Capacitance Voltage Research Articles

Intelligent Solar PV Grid Connected and Standalone UPQC for EV Charging Station Load

The insertion of renewable energy sources into the grid, as well as the development of power electronics technology to regulate loads that are not linear, had an impact on power quality (PQ). This study focuses on the PQ enhancement of grid-connected and standalone solar PV systems (SPVS) with battery energy storage device (BESD) for the Electric vehicle (EV) charging station (EVCS) load in addition to the local load. Here, a hybrid control strategy that uses both the superior qualities of the sliding mode controller (SMC) and the fuzzy logic controller (FLC) is suggested for the unified power quality conditioner (UPQC's) shunt filter. It's major goal is to achieve steady DC capacitance voltage (SVDC) during load (like EVCS, non linear balanced/unbalanced etc.) and irradiation variations, diminish of total harmonic distortion (THD) in source current and load voltage, and mitigate sag, swell disturbances, and source voltage unbalances. The created model's performance is assessed using two scenarios (grid and island) under four case studies with varying combinations of loads and grid voltage circumstances. However, to establish the superiority of the proposed technology, comparative research with standard technologies such as proportional integral controller (PIC) and SMC controllers is required. THD is reduced by the proposed method to 2.25 %, 2.36 %, and 1.71 %, It is inferior to the current approaches found in the survey.

Influence of plasma breakdown on pores and fractures in bituminous coal: A new characterization method of breakdown energy

Plasma technology has a potential application prospect in the field of coal seam permeability enhancement. However, the relationship between plasma breakdown energy and the improvement effect of coal pores and fractures is lack of in-depth research. This study proposed a novel method for characterizing the plasma breakdown energy, and three testing techniques, namely, particle size distribution, mercury intrusion porosimetry (MIP) and low-field nuclear magnetic resonance (NMR), were utilized to examine the pore and fracture distribution of coal samples obtained from Jiulong Mine under varying breakdown energy conditions. The influence between breakdown energy and pores and fractures development is revealed. The results show that: (1) The degree of coal sample fragmentation increases with the increase of plasma breakdown energy. (2) Different breakdown energy induced the development of different pore distribution patterns. At lower breakdown energy, an increase in the volume of macropores dominates. As the breakdown energy increases, there is a rapid increase in the volume of mesopores, a slight increase in minipores, and the least increase in micropores, indicating that plasma treatment primarily improves pores with diameters greater than 100 nm. The test results of the three techniques were mutually verified. (3) Compared with capacitance energy and voltage, the effective breakdown energy obtained by the integral method has a more significant linear relationship with the particle size distribution, total pore volume, and average pore diameter, indicating that the effective breakdown energy is more suitable for characterizing the crushing effect of plasma. During the plasma breakdown process, the expansion stress and thermal stress formed by the effective breakdown energy exceeded the local tensile strength of coal, leading to the generation and development of pores and fractures, which in turn led to the rupture of the coal body. The larger the breakdown energy, the larger the crushing circle formed around the ion channel, the finer the coal is crushed, and the more pore fractures are developed. These nascent pores and fractures provide channels for gas transport, which is extremely favorable for coal mine gas extraction. The research conclusions provide theoretical support for the application of plasma in fracturing and permeability enhancement in coal seams.

A Sliding-Mode Current Decoupling Control Strategy for an Active Power Filter Based on an Internal Model

