Voltage Reduction Research Articles

Optimal Allocation and Assessment of Distributed Generation Units with Multi-Objective Planning in Unbalanced Distribution Networks

—Real-world distribution networks are generally unbalanced due to unbalanced loads and asymmetric line parameters. Proper allocation of distributed generation (DG) units in unbalanced radial distribution networks to extract their maximum potential benefits is still quite difficult. Converter-coupled DG units have individual phase real and reactive power regulating ability and provide voltage unbalance compensation. This article proposes a new technique for the suitable allocation and capacity of converter-based multiple DG units considering the unbalanced operation of distribution networks. The objective function contains power loss minimization, multiphase voltage stability augmentation, and reduction of voltage unbalances among different phases in the system. A complex multi-objective optimization problem has been synthesized with the help of a Fast and Flexible Radial Power Flow (FFRPF) and solved by employing a Weighted aggregation (WA) based particle swarm optimization (PSO) approach. The performance of the proposed technique is validated on 19-bus, 25-bus, and 34-bus unbalanced radial distribution networks that consider various power factor modes of the converter-coupled DG units. The analysis of the simulation results indicates a significant enhancement in the power delivery efficiency in all the unbalanced test systems

An adaptive vector control method for inverter‐based stand‐alone microgrids considering voltage reduction and load shedding schemes

AbstractThe droop mechanism is widely utilized in a stand‐alone microgrid (MG) to regulate power‐sharing among distributed generators (DG). However, over the years, the droop phenomena are continually modified to lessen the deviation in voltage and frequency parameters caused due to classical droop. This study suggests computing the droop coefficient for voltage–current (V–I) droop to take into account for proportional power distribution among DGs. In grid utility networks, the conservation voltage reduction (CVR) strategy is widely used to curtail the use of energy. Hence, this paper investigates the CVR's performance for stand‐alone MG by performing the adaptive vector control scheme in the two‐phase d–q reference frame. In addition to it, the paper is intended to develop a coordinated control strategy for stand‐alone MG involving classical P–f droop and self‐sustained V–I droop employed to perform the function of CVR during peak demand and overloading conditions. Further, a load‐shedding control approach is also considered to cut out some segments of load during overloading conditions to operate the MG in the stable zone. The validation of the proposed strategy is conducted on MATLAB/Simulink software.

Radiation Doses in Cardiovascular Computed Tomography.

We discussed the contemporary views on the effects of ionising radiation on living organisms and the process of estimating radiation doses in CT examinations and the definitions of the CTDI, CTDIvol, DLP, SSDE, ED. We reviewed the reports from large analyses on the radiation doses in CT examinations of the coronary arteries prior to TAVI procedures, including the CRESCENT, PROTECTION, German Cardiac CT Registry studies. These studies were carried out over the last 10 years and can help confront the daily practice of performing cardiovascular CT examinations in most centres. The reference dose levels for these examinations were also collected. The methods to optimise the radiation dose included tube voltage reduction, ECG-monitored tube current modulation, iterative and deep learning reconstruction techniques, a reduction in the scan range, prospective study protocols, automatic exposure control, heart rate control, rational use of the calcium score, multi-slices and dual-source and wide-field tomography. We also present the studies that indicated the need to raise the organ conversion factor for cardiovascular studies from the 0.014-0.017 mSv/mGy*cm used for chest studies to date to a value of 0.0264-0.03 mSv/mGy*cm.

Scale-up single chamber of microbial fuel cell using agitator and sponge biocarriers

ABSTRACT Despite the high efficiency of microbial fuel cells (MFCs), MFCs cannot be a suitable alternative for treatment plants because of insufficient power generation and tiny reactors. Additionally, the increased reactor size and MFC stack result in a reduction in production power and reverse voltage. In this study, a larger MFC with a volume of 1.5 L has been designed called LMFC. A conventional MFC, called SMFC, with a volume of 0.157 L, was constructed and compared with LMFC. Moreover, the designed LMFC can be integrated with other treatment systems and generate significant electricity. In order to evaluate MFC's ability to integrate with other treatment systems, the LMFC reactor was converted into MFC-MBBR by adding sponge biocarriers. A 9.5 percent increase in reactor volume resulted in a 60 percent increase in power density from 290 (SMFC) to 530 (LMFC). An agitator effect was also investigated for better mixing and circulating substrate, which positively affected the power density by about 18%. Compared with LMFCs, the reactor with biocarriers generated a 28% higher power density. The COD removal efficiency of SMFC, LMFC, and MFC-MBBR reactors after 24 h was 85, 66, and 83%, respectively. After 80 h of operation, the Coulombic efficiency of the SMFC, LMFC, and MFC-MBBR reactors was 20.9, 45.43, and 47.28%, respectively. The doubling of coulombic efficiency from SMFC to LMFC reactor shows the design's success. The reduction of COD removal efficiency in LMFC is the reason for integrating this reactor with other systems, which was compensated by adding biocarriers.

