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This work presents a technique to actively reduce the vibrations generated by magnetic anisotropy in sinusoidal brushless motors through current injection. These vibrations are an unwanted phenomenon mainly generated by the interaction between the rotor magnets and the stator teeth. These produce vibrations which are then transmitted to the frame and other mechanical parts such as bearings, gearboxes, transmissions, and joints, thus reducing the life, performance, and reliability of these components. First, different design strategies and control algorithms to passively and actively attenuate the vibrations are reviewed. Then, a narrowband active method that attenuates a harmonic vibration through the injection of a harmonic current is presented. The effectiveness of the proposed method was demonstrated on a prototype of a Surface Permanent Magnet Synchronous Motor (SPMSM). For the motor under test, an attenuation of −13.5 dB at 650 rpm and −29 dB at 800 rpm was achieved on the main frequency component, caused by the magnetic anisotropy, which in turn corresponds to the 72nd harmonic of the rotor mechanical speed. [ABSTRACT FROM AUTHOR]

Infrared soldering as a step in module encapsulation, which would cause light-induced degradation (LID) and light- and elevated-temperature-induced degradation (LeTID) effects on solar cells, may cause efficiency mixing among solar cells that were originally in the same grade within the module after soldering. Furthermore, the problem of bright and dark regions would appear, which would result in a decrease in the CTM value. Current injection is considered to be one of the effective methods to solve the above problem. However, after the current injection treatment, there is still a 10% probability of the appearance of bright and dark regions in modules. In this work, we first adopted the conventional current injection process in monocrystalline passivated emitter and rear cells (PERCs). The effects of injected currents, temperature and time were systematically optimized, and cells with or without the current injection under the optimal parameters were illuminated with 1 sun at 85 °C for 25 h. Secondly, a piece of equipment was developed to further stabilize the performance of solar cells and improve the CTM value. The results showed that the best current injection parameters were a temperature of 185 °C, an injected current of 11 A and an injection time of 770 s. Compared with the cells without any pretreatment, the relative changes in the η, Voc, Isc and FF of the cells pretreated with the optimal conditions mentioned above were 0.23%, 0.08%, 0.02% and 0.08% larger, respectively, after 25 h of degradation. Then, solar cells processed by current injection were processed with our equipment, and the probability of a problem occurring was reduced from 10% to 2%. Meanwhile, the CTM value increased by 0.4%. Finally, a balance mechanism between H0 and H0-X has been proposed to explain the mechanism of the equipment. [ABSTRACT FROM AUTHOR]

Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

One of the main protection issues is the possible malfunctioning of protection devices under fault conditions in microgrids with integrated distributed energy resources (DERs). In this paper, a novel method of positive-negative sequence (PNS) compensation for grid connected distributed generator (DG) converters with enhanced low voltage ride-through (LVRT) capability in micro grid system is presented. The aim is to maintain the connection of the DGs by injecting the required reactive power considering the limitations imposed by grid codes. In the proposed scheme, a flexibility is provided in terms of active and reactive current injection such that the DGs can stay connected to the grid longer and produce more active power during the fault; while, in previous studies, usually a constant reactive current defined by grid codes was applied. The suitability of the proposed method in terms of utilization of current capacity of the converter is evaluated through comparative study with three other PNS current injection methods. Further, the time taken to disconnect the DGs from the grid in the event of fault is analyzed. The simulation results indicate that DGs can stay connected for longer with 99.98% utilization of converter current capacity compared to other methods. [ABSTRACT FROM AUTHOR]

To improve the breaking performances of current injection vacuum DC circuit breaker (DCCB), a double-break current injection DCCB proposed. The opening moments of the two breaks are not simultaneously, one of the breaks is arc breaking, which is used for cut off the fault current, and the other is non-arc breaking, which is used to enhance the transient recovery voltage (TRV) withstand capability. During the interruption process, let the arc-breaking contact first open, the contact starts to separate and produce arcs, then the pre-charged capacitor injects a reverse current to extinguish the arc, meanwhile, the current commutation of non-arc-breaking contact is realized by a coupling inductor. In addition, freewheeling diodes connected in parallel at the contacts to delay the occurrence of transient recovery voltage, thereby further increasing the voltage withstand capability of the CB. The principle and analysis of proposed DCCB scheme are discussed. Finally, the effectiveness of the proposed DCCB scheme is verified by simulation

In view of the existence of single-phase grounding fault arc suppression in the non-effective grounding system of distribution network, the combination of additional active compensation and arc suppression coil is often used to suppress the grounding fault arc, and the performance of active compensation system control strategy directly determines the arc suppression performance. An active arc suppression scheme based on model predictive control (MPC) is designed. Firstly, the principle of active arc suppression using injection current mode is analyzed. Then, the active arc suppression system topology of three-cascaded H-bridge multilevel inverter is adopted, and the cost function is optimized. The active arc suppression closed-loop control system based on MPC is designed. Compared with the active arc suppression closed-loop control system based on proportional integral (PI) control, the control system proposed can achieve accurate tracking of multiple harmonic currents without parameter tuning, which effectively compensates the grounding current. Simulation and experimental results show that the proposed scheme can suppress the grounding fault current more effectively and meet the requirements of reliable arc suppression in different scenarios.