With the ongoing development of electronic power technologies, harmonic pollution in the power grid has become a topic of great concern. This study takes a substation as its background. The safe and steady operation of the station’s equipment was impacted by a 10 kV bus’s harmonic current, which was significantly higher than the required amount. We propose a sliding-mode current decoupling control strategy based on an internal model to address the problems of complex harmonic current detection and distortion in the power supply current when there are nonlinear load changes in hybrid active power filters. By establishing a mathematical model for a HAPF, our proposed strategy can be used for inner current loops with the goal of stability, decoupling control between the d- and q-axes, fast-tracking harmonic reference currents, and optimizing the controller by enhancing the system’s anti-jamming performance to ensure that the system operates stably when line parameter ingressions or step changes in the load demand occur. The outer voltage loop uses the fractional-order sliding-mode control method to keep the capacitor voltage smooth and to dynamically adjust when the load changes suddenly. Finally, this filter is compared with a filter controlled by a PI in MATLAB/Simulink, and the feasibility and effectiveness of the proposed control strategy are verified based on a diode-embedded three-level parallel-type HAPF platform. The simulation and experimental results show that our sliding-mode current decoupling control strategy based on the internal mode is characterized by simplicity, stability, and fast responses.

A comparison electrical characteristics of the Au/(pure-PVA)/n-Si and Au/(CdTe doped-PVA)/n-Si (MPS) type Schottky structures using I–V and C–V measurements

In this study, both the Au/(pure-PVA)/n-Si (MPS-1) and Au/(CdTe:PVA)/n-Si (MPS-2) type Schottky diodes (SDs) were fabricated onto the same n-Si wafer in same conditions. After that, their electrical parameters were obtained from the current–voltage (I–V) and capacitance–voltage (C–V) measurements and compared to each other to determine the effect (CdTe:PVA) interlayer on the performance of MPS type SD. The saturation current (Is), ideality factor (n), rectification ratio (RR = Ifor./Irev.), zero-bias barrier height (ΦBo), and series/shunt resistances (Rs, Rsh) were derived utilizing I–V data. The values of Io, n, and ΦBo were found as 9.13 × 10–7 A, 11.07, 0.63 eV for MPS1 and 1.54 × 10–10 A, 3.97, 0.85 eV for MPS2, respectively. The C−2–V graphs were drawn for 0.7 MHz to obtain the doping concentration of donor atoms (ND), Fermi energy (EF), BH/(ΦB(C–V)), depletion layer width (WD), and maximum electric field (Em). The Nss − (Ec − Ess) profile for two SDs was produced from the I–V data by considering the voltage dependence of n and BH. The values of surface states (Nss) were changed between 4.8 × 1013 and 1.7 × 1014 eV−1 cm−2 for MPS1 and 5 × 1012 and 1.15 × 1013 eV−1 cm−2 for MPS2, respectively. All experimental results show that the (CdTe:PVA) interlayer significantly improved the quality of the MS type SDs rather than (pure-PVA) in terms of lower values of leakage/saturation current, n, Nss, and higher RR, BH, and Rsh when compared (pure-PVA) interlayer. The (CdTe:PVA) interlayer may be used instead of the conventional interlayer in the future.

Development of ferroelectricity with crystallographic phase transformation in Hf0.5Zr0.5O2 thin films upon initial stimulation of an electric field exceeding the coercive field

This study demonstrates a drastic transformation of ferroelectricity and crystallographic phase in Hf0.5Zr0.5O2 (HZO) thin films through the first stimulation of an electric field larger than the coercive field in metal-ferroelectric-metal (MFM) capacitors. Initially, capacitance–voltage (C–V) measurements in fresh MFM capacitors with voltage sweep smaller than the coercive field indicated constant capacitance value without hysteresis. Applying the electric field exceeding the coercive field subsequently, the C–V behavior changed to a typical dual-peak ferroelectric feature in positive and negative sweeps. X-ray diffraction analysis of the HZO layers before and after a single electric-field application revealed small-angle shifts in diffraction peaks, confirming a crystallographic phase transformation induced by the single electric-field stimulation exceeding the coercive field. These results suggest a possibility that the first electric field apply initiates development of ferroelectric phase transformation from a non-ferroelectric phase.