Conservation Voltage Reduction Strategy for Autonomous Microgrid with Improved Voltage-CurrentDroop-Based Inverter Control Framework

In a conventional AC distribution system, the conservation voltage reduction (CVR) strategy is widely employed to lower down the voltage of specific load to lower the power consumption. The wide applicability of demand side management (DSM) using CVR in a stand-alone microgrid through VSI-based energy sources is a thrust area, that is, not examined yet and needs to be explored. The fast dynamics and flexible control are the characteristics of the voltage-current droop method which further increases the inertia of the voltage source inverter. For utilizing these advantages of this droop method, it is required to determine the accurate droop gain to properly coordinate the distribution of power among DGs. In this paper, the voltage-current droop method is utilized to carry out the function of DSM, and a modified droop computation method for voltage-current droop is formulated to determine the impedance from initial of the DG point to the downstream end for multifeeder network. As most of the droop control techniques emulate the conventional power grid such as Q-V droop control which reduces voltage with the increase of reactive power, the research prospect is very high in devising the new droop computation method for voltage-current droop for accurate control of power. In addition to it, the work is extended to apply the benefits of voltage-current droop to execute DSM strategy in standalone MG. Moreover, the capability of the proposed estimation of droop parameter is implemented on a standalone 5-bus single-feeder multi-DGs network, and furthermore, the scheme is applied to IEEE-9 bus multifeeder multi-DGs network to show the applicability of the proposed scheme. The simulation results produced from MATLAB/Simulink are compared with the decentralized power-based droop method and conventional voltage-current droop technique to analyse the performance of the devised scheme.

Assessment of Conservation Voltage Reduction in Distribution Networks with Voltage Regulating Distribution Transformers

The application of voltage reduction in medium and low voltage grids to reduce peak power demand or energy consumption has been implemented since the 1980s using several approaches. Conservation Voltage Reduction (CVR), as one such approach, uses a voltage control device to reduce or increase the voltage setpoint on a busbar, thereby reducing or increasing the amount of active and reactive power supply in the network. Voltage regulation for CVR is always implemented according to established network planning standards in each country. Research in this field has proven that a CVR factor (CVRf) of 0.7–1.5 for peak demand reduction can be achieved. This is an evaluation metric of CVR. The aim of this research is to determine and validate CVRf for peak demand reduction by comparing actual results obtained during regular tap changes with other randomly distributed periods outside tap change operations, using a set of measurement data. It is important to understand CVR deployment capability by evaluating CVR potentials from historical random tap operations before a robust network-wide deployment is introduced. This research provides such guidance. It also provides a novel approach to determining tap changes from voltage measurements using a time-based algorithm. A CVRf ranging from 0.95 to 1.61 was estimated using a measurement dataset from a test field. The result of the entire evaluation shows that the CVRf are smaller during peak PV production and greater during peak demand periods. Further evaluation using statistical hypotheses testing and a control chart was used to validate the evaluation.

Strain Tuning of Negative Capacitance in Ferroelectric KNbO3 Thin Films

Ferroelectrics with negative capacitance effects can amplify the gate voltage in field-effect transistors to achieve low power operation beyond the limits of Boltzmann's Tyranny. The reduction of power consumption depends on the capacitance matching between the ferroelectric layer and gate dielectrics, which can be well controlled by adjusting the negative capacitance effect in ferroelectrics. However, it is a great challenge to experimentally tune the negative capacitance effect. Here, the observation of the tunable negative capacitance effect in ferroelectric KNbO3 through strain engineering is demonstrated. The magnitude of the voltage reduction and negative slope in polarization-electric field (P-E) curves as the symbol of negative capacitance effects can be controlled by imposing various epitaxial strains. The adjustment of the negative curvature region in the polarization-energy landscape under different strain states is responsible for the tunable negative capacitance. Our work paves the way for fabricating low-power devices and further reducing energy consumption in electronics.