Infrared soldering as a step in module encapsulation, which would cause light-induced degradation (LID) and light- and elevated-temperature-induced degradation (LeTID) effects on solar cells, may cause efficiency mixing among solar cells that were originally in the same grade within the module after soldering. Furthermore, the problem of bright and dark regions would appear, which would result in a decrease in the CTM value. Current injection is considered to be one of the effective methods to solve the above problem. However, after the current injection treatment, there is still a 10% probability of the appearance of bright and dark regions in modules. In this work, we first adopted the conventional current injection process in monocrystalline passivated emitter and rear cells (PERCs). The effects of injected currents, temperature and time were systematically optimized, and cells with or without the current injection under the optimal parameters were illuminated with 1 sun at 85 °C for 25 h. Secondly, a piece of equipment was developed to further stabilize the performance of solar cells and improve the CTM value. The results showed that the best current injection parameters were a temperature of 185 °C, an injected current of 11 A and an injection time of 770 s. Compared with the cells without any pretreatment, the relative changes in the η, Voc, Isc and FF of the cells pretreated with the optimal conditions mentioned above were 0.23%, 0.08%, 0.02% and 0.08% larger, respectively, after 25 h of degradation. Then, solar cells processed by current injection were processed with our equipment, and the probability of a problem occurring was reduced from 10% to 2%. Meanwhile, the CTM value increased by 0.4%. Finally, a balance mechanism between H0 and H0-X has been proposed to explain the mechanism of the equipment.

Active arc suppression devices can not accurately issue compensation current during single-phase grounding faults in the distribution network. Thus, an active current arc suppression scheme based on PI and repetitive control strategy was proposed on the basis of the analysis of the active current arc suppression principle. Based on the use of voltage feedforward links to eliminate neutral voltage disturbances, the PI and repetitive control strategy was introduced into the current closed-loop system to achieve fine-grained processing of the grounding residual current through the static-free tracking of the frequency as well as the 5 and 7 times commanded current. Compared with the traditional PI control strategy, this method used a parallel structure of PI and repetitive control to achieve accurate output compensation current by using the fast response of PI control to command current and the static-free tracking performance of repetitive control to multi-frequency AC signals. The simulation and experimental results show that compared to PI control, the PI+repeat control strategy can reduce the deviation of the injected current from the commanded current from 14.85% to 3.27%; the compensation rate of single-phase earth fault residual current under different earth resistances is improved, for example, the compensation rate increasing from 79.67% to 94.74% for an earth fault 1.4 Ω resistances, which can better achieve the goal of full compensation of earth residual current.

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposes a three-phase four-wire power flow method based on the bus frame of reference for neutral-grounded distribution systems. The proposed method integrates mathematical component models using graph theory and current-injection techniques. The accuracy of the proposed direct Z BUS method and network models for multi-grounded systems was validated using the IEEE 13-bus test system. The convergence of the proposed direct Z BUS method was tested using an IEEE 123-bus test system. Moreover, the performance of the proposed method was compared with those of the current-injection backward forward–sweep and Newton methods. [ABSTRACT FROM AUTHOR]

Crosswell electromagnetic (EM) methods are widely used in subsurface geophysical prospecting because they can achieve more effective long-distance detection than single-well methods. However, a large-diameter borehole is required to increase the magnetic moment of the magnetic dipole source. For the long-distance detection of copper ores, which is usually performed in slim holes, we present a borehole-surface current-injection-based crosswell EM logging method. Considering the cost of deploying casing, we inject a low-frequency ac directly into the ground, and converging current is formed around low-resistance anomalies in the formation. Then, the distribution of the anomalies can be inferred by detecting the low-frequency alternating magnetic field of the converging current in the receiver well. Moreover, to further improve the detection performance, we design a placement scheme for the grounding electrode for multianomaly crosswell detection based on the Gauss–Newton inversion algorithm, where the EM responses for different grounding electrode locations are analyzed. Field experiments are conducted using two slim open holes spaced approximately 1000 m apart for the detection of two copper ores. Through the processing and interpretation of measured EM signals, the conductivity imaging results of the crosswell EM method indicate that the measured distribution of anomalies is consistent with prior knowledge obtained from numerous single-well loggings, demonstrating the feasibility of the proposed application for long-distance crosswell EM logging in slim open holes.