Effect of Ultra‐Thin AlGaN Regrown Layer on the Electrical Properties of ZrO2/AlGaN/GaN Structures

Effects of the ultrathin 1 nm thick AlGaN regrown layer before gate insulator deposition on the performance of ZrO2/AlGaN/GaN metal‐insulator‐semiconductor (MIS) structures are investigated. In comparison with the reference ZrO2/AlGaN/GaN MIS high‐electron‐mobility transistors (MIS‐HEMTs), MIS‐HEMTs with AlGaN regrown layer exhibit increased maximum drain current (>1050 mA mm−1) and broader full‐width at half maximum (FWHM) of transconductance profile (11 V). Moreover, the gate leakage current in the forward direction is reduced by about four orders of magnitude while the hysteresis of the transfer curves is cut‐down to more than 40%. Compared with the control MIS‐capacitors (MIS‐caps), MIS‐caps with regrowth show highly evident sudden increase in capacitance known as “spill‐over” in the capacitance–voltage (C–V) profiles, suggesting improved ZrO2/AlGaN interfaces. Extracted electron states from the C–V profiles, reveal 6 times to 14 times reduction of interface states density within 0.2 to 0.8 eV from the AlGaN conduction band edge. Using photo‐assisted C–V measurements, the near mid‐gap electron states density of MIS‐caps is extracted with regrowth to be at least three times less than those of reference MIS‐caps. Findings in this work are very similar to those recently reported Al2O3/regrown‐AlGaN interfaces, suggesting that the regrowth technique could be universal in reducing electron states along insulator/AlGaN interfaces.

Photoelectrical characterization of heavily doped p-SiC Schottky contacts

The availability of photoelectrical characterizations of heavily Al-doped p-SiC Schottky contacts was clarified. We conducted a systematic study of four samples with different Al doping concentrations from 1 × 1018 to 5 × 1019 cm−3. Although the current–voltage (I–V) characteristics had lost rectification, reasonable Schottky barrier height (qϕ B) values were obtained up to 1 × 1019 cm−3 by capacitance voltage, photo response, and scanning internal photoemission microscopy (SIPM) measurements. In the two-dimensional characterization by SIPM, large photocurrent spots corresponding with low qϕ B were observed in an average density of 103 to 104 cm−2. However, except for these spots, a high uniformity of about 2 meV standard deviation was obtained for qϕ B over the entire observed electrodes. These results indicate that SIPM is able to characterize the inhomogeneity of heavily doped p-SiC contacts with very leaky I–V characteristics.

Pt/GaN Schottky Barrier Height Lowering by Incorporated Hydrogen

Changes in the hydrogen-induced Schottky barrier height (Φ B) of Pt/GaN rectifiers fabricated on free-standing GaN substrates were investigated using current–voltage, capacitance–voltage, impedance spectroscopy, and current–time measurements. Ambient hydrogen lowered the Φ B and reduced the resistance of the semiconductor space–charge region while only weakly affecting the ideality factor, carrier concentration, and capacitance of the semiconductor space–charge region. The changes in the Φ B were reversible; specifically, the decrease in Φ B upon hydrogen exposure occurred quickly, but the recovery was slow. The results also showed that exposure to dry air and/or the application of a reverse bias to the Schottky electrodes accelerated the reversion compared with the case without the applied bias. The former case resulted in fast reversion because of the catalytic effect of Pt. The latter case, by contrast, suggested that hydrogen was incorporated into the Pt/GaN interface oxides as positive mobile charges. Moreover, both exposure to dry air and the application of a reverse bias increased the Φ B of an as-loaded sample from 0.91 to 1.07 eV, revealing that the Φ B of Pt/GaN rectifiers was kept lower as a result of hydrogen incorporation that likely occurred during device processing and/or storage.

