Current Oscillation Phenomena Research Articles

Current Oscillation Phenomenon of MMC Based on IGCT and Fast Recovery Diode With High Surge Current Capability for HVDC Application

Integrated gate commutated thyristor (IGCT) has low loss, low cost, and high reliability in the application of modular multilevel converter (MMC). However, due to the special turn-off process of IGCT, the commutation transient is very different for IGCT in MMC. This letter reveals a current oscillation phenomenon of MMC based on IGCT and fast recovery diode (FRD). Especially, this oscillation effect becomes apparent when the FRD with high surge current capability is employed in MMC because of high junction capacitance and high stray inductance, which will threaten the safe operation of the system. This letter analyzes the current oscillation mechanism and gives the current oscillation modeling. In addition, through detailed tests under various stray inductances, the specific stray inductance range that can cause large current oscillation is obtained and an optimized inductance parameter of IGCT-MMC is proposed. The experiments show that the safe operation area of IGCT in MMC can be guaranteed maximally with the optimized parameter.

A Novel Protection Scheme for MMC-HVdc Transmission Lines Based on Cross-Entropy of Charge

MMC-HVdc transmission system has become the mainstream of power construction and plays an increasingly important role in the power system. However, the dc line fault results in shutting down of the converters, which can greatly endanger the security of the power grid. So it is essential to find a fast fault identification strategy for dc line protection technology. Besides, the existing backup protection scheme has the problems of long delay and strict communication synchronization requirements. Therefore, this paper proposes a novel protection scheme for mmc-HVdc transmission lines based on the Cross-Entropy of charge. The fault current oscillation phenomenon and fault current frequency characteristics of mmc-HVdc transmission lines are analyzed first. Secondly, this paper proposes a method to filter out distributed capacitance current by charge and eliminate the current oscillation. Finally, the difference of the charge during different faults (internal fault and external fault) is analyzed, and the Cross-Entropy is introduced to express this difference. Hence, this paper proposes a new principle of identifying faults using the Cross-Entropy of the charge. Simulation results show that the protection principle is not affected by the distributed capacitive current and does not require strict communication synchronization. It has excellent performance in intolerance to fault resistance and noise interference and can be used as backup protection for the mmc-HVdc transmission system.

Transport and Photoelectric Properties of 2D Silicene/MX2 (M = Mo, W; X = S, Se) Heterostructures.

The transport and photoelectric properties of four two-dimensional (2D) silicene/MX2 (M = Mo, W; X = S, Se) heterostructures have been investigated by employing density functional theory, nonequilibrium Green’s function, and Keldysh nonequilibrium Green’s function methods. The stabilities of silicene (SiE) are obviously improved after being placed on the MX2 (M = Mo, W; X = S, Se) substrates. In particular, the conductivities of SiE/MX2 are enhanced compared with free-standing SiE and MX2. Moreover, the conductivities are increased with the group number of X, i.e., in the order of SiE < SiE/MS2 < SiE/MSe2. An evident current oscillation phenomenon is observed in the SiE/WX2 heterostructures. When a linear light illumination is applied, SiE/MSe2 shows a stronger photoresponse than SiE/MS2. The maximum photoresponse with a value of 9.0a02/photon was obtained for SiE/WSe2. More importantly, SiE/MS2 (M = Mo, W) heterostructures are good candidates for application in designing solar cells owing to the well spatial separation of the charge carriers. This work provides some clues for further exploring 2D SiE/MX2 heterostructures involving tailored photoelectric properties.

Voltage Polarity Reversing-Based DC Short Circuit FRT Strategy for Symmetrical Bipolar FBSM-MMC HVDC System

Fault ride-through (FRT) control and protection are of vital importance for a modular multilevel converter-based high-voltage direct current (MMC-HVDC) system when dc-side pole-to-pole (PTP) or pole-to-ground (PTG) fault occurs. In this paper, a FRT strategy by reversing dc voltage polarity is proposed for symmetrical bipolar full-bridge submodule-based MMC-HVDC system. It is suitable for both PTP and PTG faults. By adopting this method, the dc voltage stress in PTG fault scenario and dc current stress in PTP fault scenario are eliminated. Meanwhile, the capability of transmitting rated active power is maintained during faults, which can minimize the impact of dc-side faults on ac grid. In addition, based on a deduced dc-side equivalent circuit, the dc line current oscillation phenomenon during FRT transient process is analyzed. An active damping control method is presented to suppress the transient oscillation. Finally, validity of the proposed FRT strategy is verified by PSCAD/EMTDC simulations.

