AC Characteristics Research Articles

Fault interaction analysis approach for hybrid AC/DC power grids

Heretofore, the comprehensive fault analysis approach for AC/DC hybrid grids has not been sufficiently investigated. Inspired by the conventional symmetrical components method, a novel “sequence component network” model based on the mapping relation is proposed to study the characteristics of AC (DC) side after DC-side (AC-side) faults in AC/DC hybrid grids. Subsequently, the AC-side electrical characteristic after DC-side faults was discussed employing the “sequence component network” model. Finally, taking into account the influence of different grounding modes, a DC-type integration system model of PV stations was established in PSCAD/EMTDC to verify the proposed approach.

Data-Driven Optimization of Transmission Section Limits and Their Adaptability for New Power Systems With High Penetration of Renewable Energy

In traditional power systems, the transmission section limits are often set to predetermined values according to the typical peak-to-valley demand modes, which may be difficult to adapt to the complex and diverse operation modes of the new power systems with high penetration of renewable energy, and it cannot consider the coupling characteristics of AC and DC transmission sections also. In order to make better use of the efficiency of the transmission sections, a mathematical model for optimizing the adaptability of the transmission section limit is firstly proposed, in which a data-driven typical demand mode extraction method based on K-means clustering is proposed according to the load forecast, renewable energy forecast and market transaction data. Then, the adaptability assessment of the section limit and the transmission requirements are carried out. Finally, the power perturbation method is used to calculate the influence factor matrix of associated transmission section limit and stability margin of its dominant fault. And the influence factors are optimized according to section limit adaptability and stability margin influence, and the best adaptable limit of the associated transmission sections are obtained. The calculation and optimization results of the actual case of the interconnection corridor between Xinjiang and the northwest main power system of China verify the effectiveness and practicability of the proposed limit optimization model, which is able to improve the flexibility and adaptability of the actual power system operation.

A Second Harmonic Current Suppressing Method Based on Negative-Order Capacitor

In microgrid system, current in dc bus may contain a lot of undesired low-order harmonics when converters are employed, especially the second harmonic current (SHC). To address the issue, this article proposes a method based on fractional-order capacitor (FOC) to suppress the SHC. The FOC, of which the order <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</i> is “−1,” has the same characteristics of dc blocking and ac conducting as conventional capacitor; while it can resonate with a conventional capacitor like an inductor, which could be called a negative-order capacitor (NOC) as well. The proposed circuit has good SHC suppression performance, faster dynamic response, and soft switching realization. It parallels on the dc side of an inverter instead of the large bus capacitor, increasing power density and reducing design cost and loss.The secondary power will only circuit between the ac side of inverter and the NOC circuit. In addition, the NOC circuit can adjust zero impedance to specific harmonics; so it can be expanded to suppress harmonic current at other frequencies in the system. The simulation and experimental results are presented to validate the feasibility of the proposed method.

Back-Gate Lumped Resistance Effect on AC Characteristics of FD-SOI MOSFET

In this work, the impact of a large lumped resistor connected to the back-gate (B-G) of an fully depleted silicon-on-insulator (FD-SOI) transistor is studied. A related transition in the frequency responses of output conductance and capacitance is evidenced experimentally by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters measurements in a large frequency range up to 40 GHz. However, present compact model does not correctly reproduce the B-G/substrate network behavior. This calls for a model accounting for both n-well and substrate networks. A small-signal equivalent circuit including distributed elements is thus proposed and compared with experimental results.

An algorithm for contingency analysis of the AC-DC networks using modified Z-bus technique

The steady state Contingency Analysis (CA) utilizes non-iterative distribution-factors (DFs) based linear estimation method of current-redistribution, to deliver approximate solutions in a shorter timeframe, which is favored over recurrent usage of iterative power flow-based non-linear techniques. However, the established principles of conventional DF-based CA cannot be directly implemented on burgeoning AC-DC networks. The DFs obtained from single unified Z-bus constructed for the entire AC-DC network leads to erroneous estimation of current redistribution post any contingency event. The reason being unified Z-bus built overlooked the characteristics of AC and DC lines. As a paradigm change toward a co-existing AC-DC network emerges, an adequate framework for understanding contingencies within such a network becomes critical. We present a quick non-iterative DF-based approach for the CA of any AC-DC network in this research by merging the use of separate AC and DC impedance matrices while accounting for the intertwined implications of the AC and DC networks. The interlinking converters (ILCs) are simulated using a reactive current bypassing approach. The proposed CA method is capable of handling contingencies occurring within ILCs, AC and the DC networks. The ETAP simulations and the Newton-Raphson (NR) technique for the AC-DC network have been utilized to corroborate the results.

