Current Change Rate Research Articles

Impact Force Analysis in Inertia-Type Piezoelectric Motors

In an inertia-type motor, a piezoelectric multilayer actuator is espoused to a transient vibration velocity as high as 1.0 m/s during slip time. This vibration velocity makes the inertia-type motors dynamic but not quasi-static. We propose a kinetic model to describe the condition under which slippage can occur between a slider and a stator. The transient current absorbed by the multilayer actuators in a stator during slip time defines the slippage behavior of the slider. A new thickness-mode force factor expression (A33), which is a relation between the transient current and the transient vibration velocity, is described in electrical domain. Impact force acting on a friction coupler produced by the actuators in the stator is proportional to the rate of change in the transient current during the sliding time. Additionally, we present the structure and characteristics of a two-phase inertia-drive-type piezoelectric motor, on which the proposed model was evaluated. Driving the multilayer actuators with truncated and mirrored sawtooth signals enhances the system dynamics. As one actuator expands and the other shrinks, their respective hysteretic nonlinearities are canceled. The motor operating frequency can be as great as 30 kHz and typically load characteristics are unloaded velocity greater than 16.0 mm/s and generated force higher than 3.0 N.

Non-equilibrium and nonlinear processes in robustness potential evaluation of reinforced concrete structural systems in ultimate states

The problems of non-equilibrium and nonlinear processes in the evaluation of reinforced concrete structural systems robustness potential in ultimate states are considered. The definition of concept of “robustness exposition” is given for a quantitative assessment of the robustness potential. A calculation model based on the generalization of the well-known classical relationship between the current relative deficit change rate of the reinforced concrete stress-strain state with respect to each fixed time value is proposed to describe in time non-equilibrium processes of structural materials force resistance depending on the mode and level of loading. On the basis of the linear creep theory, aging materials, an algorithm was developed to determine the measure of creep, corrosion-damaged concrete and reinforced concrete and to determine the parameter “robustness exposition” of a reinforced concrete statically indeterminate structural system, taking into account non-equilibrium and nonlinear processes of its deformation in time. An example of a single-span rigidly clamped reinforced concrete beam calculating the robustness potential from the position of a special limiting state criterion is considered.

Tracking snowmelt during hydrological surface processes using a distributed hydrological model in a mesoscale basin on the Tibetan Plateau

Mountain snowpack is an important water resource in high altitude and latitude regions where terrain is typically complex. However, only limited information has been published on snowmelt pathways in such regions and their de facto contributions to streamflow and soil moisture. To fill this knowledge gap, this study integrated a snowmelt pathway tracking algorithm to the high-resolution physically based Distributed Hydrology Soil Vegetation Model (DHSVM) to track snowmelt movement and to quantify snowmelt contributions during surface hydrologic processes. A simple reservoir operation scheme was also integrated into the model. The modified model was applied to a dammed mesoscale watershed in the northeastern region of the Tibetan Plateau, China, to explore relevant snow and reservoir effects. Results show that both the annual snow contribution to soil moisture (SC-SM) and the snow contribution to streamflow (SC-S) significantly decreased between 1965 and 2019. On a monthly scale, SC-SM amplitudes were highest in the upper soil layer, while peaks in deeper layers lagged behind those in upper layers. Moreover, mean monthly SC-S from all stations revealed bimodal distributions that corresponded to the snowfall season. Finally, reservoir regulation measures only exerted minimal impacts (≤2.0 %) on SC-S. If current climate change rates continue on the same trajectory, mountain snowpack reductions will be the primary cause for decreases in monthly and annual streamflow at the outlet of this basin. To mitigate climate change impacts, better water resource management is needed in this watershed.

Geospatial modeling to assess the past and future land use-land cover changes in the Brahmaputra Valley, NE India, for sustainable land resource management.

