FAM). Different CDSC blocks are applied to implement the PEM and FAM to extract the injected perturbations adaptively, under various adverse grid voltage conditions. Simulation and hardware-in-the-loop experiment results are presented to validate the effectiveness and feasibility of the proposed impedance measurement method. [ABSTRACT FROM AUTHOR]

Accurate rotor position estimation is important to ensure the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To suppress the estimated rotor position harmonic error (ERPHE) caused by inverter nonlinearities, flux spatial harmonics, and the current measurement error in high-frequency signal injection-based schemes, an adaptive iterative learning control-based online suppression method is proposed in this article. This method constructs a P-type iterative learning rotor position observer with the forgetting factor to obtain the tracking error and generate the compensation value in real time. The stability, the convergence, and the parameter sensitivity of this observer are analyzed in detail. To improve the suppression effect of the ERPHE for different loads and speeds, an iterative learning gain self-tuning strategy is investigated. The proposed method does not require the offline detection and the discrimination of harmonic frequencies, which has strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW interior PMSM drive platform. [ABSTRACT FROM AUTHOR]

This article introduces the measurement and analysis of the transient electric field (E-field) derived from the switching operation of the modular multilevel converter (MMC) and the high voltage direct current (HVdc) circuit breaker (CB) in a 200 kV converter station constructed in the Zhoushan Islands, China. It is revealed that the switching transient E-field in the converter station is a quasi-static field. Although the switching E-field pulse is a kind of electromagnetic interference to the secondary electronic circuit of the converter station, it can be used to accurately monitor the action moment of the MMC and the CB. The action moment of the MMC and the CB can be measured with an error of less than 0.005 ms based on the steep pulse front of the switching E-field pulse. This result, which is far more accurate compared to the measurement using the voltage recording system that comes with the converter station. This is of significance to the relay protection of the HVdc transmission system whose fault rapidly develops. Additionally, this method has the advantage of being noninvasive, flexible, and low cost. It has potential application value in the condition monitoring of the MMC and the HVdc CB. [ABSTRACT FROM AUTHOR]

DC bias in a transformer is a threat to the safe and efficient operation of dual active bridge (DAB) converters. Detecting a dc component in milliamperes mixed with a large ac current is difficult. This article proposes a current sensor based on ac magnetic flux (MF) cancellation. The proposed sensor utilizes a current transformer (CT) to extract the ac component in the measured current. Then, a power op-amp copies the CT signal to an additional winding to generate an ac MF opposite to that of the main ac current. Hence, the sensor range required to measure the dc is greatly reduced for a much smaller absolute measurement error. Using only a CT and a simple op-amp circuit, the proposed solution features low complexity and power consumption. The relative error in a range of 15-A ac current is 0.038%, showing a five-fold improvement compared to off-the-shelf sensors. The proposed sensor is verified on a 1-kW DAB prototype, where the dc bias is suppressed to nearly null owing to the proposed sensor. [ABSTRACT FROM AUTHOR]

The dynamics of nonresonant dual-active-bridge converter (DABC) are simultaneously affected by the transient modulation strategy and controller design. In general, inappropriate transient modulation strategies can lead to nonzero transient dc offsets in the inductor current and transformer’s magnetizing current, thus introducing excessive trajectory tracking error and time delays between the pulsewidth modulation generator and controller. Consequently, truly optimal transient responses cannot be achieved solely through a high-performance controller, unless the modulation-induced transient dc offsets can be completely eliminated. This article presents a comprehensive review of the optimized transient phase-shift modulation (OTPSM) strategies for single-phase-shift modulated DABC, and derives a novel optimal modulation method referred to as symmetric single-sided OTPSM (SS-OTPSM), which is based on a unified theoretical framework of OTPSM and an additional condition enabling a full elimination of all undesired transient dc offsets. The proposed SS-OTPSM can be easily and cost-effectively implemented in a cycle-by-cycle manner, and inherently compatible with fast controllers. Additionally, in order to more accurately match DABC’s power transfer model under SS-OTPSM, an enhanced model predictive controller (EMPC) is proposed. By a combined use of SS-OTPSM and EMPC, ultrafast and completely dc-offset-free dynamics can be achieved without measuring the inductor current. The effectiveness of the proposed schemes is verified by closed-loop simulation and experimental results. [ABSTRACT FROM AUTHOR]