Improved 4H–SiC MESFET with bulgy channel

This paper proposes an improved 4H–SiC metal semiconductor field effect transistor with a bulgy channel (BC-MESFET) whose gate-source and gate-drain drift regions are shifted downward 0.1 μm relative to the channel below the gate. By introducing recesses at both ends of the metal gate, both the DC and AC characteristics of the structure have been greatly improved. The simulation results show that the saturation current of BC-MESFET is 30% higher than that of DR-MESFET, and the breakdown voltage is 78% higher. Therefore, the maximum output power density has a significant increase of 137%. In terms of RF, since the gate-source capacitance of the BC-MESFET structure is 31% lower than that of the DR-MESFET, its characteristic frequency is also improved by 18%. In this paper, aiming at high power added efficiency (PAE), the bump height H of the buffer layer under the lower gate is optimized, and a structure with 25% higher PAE than DR-MESFET is obtained.

Modified average‐value model for high‐performance fault transient simulation of AC‐DC hybrid power networks

Due to the complicated transients and the possibility of transition from a minor fault in AC subsystems to a severe blocking event of a high-voltage direct–current (HVDC) transmission line, the study of AC-DC hybrid power systems requires both efficient and accurate electromagnetic transient (EMT) simulation. However, the computational efficiency of such simulations is restrained by the switching events when detailed models of line-commutated converters (LCCs) are used. Recently the average-value modelling technique has been developed for accelerating the simulation while still accurately capturing the transient characteristics of line-commutated AC–DC converters. This study presents the application of the average-value model in the modelling of the LCC-HVDC system and gives a further discussion about the deficiency of the model. A modified interface and the corresponding soft-switching technique are proposed for enhancing the simulation performance of the LCC-HVDC model in the transition between normal and faulty operation. The model is tested on a series of LCC-based systems including a hybrid power system with four LCC-HVDC lines to verify its efficiency and accuracy. The results indicate that the developed model can accurately predict the transients of the system both in symmetrical and asymmetrical operation while being computationally efficient.

Tunnel Magnetoresistance Sensor with AC Modulation and Impedance Compensation for Ultra-Weak Magnetic Field Measurement.

Tunnel magnetoresistance (TMR) is a kind of magnetic sensor with the advantages of low cost and high sensitivity. For ultra-weak and low-frequency magnetic field measurement, the TMR sensor is affected by the 1/f noise. This paper proposes an AC modulation method with impedance compensation to improve the performance. The DC and AC characteristics of the sensors were measured and are presented here. It was found that both the equivalent resistance and capacitor of the sensors are affected by the external magnetic field. The TMR sensors are connected as a push–pull bridge circuit to measure the magnetic field. To reduce the common-mode noise, two similar bridge circuits form a magnetic gradiometer. Experimental results show that the sensor’s sensitivity in the low-frequency range is obviously improved by the modulation and impedance compensation. The signal-to-noise ratio of the sensor at 1 Hz was increased about 25.3 dB by the AC modulation, impedance compensation, and gradiometer measurement setup. In addition, the sensitivity of the sensor was improved from 165.2 to 222.1 mV/V/mT. Ultra-weak magnetic signals, namely magnetocardiography signals of two human bodies, were measured by the sensor in an unshielded environment. It was seen that the R peak of MCG can be clearly visualized from the recorded signal.

A Novel AC/DC Power Flow: HVDC-LCC/VSC Inclusion Into the PFPD Bus Admittance Matrix

In this paper, the matrix algorithm PFPD is generalized in order to compute the power flow solution of real and large AC/DC transmission networks. In particular, it is demonstrated that the HVDC-VSC/LCC links can be seen from the AC power systems as PV/PQ constraints, which englobe both the AC and DC characteristics of the HVDC links. The proposed analytical formulation to assess the PV/PQ constraints is valid for any other numerical methods ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.,</i> Newton-Raphson and derived, Gauss-Seidel, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">etc.</i> ). Furthermore, an iterative procedure for estimating the reactive power absorption of HVDC-LCC links from the power system is proposed. In order to validate the algorithm, solution comparisons with the commercial software DIgSILENT PowerFactoy are presented. This validation procedure shows that the algorithm can analyse large and real HVAC/HVDC networks ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> , the Italian transmission one with its five HVDC links). Therefore, the conciseness, accuracy and performances of PFPD for studying real and large AC/DC power systems is confirmed.

