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This paper presents a neutral-point deviation and ripple compensating control method applied to a three-level neutral-point-clamped (NPC) converter. The neutral-point deviation and its harmonic components are analyzed with a focus on the average current flowing through the neutral-point of the dc link. This paper also proposes a control scheme compensating for the neutral-point deviation and dominant harmonic components under generalized unbalanced grid operating conditions. The positive and negative sequence components of the switching functions and ac input currents are employed to accurately explain the behavior of three-level NPC converter. Simulation and experimental results are presented to verify the validity of the proposed method.

The neutral-point voltage-balancing control is a critical issue of a neutral-point-clamped converter. The conventional control strategy is to inject the specific zero-sequence voltage to regulate the redundant vector, but it is unacceptable to the three-phase four-wire system. This paper provides a neutral-point voltage-balancing control by the dipolar modulation, and the control freedom of the zero-sequence voltage is flexible. Therefore, the proposed method is suitable for both three-phase three-wire and three-phase four-wire systems. Besides, the proposed method improves the control dynamic in a reactive power system. The proposed neutral-point voltage-balancing control is verified by the mathematical analysis and experimental results. The control dynamic, power loss estimation, and the output current performance are analyzed in this paper.

This paper applies a rigorous electromagnetic model to determine the transient distribution of potentials along a substation earth grounding grid subjected to lightning currents. The obtained results show that, in the initial period of the transient, equipment pieces that are earth grounded at distinct points of the grid and are electrically linked (for example, by aerial communication cables) experience impulsive loop currents. Such loop currents can cause equipment malfunctions, failures, and damage. A remarkable conclusion of this paper is that such loop currents can reach substantial values even in the case of soils of low resistivity. Some practical aspects are highlighted in order to reduce the risks due to the nonuniform distribution of potentials along earth grounding.

The groundings of the power distribution, signaling, and power systems of a railway system are individually performed to realize fail safe, and the groundings are often installed in close proximity. Thus, when a grounding electrode is invaded by a lightning current, its ground potential rises together with the potential of the adjacent grounding electrodes; hence, there is a possibility of a large overvoltage being applied to the connected devices. In this paper, we have investigated the potential spread between two rod-shaped electrodes widely used in the grounding of the power, signal, and distribution systems of a railway system using the finite-difference time-domain method. The results of this paper are organized in such a way that the extent of the potential spread to the neighboring grounding electrodes can be understood from information such as the grounding resistivity at the installation location of the ground electrode and the wavefront duration of the lightning current, and these findings will be useful for grounding design. We also investigate the effect of the insulator between two neighboring electrodes to prevent the potential spread.

The grounding system in a solar farm has unique characteristics due to its extended footprint and varying type of grounding components. The changing physical properties of the soil within the perimeter of a solar farm result in the nonuniform resistivity of the top soil layers. Measurements of the as-built grounding grid could indicate higher grounding resistance than that predicted by design. Once this difference is detected, it is the duty of the designer to modify the existing grounding grid such that the touch potential is below the limits specified by the applicable codes. This paper presents the analysis of the touch potentials in solar farms and also provides some recommendations to reduce these potentials when the grounding resistance is higher than that predicted by the design. An actual grounding grid design and field measurements are used in an example to illustrate the concepts introduced in this paper.

In practical engineering, electricity theft detection is usually performed on highly imbalanced datasets (i.e., the number of fraudulent samples is much smaller than the benign ones), which limits the accuracy of the classifier. To alleviate the data imbalance problem, this paper proposes simple data augmentation tricks (SDAT) to boost performance on electricity theft detection tasks. SDAT includes five simple but powerful operations: adding noises to electricity consumption readings, drifting values of electricity consumption readings, quantizing electricity consumption readings to a level set, adding a fixed value to electricity consumption readings, and adding changeable values to electricity consumption readings. In addition, eight potential tricks are also mentioned. Numerical simulations are conducted on a real-world dataset. The simulation results show that SDAT can significantly boost the performance of different classifiers, especially for small datasets. Besides, specific suggestions on how to select parameters of SDAT are provided for its migration use to other datasets.