Photocurrent response in heterojunction photodiode with quantum dot-in-well

ABSTRACTWe report the photocurrent response in heterojunction photodiode with quantum dots–quantum well. When this quantum dots–quantum well hybrid heterostructure is biased over 1.5V, the photocurrent response manifests itself a steplike enhancement, and increasing linearly with the light intensity. This phenomenon is associated with photon storage. We furtherly tested the hysteresis tropic line of the device. With the further increase of radiated intensity to 5 μW, the current oscillation phenomenon is found. At the same time, we also discuss the deference between positive bias and negative bias. Finally, the output current has the nature of a sine wave. All of the above properties are manifested in the process out of the current response.

Characteristics of Potentiodynamic Polarization Curves of Aluminum Electrodeposion Coating in Acidic Sulphate Solution

The density and anodic potentiodynamic polarization (PDP) in different diluted acidic sulphate solution of the aluminum electrodeposion coating on Q235 steel substrate, obtained in the molten salt of AlCl3,NaCl and KCl and treated by diffusion treatment, have been investigated. The results indicated that with the increase of temperature of diffusion treatment, the dencity of the coatings increases first, then reduces little. At 500°C, the dencity is biggest, 2.76g/cm3, which is almost equal to that of compact pure aluminum. As-received coating displays a current oscillation behavior on the anodic potentiodynamic polarization curves in different diluted acidic sulphate solution . And with the increase of diffusion temperature, the current oscillation behaviors donated by the current oscillation domains in solution of 180g/L H2SO4 gradually disappeared. When the temperature is up to 500°C and 700°C, no current oscillation phenomena can be observed. Based on these phenomena, a mode between the porosity of the coating, which was affected by the temperature of diffusion treatment, and current oscillation behaviors was roughly established.

Current oscillation originating from negative differential resistance in one-dimensional halogen-bridged nickel compounds

We demonstrate current oscillation phenomena using the negative differential resistance in a one-dimensional halogen-bridged nickel compound, [Ni(chxn)2Br]Br2 (chxn=cyclohexanediamine). By attaching external resistors and a capacitor to a [Ni(chxn)2Br]Br2 sample, we obtain stable current oscillation at 90 K. The oscillation and its period are explained by a simple model.

Oscillatory Phenomena during Anodic Copper Electrodissolution in Trifluoroacetic Acid Solution

This work presents the current oscillation phenomena observed in an electrochemical Cu/0.5 M CF3COOH system. The dynamical response of this new oscillator was followed by both current density-potential (j-E) and current density-time (j-t) curves. The current oscillation phenomena of the investigated system were monitored over various potential scan rates and constant applied potentials as control parameters. The increase of potential scan rate significantly decreases both the potential range of current oscillations and the frequency of oscillations. At the j-t curves both the simple and the complex (period adding) oscillations were found. Moreover, with the increase of applied potential, the increase of period of oscillations and current oscillation amplitudes were observed. It appears that the period of current oscillations exponentially grows with applied potential.

Current oscillatory phenomena based on electrogenerated superoxide ion at the HMDE in dimethylsulfoxide

