Square Of Voltage Research Articles

A Novel ANFIS-Based Islanding Detection for Inverter-Interfaced Microgrids

This paper presents a new islanding detection strategy for low-voltage inverter-interfaced microgrids based on adaptive neuro-fuzzy inference system (ANFIS). The proposed islanding detection method exploits the pattern recognition capability of ANFIS and its nonlinear mapping of relation between inputs. The ANFIS monitors seven inputs measured at point of common coupling (PCC), namely root-mean square (RMS) of voltage and current (RMS U and RMS I ), total harmonic distortion (THD) of voltage and current (THD U and THD I ), frequency ( ${f}$ ), and active and reactive powers ( ${P}$ , ${Q}$ ) that are experimentally obtained based on practical measurement in a real-life microgrid. The proposed method is composed of passive monitoring of the mentioned inputs. It does not influence power quality (PQ) and considerably decreases non detection zones (NDZs). In order to cover as many situations as possible, minimize false tripping and still remain selective; type and number of samples are introduced. Here, one of the primary goals is reducing NDZ while keeping PQ in order. Based on the sampled frequency and number of samples, we find that the proposed method has less detection time and better accuracy when compared to the reported methods. Simulations performed in MATLAB/Simulink software environment and several tests performed based on different active load conditions and multiple distributed generation, prove the effectiveness, authenticity, selectivity, accuracy and precision of the proposed method with allowable impact on PQ according to UL1741 standard.

Impact of grounding fault in PV modules on AC side and the suppression strategy based on 0‐axis control

The widely distributed large-scale photovoltaic (PV) modules suffer from a large probability of grounding fault due to their own characteristics and natural weather. This problem has been well explored in this study. Firstly, it is analysed that the grounding fault in PV modules will cause the third-harmonic voltage, DC bias voltage and common ground circulating current in the PV inverter system. Secondly, a 0-axis based control strategy is proposed to solve the above problems, which means that the zero-sequence voltage is controlled through a proportional-resonant controller in the outer loop, and the zero-sequence current is controlled in the inner loop through a proportional controller. Thirdly, the square of DC side voltage is controlled to address the non-linear relationship between capacitor energy and its voltage. Finally, the experimental results based on RTLAB platform are presented to verify the effectiveness of the proposed control strategy. In summary, this study proposes a control thought to suppress the undesirable phenomenon caused by the grounding fault in PV modules, and the method needs no status switching and hardware cost.

Calculating the mechanical characteristics of the asynchronous motor having a minimal moment in it

Problem Asynchronous electric motors (AEs) are the most common among all electric motors. This is due to the simplicity of design, high reliability, relatively low cost, better weight and overall performance, etc. The asynchronous electric drive, which has a vector control based on modern static converters with microprocessor controllers, is especially widespread now. One of the most important characteristics of the engine is its mechanical characteristics. Based on the knowledge of the dependence of the moment on the electric motor shaft on its speed of rotation in various modes of operation, it is possible to implement high-quality and efficient control. Goal. The goal is conducting the analysis of operating modes of the asynchronous motor with the calculation of its mechanical characteristics in the presence of a minimal moment in it. Methodology. Analytical methods of research, methods of the theory of electric machines and electric drives are used, as well as methods of calculating electric circuits. The method of calculating the mechanical characteristics of AE in the presence of a site with a clearly expressed minimum torque is considered. Results. The analysis of the AE is based on its G-shaped replacement scheme. The mechanical characteristics of AE in different modes of operation were considered and analyzed in details. The mechanical characteristics of the AE were calculated in the presence of a minimal moment in it. It is determined that the value of the critical slip depends on the value of the active resistance of the rotor circle. Since the current of the motor is proportional to the voltage in the first stage, and the moment is the supply voltage squared, therefore, the characteristics of the voltage drop change both qualitatively and quantitatively. Originality. The current value of the moment of the AE depends on the square of the supply voltage, the active and inductive resistance of the windings of the rotor and the stator with the given values of slip and synchronous angular velocity. For all values of the voltage, the critical velocity (critical slip) does not change, that is, it does not depend on the voltage value. The magnitude of the moment varies significantly with the change in voltage. Practical value. In real conditions, all industrial networks may be subject to voltage, therefore, it is necessary to continuously monitor how significant it is to reduce the maximum and starting moments of the drives when reducing the voltage and how much they meet the demands of the technological process. If the control of a traction electric drive based on an electric motor is considered, the fact that the voltage from the energy storage will vary with the discharge should also be taken into account. Consequently, there will be a change in both the starting and the maximum moment that this drive can develop.Keywords: asynchronous motor; mechanical characteristic; minimum torque; Clause formula; traction electric drive; electric car; electric drive system.