Satellite remote sensing and geographic information system (GIS) have revolutionalized the mapping, quantifying, and assessing the land surface processes, particularly analyzing the past and future land use-land cover (LULC) change patterns. Worldwide river basins have observed enormous changes in the land system dynamics as a result of anthropogenic factors such as population, urbanization, development, and agriculture. As is the scenario of various other river basins, the Brahmaputra basin, which falls in China, Bhutan, India, and Bangladesh, is also witnessing the same environmental issues. The present study has been conducted on the Brahmaputra Valley in Assam, India (a sub-basin of the larger Brahmaputra basin) and assessed its LULC changes using a maximum likelihood classification algorithm. The study also simulated the changing LULC pattern for the years 2030, 2040, and 2050 using the GIS-based cellular automata Markov model (CA-Markov) to understand the implications of the ongoing trends in the LULC change for future land system dynamics. The current rate of change of the LULC in the region was assessed using the 48years of earth observation satellite data from 1973 to 2021. It was observed that from 1973 to 2021, the area under vegetation cover and water body decreased by 19.48 and 47.13%, respectively. In contrast, cultivated land, barren land, and built-up area increased by 7.60, 20.28, and 384.99%, respectively. It was found that the area covered by vegetation and water body has largely been transitioned to cultivated land and built-up classes. The research predicted that, by the end of 2050, the area covered by vegetation, cultivated land, and water would remain at 39.75, 32.31, and 4.91%, respectively, while the area covered by built-up areas will increase by up to 18.09%. Using the kappa index (ki) as an accuracy indicator of the simulated future LULCs, the predicted LULC of 2021 was validated against the observed LULC of 2021, and the very high ki observed validated the generated simulation LULC products. The research concludes that significant LULC changes are taking place in the study area with a decrease in vegetation cover and water body and an increase of area under built-up. Such trends will continue in the future and shall have disastrous environmental consequences unless necessary land resource management strategies are not implemented. The main factors responsible for the changing dynamics of LULC in the study area are urbanization, population growth, climate change, river bank erosion and sedimentation, and intensive agriculture. This study is aimed at providing the policy and decision-makers of the region with the necessary what-if scenarios for better decision-making. It shall also be useful in other countries of the Brahmaputra basin for transboundary integrated river basin management of the whole region.

Contrasting population genetic responses to migration barriers in two native and an invasive freshwater fish.

Habitat fragmentation impacts the distribution of genetic diversity and population genetic structure. Therefore, protecting the evolutionary potential of species, especially in the context of the current rate of human-induced environmental change, is an important goal. In riverine ecosystems, migration barriers affect the genetic structure of native species, while also influencing the spread of invasive species. In this study, we compare genetic patterns of two native and one highly invasive riverine fish species in a Belgian river basin, namely the native three-spined stickleback (Gasterosteus aculeatus) and stone loach (Barbatula barbatula), and the non-native and invasive topmouth gudgeon (Pseudorasbora parva). We aimed to characterize both natural and anthropogenic determinants of genetic diversity and population genetic connectivity. Genetic diversity was highest in topmouth gudgeon, followed by stone loach and three-spined stickleback. The correlation between downstream distance and genetic diversity, a pattern often observed in riverine systems, was only marginally significant in stone loach and three-spined stickleback, while genetic diversity strongly declined with increasing number of barriers in topmouth gudgeon. An Isolation-By-Distance pattern characterizes the population genetic structure of each species. Population differentiation was only associated with migration barriers in the invasive topmouth gudgeon, while genetic composition of all species seemed at least partially determined by the presence of migration barriers. Among the six barrier types considered (watermills, sluices, tunnels, weirs, riverbed obstructions, and others), the presence of watermills was the strongest driver of genetic structure and composition. Our results indicate that conservation and restoration actions, focusing on conserving genetic patterns, cannot be generalized across species. Moreover, measures might target either on restoring connectivity, while risking a rapid spread of the invasive topmouth gudgeon, or not restoring connectivity, while risking native species extinction in upstream populations.

Control Strategy and Parameter Optimization Based on Grid Side Current Dynamic Change Rate for Doubly-Fed Wind Turbine High Voltage Ride Through

High voltage ride through (HVRT) control strategies for doubly-fed induction wind turbines (DFIG) have mostly focused on the rotor side converter, while the reactive power compensation capability of the grid side converter and the impact of grid side converter current transients have often been ignored on the DC bus voltage and reactive power. Therefore, a control strategy based on grid side current dynamic change characteristics is proposed, which resets the reference values of the grid side active and reactive currents for wind turbine HVRT to ensure partial absorption of reactive power on the grid side. Secondly, the key parameter in the proposed control strategy is optimization to get the most suitable DC bus voltage value with the grey wolf algorithm. Finally, the grid-integrated wind turbine simulation model is built on the MATLAB/SIMULINK and RT-Lab platforms. The simulation test results show that the proposed HVRT control strategy and its parameter optimization method are effective, DFIG can achieve HVRT when the wind turbine voltage rises to 1.3 pu.