Breakdown voltages in thrust bearings: Behavior and Measurement

This paper investigates breakdown characteristics in the bearings of variable speed electric drive trains. The analyses reveal that breakdown phenomena previously known from high-voltage technology appear to also occur in the bearing contact, though at significantly lower voltages. By loading the bearing with AC voltage of different frequencies at various mechanical load points, five states, which range from partial discharge through arc discharge to a completely conductive channel, emerge. Consistent with the concept that the magnitude of the breakdown voltage depends on the lubricant film height, the contact force, and the frequency of the AC voltage, a thicker lubricant film results in a higher breakdown voltage, analogously to a capacitor with a larger plate spacing, which requires a higher potential difference to be punctured. Furthermore, the sinusoidal frequency of the AC load correlates with the breakdown voltage. The breakdown tends to occur earlier at low frequencies, which is illustrated by the fact that at low frequencies, capacitive behaviour can only be observed at higher speeds, i.e., at a larger lubrication gap, while no voltage can be built up over the bearing at lower speeds. An increase of the contact force for the same lubricant film height lowers the breakdown voltages. The reduction of the breakdown voltage by the contact force may result from an increase of the relative permittivity of the lubricant with higher pressure and likewise of the contact area; the increased area may also increase the number of surface-roughness peaks where an increase in the electric field occurs.

Reliability Analysis of FinFET Based High Performance Circuits

In the VLSI industry, the ability to anticipate variability tolerance is essential to understanding the circuits’ potential future performance. The cadence virtuoso tool is used in this study to assess how PVT fluctuations affect various fin-shaped field effect transistor (FinFET) circuits. In this research, high-performance FinFET-based circuits at 7 nm are discussed with a variation in temperature and voltage. The idea behind the technology is the improvement of power dissipation and delay reduction at the rise of temperature and reduced supply voltage. With the use of a multi-gate predictive model, simulation is carried out employing diverse domino logic at the 7 nm technology node of FinFET files. The proposed set-reset logic circuit and high-speed cascade circuit method shows less power dissipation and delay compared to the existing current mirror footed domino, high-speed clocked delay, and modified high-speed clocked delay with a variation of temperature and supply voltage. For the proposed set-reset logic circuit and high speed cascade circuit, a Monte Carlo simulation is done to find the mean and standard deviation. FinFET simulations are run on the suggested circuit for the reduction of delay for the rise of temperature and reduction of supply voltage from 0.7 V to 0.3 V. In comparison, the proposed method results in a maximum power decrease compared to existing ones. Compared to the existing one, proposed techniques achieve a maximum delay and area reduction.

Investigating the growth of carbon traces in cardboard in oil-paper insulation

A large amount of contaminants are collected on the cardboard surface of the valve-side bushing outlet of a converter transformer that has been operating for a long period, and can cause the performance of the oil–paper insulation to degrade. The analysis of their energy spectrum has shown that these contaminants contain free carbon. To investigate causes of the formation of these carbon traces, the authors of this study analyze their law of growth on the surface of the insulating paper in the presence of pure insulating oil and insulating oil containing carbon particles. We examined the influence of carbon tracks of different lengths on the breakdown voltage along the surface of the oil–paper insulation. The results showed that carbonization on the surface of the insulating paper generated carbon traces in pure insulating oil and eventually led to the formation of conductive channels. Moreover, carbon traces were generated by carbon particles deposited on the surface of the insulating paper in insulating oil containing carbon particles. The carbon traces grew from the high-voltage electrode to the ground electrode along the direction of the electric field in both types of oils. The formation of the conductive channel through the poles of the paper in insulating oil containing carbon particles required a lower voltage and a shorter discharge time than that in pure insulating oil. As the concentration of the carbon particles increased, the rate of growth of carbon traces on the surface of the insulating paper increased such that the oil–paper insulation failed earlier than otherwise. Long carbon traces were formed on the surface of the insulating paper in case of a high concentration of carbon particles under the DC pre-pressure mode, and this led to a reduction in the breakdown voltage along the surface of the oil–paper insulation.