Low Frequency Noise and Resistivity Characteristics of Hybrid Composites with Onion-Like Carbon and Multi-Walled Carbon Nanotubes

The comprehensive study of resistivity and low frequency (10[Formula: see text]Hz–20[Formula: see text]kHz) noise characteristics of hybrid polymer composites with multi-walled carbon nanotubes (MWCNTs) and onion-like carbon (OLC) particles in one material have been carried out in the wide temperature range ((75–380) K). The characteristic dependences on the fillers density and the dominant conduction mechanisms were investigated. At low temperature ((75–170) K), the resistivity dependences on temperature are well-fitted by the Mott’s formula for the quasi-one-dimensional charge carrier variable range hopping and Arrhenius law. At temperatures above 300[Formula: see text]K, the resistance increases with temperature due to matrix expansion and decreases due to the onset of the conductivity in the matrix. Low frequency voltage noise spectra comprise of 1/[Formula: see text] and Lorentzian-type components with characteristic times in the range from 0.1[Formula: see text][Formula: see text]s to 10[Formula: see text][Formula: see text]s; the noise spectral density in the region of Ohmic resistance is proportional to the voltage square. Therefore, thermally activated charge carrier capture centers randomly modulate the sample’s resistance and control the carrier hopping. Impulse noise and more sudden changes of the noise characteristics were observed at the temperatures, where the conduction mechanisms change.

Novel protection scheme for high‐voltage direct‐current transmission lines based on one‐terminal transient AC voltage

This paper considers the distributed capacitance of transmission lines to research the protection of high-voltage direct-current (HVDC) transmission line. According to the superposition theorem, the post-fault superimposed network of HVDC system is used to analyse the characteristic of the root mean square (RMS) of specific frequency voltage (SFV) during the transient period of internal and external faults. At the parallel resonant frequency of DC filter, for internal faults, the fluctuation of the RMS of transient AC voltage is larger than that of external faults. Based on the fluctuation characteristic of single-terminal transient AC voltage, a novel protection scheme for HVDC transmission lines is proposed. Various simulation results show that the proposed protection is immune to fault resistance and performs well under different fault types.

Determination of the Boltzmann constant by the equipartition theorem for capacitors

A new experimental set-up for measurement of the Boltzmann constant is described. The statistically averaged square of voltage is measured for different capacitances C. The Boltzmann constant is determined by the equipartition theorem . For fixed capacitance, voltages could be measured for different temperatures. The set-up consists of low-noise, high-frequency operational amplifiers ADA4898-2. An instrumental amplifier is followed by an inverting amplifier, the square of the voltage is created by an analog multiplier AD633, and finally, the averaged signal is measured by a multimeter. More than ten high-school students were able to measure the Boltzmann constant with the experimental set-up in the 5th Experimental Physics Olympiad with excellent accuracy compared to the price, conditions and available time for the experiment. A new derivation of the important statistical physics theorems by Nyquist and Callen–Welton is given in an appendix at the level of introductory courses in physics studied by future teachers. To understand the work of the experimental set-up, it is only necessary to know the equipartition theorem.