Cyberattacks can be strategically counterfeited to replicate grid faults, thereby manipulating the protection system and leading to accidental disconnection of grid-tied converters. To prevent such setbacks, we propose a physics-informed spline learning approach-based anomaly diagnosis mechanism to distinguish between both events using minimal data for the first time in the realm of power electronics. This methodology not only provides compelling accuracy with limited data, but also reduces the training and computational resources significantly. We validate its effectiveness and accuracy under experimental conditions to conclude how data availability problem can be handled. [ABSTRACT FROM AUTHOR]

Currently, the architecture of Line Current Differential Relays (LCDRs) is designed to respond to internal faults on the protected line using local and remotely-communicated current measurements. However, this architecture cannot distinguish between real faults and cyber-induced attacks whose goal is to cause false tripping of the line protected by the LCDR. In this paper, we propose an Anomaly-Based Scheme (ABS) for detecting false-tripping attacks against LCDRs, in the form of relay attacks, replay attacks, general false-data-injection attacks, and time-synchronization attacks. The ABS employs the Isolation Forest algorithm, which is trained on features determined from local current measurements to confirm real faults and differentiate them from false-tripping attacks. No trip command will be issued unless the sensed fault is confirmed as a non-attack by the ABS. The performance of the proposed ABS is tested and validated using the IEEE 9-bus benchmark in PSCAD/EMTDC environment. Simulation results show that the proposed ABS: (i) can accurately detect different categories of cyberattacks, (ii) does not negatively impact the accuracy of the fault-detection function, and (iii) is robust to the change in the power system’s operating point. [ABSTRACT FROM AUTHOR]

Phasor measurement units (PMUs) used in the smart grids are vulnerable to time synchronization attacks (TSA), whose attack target is the global positioning systems (GPS). The attacker manipulates phase measurements by sending deceptive GPS signals to introduce errors in state estimation, which can affect bus power flow calculation and economic dispatching of the power system. Considering the case of multiple attacked PMUs in AC, a novel false phase data detection method is proposed in this paper. The method uses “phase coding” to extract and encode the potential relationship between amplitude and phase angle, and then builds a TSAs detection model based on a vector neural network that learns the encoded relationship vectors through dynamic routing. Finally, simulation experiments are carried out on IEEE 9, 14, 30, and 118 bus systems and real measurements provided by a province in China. The results show that the proposed method achieves the best performance among the detection methods based on the learning model. [ABSTRACT FROM AUTHOR]

This letter details the metallization process of 3-D-printed WR-28 and WR-10 waveguides using electroplating. The 3-D printing technique is stereolithography, so the printed parts are plastic-based. A two-step metallization process is followed: a premetallization with nickel spray to make the part conductive and a subsequent electroplating process, emphasizing the chemical compounds and quantities needed to improve the result obtained, as well as the metallization times and currents applied on the parts. In addition, manufacturing deviations are measured and compensated. The results obtained are compared with simulations and commercial waveguide sections. Measurements show $S_{11}$ below −33 and −21 dB for WR-28 and WR-10, respectively. Measured average losses are around 1 dB/m for WR-28 and 4 dB/m for WR-10, which is equivalent to copper with an effective surface roughness lower than $0.4~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

