Instantaneous Current Research Articles

Expansion of the Ohm's Law in Nonsinusoidal AC Circuit

In a nonsinusoidal alternating current (ac) circuit, the instantaneous impedances of the linear inductance and the linear capacitance have not been defined because no applicable law as the Ohm's law exists; hence, the analysis of the nonsinusoidal ac circuit is incomplete, and the design of the nonsinusoidal ac circuit lacks systematic consideration. This paper presents an expansion of the Ohm's law in the nonsinusoidal ac circuit by defining instantaneous impedance, instantaneous admittance, and analytic signals of the instantaneous voltage and current. It has been demonstrated that the presented definitions are reasonable generalizations of the Ohm's law in the nonsinusoidal ac circuit including ac/dc link circuit in theory analyses and experimental results in this paper. The presented expansion of the Ohm's law provides a distinct instruction for analyzing and designing nonsinusoidal circuit including ac/dc link circuit particularly for the power electronic circuit.

Instantaneous positive‐sequence current applied for detecting voltage sag sources

This study proposes a method for detecting voltage-sag sources, using only the measurements of line currents. Instantaneous symmetrical components are introduced for accommodating the transient nature of voltage sag events, where a magnitude and phase change in the instantaneous positive-sequence current is used as a criterion. The proposed method is compared with conventional phasor-based methods known from the literature. All the discussed methods for voltage sag source detection, both the already known and the proposed ones, were evaluated by applying extensive simulations, laboratory tests and field testing. When compared with the phasor-based methods, the proposed method showed faster response, a higher degree of confidence and superior effectiveness, especially for transient voltage sag events in networks with distributed generation and active loads.

Effect of pulsed electric field on electrodialysis of a NaCl solution in sub-limiting current regime

In spite of growing applications of pulsed electric fields (PEF) in membrane separation processes, there are only few theoretical studies treating mass transfer. In this paper, we propose a 1D mathematical model, which adequately describes PEF mode electrodialysis (ED) with ion-exchange membranes at sub-limiting currents. The results of simulation are compared with experimental data obtained for a laboratory-scale electrodialysis stack. We show experimentally and theoretically that the average current density and mass transfer under PEF of a sufficiently high frequency (>1Hz in the used conditions) are higher than those in conventional steady state DС mode, if a same average voltage is applied. The advantage increases with frequency and reaches a maximum at about 100Hz. When applying a pulse after a pause, we benefit by low ohmic resistance and low diffusion potential drop caused by partial concentration restoration in close vicinity of the membrane. This allows passage of an instantaneous current of a high density, which can essentially exceed the limiting current density (jlim) in steady state DC conditions. However, at low frequencies this gain rapidly vanishes by increasing concentration polarization during the pulse, thereby the mass transfer in PEF mode is lower than that in DС mode. The gain is close to zero at low currents due to linearity of I–V curve and increases with increasing current. However, within the model, the average current density cannot be higher than ilim. The gain in mass transfer rate at high frequencies increases with decreasing duty cycle, but with this the energy consumption for electrodialysis desalination in PEF mode increases, it is always higher than the energy consumption in continuous DС mode.

슈퍼캐패시터를 이용한 자동차 전압 안정화 모듈

The performance of a passenger vehicle has been greatly improved recently owing to the intensive use of electronic controllers. Many components of a vehicle, including the engine, are controlled by electronic systems installed in the vehicle. Therefore, the electrical power required for such electronics has increased significantly. However, the electrical power generated by the vehicle`s alternator, operated by the engine, is limited, and when the vehicle is started, a large instantaneous current is required. The voltage of the vehicle electrical system fluctuates to a very low level, then, it is gradually recovered. This case is very severe and can even cause damage to electronic systems. In this study, a voltage-stabilizing module comprising electric double layer supercapacitors, which could alleviate the voltage variation, was developed and tested.