Simulation Analysis of Arc Interruption Characteristics in Disconnector

Wind and solar energy are examples of clean energy that are widely developed and utilized in order to achieve the goal of carbon neutrality. Higher requirements for the safety and reliability of the power grid are put forward after they are connected to it. In the case of disconnectors, as the power system’s protection equipment, their arc interruption characteristics are closely tied to the safety and reliability of the power system. In addition, a disconnector is required to be able to break the DC arc in the photovoltaic power generation system. Therefore, this paper focuses on the arc evolution characteristics in disconnectors. A magnetohydrodynamics (MHD) model of disconnectors was built. In this model, not only are the coupling of the electromagnetic field and the airflow field considered, but also the characteristics of the external circuit. Therefore, not only can arc evolution characteristics be obtained through this simulation model, but the breaking performance will also be directly obtained. The temperature, pressure and velocity distribution are obtained to analyze the evolution process. The curve of current versus time is calculated to analyze the breaking performance. The evolution characteristics of AC and DC arcs in the disconnector are analyzed by calculation and comparison. This provides theoretical guidance for the optimal design of DC disconnectors through simulation analysis.

Monolithic Si-Based AlGaN/GaN MIS-HEMTs Comparator and Its High Temperature Characteristics

Monolithic GaN High Electron Mobility Transistor (HEMT)-integrated circuits are a promising application of wide band-gap materials. To date, most GaN-based devices behave as NMOS-like transistors. As only NMOS GaN HEMT is currently commercially available, its control circuit requires special design if monolithic integration is desired. This article analyzes the schematics of a GaN-based comparator, and three comparator structures are compared through ADS simulation. The optimal structure with the bootstrapped technique is fabricated based on AlGaN/GaN Metal–Insulator–Semiconductor (MIS) HEMT with the recessed gate method. The comparator has excellent static characteristics when the reference voltage increases from 3 V to 8 V. Dynamic waveforms from 10 kHz to 1 MHz are also obtained. High-temperature tests from 25 °C to 250 °C are applied upon both DC and AC characteristics. The mechanisms of instability issues are explained under dynamic working condition. The results prove that the comparator can be used in the state-of-art mixed-signal circuits, demonstrating the potential for the monolithic all-GaN integrated circuits.

Charged Ferroelectric Domain Walls for Deterministic ac Signal Control at the Nanoscale.

The direct current (dc) conductivity and emergent functionalities at ferroelectric domain walls are closely linked to the local polarization charges. Depending on the charge state, the walls can exhibit unusual dc conduction ranging from insulating to metallic-like, which is leveraged in domain-wall-based memory, multilevel data storage, and synaptic devices. In contrast to the functional dc behaviors at charged walls, their response to alternating currents (ac) remains to be resolved. Here, we reveal ac characteristics at positively and negatively charged walls in ErMnO3, distinctly different from the response of the surrounding domains. By combining voltage-dependent spectroscopic measurements on macroscopic and local scales, we demonstrate a pronounced nonlinear response at the electrode-wall junction, which correlates with the domain-wall charge state. The dependence on the ac drive voltage enables reversible switching between uni- and bipolar output signals, providing conceptually new opportunities for the application of charged walls as functional nanoelements in ac circuitry.

Effect of High Temperature Storage on AC Characteristics of Polymer Tantalum Capacitors

Abstract Replacement of MnO2 with conductive polymers as cathode materials in chip tantalum capacitors allows for a substantial reduction of the equivalent series resistance (ESR), improvement of frequency characteristics, and elimination of the possibility of ignition during failures. One of the drawbacks of chip polymer tantalum capacitors (CPTCs) is a relatively poor long-term stability at high temperatures. In this work, variations of capacitance, dissipation factor, and ESR in different types of capacitors including automotive grade parts from three manufacturers have been monitored during storage at temperatures from 100°C to 175°C for up to 18,000 h. Results show that ESR is the most and capacitance the least sensitive to degradation parameter. Times to parametric failures have been simulated using a Weibull-Arrhenius model that allowed for assessments of activation energies of the degradation and prediction of times to failure at the use temperature. Degradation of CPTCs was explained by thermo-oxidative processes in conductive polymers that result in exponential increasing of the resistivity with time of ageing. This process starts after a certain incubation period that depends on packaging materials and design and corresponds to the time that is necessary to form delamination between the encapsulating molding compound and lead frame. The effectiveness of the existing qualification procedures to assure stable operation of CPTCs is discussed.

InGaAs self-switching diode-based THz bridge rectifier

Here, an In0.53Ga0.47As-based self-switching diode bridge rectifier (SSDBR) is presented utilizing Silvaco TCAD computer simulations. A zero-bias self-switching diode exhibiting nonlinear current–voltage characteristics has been utilized for the device design. The output current, threshold voltage and maximum operating frequency of the device can be easily tuned by adjusting the channel width and length of the SSD, whereas the properties of conventional rectifiers are typically material-dependent. The AC and DC characteristics of the SSDBR are presented, demonstrating full wave rectification up to frequencies of 0.240 THz with a noise-equivalent power of 39.90 pW (Hz1/2)−1. Furthermore, the simulated results are validated by developing an analytical model for an InGaAs-based SSDBR.