SolSec Labs is a web-based application that provides interactive training labs for blockchain developers, especially students eager to learn more about smart contract security to gain practical knowledge (). It teaches solidity and smart contract security skills through hands-on experience. The easy-to-understand environment enables students and early developers to immediately apply newly learned secure coding practices to their ongoing projects. Currently, it consists of a total of 10 labs crafted using examples taken from the most severe real-world vulnerabilities. Every lab teaches developers about the related vulnerability; exploitation methods; preventive and remediation measures; and, finally, a step-by-step list of lab tasks to perform to secure the presented vulnerable code. [ABSTRACT FROM AUTHOR]

Feature selection is an important preprocessing step for high-dimensional data mining and machine learning; it is viewed as the selection of the optimal granularity to describe the target concept in rough set theory. Currently, research on rough sets mainly focuses on granularity selection in flat classification scenarios, while organizing hundreds of labels for hierarchical classification (HC) can provide additional external information and achieve better performance in terms of both accuracy and efficiency. However, HC also faces the following problems: 1) the current measures’ failure to characterize the uncertainty in HC; 2) the inability to select the optimal granularity of the target concept in HC; and 3) no valid approach to select features in a decision system with hierarchical classification (HieDS). To address these problems, this article introduces HC into rough set theory and proposes an approach to granularity selection for HC. First, we introduce the knowledge distance to reflect the uncertainty of HC and define related important characteristic functions to describe a HieDS. Then, from the perspective of uncertainty, granularity selection for the target concept and feature selection are presented based on these characteristic functions. Finally, we experimentally realize granularity selection and demonstrate excellent performance of feature selection in a HieDS in terms of both feature selection and classification accuracy. [ABSTRACT FROM AUTHOR]

Roller bearings are important rotating components of engines and have been widely used in the commercial, aerospace, railway transportation, and military fields. The inner race of a bearing that operates at high speeds can attain a temperature of almost 200 °C. Therefore, accurately measuring the speed of bearing inner race under a high-temperature thermal load is vital to ensure that engine is working properly. Herein, we propose a wireless method for measuring the bearing speed. The proposed method has a higher temperature application range and better accuracy than previous used methods. It measures the bearing’s inner race speed based on the eddy current effect and impedance matching. Adding a silver/copper layer to the surface of the bearing substrate changes its conductivity, magnetic permeability, and the equivalent impedance of the antenna. After passing through the coupler and detection circuit, the signal is output to the oscilloscope as a periodic voltage. The rotational speed of the bearing’s inner ring is measured by calculating the periodicity of the waveform. A bearing speed test platform is built and used for multiple groups of bearing speed measurements at 20 °C, 100 °C, and 200 °C on the platform. The results indicate that the method provides excellent stability and accuracy in the range of 0–1000 rpm, with a stable relative error of less than 1.64% and a maximum hysteresis of 1.72%. The maximum repeatability is 1.63658% (1000 rpm, 200 °C), and the maximum uncertainty is 0.66782 (1000 rpm, 200 °C). [ABSTRACT FROM AUTHOR]

The conventional approach of contactless current sensing using Rogowski’s coil is associated with unavoidable design constraints that limit the sensitivity, rise time, settling time, and bandwidth of operation. This article discusses some novel coil designs for contactless current measurement along with an electron device that works based on a brace-shaped Hall plate for dynamic precision adjustment. Experimentally, these proposed coil models achieve a sensitivity of 5.76 mV/A and a nonlinearity of 0.09%, which are better than their conventional counterparts. Apart from this, a mathematical analysis related to this work with different core materials and geometrical parameters confirms that these coils are also superior based on rise time, peak time, settling time, and sensitivity compared with their conventional counterparts. The dynamic precision adjustment device, made up of a brace-shaped Hall plate, utilizes novel materials, such as TiO2 and NiO, to make the device impedance more sensitive to control frequency and voltage. Experimentally, the impedance across the electron device varies between 0.0153 $\text{M}\Omega $ and 0.387 $\text{M}\Omega $ for every change in voltage and frequency in MHz of the switched mode control signal. This impedance-sensitive characteristic makes the output of the proposed sensor more efficient in achieving dynamic precision control even at a small range of operating conditions. [ABSTRACT FROM AUTHOR]