Silicon heterojunction (SHJ) solar cells have garnered significant attention recently due to their excellent performance, benefiting from the outstanding passivation quality of intrinsic/doped hydrogenated amorphous silicon (a‐Si:H) bilayers. Herein, it is found that current injection at elevated temperatures can enhance the electrical performance of SHJ solar cells. The kinetics study clarifies that activation energy of 0.5 eV is obtained for this enhancement phenomenon. By using photoluminescence (PL) images, it is demonstrated that the performance enhancement can be mainly attributed to the reduction of electrically active defects. The underlying mechanism is focused on the diffusion and passivation effect of hydrogen, which could be valuable for understanding the kinetics of the current injection‐induced enhancement phenomenon in the SHJ cells. This approach serves as an alternative method of light soaking to reach the effect of performance enhancement of SHJ cells, making it more competitive in the photovoltaics industry. [ABSTRACT FROM AUTHOR]

In this study, the design of a direct down-conversion, double-balanced Gilbert Mixer at 432 MHz is presented. The proposed circuit achieves a 13.4 dB double-sideband noise figure with an associated flicker corner frequency of 250 kHz. The conversion gain of the mixer is approximately 10.2 dB, with an IIP3 of 8.2 dBm simulated in the post-layout setup at a 1 MHz intermediate frequency. The design of the mixer has been accomplished using the UMC 180 nm CMOS process, and its layout occupies an area of 0.0135 mm 2 . At the supply voltage of 1.8 V, the mixer consumes approximately 5.15 mW of power. [ABSTRACT FROM AUTHOR]

Active arc suppression devices can not accurately issue compensation current during single-phase grounding faults in the distribution network. Thus, an active current arc suppression scheme based on PI and repetitive control strategy was proposed on the basis of the analysis of the active current arc suppression principle. Based on the use of voltage feedforward links to eliminate neutral voltage disturbances, the PI and repetitive control strategy was introduced into the current closed-loop system to achieve fine-grained processing of the grounding residual current through the static-free tracking of the frequency as well as the 5 and 7 times commanded current. Compared with the traditional PI control strategy, this method used a parallel structure of PI and repetitive control to achieve accurate output compensation current by using the fast response of PI control to command current and the static-free tracking performance of repetitive control to multi-frequency AC signals. The simulation and experimental results show that compared to PI control, the PI+repeat control strategy can reduce the deviation of the injected current from the commanded current from 14.85% to 3.27%; the compensation rate of single-phase earth fault residual current under different earth resistances is improved, for example, the compensation rate increasing from 79.67% to 94.74% for an earth fault 1.4 Ω resistances, which can better achieve the goal of full compensation of earth residual current. [ABSTRACT FROM AUTHOR]

In this article, a simple series-connected 24-pulse rectifier with a passive auxiliary current injection circuit (ACIC) is proposed. The proposed rectifier consists of a 12-pulse rectifier and an ACIC. The ACIC includes a circulation current forming circuit, an auxiliary single-phase transformer (AST), and an auxiliary single-phase full-bridge rectifier (ASFR). The ASFR extracts alternating square-wave current from the dc side and injects it into the outputs of three-phase rectifier bridges to increase the output state of these bridges. The operating mode of the proposed rectifier is analyzed, and the functional relationship between the input current and turns ratio of AST is established. The AST turns ratio that minimizes the input line current total harmonic distortion (THD) is derived. The voltage and current rating of AST are calculated, and the design method of capacitors C1 and C2 in ACIC is given. Under the optimal turns ratio, the ACIC extends the 12- to a 24-pulse rectifier. The resulting 24-pulse rectifier draws near-sinusoidal input currents with less than 5% THD. The AST in ACIC has a very low kilovolt-ampere rating (1.96% Pd), and the current ratings of ASFR are small. The theoretical analyzes are provided and experimentally verified using a 1.7 kW experimental prototype. [ABSTRACT FROM AUTHOR]

The fault current of generation with renewable energy sources that use inverters (FERUI) between the grid and generation, is limited due to limitations of the electronic components, so a dispute arises related to the viability of the overcurrent relay in FERUI applications. These disputes arise due to the unavailability of FERUI fault current characteristics. The problem is further complicated by the numerous fault current controls, where various current characteristics can be obtained. This document aims to establish the various fault current characteristics of FERUI, meeting the requirements of the Brazilian grid code. From these characteristics, disputes related to the feasibility of overcurrent relays for FERUI applications can be resolved and the appropriate types of control that allow satisfactory performance can be identified. [ABSTRACT FROM AUTHOR]

Based on a self-biased architecture, this paper presents a novel adaptive fast-locking, wide operating range and low-jitter phase-locked loop (PLL). A current injection and adaptive bandwidth technology with minimum area overhead is employed to speed up the loop equilibrium acquisition process, without any adverse impact on the steady-state loop dynamics and the jitter performance. The proposed start-up circuit resets the loop to an appropriate initial state in order to shorten the initial ramp-up interval of the voltage-controlled oscillator (VCO), also resulting in cutting down the pull-in time. In addition, a proportional factor is introduced to give some kind of flexibility in the circuit design optimization. The proposed adaptive fast-locking self-biased PLL (AFL-SPLL) is designed and realized in a prototype based on TSMC 28 nm CMOS process, having a supply voltage of 0.9 V and an area of 0.0281 mm2. This PLL demonstrates a tuning range of 1 to 3 GHz and power consumptions from 0.91 mW at 1 GHz to 4.6 mW at 3 GHz operating frequency. The experimental results show that the capture process has been accelerated by up to 84.7% over large division ratios, yet the capture performance did not deteriorate at all for small division ratios. Meanwhile, the circuit implementation gave almost no area increase and yet achieved a reduction in the lock-in time of about 6.5 times, namely from 23.5 μs (without the adaptive locking) to only 3.6 μs (with the adaptive locking) on the maximum operation frequency condition of 3 GHz. [ABSTRACT FROM AUTHOR]