Research on the Influence of Coil LC Parallel Resonance on Detection Effect of Inductive Wear Debris Sensor.

The coil structure of the inductive wear debris sensor plays a significant role in the effect of wear debris detection. According to the characteristics of LC parallel resonance, the capacitor and coil are connected in parallel to make sensor coils in the LC parallel resonance state, which is beneficial to improve the ability to detect wear particles. In this paper, the mathematical model of output-induced electromotance of the detection coil is established to analyze the influence of the structure on the detection sensitivity and enhance the sensor’s current rate of change to the disturbance magnetic field, which is essential to resist noise interference. Based on the coherent demodulation principle, the AD630 lock-in amplifier is applied to the test platform to amplify and identify weak signals. In addition, experiments are designed to test the output signals of debris under the condition of different original output voltages of the sensor with a parallel structure. Meanwhile, the near-resonance state of the detection coil with LC parallel circuit is tested by output signal information. Results show that the sensor detection sensitivity will be effectively improved with the LC parallel coil structure. For the sensor structure parameters designed in this paper, the optimal raw output amplification voltage for abrasive particle detection is 4.49 V. The detection performance of ferromagnetic particles and non-ferromagnetic particles is tested under this condition, realizing the detection ability of 103.33 μm ferromagnetic abrasive particles and 320.74 μm non-ferromagnetic abrasive particles.

Extracellular microRNA and cognitive function in a prospective cohort of older men: The Veterans Affairs Normative Aging Study.

Background: Aging-related cognitive decline is an early symptom of Alzheimer’s disease and other dementias, and on its own can have substantial consequences on an individual’s ability to perform important everyday functions. Despite increasing interest in the potential roles of extracellular microRNAs (miRNAs) in central nervous system (CNS) pathologies, there has been little research on extracellular miRNAs in early stages of cognitive decline. We leverage the longitudinal Normative Aging Study (NAS) cohort to investigate associations between plasma miRNAs and cognitive function among cognitively normal men.Methods: This study includes data from up to 530 NAS participants (median age: 71.0 years) collected from 1996 to 2013, with a total of 1,331 person-visits (equal to 2,471 years of follow up). Global cognitive function was assessed using the Mini-Mental State Examination (MMSE). Plasma miRNAs were profiled using small RNA sequencing. Associations of expression of 381 miRNAs with current cognitive function and rate of change in cognitive function were assessed using linear regression (N = 457) and linear mixed models (N = 530), respectively.Results: In adjusted models, levels of 2 plasma miRNAs were associated with higher MMSE scores (p < 0.05). Expression of 33 plasma miRNAs was associated with rate of change in MMSE scores over time (p < 0.05). Enriched KEGG pathways for miRNAs associated with concurrent MMSE and MMSE trajectory included Hippo signaling and extracellular matrix-receptor interactions. Gene targets of miRNAs associated with MMSE trajectory were additionally associated with prion diseases and fatty acid biosynthesis.Conclusions: Circulating miRNAs were associated with both cross-sectional cognitive function and rate of change in cognitive function among cognitively normal men. Further research is needed to elucidate the potential functions of these miRNAs in the CNS and investigate relationships with other neurological outcomes.

Impacts of large projects on the sediment dynamics and evolution of the Hengsha Shoal in the Yangtze Delta

Global deltas are facing severe challenges under the impacts of riverine sediment decline and large estuarine projects. Comparing with abundant research on the Yangtze subaqueous delta, the shoals in shallow waters are poorly understood. The Hengsha Shoal, Yangtze Delta, China, expands during the past ∼65 years, with only slight changes during the pre-projects period and remarkable variations in the projects period. It's now half-surrounded by the Hengsha Reclamation Project and the Deep Waterway Project, both facilitating the recent expansion. The current vertical net rate of change in the study area is −2.2 cm/yr, suggesting an overall balance between sediment deposition and erosion. Spatially, the Hengsha Shoal is currently changing from horizontal expansion to vertical accretion. Considering the spatial patterns of erosion/deposition and residual currents and sediment, modern geomorphic changes in the Hengsha Shoal appear to be dominated by internal sediment transport from deep to shallow waters. Considering further possible changing conditions, the future evolution of this shoal and the resulting potential ecological impacts should be studied further. This case study demonstrates that sediment dynamics in semi-artificial shoals can be totally different from the subaqueous delta, highlighting the importance of human engineering in governing large deltas globally.