Fish detection in shallow water conditions or close to the bottom poses specific challenges, which often can hardly be addressed using typical acoustical or optical means. This significantly limits the possibilities of fish population monitoring and the use of fish detection for optimizing fishing techniques in such environments. Here, we investigate the potential of electrical impedance spectroscopy (EIS) as a remote-sensing technique for fish detection, to address this issue. The approach utilizes a set of electrodes to generate a low-intensity alternating electric current through water and to measure the impedance. We conducted a number of experiments in which a fish was swimming in a glass tank. We measured changes in impedance at different frequencies, using different electrode arrangements, while simultaneously tracking the fish position with a pair of cameras. We also created numerical models of the experimental setup using the finite-element method. The results of simulations were compared to the experimental data to test the accuracy of predictions and to determine if such a model could be a useful tool for designing detection setups for specific environmental conditions. We measured the robustness of the system to the presence of air bubbles as a potential source of disturbances. Our results show a clear correlation between the observed drops in both real and imaginary parts of the measured impedance and the position of the fish. Model simulations showed qualitatively and quantitatively similar results, indicating that such models could be suitable for practical applications. [ABSTRACT FROM AUTHOR]

Activation energy represents the average rate of interaction between aging by-products and cellulose. Activation energy is a crucial parameter that can be used to identify the remaining life of insulation in high voltage (HV) equipment. Existing noninvasive methods take a significantly longer time to sense activation energy for given insulation. This is primarily due to the volume of data required for such analysis, which generally takes significant time to measure. This work reports a noninvasive and effective approach to predict activation energy of oil–paper insulation using a dielectric response that is recorded for a very short span of time. The proposed method requires polarization current data sensed for a few seconds (15–20 s) to operate. The initial decay rate (DR) of the sensed data is found to be sensitive to the activation energy. This feature of the initial DR is utilized to sense the value of activation energy within a short duration. The proposed technique utilizes the current sensor (present within an electrometer) more efficiently. This facilitates the measurement of a highly accurate polarization profile and ensures reliable activation energy estimation. The proposed methodology has been successfully applied to data collected from a few real-life transformers. Reported results show that the suggested method provides satisfactory results with good accuracy. [ABSTRACT FROM AUTHOR]

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In this work, we study the current coupled to a simplified Unmanned Aerial Vehicle (UAV) model using a dual computational and experimental approach. The simplified surrogate structure reduced the computational burden and facilitated the experimental measurement of the coupled currents. For a practical system, a wide range of simulations and measurements must be performed to analyze the induced current variations with respect to properties of the incident excitation waveform, such as the frequency, angle of incidence, and polarization. To simplify this analysis, Characteristic Mode Analysis (CMA) was used to compute the eigen-currents of the UAV model and predict where and under which RF excitation conditions the coupled current is maximized. We verified these predictions using direct experimental measurement of the coupled currents. The presented simulations and measurements show the usefulness of CMA for studying electromagnetic coupling to practical systems.

Nowadays the percentage of power electronic devices, which use shunts for sensing of electrical signals, is increasing significantly. This method of measurements is simple, reliable and low-cost, however it requires careful elaboration of schematics and meticulous design of printed circuit boards. The author provides a detailed insight into the design of power converter Printed Circuit Boards (PCBs) with shunt-based sensing circuits and provides recommendations on improvement of signal measurements. He analyses the most popular design mistakes and illustrates their impact on measuring signals, which can be used for mistake localization. This paper demonstrates that the properly designed schematic can be turned into poorly operating PCB and recommends measures to avoid it. The author shares his more than 20-years experience and illustrates his statements with examples from real life. Although this paper is mainly addressed to young engineers, it could also be useful for experienced researchers, who work in neighboring areas and do not gain experience in PCB design.