A Comparative Analysis of Parameter Estimation Strategies for Mathematical Modeling of Ion Channel Gating

Mathematical modeling in cardiac electrophysiology is well established; however, the veracity of model predictions for pharmacological design and testing is unclear. Ion channel gating is often modeled with Markov schemes that reflect different occupancy states of the channel. Although experimental data are always used to constrain the parameters of these models, it often remains unclear whether a set of parameter values is unique, or whether alternative parameter sets could fit the data equally well. Here we have compared alternative parameter estimation strategies to build a patient-specific approach to in-silico drug testing. Using a published Markov representation of the cardiac Na+ channel, we aimed to optimize the value of rate constants regulating the channel's transition between different states. Data derived from voltage-clamp experiments, performed by implementing a traditional voltage square steps protocol in HEK293 cells, were used to test the following approaches: (1) “broad fitting algorithm” using population-based mathematical modeling; (2) optimization through genetic algorithm; and (3) optimization through direct search simplex algorithm. We generated a population (n=10000) of channel variants by randomizing Markov model rate constants and used it to replicate the electrophysiology results. While approaches (2) and (3) identify a single solution that matches the experimental findings, approach (1) provided a population (n=48) of channel variants that reproduce distinctive features of experimental activation and inactivation curves. We conclude that adopting a population-based strategy allows us to find several parameter sets that are all compatible with experimental results and cannot be captured by other common optimization strategies. These solutions recreate the level of experimental variability and account for the fact that different rate constants can compensate for one another. Evaluation of the three algorithms on action potential clamp and dynamic clamp experiments is currently ongoing.

Coherent emission from the stack of Josephson junctions with the non-uniform inductive interaction

During last decade, considerable efforts were made to achieve coherent emission from stacks of many Josephson junctions. It is known that strong emission from a junction in the presence of external magnetic field appears at the so-called Fiske steps in the IV-characteristic at voltages which correspond to frequencies of geometrical resonances. However, it is possible to obtain resonant steps in long junctions without external magnetic field. The periodical movement of fluxons is excited due to some disorder in the distribution of critical currents along junctions. The so-called zero-field steps are formed in the IV-curve due to the interaction of fluxons with oscillations of voltage at Josephson frequencies. We investigated numerically IV-characteristics and the dependence of the average square of ac voltage at the end of the stack of two long Josephson junctions on the average voltage. Junctions interacted inductively with each other. We introduced not only the Gaussian distribution of critical currents along junctions but also the Gaussian distribution of coefficients of the interaction between junctions (mutual inductances). Zero-field steps in the IV-characteristic were found at voltages which corresponded to frequencies of in-phase collective modes in the stack as well as to frequencies of uncoupled junctions. Zero-field steps appeared in the hysteretic region of the IV-curve. There appeared also jumps of voltage from the resistive branch to the zero-field step. We showed that there existed distributions of mutual inductances along junctions which provided jumps to voltages at which the average square of ac voltage at the end of the stack (which is proportional to power of emission) was larger than that for the stack with the uniform distribution of mutual inductances.

Electrical analysis of triboelectric nanogenerator for high voltage applications exampled by DBD microplasma

Triboelectric nanogenerator (TENG) is a natural high voltage and low frequency power source by transferring ambient motion into electrical energy. To improve the output performance of the rotary freestanding TENG (RF-TENG) with the capacitive impedance load used in high voltage field, where the dielectric barrier discharge (DBD) microplasma as an example, an efficiently and effectively electrical analysis for the whole system is explored. Firstly, a simply experimental method with 99% reliability shows the root mean square (RMS) of open-circuit voltage in our RF-TENG is around 3500-4000V and the internal capacitance is 100–130 pF with frequency from 10 Hz to 30 Hz. Then, the experiments of DBD microplasma directly driven by the RF-TENG under different conditions have been conducted and the results fit well with the simulation in discharge current and voltage. Moreover, a 10–30 folds jumping of the discharge current and real-time power have been observed. Finally, by increasing the input frequency or decreasing gas thickness, the discharge intensity and efficiency have been enhanced, meanwhile over 10 times increase on discharge power (RMS) has been achieved. This work will not only help to understand the characteristics of the microplasma at low frequency (<50 Hz) but also benefit the further researches on the directly high voltage application of the RF-TENG.