High-performance nanopattern triboelectric generator by block copolymer lithography

Large-area nanopatterning is introduced on a flexible gold substrate by block copolymer (BCP) lithography. We fabricate ultrahigh power energy harvesting nanogenerators based on contact-electrification principle exploiting the effective contact area enhancement by block copolymer lithography. Owing to the facile and effective surface area enhancement by BCP nanopatterning, significant enhancement of triboelectric charge induction is attained. Output currents from TENG increased at least 16 times after BCP nanopatterning. This nanogenerator can generate remarkably high output voltage and current, which can directly light up 504 serially connected LEDs. The resultant nanogenerator attains the maximum instantaneous current of 1.6mA and output power of 93.2W/m2. Electrical energy generated by single cycle of impact force is 0.54mJ, and the average electrical energy is 114.89mW. Those values indicate one of the highest device performance ever reported for the TENGs based on contact-separation mode thus far.

防食基準電位におけるアノード電流の埋設鋼管の防食への影響

Cathodic protection is being applied to buried steel pipelines and polarized potential of pipelines is kept less noble than the protection potential criterion, -0.85 V vs. Cu/CuSO4. However, instantaneous anodic current has been infrequently observed in some fields even though polarized potential of pipelines is kept less noble than the protection potential criterion. In this study, the influence of instantaneous anodic current on corrosion protection of buried steel pipelines under cathodic protection was evaluated and the oxidation reaction causing anodic current was investigated to some extent. As a result, it was found that most of the anodic current was not attributed to corrosion reaction and the maximum value of corrosion rate of steel was as little as 1.8 μm/year. Therefore, it was considered that there was no matter on buried steel pipelines even though the instantaneous anodic current occurred under the protection potential criterion. It was estimated that some part of the anodic current was attributed to the oxidation reactions of components in soil and of rust on the steel surface.

The Contribution of Conductor Temperature and Sag Monitoring to Increased Ampacities of Overhead Lines (OHLs)

The electric utility industry is restructuring itself to operate in a competitive wholesale market. However, the transmission system remains a regulated entity that connects deregulated generation with the end consumer. In many countries, the pace of investment in OHLs has lagged behind the rate of load growth and generated additional capacities, due to public, regulatory, environmental and financial obstacles to the construction of new transmission facilities. Consequently, many OHLs reached critical values of ampacity and sag. Many renewable energy sources, especially hydro plants, solar or wind farms also require dynamic operation of the power grid. OTLM – Overhead Transmission Line Monitoring system is adding new dimensions to the operation of OHLs enables more efficient performance while at the same time enhances the safety of system operation. A maximum utilization of the OHL ampacity is only possible, if the operators have accurate data about the actual ground clearance, crossed lines, vegetation, instantaneous conductor temperature and current. With the measurements captured and processed by OTLM, the operator of the transmission network can optimize and determine the operation mode of OHLs. Software solutions also provide the means for a short-term prediction of conductor temperature. Temperature data along with data gained by laser scanning or similar measurements and diagnostics of the OHLs is necessary to up-rate OHL projects. This paper is supported with case studies, which prove that temperature and sag monitoring is an essential part of the transmission smart-grid.

Smart Inverter with Active Power Control and Reactive Power Compensation

Conventional grid-tied single phase inverters of renewable power generators (solar PV systems typical) have limited reactive power compensation capability and do not have active power control. This paper presents a novel control strategy which provides active power control with reactive power compensation for a DC/AC inverter connected to a single-phase AC grid, which supplies electricity to local loads. By sampling the instantaneous current on the grid at the local load side, which represents the domestic load current, an orthogonal signal is constructed using second order generalised integrator. The active and reactive current of the local loads are then rapidly detached from the orthogonal signal through specific trigonometric calculation. The reference current for the inverter output are produced by combining the active current and the reactive current which is detached from the domestic load current. Comparing the reference current with the inverter output current generates the PWM signals which are used to control the IGBT devices of the inverter bridge with capacitive impedance output to achieve domestic reactive compensation for inductive loads. The output current remarkably improves the load capacity of the grid and reduces the demand of reactive power from the gerid.