This work presents a closed-form analytic approach to calculate the distortion introduced in resistive current measurements due to thermal properties of shunt resistors. As a shunt’s resistance varies with temperature, the sensed voltage becomes distorted. This non-linear effect depends on the thermal interface, dissipated power and material properties of the shunt resistor. It is presented, how to simplify the non-linear equation of the shunt temperature and calculate the resulting voltage spectrum, without the use of computationally extensive time-to-frequency-domain transforms. The results of the presented method match simulations including the non-linear behaviour, enabling a quick search through a solution space. The method is experimentally verified by use of a linear amplifier with an output distortion of −90 dB at low frequencies. In the experiment, a total harmonic distortion of up to −70 dB is observed in several shunt resistors covering a range of different thermal properties. Based on the presented method, shunt resistors can be chosen according to the minimum distortion required in a given application. Depending on the frequencies of interest, shunt resistors with a high temperature coefficient might still offer sufficient distortion performance.

Abstract Zero‐sequence currents in high‐voltage power systems during normal operation can have a significant influence on nearby infrastructure. It is therefore necessary to gain insight into typical levels of zero‐sequence currents in a variety of operational situations. Measurements can provide this insight. When performing measurements, one needs to know the uncertainty associated with the measurement to draw accurate conclusions. The measurement uncertainty associated with three different practical strategies to measure zero‐sequence currents during normal operation are studied: a direct and indirect measurement strategy using current clamps and oscilloscopes and a measurement strategy using phasor measurement units (PMU). Measurement uncertainty is studied using two methods: by analytical expressions and by Monte Carlo simulations. Both methods give consistent outcomes for the measurement uncertainty and show the same tendencies of the zero‐sequence current measurement uncertainty as a function of the positive‐sequence current. This paper studies measurement strategies with error sources based on realistic measurement devices that could be used in practice. The following outcomes were found: in the direct strategy, the primary current transformers are the largest uncertainty sources; in the indirect strategy, the current clamps are the largest uncertainty sources; in the PMU strategy, the PMU total vector error is the largest uncertainty source.

A simple structure E-plane decoupled millimeter wave (mmW) multiple-input multiple-output (MIMO) antenna based on current cancellation model is proposed in this communication. First, a coupling model of E-plane MIMO antenna is established by analyzing the coupling current. Then, a high-isolation two-element E-plane MIMO antenna loaded with decoupling branch Bar-L is designed by current cancellation method. Finally, a high-isolation four-element E-plane MIMO antenna is designed, fabricated, and measured to verify the applicability of the decoupling method in large arrays. The measured results show that the antenna achieves $\vert \text{S}_{\mathbf {11}}\,\,\vert < -10$ dB in band of 25.5–26.5 GHz, and the measured isolation of adjacent ports in this band is greater than 35 dB, which effectively improves the isolation without deteriorating other performance. The proposed antenna with a simple structure is suitable for mmW MIMO systems requiring high isolation. [ABSTRACT FROM AUTHOR]

Existing robust state estimation methods are generally unable to distinguish model uncertainties (state outliers) from measurement outliers as they only exploit the current measurement. In this article, the measurements in a sliding window are, therefore, utilized to better distinguish them, and an adaptive method is embedded, leading to a sliding window variational outlier-robust Kalman filter based on Student’s t-noise modeling. Target tracking simulations and experiments show that the tracking accuracy and consistency of the proposed filter are superior to those of the existing state-of-the-art outlier-robust methods thanks to the improved ability to identify the outliers but at a cost of greater computational burden. [ABSTRACT FROM AUTHOR]