Timing error detection and correction for power efficiency: an aggressive scaling approach

Low-power consumption has become an important aspect of processors and systems design. Many techniques ranging from architectural to system level are available. Voltage scaling or frequency boosting methods are the most effective to achieve low-power consumption as the dynamic power is proportional to the frequency and to the square of the supply voltage. The basic principle of operation of aggressive voltage scaling is to adjust the supply voltage to the lowest level possible to achieve minimum power consumption while maintaining reliable operations. Similarly, aggressive frequency boosting is to alter the operating frequency to achieve optimum performance improvement. In this study, an aggressive technique which employs voltage or frequency varying hardware circuit with the time-borrowing feature is presented. The proposed technique double samples the data to detect any timing violations as the frequency/voltage is scaled. The detected violations are masked by phase delaying the flip-flop clock to capture the late arrival data. This makes the system timing error tolerant without incurring error correction timing penalty. The proposed technique is implemented in a field programmable gate array using a two-stage arithmetic pipeline. Results on various benchmarks clearly demonstrate the achieved power savings and performance improvement.

Low frequency energy harvesting with a variable potential function under random vibration

This paper presents the study of a low frequency vibration energy harvester by applying a variable double potential function under Gaussian white noise. The energy harvester is composed of a piezoelectric cantilever with a magnetic tip and a second cantilever, this one perpendicular to the piezoelectric cantilever, that also has a magnetic tip. This differs from traditional designs where a fixed magnet opposes the piezoelectric cantilever. Three coupled differential equations represent a model of the nonlinear coupled system. The power spectral density and root mean square of the output voltage are obtained for various base excitation levels. The simulations are validated using experimental results. The optimal distance, where maximum output is generated, is found at the transition distance from mono- to bi-stable regions. Unlike the traditional fixed magnet design where the optimal distance changes with the noise level, in the proposed design the optimal distance remains the same regardless of the noise intensity. This is because of a variable potential function that enables effective conversions of potential and kinetic energies. The effect of different parameters of the system on the output voltage and power is investigated. The results show that the proposed structure can improve the efficiency of vibration harvesting in the low frequency range regardless of excitation levels.

Hybrid energy harvesting from mechanical vibrations and magnetic field

This letter proposes a hybrid energy harvesting scheme to collect the energy from mechanical vibrations and the magnetic field simultaneously. The structure consists of a magnetostrictive substrate bonded with a piezoelectric sheet. The theoretical modeling and experimental investigations are conducted and their results are in good agreement. The effects of phase differences between the harmonic vibration and the AC magnetic field on the behaviors of the energy harvester are investigated. The open circuit voltages are larger than those from either vibration energy or magnetic energy in most phase values, and the energy capacity is mainly determined by the dominant component. The energy harvesting performances of the Galfenol alloy and the nickel alloy are examined, respectively. The results show that the Galfenol alloy is more sensitive to the AC magnetic field, which can enhance the root mean square of the output voltage. Furthermore, the existence of the bias magnetic field (DC magnetic field) can significantly increase the output voltages of the cantilever. The optimal output power of the hybrid energy harvester can increase to 14.82% and 30.40% when compared with the vibration and magnetic excitations, respectively. These findings demonstrate a feasible energy harvesting idea of taking advantage of the ambient vibration and the magnetic energy simultaneously. This letter presents advancements in improving the energy capacity and the reliability.