Benthic-pelagic uncoupling between the Northern Patagonian Frontal System and Patagonian scallop beds

Availability of planktonic food in the bottom is the most important factor to explain the persistence and recurrent localization of Patagonian scallop (Zygochlamys patagonica) populations. The establishment of the scallop Sea Bay bed (SBB) has been related with food supply from the Northern Patagonian Frontal System (NPFS). In this article outputs from high resolution numerical models combined with particle tracking methods were used to identify for the first time potential physical mechanisms of food transfer. The model results showed no evidence of benthic-pelagic coupling between the NPFS and the SBB. They also revealed that the dominant instantaneous semidiurnal tidal currents and the mean N–NE flow on the inner-middle Patagonian shelf are the main dynamical mechanisms preventing particles released at the surface of the NPFS to reach the SBB area. Sensitivity studies changing the stochastic numerical method for solving the particle trajectories, the release month and location of the particles, the magnitude of the horizontal turbulent diffusion coefficient and the frequency of the wind forcing did not alter this conclusion significantly.

Optimization Research on the Circuit Breaker Instantaneous Characteristic Experiment Based on Neural Network

The circuit breaker’s instantaneous characteristic test equipment controlled by computer is introduced in this paper. There are still some problems in the design. To address those issues, compensation coefficient is presented in order to improve the accuracy of instantaneous current. Based on analyzing the influencing factors of instantaneous current and establishing equivalent model, neural network control method is adopted. Under LabVIEW software environment, neural network which has been trained by MATLAB script node is called to compute the compensation coefficient. In order to enhance system adaptability, the neural network online adjustment is achieved by changing training samples. The accuracy of instantaneous current is further improved.

Two‐loop power‐flow control of grid‐connected microgrid based on equivalent‐input‐disturbance approach

This study employed the equivalent‐input‐disturbance (EID) approach to devise a two‐loop power‐flow control system that controls the output current of an inverter so as to regulate the flow of active and reactive power between a distributed generation unit and a utility grid. It actively eliminates disturbances that degrade the power quality of a microgrid. The pq theory and an all‐pass filter are employed to generate an instantaneous reference current for the control system based on the prescribed active and reactive power of a utility grid terminal. The inner loop consists of a disturbance compensator and a state observer. The disturbance compensator uses information acquired from the state observer to estimate disturbances, such as drops and harmonics in the grid voltage, and compensates for them by incorporating the equivalent input disturbance into the control law. The outer loop consists of a resonance‐based internal model and a state‐feedback controller, which enables the output current of inverter to track the instantaneous reference current. The small‐gain theorem ensures the stability of the system. The system improves the power quality and guarantees that the flow of active and reactive power from the grid and inverter has low harmonic distortion. Simulations demonstrated the effectiveness of the system. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Series arcing detection by algebraic derivative of the current

We present in this paper an algebraic derivative method of the line current in order to detect the presence of series arcs in an AC or DC electrical installation. The first derivative is computed from a limited Taylor-McLaurin series transposed in Laplace space. The temporal estimation is achieved by integration over a sliding window of the product of a particular polynomial with the instantaneous current. The discrete version can be synthesized by a simple FIR filter.The tests, with and without series arc, are conducted on experimental currents (3–12A) measured on domestic loads (resistors, vacuum drill, dimmer). The sampling frequency is set to 1MHz.Short integration times (50μs in AC and 200μs in DC) are sufficient to observe, with high contrast, the derivative peaks due to the arc ignition. The detection is then performed by comparing the derivation filter output to its instantaneous noise level. The response time is equal to the integration duration.This method, simple to set up and easy to implement, is ideally suited for installations that do not use load switching current.