A Physics-based Transient Simulation and Modeling Method for Wide-frequency Electrical Overstress Including ESD

Circuits design that meets various IEC electrical overstress (EOS) standards is still a challenge, for that different kinds of EOS are at different frequency bands. In this paper, a physics-based transient simulation and modeling method is proposed, which can simulate wide-frequency EOS including electrostatic discharge (ESD) and AC characteristics. In this method, the physical model is used to characterize the nonlinear semiconductor devices in the finite-difference time-domain (FDTD)-SPICE co-simulation. Moreover, the modeling and physical parameters extraction method of the ESD protect devices, the transient voltage suppressor diode, is demonstrated. Taking an EOS protection circuit for example, it is modeled and simulated by the proposed method. Moreover, the circuit is also simulated by the widely-used System-Efficient ESD Design (SEED) method, in which the TVS diode is modeled based on 100 ns Transmission Line Pulse (TLP) measurements. The experiments show that both this method and SEED method can characterize the IEC system-level ESD behaviors well. However, the error of the SEED is about 219.2% at 10 MHz AC characteristics, but the maximum error of the proposed method is only 7.8%. Hence, compared with the widely-used SEED method, this method is more accurate when characterizing the EOS event during AC operation and switching.

Design optimization of high-frequency AlGaN/GaN HEMT on BGO substrates

In this paper, a T gate head AlGaN/GaN high-electron-mobility transistor (HEMT) on BGO substrate is proposed and optimization is done for channel length, gate length and gate position. The dc and ac characteristics of the devices under consideration are analysed using Silvaco TCAD software. The threshold voltage and transconductance of the proposed HEMT are extracted from the DC characteristics. The unity gain cut-off frequency (fT) and maximum oscillation frequency (fmax) are analysed for comparing the radio frequency characteristics. The T gate AlGaN/GaN HEMT on BGO substrate with channel length of 200 nm, gate length of 20 nm, gate source distance of 100 nm and gate drain distance of 80 nm exhibits optimum values for fT and fmax of 265 GHz and 900 GHz. The RF performance of the optimized device is compared with other related recent technologies and found that the proposed device is superior among them.

27‐3: Optimizing Charge Transport and Reducing Excitonic Loss Channels in Fluorescent Doped TADF OLEDs

A combined experimental and simulation study on a set of 4 OLEDs with 2 systematically varied guest dopants in the emission layer is presented. A numerical electro‐optical model is employed, demonstrating one consistent parameter set that describes both steady‐state and ac characteristics of all devices. The model accounts for charge transport and trapping, polar layers, and excitonic loss processes inducing an efficiency rolloff that can be correlated with the shape of the emission zone and the guest dopant concentrations. Furthermore, starting from the resulting parameter set, we show routes for optimized devices with a reduced roll‐off.

Application of response surface methodology for color removing from dyeing effluent using de-oiled activated algal biomass

BackgroundConservation of the ecosystem is a prime concern of human communities. Industrial development should adopt this concern. Unfortunately, various related activities release lots of noxious materials concurrently with significant leakage of renewable resources. This work presents a new biosorbent activated de-oiled microalgae, Chlorella vulgaris, (AC) for biosorption of Acid Red 1 (AR1) from aqueous solution simulated to textile dyeing effluent. The biosorption characteristics of AC were explored as a function of the process parameters, namely pH, time, and initial dye concentration using response surface methodology (RSM).ResultsOptimization is carried out using the desirability approach of the process parameters for maximum dye removal%. The ANOVA analysis of the predicted quadratic model elucidated significant model terms with a regression coefficient value of 0.97, F value of 109.66, and adequate precision of 34.32 that emphasizes the applicability of the model to navigate the design space. The optimization depends on the priority of minimizing the time of the process to save energy and treating high concentrated effluent resulted in removal % up to 83.5%. The chemical structure and surface morphology of AC, and the dye-loaded biomass (AB) were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and transmission electron microscope (TEM). The activation process transforms the biomass surface into a regular and small homogeneous size that increases the surface area and ultimately enhances its adsorption capacityConclusionThe optimization of the process parameters simultaneously using RSM performs a high-accurate model which describes the relationship between the parameters and the response through minimum number of experiments. This study performed a step towards an integrated sustainable solution applicable for treating industrial effluents through a zero-waste process. Using the overloaded biomass is going into further studies as micronutrients for agricultural soil.

Experimental study on V-A characteristics of AC and DC metal oxide varistors under different temperatures

Experimental study on V-A characteristics of AC and DC metal oxide varistors under different temperatures

Methods to Determine the Characteristics of AC Cryogenic Current Leads

Methods to Determine the Characteristics of AC Cryogenic Current Leads