Speed control of a DFIG-based wind turbine using a new generation of ADRC

ABSTRACT This paper represents a new generation of adaptive disturbance rejection control (ADRC) which is more robust against disturbances than conventional ADRC. The non-derivability of the fal function employed in the traditional ADRC has negative impacts on its operation, so alternate functions will be used which are derivable at all segments. In this regard, odd hyperbolic and trigonometric functions were employed. The performance of the proposed structure was investigated to control the doubly fed induction generator (DFIG) speed. To enhance the efficiency of the suggested ADRC, fractional-order calculations and fuzzy logic were utilized simultaneously. The results in MATLAB platform indicate that: 1) With constant wind speed and changing reference speed, using new fal functions in fuzzy fractional-order ADRC (FFOADRC) has improved the performance compared to the PI regulator and FFOADRC with default fal function. 2) During wind speed variations and using new fal functions, the DFIG speed reaches the final steady amount as over damping, while this condition is critical damping when using FFOADRC with default fal function. 3) During network voltage reduction, using new FFOADRCs leads to fewer oscillations in the stator flux, DC-bus voltage, and DFIG speed, which shows their better performance than PI regulator and traditional ADRC.

Multi-Wavelength-Recognizable Memristive Devices via Surface Plasmon Resonance Effect for Color Visual System.

Photoelectric memristor has attracted many attentions thanks to their promising potential in optical communication chips and artificial vision systems. However, the implementation of an artificial visual system based on memristive devices remains a considerable challenge because most photoelectric memristors cannot recognize color. Herein, multi-wavelength recognizable memristive devices based on silver(Ag) nanoparticles (NPs) and porous silicon oxide (SiOx ) nanocomposites are presented. Rely on the effects of localized surface plasmon resonance (LSPR) and optical excitation of Ag NPs in SiOx , the set voltage of the device can be gradually reduced. Moreover, the current overshoot problem is alleviated to suppress conducting filament overgrowth after visible light irradiation with different wavelengths, resulting in diverse low resistance states (LRS). Taking advantage of the characteristics of controlled switching voltage and LRS resistance distribution, color image recognition is finally realized in the present work. X-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (C-AFM) show that the light irradiation plays an important role on resistive switching (RS) process: the photo-assisted Ag ionization leads to a significant reduction of set voltage and overshoot current. This work provides an effective method toward the development of multi-wavelength-recognizable memristive devices for future artificial color vision system.

Improvement in Electrochemical Performance of Lithium Rich Li2RuO3 Cathode With Co-doping Strategy

Lithium-rich layered oxides based on Ru are interesting as cathode materials because they have high energy density and reversible capacity. However, due to the problems of weak structural stability and voltage decay, their commercial utility is limited. To address this, we use a DFT+U quantum mechanics to investigate the co-doping strategy on Li2RuO3 (LRO) for improved battery performance. In particular, the effect of two co-dopants Ti and Co has been studied. The co-doping strategy has been found to significantly improve the structural and thermal stability of LRO. By slowing the oxygen removal reaction, Ti and Co improve structural stability. Co-doping with Ti and Co increases the maximum open circuit voltage at least by 5.5% and decreases the voltage reduction by a minimum of 44%. Bandgap is also increased by a minimum of 6% with co-doping. In particular, Li2Ru0.5Ti0.375Co0.125O3 provides the highest maximum voltage of 4.4V with 61% decrease in the voltage reduction and 40% lower bandgap (0.45eV).

Conservation Voltage Reduction in Modern Power Systems: Applications, Implementation, Quantification, and AI-Assisted Techniques

Conservation voltage reduction (CVR) is a potentially effective and efficient technique for inertia synthesis and frequency support in modern grids comprising power electronics (PE)-based components, aiming to improve dynamic stability. However, due to the complexities of PE-based grids, implementing the CVR methods cannot be performed using traditional techniques as in conventional power systems. Further, quantifying the CVR impacts in modern grids, while focusing on dynamic time scales, is critical, consequently making the traditional methods deficient. This is an important issue as CVR utilization/quantification depends on grid conditions and CVR applications. Considering these concerns, this work offers a thorough analysis of CVR applications, implementation, and quantification strategies, including data-driven AI-based methods in PE-based modern grids. To assess the CVR applications from a new perspective, aiming to choose the proper implementation and quantification techniques, they are divided into categories depending on various time scales. CVR implementation methods are categorized into techniques applied to PE-based grids and islanded microgrids (MGs) where different control systems are adopted. Additionally, to address the evaluation issues in modern grids, CVR quantification techniques, including machine learning- and deep learning-based techniques and online perturbation-based methods are evaluated and divided based on the CVR application. Concerns with the further utilizing and measuring of CVR impacts in modern power systems are discussed in the future trends section, where new research areas are suggested.