Reflections on the Future Electric Power Grid Monitoring System

A shortcoming of the contemporary power grid monitoring is that the system does not know its own state. Instead of taking automatic note of energy-flow disruptions, one deals with haphazard telephone reports of “no light in our house”. We propose a novel monitoring system that requires no restructuring of the power distribution network and can be applied both to the existing grids and the future “smart grids”. The proposed system is based on a network of inexpensive sensors, installed on every connecting line and communicating measured data to a central processing unit. Our approach is topological in nature, based on the connectivity aspects of the power grid embodied in Kirchhoff's current law that must be valid at every node of the network. We argue that the state of the network can be adequately characterized by specifying the RMS currents and the direction of energy flow in all connecting lines. It is essential that in this description one does not have to know the magnitude of the energy flow, only its direction. This eliminates the need to measure voltage, which would be prohibitively costly on the massive scale. In contrast, the relative phase between the current and voltage can be measured easily. Another essential point is that the instantaneous RMS currents are impractical to record and communicate, hence local averaging is required. Since Kirchhoff's law should remain valid upon averaging, the latter must be carried out at each sensor synchronously over the entire network with global synchronization provided by the GPS.

A novel control method for series hybrid active power filter working under unbalanced supply conditions

In this paper a new control algorithm for a Series Hybrid Active Power Filter (SHAPF) is proposed. With the proposed control algorithm, the series active power filter simultaneously compensates for source voltage unbalance and source current harmonics generated by non-linear loads. The proposed control algorithm is based on the generalised instantaneous power theory where the instantaneous inactive power is represented as a second order tensor. The reference voltage is directly associated with three-phase instantaneous voltages and currents and are separated in three-phase co-ordinate systems. Therefore, the calculation of the compensation reference voltage is much simpler than the other available control algorithms. It can be applied for both voltage and current harmonic generating loads connected across balanced and unbalanced source voltages. The mathematical formulation of the proposed control algorithm with its applications to SHAPF is presented. The validity of the proposed control algorithm is verified with extensive experimental study and results are reported.

Switches Faults Analysis of Voltage Source Inverter (VSI) using Short Time Fourier Transform (STFT)

Three-phase voltage source inverter (VSI) play a very important role in the present industrial life. The knowledge and information about faults characteristic of the VSI is important to prevent failure of equipment, data losses, high maintenance and economic losses. Therefore, to insure a continuous and safety operation of the VSI, switches faults analysis implemented to prevent further damages and the commonly open and short circuit faults are happened within the VSI. This paper present the analysis of switches faults VSI by using linear time-frequency distribution (TFD) which is short time Fourier transform (STFT) by simulation using MATLAB. STFT are appropriate technique to analyze non-stationary that consist of multi-frequency component and magnitude that represent signal in time-frequency representation (TFR). From the TFR obtained, parameters of the signals are estimated such as instantaneous average current, instantaneous of root means square (RMS) current, fundamental RMS current, total harmonics distortion (THD), total nonHarmonics distortion (TnHD) and total waveform distortion (TWD). According the analysis of switches faults parameters VSI is presented. Based on the signal parameters, characteristic of signal are calculated. The end of research, various characteristics of parameter VSI faults are clearly differentiate between open and short switches faults. The information of analysis switches faults is usefull to industrial application in the process for identifying fault detection and can fault can be identify early.

Open and Short Circuit Switches Fault Detection of Voltage Source Inverter Using Spectrogram

In the last years, fault problem in power electronics has been more and more investigated both from theoretical and practical point of view. The fault problem can cause equipment failure, data and economical losses. And the analyze system require to ensure fault problem and also rectify failures. The current errors on these faults are applied for identified type of faults. This paper presents technique to detection and identification faults in three-phase voltage source inverter (VSI) by using time-frequency distribution (TFD). TFD capable represent time frequency representation (TFR) in temporal and spectral information. Based on TFR, signal parameters are calculated such as instantaneous average current, instantaneous root mean square current, instantaneous fundamental root mean square current and, instantaneous total current waveform distortion. From on results, the detection of VSI faults could be determined based on characteristic of parameter estimation. And also concluded that the fault detection is capable of identifying the type of inverter fault and can reduce cost maintenance.