This paper reviews architectures and circuit implementations of on-chip sinusoidal signal generators (SSGs) for electrical impedance spectroscopy (EIS) applications. In recent years, there have been increasing interests in on-chip EIS systems, which measure a target material’s impedance spectrum over a frequency range. The on-chip implementation allows EIS systems to have low power and small form factor, enabling various biomedical applications. One of the key building blocks of on-chip EIS systems is on-chip SSG, which determines the frequency range and the analysis precision of the whole EIS system. On-chip SSGs are generally required to have high linearity, wide frequency range, and high power and area efficiency. They are typically composed of three stages in general: waveform generation, linearity enhancement, and current injection. First, a sinusoidal waveform should be generated in SSGs. The generated waveform’s frequency should be accurately adjustable over a wide range. The firstly generated waveform may not be perfectly linear, including unwanted harmonics. In the following linearity-enhancement step, these harmonics are attenuated by using filters typically. As the linearity of the waveform is improved, the precision of the EIS system gets ensured. Lastly, the filtered voltage waveform is now converted to a current by a current driver. Then, the current sinusoidal signal is injected into the target impedance. This review discusses the principles, advantages, and disadvantages of various techniques applied to each step in state-of-the-art on-chip SSGs. In addition, state-of-the-art designs are compared and summarized. [ABSTRACT FROM AUTHOR]

Improving current injection into r- and m-planes of nanowires (NWs) is essential to realizing efficient GaInN/GaN multiple quantum shell (MQS) NW-based light-emitting diodes (LEDs). Here, we present the effects of different p-GaN shell growth conditions on the emission characteristics of MQS NW-LEDs. Firstly, a comparison between cathodoluminescence (CL) and electroluminescence (EL) spectra indicates that the emission in NW-LEDs originates from the top region of the NWs. By growing thick p-GaN shells, the variable emission peak at around 600 nm and degradation of the light output of the NW-LEDs are elaborated, which is attributable to the localization of current in the c-plane region with various In-rich clusters and deep-level defects. Utilizing a high growth rate of p-GaN shell, an increased r-plane and a reduced c-plane region promote the deposition of indium tin oxide layer over the entire NW. Therefore, the current is effectively injected into both the r- and m-planes of the NW structures. Consequently, the light output and EL peak intensity of the NW-LEDs are enhanced by factors of 4.3 and 13.8, respectively, under an injection current of 100 mA. Furthermore, scanning transmission electron microscope images demonstrate the suppression of dislocations, triangular defects, and stacking faults at the apex of the p-GaN shell with a high growth rate. Therefore, localization of current injection in nonradiative recombination centers near the c-plane was also inhibited. Our results emphasize the possibility of realizing high efficacy in NW-LEDs via optimal p-GaN shell growth conditions, which is quite promising for application in the long-wavelength region.

The structure of the low-voltage distribution network often changes. The change of topology will affect fault detection, fault location, line loss calculation, etc. It leads to fault detection error, inaccurate positioning and abnormal line loss calculation. This paper presents a new method to automatically identify the topology of a low-voltage power grid by using the injection current signal. When the disturbance current signal is injected into the low-voltage line, the current upstream of the injection point will change, and the current downstream of the injection point will not be affected. It is proved theoretically by using the superposition principle. With this method, the disturbance current signal can be injected into the line in turn, and the topology can be identified by observing the change of the current in line. The correctness of the method is proved by Matlab simulation and laboratory verification.

Abstract As a basis for the electrical tomography of laboratory-scale rock samples (~ 10 cm), we developed a procedure for stable, multi-point, electrical measurement on rock samples that is effective even at high contact and sample resistance. Electrodes were strongly attached to the surface of high-resistivity rock using conductive and adhesive epoxy. Sustained current injection for long periods into high-resistance rocks was fulfilled using a constant direct current source with high internal resistance. Accurate voltage measurement across the high-resistance rock was accomplished by differential measurement using two high input resistance voltmeters. Measurements of high resistance also require a stable measurement environment: the temperature and humidity in the laboratory were controlled using an air conditioner, a humidifier, a dehumidifier, and a vinyl tent. Signal noise arising from human activities was eliminated by the remote operation of the measuring equipment and switching terminal. The proposed measurement procedure was evaluated in terms of the stability and accuracy of measured values and its applicability to electrical tomography. To assess measurement stability, we performed multiple measurements of a dry granite sample at various levels of absolute humidity. Our procedure recorded highly reproducible measurements under each humidity condition. The observed changes in measured values with absolute humidity indicate the importance of stabilising the temperature and humidity conditions in the laboratory. Applying our technique to multiple plastic samples with known resistivity confirmed its accuracy. To evaluate its applicability to electrical tomography, we measured the potential distribution on a dry granite surface in response to an injected current using a simple 40-electrode array. The potential distribution measured by our procedure agreed well with that predicted by forward modelling, demonstrating the robustness of our procedure in array measurements, and thus indicating its potential applicability to tomographic measurements for a variety of targets even under severe conditions including the relative dryness of ambient humidity.