Pulsed plasma thruster exhaust reconstruction

The transient exhaust of an ablative pulsed plasma thruster is characterized experimentally for three capacitances and three discharge voltages, for discharge energies below 11 J. A novel analysis technique is introduced, which reconstructs the exhaust as a superposition of different Maxwellian-like ion groups. Each ion group is characterized by its own mean velocity, thermal spread, initial density, generation time and divergence rate. The time series of three probes working in the ion saturation regime are used to determine the model parameters by least-squares fitting. This approach allows a higher level of accuracy and insight than time-of-flight analysis based on direct feature correlation alone. A good fit of the main part of the discharge time series is achieved with just three ion groups, with mean velocities ranging in 50–70, 30–45 and 10–25 km s−1 respectively. Each ion group differs in the lateral divergence rate and axial thermal spread, and potentially corresponds with a different charge/mass ratio and/or creation time. Some trends with bank capacitance and discharge voltage are identified and discussed.

An ANN-Based Output-Error-Driven Incremental Model Predictive Control for Buck Converter Against Parameter Variations

DC/DC buck converters have been widely applied in the power processing of distributed energy resources (DERs) penetrated DC microgrid. Model predictive control (MPC) provides optimal control for the buck converter, but it often requires multiple sensors or complex observers to realize zero-steady-state-error control against parameter variations. An output-error-driven incremental MPC (OEDIMPC) for buck converter is proposed in this paper. Different from the traditional concept of calculating the optimal duty cycle, the proposed MPC calculates the optimal rate of change of the duty cycle by using a reduced-state output-error-driven prediction model. As a result, the OEDIMPC achieves zero-steady-state-error control against parameter variations, including load value, input voltage, output inductor, and output capacitor, with significantly improved dynamic performance and minimal sensor and observer requirements Besides, small- and large-signal analyzes are used to study the stability boundary of the OEDIMPC under parameter variations, and a shallow layer artificial neural network (ANN) is utilized to realize the OEDIMPC on the hardware. The proposed technique has been evaluated experimentally on a buck converter with resistor load and constant power load (CPL), confirming its effectiveness.

Low-cost pyrolysis of biomass-derived nitrogen-doped porous carbon: Chlorella vulgaris replaces melamine as a nitrogen source.

Porous carbon generated from biomass has a rich pore structure, is inexpensive, and has a lot of promise for use as a carbon material for energy storage devices. In this work, nitrogen-doped porous carbon was prepared by co-pyrolysis using bagasse as the precursor and chlorella as the nitrogen source. ZnCl2 acts as both an activator and a nitrogen fixer during activation to generate pores and reduce nitrogen loss. The thermal weight loss experiments showed that the pyrolysis temperatures of bagasse and chlorella overlap, which created the possibility for the synthesis of nitrogen-rich biochar. The optimum sample (ZBC@C-5) possessed a surface area of 1508 m2g-1 with abundant nitrogen-containing functional groups. ZBC@C-5 in the three-electrode system exhibited 244.1F/g at 0.5A/g, which was extremely close to ZBC@M made with melamine as the nitrogen source. This provides new opportunities for the use of low-cost nitrogen sources. Furthermore, the devices exhibit better voltage retention (39%) and capacitance retention (96.3%). The goal of this research is to find a low cost, and effective method for creating nitrogen-doped porous carbon materials with better electrochemical performance for highly valuable applications using bagasse and chlorella.

Hardware-in-the-loop setup for enhanced modular multi-level converter with reduced circulating currents

Owing to its essential features, such as modularity and exceptional power quality, the modular multilevel converter (MMC) emerges as the optimal converter topology for high-voltage direct current (HVDC) applications. Traditionally, MMCs are controlled through a method called nearest level modulation (NLM), which generates N+1 AC output voltages, where N represents the number of sub modules (SMs) per arm. In this paper, we introduce a modified NLM technique designed to yield 2N+1 and 4N+1 levels, with a focus on efficiently controlling internal dynamics. The proposed MMC is evaluated using a hardware-in-the-loop (HIL) environment to obtain real-time simulation outcomes. This MMC topology demonstrates a reduction in circulating currents and capacitor voltage ripple.