A study on the current oscillation based on the electrogenerated superoxide ion ( O 2 - ) at a hanging mercury drop electrode (HMDE) in dimethylsulfoxide solution containing tetra- n-alkylammonium perchlorate as the electrolyte was carried out. Cyclic voltammetric, potential step chronoamperometric, normal and reverse pulse voltammetric techniques were employed in this study. A bare glassy carbon electrode, a liquid hemispherical mercury (Hg) drop-coated gold (Au) electrode and a Hg film-coated Au electrode were also used as working electrodes to understand the mechanism of the current oscillation. The experimental conditions were optimized for a simple, regular and reproducible current oscillation. The specific adsorption phenomenon of iodide ion and the adsorption of the alkyl chain of the supporting electrolyte on the HMDE surface were also considered to clarify the experimental factors governing the current oscillation phenomenon. It has been concluded that the oscillation is mainly due to the promoted oxidation (dissolution) of the HMDE itself by the adsorption of O 2 - , resulting in the formation–destruction of a passive film such as Hg 2 ( O 2 - ) 2 on the electrode surface. A probable mechanism for the observed current oscillation is discussed.

Dynamic-Field-Induced Oscillatory dc Current in Colloidal Crystallite

The one-dimensional variable range hopping conductivity model1-3 was applied to a very simple model system, monodispersed hard spheres suspended in an insulating oil, to understand dynamic-field-induced dc current oscillation phenomenon that was experimentally observed in the electrorheological fluid,1,4 a typical colloid crystallite arrayed with an external electric field. The relationship between the oscillatory dc current and the applied mechanical field is established, agreeing well with previous experimental results. Our finding suggests that this kind of colloidal crystal can be potentially used as a convenient electronic device to mutually transfer electronic and mechanical signals or to real-time analyze mechanical signals, which would be useful in mechanical measurement, such as in seismographs.

Negative Resistance and Current Oscillation Phenomena in Oriented Polypropylene Films

The conduction characteristics in oriented polypropylene (OPP) film were studied over field intensities between 10 and 300 MV/m and a range of temperature from 5 to 55°C. The range of the conduction characteristics observed at 15°C was divided into five regions with increasing field intensity. Particularly, in the region from 70 to 82 MV/m voltage‐controlled negative resistance was displayed. In the negative resistance region, current oscillations were also observed and the mobility of carriers was . The negative resistance characteristics could be explained by Gibbons' theory.

Microelectrode study of gallium deposition from Chlorogallate melts

AbstractMicroelectrodes are used to extract thermodynamic, transport, and kinetic data for the gallium trichloride/1‐methyl‐3‐ethylimidazolium chloride room‐temperature molten salt that has been used by the authors to form GaAs thin films. The gallium electrodeposition process, which must be understood for the analysis of the GaAs deposition process, is simulated numerically. A plausible gallium deposition mechanism is identified. Microcylinder electrodes are shown to be advantageous for the acquisition of physicochemical constants. Microdisk electrodes are employed to investigate current oscillation phenomena that appear to be related to metal crystallization processes.

Charge-density-wave transport in quasi-one-dimensional conductors. I. Current oscillations.

We present a detailed experimental study of current oscillation phenomena in charge-density-wave (CDW) transport. The amplitude and harmonic content of the quasiperiodic component of the current oscillations remain large and approximately constant even at very high electric fields, suggesting that the form and magnitude of the impurity pinning potential are approximately independent of applied field. A simple single-coordinate model of CDW motion in a nonsinusoidal pinning potential, motivated by the quantum tunneling theory of CDW depinning, accounts for all the qualitative features of our results. Nearly perfect velocity coherence seems to be characteristic of weak-impurity-pinned CDW's in high-quality ${\mathrm{NbSe}}_{3}$. However, other types of crystal defects together with contact effects act to broaden the observed distribution of CDW velocities. This velocity distribution plays a crucial role in the ``ringing'' observed in the CDW response to a current pulse, and also in generating the broadband noise.

Current oscillations in charge-density-wave transport.

Detailed measurements of current-oscillation phenomena in Nb${\mathrm{Se}}_{3}$ and Ta${\mathrm{S}}_{3}$ show that the harmonic content and amplitude of the oscillations remains large even at very high electric fields. These results are well described by overdamped motion in a nonsinusoidal pinning potential of the general type previously proposed by Bardeen. Transient "ringing" in the voltage response to a current pulse is attributed to charge-density-wave dephasing. This dephasing is associated with crystal defects, such as dislocations, and with contact effects.