Land Cover Change Effects on Stormflow Characteristics across Broad Hydroclimate Representative Urban Watersheds in the United States

Urban development alters stormflow characteristics and is associated with increasing flood risks. The long-term evaluation of stormflow characteristics that exacerbate floods, such as peak stormflow and time-to-peak stormflow at varying levels of urbanization across different hydroclimates, is limited. This study investigated the long-term (1980s to 2010s) effects of increasing urbanization on key stormflow characteristics using observed 15 min streamflow data across six broad hydroclimate representative urban watersheds in the conterminous United States. The results indicate upward trends in peak stormflow and downward trends in time-to-peak stormflow at four out of six watersheds. The watershed in the Great Plains region had the largest annual increasing (decreasing) percent change in peak stormflow (time-to-peak stormflow). With the current change rates, peak stormflow in the Great Plains region watershed is expected to increase by 55.4% and have a 2.71 h faster time-to-peak stormflow in the next decade.

Microbiota mediated plasticity promotes thermal adaptation in the sea anemone Nematostella vectensis

At the current rate of climate change, it is unlikely that multicellular organisms will be able to adapt to changing environmental conditions through genetic recombination and natural selection alone. Thus, it is critical to understand alternative mechanisms that allow organisms to cope with rapid environmental changes. Here, we use the sea anemone Nematostella vectensis, which has evolved the capability of surviving in a wide range of temperatures and salinities, as a model to investigate the microbiota as a source of rapid adaptation. We long-term acclimate polyps of Nematostella to low, medium, and high temperatures, to test the impact of microbiota-mediated plasticity on animal acclimation. Using the same animal clonal line, propagated from a single polyp, allows us to eliminate the effects of the host genotype. The higher thermal tolerance of animals acclimated to high temperature can be transferred to non-acclimated animals through microbiota transplantation. The offspring fitness is highest from F0 females acclimated to high temperature and specific members of the acclimated microbiota are transmitted to the next generation. These results indicate that microbiota plasticity can contribute to animal thermal acclimation and its transmission to the next generation may represent a rapid mechanism for thermal adaptation.

An RLL Current Sharing Snubber for Multiple Parallel IGBTs in High Power Applications

A resistor–inductor–inductor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(RLL)</i> snubber is proposed for high-power power electronic devices that use insulated gate bipolar transistors (IGBTs) in parallel. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLL</i> snubber provides current sharing for parallel IGBTs by utilizing series inductors to decrease the rate of current change in turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> transients. Compared with other methods, the proposed snubber incorporates only passive components without additional sensors or control circuits, which shows its advantages of simple structure, strong applicability, and easy implementation. In order to further expand its application scope, the topologies of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLL</i> snubber for multiple IGBTs in parallel are designed and improved. Experimental results of 5 and 6 parallel IGBTs validate the feasibility and effectiveness of the proposed snubber.

Phase Current Reconstruction Error Suppression Method for Single DC-Link Shunt PMSM Drives at Low-Speed Region

The extensive application of vector phase shift modulation method in permanent magnet synchronous motor drive systems with single dc-link current sensor results in obvious current ripple in the low-speed region. The patterns of these ripples vary greatly in different sectors, leading to nonnegligible phase current reconstruction errors. In this article, an estimation of the local average current change rate (ELAC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> R) based reconstruction error suppression method within the switching cycle is proposed to resolve this problem. By comparing the actual and the ideal sampling points, the increase of current ripple and the reconstruction error caused by the combination of the vector phase shift and the single current sensor sampling in the low-speed region are modelled and analyzed. Then according to equivalent modelling of the current ripple between the ideal and the actual sampling points, the more accurate phase current information can be quickly obtained based on the sampling value. The compensation process is significantly simplified and the computation burden of the processor is reduced. Experimental results show that the performance of current reconstruction can be improved effectively with less harmonic content with the proposed method.