Advances on no-insulation REBCO coil technology has made understanding and controlling contact resistivity increasingly important. Praffin (wax) impregnation is a process that has been used for improving mechanical stability of insulated and no-insulation REBCO coils. Wax impregnation is beneficial in both no-insulation coils and insulated coils with additional copper stabilizer or multiple conductors. In the latter scenario, contact resistance between conductor and additional stabilizer is also important. It is crucial to understand the effects of wax impregnation on contact resistivity (Rct). We designed and built an apparatus to use short REBCO samples which simulates the behavior of Rct in a pancake coil during the wax impregnation process. Rct was measured at 77 K before and after the wax impregnation. In addition, a single pancake coil was wound to test the effect of wax impregnation. This coil simulates the NHMFL 32 T magnet Coil A in winding stresses. Rct was measured at 77 and 4.2 K before and after wax impregnation. We found that wax impregnation does not significantly change contact resistivity. This means that wax impregnation can be used in coils without compromising the current sharing ability between turns. The experimental process and results are discussed. [ABSTRACT FROM AUTHOR]

High critical current density is desired for cables adopted in fusion or accelerator applications. The bending diameter of REBCO tapes is very important for the preparation of such cables. The bending diameter of REBCO tape is related to many factors. It is necessary to identify the most important factors determining the bending diameter by experiments. In this article, a new measurement method for bending diameter is developed. Short samples are taken from individual tapes in a large batch and connected in series into one long piece for bending diameter measurement. This way, a large batch of tapes can be efficiently assessed in one go. The samples prepared by Shanghai Superconducting Technology Co., Ltd. (SST) have been tested. It is concluded that the critical bending diameter of the tapes, which we define that the critical current attenuation is less than 10%, is closely related to its thickness, stiffness, superconducting layer thickness, and copper plating thickness. The composition of the superconducting layer has little effect on it. By testing the tapes prepared by SST in large quantity, it is found that when the REBCO faces inward during bending, tapes plated with 5 and 10 μm copper on one side only have smaller critical bending diameter than tapes plated with copper on both sides. The current has no attenuation when the bending diameter is 2.6 mm. When REBCO faces outward, copper plating has little effect on the critical bending diameter, which varies between 6 and 14 mm. [ABSTRACT FROM AUTHOR]

The transcutaneous energy transmission system (TETS) has been studied for wireless power supply in ventricular assist devices embedded in the body. To be approved as a medical device, it is necessary to measure the high-frequency patient leakage current (Ip) and to suppress it to a safety limit below 10 mA. However, it is difficult to suppress because the terminal voltage and the frequency of the transmitting coil are extremely high (500 V and 400 kHz). In this study, we propose an original measurement method for Ip in TETS and measure the Ip. Furthermore, the suppression method of Ip is investigated using a high-frequency isolation transformer (HFIT) and an insulation sheet for transmitting coils. Consequently, an Ip of 17.14 mA is obtained when the HFIT without countermeasures and an insulation silicone sheet is used (Type A), whereas an Ip of 7.68 mA is obtained when using two series-connected HFITs and an expanded polystyrene sheet with a thickness of 3.58 mm (Type B). Thus, it is possible to drastically suppress Ip below 10 mA. Additionally, we define the combined capacitance CCom based on the series connection of the capacitance of the insulation transformer Cp and that of the insulation sheet Cc and calculate the theoretical Ip. The theoretical Ip decreases from 20.8 mA for Type A to 5.6 mA for type B. The calculation results of Ip are mostly in agreement with the measurement results, indicating that a reduction in CCom is important for suppressing Ip of the TETS. [ABSTRACT FROM AUTHOR]

The distributed parameters of a non-uniform transmission line (NTL) are assumed to depend on a finite set of unknown parameters, for example, their spatial Fourier series coefficients. The line equations are set up taking random voltage and current line loading into account with the random loading being assumed to be white Gaussian noise in the time and spatial variables. Bypassing over to the spatial Fourier series domain, these line stochastic differential equations (SDEs) are expressed as a truncated sequence of coupled stochastic differential equations for the spatial Fourier series components of the line voltage and current. The coefficients that appear in these stochastic differential equations are the spatial Fourier series coefficients of the distributed line parameters and these coefficients in turn are linear functions of the unknown parameters. By separating these complex stochastic differential equations into their real and imaginary part, the line equations become a finite set of SDEs for the extended state defined to be the real and imaginary components of the line voltage and current as well as the parameters on which the distributed parameters depend. The measurement model is assumed to be white Gaussian noise corrupted versions of the line voltage and current sampled at a discrete set of spatial points on the line and this measurement model can be expressed as a linear transformation of the state variables, i.e, of the spatial Fourier series components of the line voltage and current plus a white measurement noise vector. This work uses sparse matrix factorization using Kronecker product to implement the Fourier unitary transform. This work implements perturbation theory for non-uniform transmission line. The extended Kalman filter (EKF) equations are derived for this state and measurement model and our real timeline voltage and current and distributed parameter estimates show excellent agreement with the true values based on MATLAB simulations. The use of sparse matrix factorization using Kronecker product ease the mathematical complexity and provides compact representation. [ABSTRACT FROM AUTHOR]