Electric charge accumulation on fibrous dielectric media during manufacturing processes can easily attain high levels of electrostatic hazard. In a previous paper, the authors addressed the problem of the accelerated discharge of such materials using a commercial ion generator. The aim of this paper is to evaluate the various factors that influence the efficiency of charge neutralization performed using a wire-type corona electrode energized from either a sinusoidal or a triangular ac high-voltage supply. The experiments were performed on 400-μm-thick nonwoven sheets of polypropylene and polyester, in ambient air. The samples were charged for 10 s using a triode-type corona electrode system of negative polarity. The surface potential on the charged medium, which was in contact with the grounded electrode, was then measured with an electrostatic voltmeter. After 10 min, the medium was moved beneath a neutralizing electrode, connected to a high-voltage amplifier. The efficiency of the neutralization was quantified by the ratio between the surface potential after and prior to the charged sample exposure to ac corona discharge. The experimental design methodology was employed for evaluating the effects of two factors, namely, amplitude (range: 16-24 kV) and frequency (range: 20-400 Hz), of the neutralizing voltage. The potential at the surface of the nonwoven fabrics after neutralization was found to vary insignificantly with thermal conditioning and signal waveform but was significantly lower for higher frequencies and amplitudes.

When using the boundary biased-probe method, the nonlinear curve attained in experiments is contradictory to the linearity expected when Tassicker's formula is applied to this method. In this paper, the authors analyze the probe model theoretically and obtain a nonlinear relation. Their analysis shows that the space charge near by the biased probe is the main cause of this nonlinearity. This space-charge effect was ignored in Tassicker's formula. Their theoretical analysis and experimental results show that Tassicker's formula can be improved, in particular, when the electric field region is rich in space charge. In this paper, the authors propose a way to improve Tassicker's formula.

The main objective of this paper is to develop a novel two-stage-type electrostatic precipitator to collect finely ground lignocellulosic particles. To prevent the danger of explosion of such a powdery material, ion generation and particle charging processes are separated. Main results show that the particles can be highly charged in a two-coaxial-cylinders triode-type device, which also facilitates their collection. For instance, the collection efficiency reaches 92 % for particle size of about 0.3 μm, and exceeds 99% for particle size greater than 2 μm.

The aim of this paper is to evaluate the collection efficiency of submicron particles using electrically charged nonwoven filter media. A triode-type electrode arrangement consisting of a high-voltage wire-type ionizing electrode, a metallic grid, and grounded plate electrode is employed to control the distribution of electric charges deposited on the media. Surface electric potential measurement is carried out to study the evolution in time and the repartition in space of deposited charges. The collection efficiency is estimated by measuring the particle concentrations downstream and upstream of the charged filter media. The main results show good correlation between the surface potential level and the collection efficiency of submicron particles for several charging conditions. In particular, filtration performance increases with increasing the corona current through the media during the charging process. Increasing the electric field between the grid and the media during corona charging has also a positive effect on the collection efficiency. Results indicate that high collection performances could not be achieved using thin monolayer media.

The ability of polymers to acquire and retain electrostatic charges is valued in designing new equipment like electrostatic separators, electret filters, and powder coating devices. Several recent studies have pointed out the beneficial effect of electric charges on the lubricated contacts. The aim of this paper is to compare two physical mechanisms of electric charging of polymers: 1) triboelectric effect; and 2) corona discharge. The experiments are performed with 5-mm-thick samples of Acrylonitrile-butadiene-styrene, poly-vinyl-chloride, and polypropylene. The cartography of the electric potential is made using the induction probe of an electrostatic voltmeter. The tribocharging is done by back and forth movement of two polymer plates in conformal contact with each other (speed: 7 to 30 mm/s; constant normal force: 10 N). Uniform corona charging is performed by moving the sample in the space charge zone generated by a wire-type high-voltage electrode used in a triode configuration with the potential of the grid electrode set at 1 and 2 kV. The electric potential at the surface of tribocharged polymers is less uniform, but decays slower than that of corona-charged samples.

This paper presents a method of analysis of grounding systems located inside or near a hemi-oblate spheroidal soil heterogeneity. This type of soil is particularly useful for modeling grounding grids close to certain types of finite inhomogeneities, such as lakes or some types of backfill materials. The developed analytical framework is based on a moment method and involves solving Poisson's equation in an oblate spheroidal coordinate system. Computation results obtained using this modeling approach for several electrodes and hemispheroidal geometries are compared with those obtained using other numerical and analytical techniques. In all cases, good agreement has been achieved.

This paper presents the analysis of grounding systems including freely oriented conductors and metallic plates of arbitrary shapes in horizontal multilayer soils. The analysis method yields not only the scalar potential but also the electric field and current density in the soil in the low frequency limit. Numerical results are provided for various configurations such as a single plate, a plate with rods, parallel plates, a box, or cylinders formed by multiple plates and are verified against available analytical methods.