A bioinspired structure modification of piezoelectric wind energy harvester based on the prototype of leaf veins

This paper describes a novel leaf-like piezoelectric wind energy harvester based on the venation growth algorithm, which are derived from the prototype of dicotyledonous plant leaves that have the netted distributions of veins. Some triangle polyvinylidene fluoride (PVDF) leaves are designed and fabricated to be the energy harvesting element that is driven by the vortex induced vibration in the wind flow behind a bluff body. Wind tunnel experiments were carried out to investigate and compare the performances of energy harvesting capacity of different elements. Experimental results show that the output powers of the veined structures are 4–6 times higher than that of the structure without veins. The largest root mean square of open circuit output voltage reaches 1.094 V under the wind velocity of 11 m/s for the 110 μm thickness PVDF leaf with veins. The dynamic analysis indicates that the veins can greatly influence the mechanical coupling properties between the harvesters and the wind flow although the system has not reached a typical state of instability. It is confirmed that the presence of veins has an important effect on the efficiency of the energy harvesting system.

TCSTM: A task-characteristic-considered steady-state thermal model of multicore processors

Because the power density and temperatures of multicore processors are increasing to the extent that their performance and reliability are degraded, it is crucial to estimate the powers and temperatures of multicore processors accurately and rapidly at the early design stage. In this paper, to improve the accuracy, a task-characteristic-considered steady-state thermal model (TCSTM) of multicore processors is presented. First, a metric, namely, task characteristic, is explicitly defined to characterize the behavior of a workload. The task characteristic is expressed by a column vector Hcycle=[hmemory,hbranch,hinteger,hfloat]′, in which each element respectively denotes the number of memory instructions, branch instructions, integer instructions and floating point instructions per cycle. Second, the dynamic power of a core is modeled as a linear function of the task characteristic, running frequency and the square of voltage. The leakage power is approximated as a linear model of the temperature and voltage. The voltage-given and temperature-interval-limited linear regression (VTLR) method is employed to reduce the complexity of the steady-state model. Third, the steady-state temperature of a core is derived as a function of the task characteristic, frequency, voltage and the number of active cores. To the best of our knowledge, this is the first work to introduce the task characteristic into the steady-state thermal model. Finally, not only the relationships between the frequency, the number of active cores and hot-spot temperatures but also the impact of the number of frequency-scaled cores on hot-spot temperatures are investigated experimentally. The experimental results demonstrate that the proposed steady-state model achieves satisfactory accuracy in terms of the estimation of the dynamic and leakage power and the prediction of hot-spot functional units.

Dynamic Characterization of a Bistable Energy Harvester Under Gaussian White Noise for Larger Time Constant

In this paper, the system parameters of a nonlinear bistable energy harvester excited by Gaussian white noise was investigated. Using Fokker–Planck–Kolmogorov equation, the probability distribution functions of displacement and velocity of the oscillator are obtained. The effect of various system parameters on the probability distributions of displacement and velocity of the oscillator and the mean square of the output voltage are investigated when the time constant of the piezoelectric circuit takes a larger value to achieve maximum voltage gain. The maximum peak values of the joint probability distribution of displacement and velocity of the oscillator decrease with the larger values of noise strength. The effect of parameters of bistable potential function on mean square of output voltage was also investigated. The system equations are numerically solved and mean square value of output voltage is numerically estimated and is seen to be increased as noise intensity increases and decreased as viscous damping increases. The result also shows that better power output can be achieved when the time constant takes larger value.

Method of Measuring the Mismatch of Parasitic Capacitance in MEMS Accelerometer Based on Regulating Electrostatic Stiffness.

For the MEMS capacitive accelerometer, parasitic capacitance is a serious problem. Its mismatch will deteriorate the performance of accelerometer. Obtaining the mismatch of the parasitic capacitance precisely is helpful for improving the performance of bias and scale. Currently, the method of measuring the mismatch is limited in the direct measuring using the instrument. This traditional method has low accuracy for it would lead in extra parasitic capacitive and have other problems. This paper presents a novel method based on the mechanism of a closed-loop accelerometer. The strongly linear relationship between the output of electric force and the square of pre-load voltage is obtained through theoretical derivation and validated by experiment. Based on this relationship, the mismatch of parasitic capacitance can be obtained precisely through regulating electrostatic stiffness without other equipment. The results can be applied in the design of decreasing the mismatch and electrical adjusting for eliminating the influence of the mismatch.