This paper introduces a current differential protection scheme, appropriate for application in medium voltage active distribution systems, where it is desired to keep the greatest possible number of loads and DG units energized during a fault. Conventional two-terminal percentage current differential relays are used to form successive, time-current-coordinated, differential protection zones. Multiple time-delayed differential elements in each protection zone guarantee coordination with the zone's lateral protection devices, as well as between successive differential protection zones. Sensitive time-delayed differential elements protect against relatively high-resistance faults, while instantaneous differential elements minimize protection speed whenever possible. Additional emergency differential elements deal with post-fault topology changes and breaker failure conditions enhancing the overall scheme's performance. The proposed scheme is applied to a model of real medium voltage distribution system with distributed generation, considering a ring topology operation. A detailed simulation-based study proves the applicability and enhanced performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

The existing methods for multi-point harmonic contribution evaluation usually require some preconditions, such as the node harmonic current is equivalent to the harmonic emission current and the number of measurements is not less than the number of sources. However, these requirements may not be satisfied in practice. In this context, this paper proposes an improved sparse component analysis (SCA) method to solve the underdetermined blind source separation model, which is used to describe the harmonic state under incomplete measurements. The improved SCA adopts a new two-stage technique. First, the mixing matrix containing harmonic transfer impedances is estimated through the synchrosqueezing S-transform. Then, the source signal vector containing harmonic emission currents is reconstructed through the modified subspace projection. By matching the harmonic impedances and currents, the multi-point harmonic contribution evaluation is further achieved. The efficiency of the proposed method is verified by simulations and field case studies. The results demonstrate that the proposed method outperforms the existing methods in terms of accurately estimating the harmonic emission currents and quantifying the harmonic contributions under incomplete measurements. [ABSTRACT FROM AUTHOR]

In this paper, a self-adaptive protection system is proposed for adjusting the time dial (TD) of reclosers found in electrical power distribution systems (EPDSs). The self-adjustment is carried out in both phase and ground protection. The methodology considers the fuses along the feeder to obtain the fuse-saving philosophy. This feature allows less interference on the protection system already implemented by the electrical power distribution utilities. This methodology also allows using other frameworks, such as the estimation of the fault distance. The software used for computer modeling and simulation was PSCAD™/EMTDC™. The flexibility provided by the method, which allows the incorporation of new logic and changes in decision-making, resulted in an adaptive method with a good performance against different locations, types, and fault impedance. It also resulted in better coordination between the protection devices (PDs). The results compared with well-coordinated conventional protection have shown significant performance gain with the adaptive system. [ABSTRACT FROM AUTHOR]

Fault response of an inverter based resource (IBR) is dictated by its control scheme, making it markedly different from the response of a synchronous source. This has led to misoperation of distance relays when fed by IBRs. Published literature is mostly focused on changing the control design of inverters, but this approach is not practical, as these controls are proprietary and beyond the reach of utilities. To resolve this issue, this paper proposes a method for a source-agnostic distance relay that works in time-domain. Using only single ended measurements, the relay detects, classifies and locates any fault on the line it monitors. The method does not require any polarization technique. It is shown to work for unbalanced lines of any length, for transmission or distribution system with any number (even 100%) of IBRs, is immune to load encroachment, decaying dc offset and prefault currents. With very limited communication, it is also shown to be immune to fault resistance. [ABSTRACT FROM AUTHOR]