A Switched-Capacitor Multilevel Inverter With Modified Pulsewidth Modulation and Active DC-Link Capacitor Voltage Balancing

Although switched-capacitor (SC) multilevel inverters (MLIs) offer self-voltage balancing of flying capacitors and voltage gain higher than unity, the advantages come at the cost of high current stress and power loss in the SC circuit and DC source. Moreover, the voltage balancing is often restricted to a limited range of modulation index. Another problem of MLIs with neutral-point clamped (NPC) front end is with DC-link capacitor voltage balancing under unbalanced load conditions, imploring sensor-based closed-loop control. This paper proposes a unity gain five-level active-NPC SC-MLI with inrush charging current attenuation and actively balanced DC-link capacitor voltages under all load conditions and over the entire range of modulation index and power factor. The modified pulse-width modulation results in most switches operating at a low switching frequency, minimizing switching losses in the SC circuit. The proposed MLI attains a maximum efficiency of 98.04% at an output power of 510 W. Experiments on a 2 kVA laboratory prototype validate the theoretical analysis. Results from transformerless grid-connected solar PV system show that the proposed MLI can inject power into the grid with a unity power factor under conditions of varying irradiance and provide the grid with reactive power as well.

Topology and Hybrid Modulation of Six-Level Switched-Capacitor HC Converter With Improved DC-Link Capacitor Voltage Balancing

Topology and Hybrid Modulation of Six-Level Switched-Capacitor HC Converter With Improved DC-Link Capacitor Voltage Balancing

Impact of TiO2, ZnO, and Methylene Blue Doping on the Dielectric anisotropy of planar 8CB nematic liquid crystal

In this study, the impact on the dielectric properties of 8CB with the dispersion of TiO2, ZnO, and methylene blue (0% to 5%) is examined. Employing capacitance–voltage (C–V) measurements across frequencies ranging from 10 kHz to 2 MHz, we explore the combined effects of dispersed photoactive nanoparticles and mono/polymeric materials like MB. Our investigation provides novel insights into the nuanced variations induced by transition-metal oxide loaded 8CB, highlighting the role of their oxidation states, and elucidates the influence of larger photoactive monomers on 8CB’s dielectric polarizability. The study found that the dielectric anisotropy was strongly influenced by frequency and doping, changing sign at a critical frequency. Our work represents the first comparative analysis incorporating these oxides alongside photoactive materials like MB.

Reduced sensor Lyapunov‐based control for active power decoupling circuit

SummaryThe double‐line frequency ripple power exists inherently in single‐phase power converters. To address this problem, active power decoupling (APD) technique is widely used. It diverts the ripple power into a small energy storage element by introducing passive and active power devices. This inevitably involves more voltage and current sensors for corresponding control, which raises the cost while decreasing reliability and power density. In this paper, a Lyapunov‐based methodology is proposed to achieve APD control without adding any sensor. According to the designed controller laws, the practical decoupling capacitor voltage will converge to its reference. The decoupling voltage reference is given by taking into account buffering the double‐line frequency ripple power. Afterward, the robustness against parameter perturbations of the proposed method is discussed. Finally, the experimental results verify the feasibility of the proposed control strategy.

Model Predictive Control for Cascaded H-Bridge PV Inverter with Capacitor Voltage Balance

We designed an improved direct-current capacitor voltage balancing control model predictive control (MPC)for single-phase cascaded H-bridge multilevel photovoltaic (PV) inverters. Compared with conventional voltage balancing control methods, the method proposed could make the PV strings of each submodule operate at their maximum power point by independent capacitor voltage control. Besides, the predicted and reference value of the grid-connected current was obtained according to the maximum power output of the maximum power point tracking. A cost function was constructed to achieve the high-precision grid-connected control of the CHB inverter. Finally, the effectiveness of the proposed control method was verified through a semi-physical simulation platform with three submodules.