Global earthing systems (GESs), which are created by the interconnection of local earthing systems, should guarantee the absence of dangerous touch voltages. According to international standards, one of the reasons for this safety characteristic of GESs is that medium-voltage and low-voltage grounding systems form a quasi-equipotential area. Typical examples of GESs are in city centers due to the high number of interconnected grounding systems in the area. For this reason, in addition to ground grids, other metallic parts with different primary functions shall be also considered, e.g., water and gas pipes, tramway tracks, and building foundations can modify the electric potential distribution in the area. In this paper, a model based on the Maxwell's subareas method (MaSM) is used to evaluate how buried metallic parts, which are not intentionally connected to ground grids, modify the electric potential on the soil surface. First, the MaSM model is validated with experimental measurements on a simple electrode configuration. The measured voltages are compared with the MaSM results and with the results obtained with a finite-element method model simulated with COMSOL Multiphysics. Then, the simulations are carried out on a realistic urban test case.

This paper presents an analysis of high-voltage direct current sea electrodes using different numerical techniques. The large volume of sea water that must be included in the analysis is represented using infinite (inclined layer model) and finite models (finite volume and hemispheroidal models). The comparison between the results obtained using these models is based on the potential rise of the electrode, the sea potential rise in the vicinity of the electrode, and the computational burden for utilizing each model. The analysis shows that the results obtained using finite models can predict the performance of the electrode more accurately and realistically.

The electrophotographic properties of a newly developed organic photoconductor and triboelectric magnetic toner were investigated for a nonimpact printer with a diode laser. The photoconductor was composed of a metal-free phthalocyanine layer and an oxazole-derivative-doped polymer layer. The photoconductor had a charge acceptance of -1000 V and a light sensitivity of more than 0.1 m 2 /mJ at 780 nm. The magnetic toner had a resistivity as high as 10 14 ? cm and could accept triboelectric charge of -3.5 ?C/g. Chrome dye was employed for a negative charge control agent to affect the sign and magnitude of triboelectric charge on toner particles. Using the developed organic photoconductor and triboelectric magnetic toner, good quality prints on plain paper were obtained with the new diode laser printer. Toner mass density deposited on the photoconductor was improved by more than 20 percent as compared with that of conventionally used conductive or high-resistance magnetic toners. It was found that the triboelectric magnetic toner had a very high transfer efficiency of as large as 80 percent, even on plain paper.

A new solid-state scanning ink jet recording technique, called slit jet recording, is proposed. This technique uses a recording head with one slitlike ink-issuing opening having a number of recording electrodes arrayed along a horizontal scanning direction. The ink is emitted from the ink-issuing opening due to the electrical potential difference between a driven recording electrode and a counterelectrode located behind the recording paper. The ink strikes the paper and forms a recording dot. Many recording electrodes can be driven simultaneously by video signals which enhance the total copy recording speed over that for conventional techniques using a single nozzle. The head of this ink jet recording apparatus is remarkably simple in construction and can be fabricated without difficulty. Improvements in reliability and maintainability can also be expected, as the simple structure of the ink-issuing opening reduces clogging and facilitates easy cleaning as compared with other equipment having a large number of nozzles. The recording principle and characteristics and ink-issuing characteristics are described, and the results of a trial recording are presented. The results show that an ISO A4 size (210 mm x 297 mm) full-color copy can be recorded in about 30 s at an 8-dot/ mm rate.

The triode electrode system is frequently employed for accurately controlling the corona charging of insulating materials. The primarily aim of this paper is to characterize this electrode system by current–voltage and current density distribution measurements. The electrostatic aspect of the electric field generated by the triode electrode system is also numerically analyzed using a charge simulation program. The ionizing element of the electrode system is a thin tungsten wire (diameter: 200 $\mu\hbox{m} $ ) attached to a cylinder (diameter: 26 mm) and distanced at 34 mm from its axis. The wire-cylinder assembly is a “dual” electrode, facing a grid electrode, connected to a well-defined potential, and grounded plate electrode (aluminum, 250 mm $\times$ 130 mm) . The interelectrode spacing has a very significant influence on the current–voltage characteristics of the triode system and on the extension of the corona discharge generated by it. The experimental results obtained for different geometries of the electrode system are interpreted in the light of the numerical modeling of the electric field, in order to make some recommendations regarding its design: reduce/increase the wire-grid distance in order to diminish the operating high voltage/expend the surface affected by the corona discharge.