Сontrol strategy of shunt active filter for three-phase four-wire power system with multivariate proportional-vector formation of instantaneous source currents

It is shown that most of the existing control strategies оf shunt active power filters (APF) for three–phase four-wire power system are equivalent to formation of instantaneous source current vector proportional to the referent voltages vector which coincides with the instantaneous vector of the phase voltages or is its part with improved spectral composition. Control system of APF was proposed that realize the multivariate proportional-vector formation of instantaneous source currents. Depending on the application conditions one of the twenty control methods optimal for certain quality characteristics can be selected.Reference 9, figures 1, tables 2.

In‐Situ Investigation of Quantitative Contributions of the Anode, Cathode, and Electrolyte to the Cell Performance in Anode‐Supported Planar SOFCs

A novel method that embeds Pt voltage probes into the triple‐phase boundary (TPB) is developed. Moreover, the quantitative contributions of the anode, the cathode, and the electrolyte to cell performance are investigated in situ for anode‐supported planar solid oxide fuel cells (SOFCs). The voltage and maximum output power density (MOPD) measured by the probes, which are placed on both sides of the electrolyte, account for 97.3% and 94.4%, respectively, of those of the cell during the instantaneous current–voltage testing. When the stack is discharged at 0.32 A cm−2 for 200 h, the voltage drops of the anode, the cathode, and the electrolyte account for 76.9%, 15.4%, and 7.7%, respectively, of the total voltage drop of the unit cell. The ohmic resistance of the unit cell primarily depends on the resistance that results from the TPB. The variation in cell resistance is mainly attributed to the increase in anode polarization resistance caused by Ni particle agglomeration. However, cell voltage is more sensitive to the TPB ohmic resistance, which may be the primary factor for SOFC degradation.

Dimerization, trimerization and quantum pumping

We study one-dimensional topological models with dimerization and trimerization and show that these models can be generated using interaction or optical superlattice. The topological properties of these models are demonstrated by the appearance of edge states and the mechanism of dimerization and trimerization is analyzed. Then we show that a quantum pumping process can be constructed based on each one-dimensional topological model. The quantum pumping process is explicitly demonstrated by the instantaneous energy spectrum and local current. The result shows that the pumping is assisted by the gapless states connecting the bands and one charge is pumped during a cycle, which also defines a nonzero Chern number. Our study systematically shows the connection of one-dimensional topological models and quantum pumping, and is useful for the experimental studies on topological phases in optical lattices and photonic quasicrystals.

Digital multimeter-based immunosensing strategy for sensitive monitoring of biomarker by coupling an external capacitor with an enzymatic catalysis

A new digital multimeter (DMM)-based immunosensing system was designed for quantitative monitoring of biomarker (prostate-specific antigen, PSA used in this case) by coupling with an external capacitor and an enzymatic catalytic reaction. The system consisted of a salt bridge-linked reaction cell and a capacitor/DMM-joined electronic circuit. A sandwich-type immunoreaction with target PSA between the immobilized primary antibody and glucose oxidase (GOx)-labeled detection antibody was initially carried out in one of the two half-cells. Accompanying the sandwiched immunocomplex, the conjugated GOx could catalyze the oxidation of glucose, simultaneously resulting in the conversion of [Fe(CN)6]3− to [Fe(CN)6]4−. The difference in the concentrations of [Fe(CN)6]3−/[Fe(CN)6]4− in two half-cells automatically produced a voltage that was utilized to charge an external capacitor. With the closing circuit switch, the capacitor discharged through the DMM, which could provide a high instantaneous current. Under the optimal conditions, the resulting currents was indirectly proportional to the concentration of target PSA in the dynamic range of 0.05–7ngmL−1 with a detection limit (LOD) of 6pgmL−1. The reproducibility, precision, and selectivity were acceptable. In addition, the methodology was validated by analyzing 12 clinical serum specimens, receiving a good accordance with the referenced values for the detection of PSA.