Acoustic vortex beam created with a continuous phase ramp lens and resulting radiation torque response of a sphere

An acoustic vortex beam was created in water using a lens with a phase ramp placed in front of a focused transducer. The lens was made from a polystyrene disk and CAD machine milled to have a continuous ramp in height about the center axis, with the ramp step height corresponding to a 2π phase difference between waves propagating in water and polystyrene at 500 kHz. This causes the transmitted beam through the lens to exit as a vortex beam with an angular phase ramp. It has been predicted [L. Zhang and P. L. Marston, J. Acoust. Soc. Am. 136, 2917–2921 (2014)] that the torque exerted by a vortex beam on an impenetrable sphere in a viscous fluid is proportional to the incident intensity due to dissipation of angular momentum in the viscous boundary layer near the sphere. This should result in steady rotation of the sphere with viscous drag proportional to angular velocity. Our upward-directed vortex beam was used to trap and spin a Styrofoam (closed foam) ball floating at the water surface. The spin rate was approximately proportional to the square of the source voltage as expected. [Work supported by ONR.]

A DC-Link Voltage Fast Control Strategy for High-Speed PMSM/G in Flywheel Energy Storage System

This paper presents a dc-link voltage fast control strategy for high-speed permanent magnet synchronous motor/generator of flywheel energy storage system (FESS) to ensure fast dynamic performance within its wide operation range. Instead of the conventional strategy with cascaded outer dc-link voltage loop and inner current loop, the proposed strategy is a direct voltage control strategy without an intermediate current loop. The nonlinear dc-link voltage loop model is globally linearized by treating the square of dc-link voltage as the state variable, and lumping the nonlinear and uncertain terms in the power balance equation as the total disturbance. An extended state observer (ESO) is designed to observe the total disturbance, and a control law that compensates the speed variation and the total disturbance is proposed. The inner dynamic of the proposed ESO is analyzed, and the tracking performance and antidisturbance capability of the proposed strategy is hereby derived. Finally, the proposed strategy is validated on a high-speed FESS test bench.

Influence of sinusoidal and square voltages on partial discharge inception in geometries with point‐like termination

High-voltage equipment involves both electrical and electronic components. In electrical power network, which consists of rotating machine, power transformers and transmission lines, field enhancement at critical regions can lead to local breakdown [partial discharges (PD)]. The continuous occurrence of PDs can lead to complete breakdown. While in large power equipment sharp edges can be avoided, this is not the case in power converter due to the miniature nature of the semiconductor device. Sharp edges can also be present in any power equipment in the shape of conducting particles, either stuck at a barrier or freely moving in the bulk oil. This creates high-field regions, prone to PD activities. Different power equipment operates at different voltages such as AC, DC, square voltage, pulse voltage, fast-rise transient voltage etc. This study presents the influence of sinusoidal voltage, slow- and fast-rise square voltage on PDs in two different geometries using optical PD measurement technique. Fast-rise square voltage has the lowest PD inception voltage while the sinusoidal voltage has the highest. This is may be due to the influence of homo- and hetero-charges. Fast-rise square voltage displayed higher PD magnitude at inception which may be connected to the rise time of the voltage.

KN.U-K2 International Laboratory Comparison of Ultrasound Power Measurements Emitted from an Ultrasonic Transducer

An international comparison of ultrasound power measurements was conducted among the ultrasound laboratories of the Korea Research Institute of Standards and Science (KRISS), the National Metrology Institute of Japan (NMIJ) and the National Institute of Standards (NIS, Egypt). The measurand for comparison is the electro-acoustic radiation conductance G, which is defined as the amount of ultrasound power divided by the square of the input signal voltage to the transducer. The reference device is an ultrasonic transducer, model number KRISS-2MHz-14LN, manufactured by KRISS using a Lithium-Niobate (LiNbO3) piezoelectric single crystal. This comparison, reference number KN.U-K2, was piloted by KRISS, including the preparation of the protocol and the reference device, and the analysis of measurement results by the participants. This paper reports the comparison results.