A SOGICON type instability in silicon

A current oscillation phenomenon in SOGICON type Si device fabricated by the use of a planar process is studied. The oscillation is generated in the region between anode and notch which is located at the center on the sample. A considerably high electric field is observed in the notch region. Considering the hot-electron effect due to the high electric field, the mechanism underlying the current oscillation is discussed.

Phase coherence in the current-carrying charge-density-wave state: ac-dc coupling experiments in NbSe3

Various experiments which involve the joint application of dc and ac driving fields, $V={V}_{\mathrm{dc}}+{V}_{\mathrm{ac}}cos(\ensuremath{\omega}t)$, are reported for the charge-density-wave (CDW) state of the linear-chain compound Nb${\mathrm{Se}}_{3}$. Steps are observed in the dc $I\ensuremath{-}V$ characteristics when ac driving fields are applied. The complex ac response ${\ensuremath{\sigma}}_{\mathrm{ac}}(\ensuremath{\omega})$ is also strongly influenced by the application of dc fields, with sharp changes occurring in ${\ensuremath{\sigma}}_{\mathrm{ac}}(\ensuremath{\omega})$ for well-defined driving frequencies and bias fields. These phenomena are the consequence of interference effects between the applied ac signal and the intrinsic current oscillations. In both cases, the ac "interference" frequency is proportional to the excess current ${I}_{\mathrm{CDW}}$ carried by the charge-density wave. We analyze our experiments in terms of a simple nonlinear equation proposed previously to account for the field- and frequency-dependent response and current oscillation phenomena. The equation is formally identical to the equation describing a resistively shunted Josephson junction (Stewart-McCumber model). Analysis in terms of this equation leads to a highly coherent sample response where the specimen can be described by a single degree of freedom. Our observations are also discussed in light of recent theories of CDW pinning and dynamics.

Nonlinear and frequency-dependent transport phenomena in low-dimensional conductors

Nonlinear and frequency-dependent electrical conductivity is more a rule than an exception in materials with highly anisotropic electronic structure. Disorder leads to localization of the electronic wave functions, and the temperature-( T), electric field-( E), and frequency (ω)-dependent transport are due to random transfer rates between localized single particle states, a process fundamentally different from band transport. Interactions lead to collective modes, represented by a periodic modulation of the charge or spin density. The charge density wave (CDW) mode is pinned by impurities, but for small pinning forces, it can be depinned by moderate electric fields, leading to nonlinear conductivity due to a sliding CDW. Both classical and quantum models account for the field and frequency dependent response; they also describe current oscillation phenomena and effects which arise when both dc and ac excitations are applied. For strong pinning the collective mode cannot be depinned at small electric field strengths, but nonlinear (soliton) excitations of the collective modes may be responsible for the nonlinear conductivity observed. In all these cases field-and frequency-dependent transport is strongly related. This feature is reproduced by various models, and therefore a detailed study of σ( T, E,ω) is called for to distinguish between the various sources of novel transport phenomena in these new types of solids.

Current Oscillation Phenomena in Nonohmic ZnO Ceramics

Current Oscillation Phenomena in Nonohmic ZnO Ceramics

Formation of the Stationary Domain under the Strong Magnetic Field in CdS

The effect of a transverse magnetic field on the acoustoelectric effect in semiconducting CdS is investigated. The ultrasonic amplification factor increases with the magnetic field strength. The formation of the stationary domain by the addition of a magnetic field gives a damping effect upon the current oscillation phenomenon. For the current oscillation being damped by the increase of the magnetic field, it may be considered as the geometrical effect of the crystal plays a lot of role in the nucleation of the stationary domain.

Carrier transport and current oscillation in Bi12GeO20 in the ``relaxation semiconductor regime''

New transport and low-frequency current oscillation phenomena have been observed in a photoexcited Bi12GeO20 single crystal in the temperature range 77–110 K. These phenomena can be explained on the basis of the relaxation semiconductor regime where the dielectric relaxation time exceeds the minority-carrier lifetime. Experiments strongly suggest that sublinear dependencies in the current-voltage characteristic and the current oscillation in the higher bias range are general features of the relaxation regime.