This paper introduces a variable magnet switched reluctance motor (VM‐SRM) drive that can be characterized with adjustable performance. It consists of a switched reluctance (SR) motor with low coercive force (LCF) magnets buried on stator yoke and a modified asymmetric half bridge (AHB) converter. Magnetization level of the LCF magnets is adjusted by injecting a current pulse to a phase winding of the VM‐SRM. The magnetization process does not need any extra coil and provides a simplicity owing to modified AHM converter. Possible magnetic saturation that limits the magnetization level is overcome by injecting current pulses to two phase windings at the same time. Thus, LCF magnets can be used with their full capacity. The presented analysis results demonstrate that proposed VM‐SRM drive provides a variable performance and might be a candidate for future variable speed applications. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Solar energy remains one of the best renewable energy options available, as it is abundant, clean and reliable. Due to the susceptibility of the PV system to grid failure, conventionally, the PV inverter would shut down. However, many countries have implemented grid codes to ensure and regulate the operation of photovoltaic systems during grid failures. Modern technologies have equipped PV inverters with Low Voltage Ride Through (LVRT) capability. This document discusses current controllers for current injection under LVRT conditions. These controllers have been classified into two main categories: linear controllers and nonlinear current controls. In addition, a comparative analysis has been presented, discussing the advantages and disadvantages of these control schemes. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Solid-state transformers (SSTs) have a great ability to improve power quality problems. In this article, an effective strategy is proposed to improve voltage unbalance conditions by these transformers. A searching optimization algorithm is presented to estimate the optimal required negative-sequence current vector. Injection of this current vector into a medium-voltage network provides maximum compensation in the voltage unbalance factor. In this method, the amplitude of the negative-sequence current vector is determined based on the current limitation of the SST and its phase angle is optimized to maximum improve the voltage unbalance conditions. Parametric analysis proves that the proposed injection current vector is unique. This negative-sequence current vector is obtained based on a simple process that is presented in the form of a flowchart. Independence from the extraction of positive and negative sequences of the measured currents is one of the main advantages of the proposed control method. Simulation and experimental results by using a laboratory three-stage SST approve the proposed optimization method. These results show that SSTs can acceptably decrease grid unbalanced voltage by an optimal injection current. [ABSTRACT FROM AUTHOR]

Rationally manipulating the functional substituents plays a crucial role in tuning the luminescence and lasing properties of organic gain media. Herein, a cyanophenyl‐moiety, which exhibits relatively weaker electron affinity, is connected to 2,6‐dicarbonitrile diphenyl‐1λ5‐phosphinine (DCNP) via para‐linking. Resultantly, the appreciated locally‐excited characteristics ensuring a large oscillator strength and high radiative rate can be reserved in DCNP‐4‐(4‐cyanophenyl) (DCNP‐pCN). Interestingly, the weak charge‐transfer state from the relative donor (D)/acceptor (A) interplay enables small singlet‐triplet splitting (ΔEST ≈ 0.45 eV). Thus the triplets generated on DCNP‐pCN can be efficiently scavenged by 4,4'‐bis[(N‐carbazole)styryl]biphenyl (BSBCz), which is used as the host with a lower‐lying triplet energy level for DCNP‐pCN. Moreover, benefitting from the mediation between the conjugated length extension and weak D/A interplay, the emission spectrum cannot be largely shifted, which can effectively suppress the overlap between the lasing emission of DCNP‐pCN and the excited‐state absorption of BSBCz, thereby avoiding detrimental singlet‐triplet annihilation. Thus, high‐quality distributed feedback lasings with ≈2.0 μJ cm−2 thresholds are achieved, and the organic light‐emitting diodes exhibit external quantum efficiency exceeding 2.0% without efficiency rolloff under high current injection, indicating the potential for electrical‐pumping organic lasings. [ABSTRACT FROM AUTHOR]