This paper addresses the numerical investigation of an electrohydrodynamic (EHD) plume induced by a sharp blade electrode in a dielectric liquid. Different injection laws, namely, autonomous and nonautonomous ones, are considered, and the importance of the blade shape is emphasized, especially for nonautonomous injection laws. Different flow regimes arise according to the value of the Reynolds number based on the ionic mobility and the distance $d$ between the blade and the vertical plate. It is found that the critical Reynolds number for which the transition between steady and unsteady regimes occurs depends on the injection law, on the blade shape, on the $M$ parameter, and on the injection strength $C$ . For much higher Reynolds number, the flow turns to be chaotic and behaves as a jet flow with the development of a Kelvin–Helmoltz instability. The use of different sharp blades indicates that a higher electric field at the tip of the blade plays a significant effect on the development of the EHD plume. The plumes have been characterized by their charge density distribution which shows, in the early stages of the simulation, that its dynamics is significantly dependent on the blade shape as well as on the nonautonomous injection law.

This paper presents a comparative study of two types of low cost single-phase wound-field switched flux machines with DC field and AC armature windings having the same coil-pitch of 2 slot-pitches and having different coil-pitches of 1 and 3 slot-pitches, respectively. Both can share the same stator lamination but the later can have shorter end-windings and lower iron loss for the 12-slot/6-pole configuration. The performance, including back-EMF, cogging torque, and static torque, of both machines are analysed and compared by two-dimensional (2-D) finite element analysis (FEA) and validated by experiments on the prototype machines.

Neutralization of the residual electric charge is often a prerequisite for the optimal processing of insulating granules, thin films, or textile media. The aim of the present paper is to evaluate the factors that might affect the ability of AC corona discharge to eliminate the charge at the surface of polyethylene granular materials. The effectiveness of the neutralization is evaluated from the measurement of surface potential distribution before and after exposing the samples to a flux of bipolar ions. The corona discharge was generated by energizing at various high-voltage levels (16 kV, 20 kV, and 25 kV), and frequencies (1 Hz, 20 Hz, 50 Hz, 100 Hz, 200 Hz, 400 Hz) a wire-type corona electrode suspended at 30 mm above the granular layer disposed at the surface of a grounded plate. The results show that the neutralization efficiency can be improved by increasing the frequency of the high-voltage. An optimal value voltage can be experimentally determined for the case of practical interest when the frequency of the power supply is 50 Hz. In the same case, successive exposures to the AC corona discharge may enhance the efficiency of the neutralization.

Electric charging of nonwoven materials employed as filter media improves their particle collection efficiency by the electrostatic particle capture mechanism that enhances the conventional mechanical filtration without causing an increase of the pressure drop. The aim of this paper is to provide a better understanding of the corona-charging process of such materials, by analyzing some of the factors that affect the repartition of the electric potential at the surface of the respective media. The experiments were carried out on two types of polypropylene samples: nonwoven fabrics and films. The experimental results show that the area occupied by the charge increases with both the charging voltage to the corona electrode and the duration of the charging process. The same area increases also with the time elapsed from the end of the charging, which points out the charge redistribution at the surface of the media by a surface conduction mechanism.

This paper provides and analyzes a simple, robust, and universal model for rotor position estimation for synchronous machines. The rotor position is estimated using an equivalent electromotive force (EMF) model of a synchronous machine or, alternately, using a sliding-mode observer (SMO) based on the equivalent EMF model. The SMO provides fast convergence and low sensitivity to parameter variations. Experimental results with a 3.7-kW interior-permanent-magnet machine have validated the effectiveness of the proposed equivalent EMF scheme.

Surface potential and electric field measurement techniques are widely used for the investigation of the corona charging of dielectric surfaces in a wide range of industry applications. The aim of this paper is to estimate which of these techniques are the most appropriate for characterizing the charging state of nonwoven fibrous dielectrics and point out the “noise factors” that might distort the results of the measurements. The experiments were performed on samples of nonwoven polypropylene sheets, in contact with or at a well-defined distance from a grounded plane electrode. The effect of the variability of the position of the probes with respect to the samples was also investigated. Several recommendations have been formulated regarding the use of these techniques for monitoring the charging state of nonwoven fabrics in industry applications.