A modeling framework for predicting the effect of the operating conditions and component sizing on fuel cell degradation and performance for automotive applications

In this study, durability and performance prediction were integrated in the sizing process of the FC stack of a fuel cell range-extender (FCREx) vehicle together with the design of a dynamics-limited control strategy. For that purpose, a FCREx vehicle model integrating a FC stack, balance of plant, battery, H2 tank and vehicle body (C-class SUV) validated in previous studies was used. To predict FC stack degradation rate, a novel semi-empirical multi-layered degradation modeling framework for automotive application is proposed and developed. Degradation rates are calculated based on reference degradation rates measured at reference and known conditions (1st layer) and scaled with the electrochemical phenomena (2nd layer) and the operating conditions (3rd layer) through scaling functions based on physical tendencies. Results show how increasing the FC stack power decreases H2 consumption but increases durability, while increasing the dynamic limitations on the control strategy increases both H2 consumption and durability. The isolated effect of sizing implied a decrease in H2 consumption of ∼3% and an increase in FC stack durability of ∼53% when comparing the 40 kW and 100 kW designs. In contrast, the effect of dynamic limitations was significantly perceived in the 40 kW design which implied an increase in H2 consumption close to 8% and an increase in durability of 294% when comparing the infinite dynamics and the highest dynamically restricted cases. Nevertheless, the effect of sizing is neglected under high dynamic limitation and limiting the current density change rate to 0.001 A/cm2s may prevent the control strategy from fulfilling the charge sustaining mode in aggressive driving. Based on these results, a set of recommendations were elaborated for FC stack and FCV manufacturers aiming to apply FCREx architecture to passenger car vehicles.

Self-Stretchable Fiber Liquid Sensors Made with Bacterial Cellulose/Carbon Nanotubes for Smart Diapers.

Liquid sensors for detecting water and body fluids are crucial in daily water usage and health monitoring, but it is challenging to combine sensing performance with high tensile deformation and multifunctional applications. Here, a substrate-free, self-stretchable bacterial cellulose (BC)/carbon nanotube (CNT) helical fiber liquid sensor was prepared by the solution spinning and coiling process using BC as the water-sensitive matrix and CNTs as the active sensing materials. The BC/CNT (BCT) fiber sensor has a high stretch ratio of more than 1000% and a rapid response for a current change rate of 104% within 1 s, which is almost unaffected under washing and various stretching or knotting deformations. By combination of the BCT fiber, we can design smart diapers or water level detectors, which rapidly monitor the status of smart diapers or water level, and the monitoring result can be transferred on time through an alarm device or smartphone. In short, the scalable and continuous preparation of the self-stretchable BCT helical fiber will provide a capacious platform for the development of a wearable sensor applied in daily life (such as smart diapers, water level detection, etc.).

A self-powered triboelectric multi-information motion monitoring sensor and its application in wireless real-time control

With the advantages of low power consumption, low cost and miniaturization, self-powered sensors have a wide range of applications in the human-machine interface, Internet of Things (IoTs), sports monitoring and versatile fields. Here, a novel and easy-processing self-powered triboelectric multi-information motion monitoring sensor (TM3S) is proposed and systemically investigated under the conditions of rolling and sliding motion. The relationships between electrical signals (charge, rate of charge change, current, rate of current change, voltage, etc.) and kinetic parameters (displacement, direction, velocity, acceleration, etc.) are established and verified with various motion states. The results show that TM3S can precisely detect the displacement, direction, velocity, and acceleration of the moving object, demonstrating excellent performance in motion monitoring. Furthermore, a wireless self-powered motion monitoring system based on TM3S is developed, which can detect the movement of a sliding mouse in real time, wirelessly transmit sensing data instantaneously, and achieve real-time control in human-machine interface. The real-time motion monitoring system exhibits two significant advantages of high sensitivity and self-powered nature, showing huge potential in low power consumption IoTs and intelligent human-machine interaction.