As a basis for the electrical tomography of laboratory-scale rock samples (~ 10 cm), we developed a procedure for stable, multi-point, electrical measurement on rock samples that is effective even at high contact and sample resistance. Electrodes were strongly attached to the surface of high-resistivity rock using conductive and adhesive epoxy. Sustained current injection for long periods into high-resistance rocks was fulfilled using a constant direct current source with high internal resistance. Accurate voltage measurement across the high-resistance rock was accomplished by differential measurement using two high input resistance voltmeters. Measurements of high resistance also require a stable measurement environment: the temperature and humidity in the laboratory were controlled using an air conditioner, a humidifier, a dehumidifier, and a vinyl tent. Signal noise arising from human activities was eliminated by the remote operation of the measuring equipment and switching terminal. The proposed measurement procedure was evaluated in terms of the stability and accuracy of measured values and its applicability to electrical tomography. To assess measurement stability, we performed multiple measurements of a dry granite sample at various levels of absolute humidity. Our procedure recorded highly reproducible measurements under each humidity condition. The observed changes in measured values with absolute humidity indicate the importance of stabilising the temperature and humidity conditions in the laboratory. Applying our technique to multiple plastic samples with known resistivity confirmed its accuracy. To evaluate its applicability to electrical tomography, we measured the potential distribution on a dry granite surface in response to an injected current using a simple 40-electrode array. The potential distribution measured by our procedure agreed well with that predicted by forward modelling, demonstrating the robustness of our procedure in array measurements, and thus indicating its potential applicability to tomographic measurements for a variety of targets even under severe conditions including the relative dryness of ambient humidity. [ABSTRACT FROM AUTHOR]

The article describes a method for active reduction of magnetic noise generated by a magnetic field that exists in the airgap of an induction motor. In this article a mathematical model of the process of magnetic noise excitation in a stators is presented. The model take into account that magnetic field waves, radial magnetic force waves (so-called Maxwell forces) and stator deformation waves (magnetic noise) are characterized by their own values of amplitude, mode number, frequency and phase shift. By comparing the equations for calculating the stator mechanical impedance, the amplitude of the radial magnetic force and the simplified magnetic noise equation, the relationships between these variables were established. The method of active reduction of magnetic noise proposed in the article is based on the use of these relationships. The novelty of the proposed method lies in the use of the filtered spectrum of output signal of the accelerometer installed on the stator to determine the most intense harmonics of the magnetic field in the motor airgap in order to further suppress them. The compensation signal generated by a special device adapts not only in frequency, but also in phase and amplitude of each vibration-disturbing harmonic. [ABSTRACT FROM AUTHOR]

In tackling the challenges associated with partial shading scenarios in solar photovoltaic (PV) arrays, this study introduces a groundbreaking approach to dynamic reconfiguration: the Optimal Battery-based Electrical Reconfiguration (OBER). Unlike conventional methods like the Couple Matching (CM) algorithm, OBER directly addresses the impact of shading on PV performance. By strategically connecting the strongest and weakest rows of both genders, OBER aims to overcome performance disparities induced by shading. A key innovation in OBER is the use of an external battery to augment energy in the weakest row, resulting in a substantial increase in array current and overall power output. Using MATLAB simulation, this study compares OBER with traditional methods like the New Column Index Method (NCIM), Square Dynamic Reconfiguration (SDR), and CM across ten partial shading scenarios. The proposed OBER outperforms TCT, NCIM, SDR, and CM in P max generation by 8.3% to 46.5%. OBER proves to be a transformative approach, promising efficiency enhancements and positioning itself as a key advancement in dynamically responsive solar PV systems. The experimental validation of OBER's performance reinforces its potential to significantly increase power output, providing a promising solution for optimizing solar PV arrays under challenging shading conditions. • OBER introduces a solution for PV shading challenges. • It strategically connects rows without gender alignment. • The breakthrough involves an external battery boosting the array power. • OBER outperforms traditional methods by 8.3% to 46.5% in MATLAB simulations. • Effectiveness in diverse shading patterns showcases adaptability. [ABSTRACT FROM AUTHOR]

This article presents a current injection power flow analysis and optimal generation dispatch method for bipolar DC microgrids. In bipolar DC systems, despite a certain local voltage being balanced by the converter control, voltage unbalance can occur at buses that are electrically far from the balanced voltage. In addition, from the aspect of system operation, the optimization of operation cost and voltage unbalance has not been fully investigated yet. Herein, for steady-state analysis, the current injection Newton-Raphson power flow for a bipolar DC microgrid is developed using static models of the network, voltage balancer, sources, and loads. Afterwards, the optimization problem is formulated based on voltage sensitivity, which can be obtained from the Jacobian matrix, to reduce the operation cost while resolving the voltage unbalance. The problem of quadratic programming can be solved sequentially to find the final optimal solution. The case study validates that the power flow method is sufficiently accurate compared to the simulation in PSCAD/EMTDC and that optimal generation can be achieved while reducing the operation cost and mitigating voltage unbalance. [ABSTRACT FROM AUTHOR]