AC electroosmotic pumping of fluids in a microchannel with two thin coplanar electrodes, deposited on one dielectric wall and placed in an aqueous solution, is studied in this paper. Two different numerical formulations are compared. In the first one, the transport equations (mass, molar, and momentum balances) for the ion concentration and the Poisson equation for the electric field are solved simultaneously in the time domain without any simplification of the computational domain except that the dielectric walls are neglected. In the second one, a time average model is assumed, and the Debye layer is represented by an approximate 1-D model. In both cases, the finite-element method implemented in the COMSOL commercial software is used as a numerical tool. The results for the electric field, space charge, and velocity distributions are compared with a qualitative agreement between both models.

Recent work has demonstrated that airborne bacteria can carry high net charges which may influence their deposition onto surfaces. This paper investigated the relationship between surface electric potential relative to ground and the deposition rate of airborne bacteria. Nutrient-agar settle plates were charged to potentials of +/-5, +/- 2.5, and 0 kV and microbial deposition (CFU/cm2middoth) enumerated in an office restroom environment. Results showed that deposition rates were enhanced in proportion to the surface potential to a maximum of approximately twofold. The results were consistent with framework modeling of the relative contributions of electrostatic attraction (ESA), sedimentation, and diffusion deposition rates. It is concluded that ESA can significantly increase deposition rates under selected conditions. This has implications for health-care settings and may provide a basis for application of particle-deposition-reduction engineering controls that have been successfully employed in the semiconductor industry.

In an isothermal liquid, only the Coulomb force which is the force acting on the free charges, can contribute to the net electrohydrodynamic (EHD) motion. In the absence of a direct charge injection or induction, the charges can be generated through the dissociation process of the fluid. The generated charges by dissociation are redistributed by the applied electric field, resulting in the heterocharge layers around the electrodes. The pumping of an isothermal liquid without ion injection is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes. This type of pumping is referred to as the conduction pumping. This paper investigates the pressure head generated by the conduction pumping mechanism theoretically through the numerical solutions. For this purpose, a theoretical model for the static case (i.e., without a fluid motion) is established and a numerical code using finite volume method is developed. Electric potential, electric field, charge density, and electric body force distributions for the selected electrode configuration are presented. The generated pressure as a function of the applied voltage is also presented. The numerical results confirm the EHD conduction pumping concept theoretically.

Although the mobility constant of an ionic species can be easily measured at low electric potentials, at high potentials the constant often appears to be dependent on the potential or apparent electric field. Clearly, if the mobility varies with the applied potential, then the concept of a mobility constant becomes ambiguous. This paper examines the assumptions normally made to convert raw data to a mobility. The examination shows the ambiguity arises when the space-charge effect is ignored in the analysis at high potentials, Using the charge-injection equation, the result shows the mobility at high electric fields can still be considered a constant. The analysis predicts the nonlinear rise in the measured current density at high field, without the need to impose a nonconstant mobility. Conversely, the result shows the true mobility can be obtained by extrapolating the apparent mobility to zero electric field.

In this paper, a new modulation method is proposed for a $Z$ -source three-level T-type inverter $(3\mbox{LT}^2{I})$ . The $Z$ -source $3\mbox{LT}^2{I}$ combines the merits of the $Z$ -source two-level inverter and the advantages of the $Z$ -source neutral-point-clamped inverter. Although the previous literature has proved that the space vector modulation (SVM) technique for $Z$ -source $3\mbox{LT}^2{I}$ produces the desired voltage transfer gain with minimized switching loss, it cannot deal with the neutral-point (NP) potential balance issue. Therefore, an improved SVM method addressing this problem for $Z$ -source $3\mbox{LT}^2{I}$ is proposed. The method simplifies the space-vector diagram of a $Z$ -source $3\mbox{LT}^2{I}$ into that of a $Z$ -source two-level inverter. In order to obtain NP potential balance, the pattern of the conventional symmetric SVM is changed by properly adding or subtracting a percentage of the minimum gate-on time. The upper and lower shoot-through states can be inserted into the improved symmetric SVM, thus offering av few advantages, including boosting ability, NP potential balance, and low switching loss. The considerate stable NP voltage and the boosting gain have been experimentally proven by results from a prototype inverter.

It is often necessary to reduce the total energy released by an accidental spark discharge from a dc high-voltage terminal. The paper presents the results obtained with two experimental setups designed to investigate the effects of inserting a corona element in series with such terminals. The spark discharge onto a 23-cm diameter spherical probe was measured for the same terminal voltage with and without the corona element. Depending on the capacitances of the high-voltage circuit and of the corona element, and on the corona current-voltage characteristics, the reduction of the spark energy may reach one order of magnitude or more.