State-of-the-art capacitor online monitoring methods are designed for the whole dc bank. The capacitance or equivalent series resistance of the dc bank, as an aging indicator, is obtained by the sensors installed at the dc terminal, or derived from the state equation of the system. The difference of capacitor parameters from manufacturing and the arrangement of the dc bank will result in uneven thermal stress for the capacitors. Due to the restriction of the low stray inductance specification and high power density requirement, the traditional online monitoring circuits are hard to be designed for the single capacitor in the dc bank. In this article, a Rogowski coil based online monitoring circuit has been designed for the single capacitor in the dc bank. A new aging criterion has been established for aluminum electrolytic capacitors based on the accelerated aging test. To achieve a compact integration design, a six-layer printed-circuit-board-type Rogowski coil is designed under an optimized frequency. A 2-kW single-phase inverter is built to verify the theoretical analysis and practical performance of the monitoring circuit. [ABSTRACT FROM AUTHOR]

The current shunt with high bandwidth and low parasitics is critically needed to satisfy the soaring current slew rate of the wide-bandgap (WBG) device. However, the existing lumped parameter model is inappropriate to model and design the next-generation ultrahigh bandwidth current shunt, leading to the unclear bandwidth limitation, inextricable invasive effect, and lacked design guidance. In this letter, by introducing the transmission line theory, it is revealed that, due to the impedance mismatch, the strong signal reflection inside the current shunt results in the high-frequency parasitic inductance, which severely deteriorates its bandwidth. On this basis, the concept of the impedance-matching shunt (IM-shunt) is then proposed to derive the mathematical model-guided design methodology for the high-performance current shunt. With the aid of the proposed concept, the current shunt with > 3 GHz bandwidth and < 0.1 nH parasitics is developed. The comparative experiments further ensure the accurate and nonintrusive characterization of the switching trajectories for the WBG application. [ABSTRACT FROM AUTHOR]

In this paper, we study a new variant of trajectory similarity search from the context of continuous query processing. Given a moving object from $s$ s to $d$ d , following a reference route $T_r$ T r , we monitor the trajectory similarity between the reference route and the current partial route at each timestamp for online detour detection. Since existing trajectory distance measures fail to adequately capture the deviation between a partial route and a complete route, we propose a partial trajectory similarity measure to bridge the gap. In particular, we enumerate all the possible routes extended from the partial route to reach the destination $d$ d and calculate their minimum distance to $T_r$ T r . We consider deviation calculation in both euclidean space and road networks. In euclidean space, we can directly infer the optimal future path with the minimum trajectory distance. In road networks, we propose an efficient expansion algorithm with a suite of pruning rules. Furthermore, we propose efficient incremental processing strategies to facilitate continuous query processing for moving objects. Our experiments are conducted on multiple real datasets and the experimental results verify the efficiency of our query processing algorithms. [ABSTRACT FROM AUTHOR]

Aiming at improving the fault-tolerant performance of switched reluctance generators, a new power converter with fault-tolerance capability is proposed in this paper. The structure of the converter is simple and there is only one transistor in each of the working modes, which makes fault diagnosis easier. To obtain more fault information, an improved current measurement method is proposed. The phase current is obtained by solving current equations obtained by current sensors and rotor positions. Open-circuit and short-circuit faults can be determined by comparing the consistency of the current slope and gate signal. Fault locations can be determined by comparing the relationships among the magnitude of the bus current, the phase current, and the corresponding thresholds. Open-circuit transistors can be replaced by fault-tolerant strategy, which returns the power converter to normal and maintains the stable operation of the system. Simulations and experiments show that the open-circuit and short-circuit faults of transistors can be diagnosed by the proposed strategy. [ABSTRACT FROM AUTHOR]