When the permanent magnet synchronous machine (PMSM) based electric vehicles (EV) are in the postcrash situations, the dc-bus capacitor voltage requires to be reduced quickly for the sake of electric shock risk prevention. Currently, due to the advantages of low cost, compact structure, and high reliability, the pure-winding-based discharge strategies are attracting increasing attentions. However, there are no theoretical criteria for judging whether a pure-winding-based method is suitable for bleeding a particular PMSM-based EV drive, not to mention the rules for opting for an effective discharge strategy among the instant nonzero d-axis, zero q-axis (NDZQ), long-cycle NDZQ, and the nonzero d-axis, nonzero q-axis (NDNQ) current control techniques. This article discusses the applicable occasions of the instant NDZQ, long-cycle NDZQ, and NDNQ discharge methods based on parametric analysis. On this ground the principles for determining whether an EV drive can adopt a pure-winding-based method for discharge are given. Meanwhile, the implementation procedures of the proposed criteria are detailed clearly. Finally, the proposed selection criteria are used for evaluating five different EV drives so as to select the corresponding winding-based discharge strategy for each system, and the effectiveness is verified by simulation or experiments. [ABSTRACT FROM AUTHOR]

The aim of this study is to improve the three-phase unbalanced voltage at the secondary side of a distribution transformer. The proposed method involves compensation sources injecting three different single-phase currents into the connected point of a grid. The computations of optimal single-phase currents are performed using the circuit analysis method and particle swarm optimization algorithm. An unbalanced three-phase power distribution system model is constructed, including a transformer Δ–Δ connection, V–V connection, load balance, load unbalance combination, and three single-phase compensation current sources. The results show that the voltage unbalance rate of the electricity user side is improved to less than 1%, and the three-phase total compensation apparent power is approximately 0 VA. In the future, the application of the model as an auxiliary service could be achieved by adding an energy storage system.

A distributed feedback dual-gate graphene-channel field-effect transistor (DFB-DG-GFET) was fabricated as a current-injection terahertz (THz) light-emitting laser transistor. We observed a broadband emission in a 1–7.6-THz range with a maximum radiation power of ~10 μW as well as a single-mode emission at 5.2 THz with a radiation power of ~0.1 μW both at 100 K when the carrier injection stays between the lower cutoff and upper cutoff threshold levels. The device also exhibited peculiar nonlinear threshold-like behavior with respect to the current-injection level. The LED-like broadband emission is interpreted as an amplified spontaneous THz emission being transcended to a single-mode lasing. Design constraints on waveguide structures for better THz photon field confinement with higher gain overlapping as well as DFB cavity structures with higher Q factors are also addressed towards intense, single-mode continuous wave THz lasing at room temperature.

Saturation and cross‐coupling effects have a significant impact on the magnetic behaviour of a permanent magnet synchronous motor (PMSM), which cannot be analysed by the conventional linear model in the direct and the quadrature axis. This study introduces a precise two‐axis flux linkage model for PMSMs to offer a better depiction of the relationship between the flux linkages and corresponding currents. A parameter determination methodology is developed to identify the model parameters for a PMSM, and based on these works; the condition of a PMSM can be estimated. The process requires no geometrical parameter of the machine and little computational effort. Once the model parameters are determined, the torque estimation of a PMSM is simple enough to be made in real‐time in a motor drive controller. Finite‐element analysis and experimental results demonstrate the feasibility and accuracy of the improved model. It follows that the proposed non‐linear PMSM model based on current injection and bivariate function approximation can significantly enhance modelling precision of flux linkage and inductance over the entire range of current excitation in the application of PMSM drive. [ABSTRACT FROM AUTHOR]

An islanding detection technique, based on monitoring of impedance based parameter at the terminal of distributed generators (DG) through the low frequency current injection is proposed in this paper. To reduce the power quality issues, current injection is initiated only during the grid disturbances. The disturbances are identified by comparing the frequency data of the DG bus with respect to reference substation bus. After the disturbance identification, a low frequency current is injected through the inverter d-axis current controller. An impedance based parameter is formulated to check the status of operation of microgrid. The islanding detection parameter is a function of Thevenins impedance seen at the inverter DG terminals. The main advantage of the proposed method is that, the power quality degradation associated with current injection methods is considerably minimized. Further, the considered islanding detection parameter is independent of the operating condition of inverter based DG. Various islanding and non-islanding cases are simulated to study the selectivity of the proposed technique. The simulation and control hardware in the loop test results show the effectiveness of the proposed technique in identifying islanding in less than 170ms. [ABSTRACT FROM AUTHOR]