On the accuracy of short-term COVID-19 fatality forecasts

BackgroundForecasting new cases, hospitalizations, and disease-induced deaths is an important part of infectious disease surveillance and helps guide health officials in implementing effective countermeasures. For disease surveillance in the US, the Centers for Disease Control and Prevention (CDC) combine more than 65 individual forecasts of these numbers in an ensemble forecast at national and state levels. A similar initiative has been launched by the European CDC (ECDC) in the second half of 2021.MethodsWe collected data on CDC and ECDC ensemble forecasts of COVID-19 fatalities, and we compare them with easily interpretable “Euler” forecasts serving as a model-free benchmark that is only based on the local rate of change of the incidence curve. The term “Euler method” is motivated by the eponymous numerical integration scheme that calculates the value of a function at a future time step based on the current rate of change.ResultsOur results show that simple and easily interpretable “Euler” forecasts can compete favorably with both CDC and ECDC ensemble forecasts on short-term forecasting horizons of 1 week. However, ensemble forecasts better perform on longer forecasting horizons.ConclusionsUsing the current rate of change in incidences as estimates of future incidence changes is useful for epidemic forecasting on short time horizons. An advantage of the proposed method over other forecasting approaches is that it can be implemented with a very limited amount of work and without relying on additional data (e.g., data on human mobility and contact patterns) and high-performance computing systems.

Independent closed loop control of di/dt and dv/dt for high power IGBTs

As the insulated gate bipolar transistor (IGBT) modules have their own specific characteristic switching forms, their turn-on and turn-off times are changed according to practical applications. For the conventional gate drives, gate resistors are used to adjust the turn-on and turn-off times which change switching losses that have a significant amount in total losses. Collector current rate of change, $di_{C}/ dt$ and collector-emitter rate of change, $dv_{CE}/ dt$ are dependent on each other and they affect operating parameters in high power converters. Relations between current and voltages during the switching transitions are given and effects of the changes in electrical parameters for the operation of IGBT are described. Thereafter, closed-loop gate drive with analog control that performs independent control of $di_{C}/ dt$ and $dv_{CE}/ dt$ of a new generation IGBT module platform for high power applications is proposed. Unlike conventional gate drives, proposed closed-loop drive makes constant $di_{C}/ dt$ possible while $dv_{CE}/ dt$ is decreased to increase the efficiency of the power conversion system. This leads to decrease of the switching losses without changing the electromagnetic interference (EMI), IGBT voltage, and current stresses which are related with the rate of change of collector current. Simulations are performed in a double pulse test circuit in which new package next high power density dual (nHPD$^{2}$) family MBM450FS33F Hitachi dual IGBT with 3300V 450A ratings is modelled.

Joint modeling of time to diabetic retinopathy and change in fasting blood sugar among type 2 diabetic patients, Northwest Ethiopia

This study aimed to assess changes in fasting blood sugar (FBS) levels, time to diabetic retinopathy (DR) and its predictors among type 2 diabetes patients in Ethiopia. An institution-based retrospective follow-up study was conducted at the University of Gondar Comprehensive Specialized Hospital. The linear mixed effect model and Cox proportional hazard models were fitted separately, and later, the two models were fitted jointly using R software. Variables with a p value < 0.05 were considered significant predictors in the adjusted analysis. The incidence rate of DR was 2 per 100-person year of observation with a median follow-up time of 90.8 months (IQR 63.4). The current value and rate of change in FBS level were significant predictors of time to DR (AHR = 1.35; 95% CI 1.12–1.63) and (AHR = 1.70; 95% CI 1.21–2.39), respectively. Hypertension (AHR = 2.49; 95% CI 1.32–4.66), taking > 1 antidiabetic oral agent (AHR = 4.90; 95% CI 1.07–20.0) and more than 10 years duration (AHR = 0.17, 95% CI 0.06–0.46) were predictors of time to DR. This study revealed that the current value of FBS and the rate of FBS change were significantly associated with the time to DR.

A New Approach for Solving the False Balance of a Closed-Loop Fluxgate Current Transducer

The closed-loop fluxgate current transducer (CFCT) is the only current sensor whose measurement accuracy can reach a level of the parts per million (ppm) at present. However, the false balance, which makes the CFCT unable to work, caused by an excessive offset current is the inherent flaw of the CFCT. The high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> (rate of current change) of the primary current is the main factor resulting in the offset current overload. Therefore, the CFCT is currently only applied for steady-state direct-current measurements. In this article, an approach is proposed to eliminate the false balance of the CFCT in the dynamic process by adding a feedforward branch, which provides a follow-up bias point for the CFCT to make the CFCT always work in a small-signal range, where a risk of magnetic saturation does not arise. The zero-flux state of the CFCT still only depends on the feedback branch, so its high measurement accuracy is maintained. The experiments prove that the CFCT can measure a flat-top pulsed current with an accuracy of the ppm level by this method.