The impact of sputtering pressure on the TiO2/p-Si interface and its implications for hole-blocking and photodetection

One convenient approach to minimize the surface recombination loss in Si is to passivate the surface dangling bonds by depositing a thin TiO2 layer on the bulk Si. Besides, the p-Si/TiO2 interface can initiate hole-blocking and facilitate efficient electron transport through the TiO2 layer; thereby, promoting the extraction of electrons for efficient onward utilization. In this context, the current investigation involves studying how the Ti3+ donor states, produced by deliberately introducing O-vacancies controlled by changing the plasma pressure in the RF-magnetron sputtering chamber during the growth of the TiO2 thin films, can change the material's Fermi level and work function and modify the band bending and band offset as well as the fixed oxide charge density in the p-Si/TiO2 heterojunction interface. The TiO2/p-Si interface has been studied through capacitance-voltage (C-V) analysis to determine the interface parameters such as fixed oxide charge, the density of interface traps, and the dielectric constant of TiO2. The studied hole-blocking property of the interface has been correlated to the photoresponsivity of the metal-oxide-semiconductor (MOS) structure. The MOS device fabricated at a pressure of 30 mTorr displays a large saturation current (15.95 μA cm–2) when subjected to a positive gate bias, facilitated by the relatively low conduction band offset (ΔEC ∼0.20 eV), significant positive fixed oxide charge (+1.18 ×1011 cm–2) and the interface trap density (1.03 ×1012 cm–2), which enhanced the transport of minority carrier electrons from the p-Si to the metal, resulting in a good photo responsivity ∼0.158 AW–1 and photo gain of ∼37.5 under white light illumination. Optimum hole-blocking and surface passivation characteristics of the TiO2/p-Si interface together may facilitate fabricating improved heterojunction Si solar cells.

Simulation of grid/standalone solar energy supplied reduced switch converter with optimal fuzzy logic controller using golden BallAlgorithm

This article presents the utilization of a shunt active power filter (SHAPF) in combination with an Energy Storage System (ESS) and a Solar Energy System (SES). Voltage source converters (VSC) are connected in parallel to a direct current (DC) bus. The membership function (MSF) of fuzzy logic controller (FLC) for the shunt control system is optimally adjusted using the golden balloptimization algorithm (GBOA). The present effort aims to achieve the following primary objectives: 1) Quick implementation to stabilize the voltage of the DC Link capacitor (DCLCV); 2) Mitigation of harmonics and improvement of power factor (PF); 3) Satisfactory performance under load as well as solar power varying conditions. The effectiveness of the optimally designed controller is evaluated by studying four test scenarios with grid and standalone conditions. The results are then compared to the existing sliding mode (SMC) and fuzzy logic controllers (FLC).

A cleaner lignin-induced 3D porous MXenes hybrid electrode with enlarged voltage and high capacitance retention

Conventional supercapacitors face narrow voltage and an inevitable reduction in capacitance retention during operation, significantly preventing its further commercial application. So, biomass-derived composite materials have attracted intensive attention, especially for pseudocapacitive supercapacitors. Herein, a high-end utilization strategy of lignin to induce a 3D porous layered MXenes/graphene oxide hybrid electrode (LGM2-80) and homologous gel electrolytes with low interface resistance for lignin-derived supercapacitors is demonstrated by a simple hydrothermal method. A more uniform distribution and smaller nanospheres ≈<10 nm of lignin prevent the restacking and increase the interlayer spacing of graphene oxide, also play an adhesive role between graphene oxide and MXene, guaranteeing the maximization of the pseudocapacitance effect between lignin and MXene. Consequently, the LGM2-80 electrode showed a wide operating potential (−0.7∼1.0 V), breaking through the bottleneck of MXene-derived devices with limited working voltage (typically≤0.6 V). Furthermore, the lignin-derived symmetric quasi-solid-state supercapacitor (LGM2-80//lignin gel//LGM2-80) possesses an excellent capacitance retention rate of 149 % at 5,000 cycles, which is far exceeding the current reported supercapacitors. This innovative use of lignin opens up new perspectives for ultra-voltage and ultra-high capacitance retention of advanced supercapacitors.