Due to the intermittent nature of renewable sources, the generation of power is varied which is the main problem in renewable energy system. Miss-matching between the power generation and load power causes a deviation from the desired voltage and frequency in power supply. Therefore, a new efficient smart grid system is required for an optimal power flow management. In this paper, a hybrid approach is presented for power flow management of HRES connected smart grid system. The novelty of the proposed approach is the combined execution of IHHO with SOA named as I2HOSOA technique. In the established work, the HHO is integrated by crossover and mutation function, it is known as IHHO. The main contribution of the proposed strategy is to control the power flow based on source and load side parameters variations. In the proposed approach, the control signals of the voltage source are developed by the IHHO based on the variety of power exchange between the source and load side. Similarly, the online control signals are located by the SOA procedure by utilizing the parallel execution against the active and reactive power varieties. The multi-objective function is shaped by the grid required active and reactive power varieties created based on accessible source power. Here, the control parameters of the power controller are enhanced by the proposed technique based control models in light of the power flow varieties. The comparison between established and existing methods is analyzed in terms of reactive current injection, grid code, current amplitude limitation control, active power control, zero active power oscillations, and injection of active and reactive power. Furthermore, the statistical evaluation of established, and existing methods of mean, median, and standard deviation, is evaluated. Finally, the proposed model is executed in MATLAB/Simulink working platform and the execution is compared with the existing techniques. [ABSTRACT FROM AUTHOR]

Accurate temperature information is crucial to dual three-phase permanent magnet synchronous machine (DT-PMSM) drives. Therefore, this article proposes two efficient models for permanent magnet temperature estimation of DT-PMSMs. The proposed models are derived through current injection in the reference frame that does not contribute to torque production. Through current injection, the proposed models can fully explore the two sets of machine equations to cancel winding resistance and machine inductances. To improve the estimation performance, inverter nonlinearity is compensated in the first model and cancelled in the second model. In comparison to existing methods, the proposed approach is computationally efficient and robust to parameter variation, magnetic saturation, and inverter nonlinearity. Moreover, the current injection will not affect the machine torque production and control performance. The proposed estimation approach is evaluated on a laboratory DT-PMSM under various operating conditions. [ABSTRACT FROM AUTHOR]

A turn-to-turn short-circuit fault usually causes excessive fault current because of very low impedance associated with a few fault turns. It should be dealt with promptly to avoid further damages to the machine, especially for a permanent magnet (PM) machine. In order to limit the turn fault current, a novel turn fault mitigation strategy based on current injection technique for a triple redundant 3 × 3-phase PM synchronous reluctance machine (PMA SynRM) is investigated in this paper. First, the flux linkage of the fault phase where the fault turns are located is estimated considering the influence of PM and currents in the healthy and fault three-phase sets. This flux linkage, including that of the fault turns, is subsequently reduced by injecting specific currents to the fault three-phase set, leading to much smaller fault current. The proposed current injection method does not affect the operation of the healthy three-phase sets that continue to produce torque. The effectiveness of the proposed method is validated by extensive finite-element (FE) simulation and experimental tests on a prototype 3 × 3-phase fault-tolerant PMA SynRM drive. [ABSTRACT FROM AUTHOR]

The output of a photovoltaic array is reduced considerably when PV panels are shaded even partially. The impact of shading causes an appreciable loss in power delivery, since the PV panels are connected in series and parallel to contribute to the required voltage and power for the load. The prevailing research on mitigating the shading impact is mostly based on complex reconfiguration strategies where the PV panels are subjected to complex rewiring schemes. On the other hand, to disperse the shading many studies in the literature defend the physical rearrangement of the panels. The available intensive reconfiguration schemes, such as the series parallel (SP), bridge link (BL), honeycomb (HC), and total cross tied (TCT) schemes, try only to mitigate the shading impact and there is no scope for compensation; as a result, a loss of output power is inevitable. In the proposed research work, both the mitigation of and the compensation for the losses incurred due to shading are studied. In this work, an optimal reconfiguration scheme is adopted to reduce the shading impact and a power electronic circuit with a battery source is designed to compensate for the shading losses in all aspects. In the optimal reconfiguration scheme, a bifurcation strategy is adopted in each column and the electrical connections of the PV panels are interchanged such that the shading impact is dispersed. The power electronic circuit consists of a half-bridge buck converter with a battery source that injects the current required by a shaded column. This setup compensates for the shaded PV array’s power and improves the efficiency of the total system. The proposed scheme was implemented in a 3200 W system and subjected to various shading patterns, including single panel shading, corner shading, long and wide shading, and random shading. The proposed scheme was simulated in the MATLAB Simulink environment and compared with static 4 × 4 PV array configurations, including the series parallel (SP), bridge link (BL), honeycomb (HC), and total cross tied (TCT) configurations. The comparative performance was assessed in terms of mismatch power loss, fill factor, and efficiency. The proposed system is suitable for all shading patterns and was proved to be very efficient even in the worst shading, where 1353 W was saved.

At 20 kV radial distribution systems supplied by the substation in a considerable distance from the load centre, will cause occurred its voltage drop significantly. The integration of distributed generation on the distribution networks will be one of the solutions to reduce the drop voltage. This paper proposes a way to analyze the effect of integration multiple distributed generation (DG) in radial distribution networks to the voltage drop. This analysis uses the injection current method of the load and the DG on each bus. The analysis results showed that the penetration of 5 units of DG on the distribution network will reduce its voltage drops significantly, especially on the adjacent bus with DG.