Design and Analysis of Solid State DC-AC Transformer

Multimodal single/dual stage conversion (BSDC) based on a new solid-state DC-AC transformer (SDAT) is proposed. The suggested conversion can perform variable or constant DC voltage operation. A variable DC voltage is controlled dynamically in response to changes in DC input side voltage, allowing the DC-DC conversion stage to always operate at its best. New DC-AC power conversion of 2 port two-way choppers (TBDC) and two-way rectifier/inverter conversion (BRIC) was planned for the implementation of the proposed SDAT. SDAT, consisting of a bi-directional step-down-step-up converter and a bi-directional step-up-step-down converter, has been used as a prototype model to check the suggestion system. Functional concepts of this BSDC converter with TBDC are designed and simulated on the MATLAB/simulink environment network. PWM and control methods have been applied for SDAT to accomplish a wide variety of voltage and power loss reduction in the proposed device. Test bench model hardware is designed and tested to validate the effectiveness and benefits of the proposed approach.

A Selective Bit Dropping and Encoding Co-Strategy in Image Processing for Low-Power Design in DRAM and SRAM

A novel and efficient way of image processing is proposed in this paper, which fully exploits the features of DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory) as well as the human visual system. The proposed strategy first approximates and encodes the image to effectively reduce the number of bit-‘1’ in the original pixel data, then the processed data is pushed into the off-chip DRAM, and later written into the on-chip SRAM for further computation. Since the storage power consumption of DRAM is proportional to the number of bit-‘1’, while the write power consumption of SRAM is linear relative to the switch probability and the square of the supply voltage, fewer bits-‘1’ in the processed pixel data will decrease the power consumption of DRAM and SRAM, yet accompanied by negligible influence on output quality as our proposed method has the advantages of both approximate computation and error compensation. Thus, a tradeoff is finally achieved between storage power consumption and output quality. In the experimental simulations, 39.8% power reduction for DRAM and 25.9% write power reduction for SRAM have been achieved. Regarding output quality, Discrete Cosine Transform (DCT), quantization, inverse quantization and inverse DCT (IDCT) are employed to process the approximated data. The simulations shows average 3.36 dB losses in Peak-Signal-Noise-Ratio (PSNR). Based on this strategy, an approach of priority-based reduction in supply voltage for insignificant pixel data is introduced to achieve further reduction in power consumption for SRAM. Undoubtedly, a lower supply voltage will increase the probability of read error from SRAM. However, with our proposed approximate coding strategy, the output quality is barely impacted by the lower supply voltage.

Passive Cooling Module to Improve the Solar Photovoltaic (PV) Performance

Solar energy is a renewable clean energy. Photovoltaic (PV) cells or solar panels use the sun light as the main source to produce electricity. However, the operating temperature has a significant impact on the PV conversion process and its performance. PV cell technology performance is sensitive to the operating temperature. Increasing cell temperature causes a significant reduction in the output voltage which in turn leads to reducing electrical efficiency. In other words, when the temperature rises, the output current rises exponentially which leads to output voltage to fall. Therefore, PV efficiency decreases. This paper aims to develop a new PV panel passive cooling system that enhances the efficiency of the panel and improves its performance. The design is based on air channels and air chimneys. Overall, cooled solar panels are efficient and cost-effective as their performance is better and their efficiency is higher than the non-cooled solar panels. Our project is designed to serve UAE’s 2021 vision (increased dependence on clean energy and green development), reduce pollution in the environment, and save energy for the next generations. The goal of this research is to lower the temperature of the PV panel., therefore, enhancing the efficiency as well as improving the performance by cooling the PV panel. So, It has the potential to alleviate the problem of overheating solar panels.

A Simplified PWM Strategy for Open-Winding Flux Modulated Doubly-Salient Reluctance Motor Drives With Switching Action Minimization

In this article, a simplified pulsewidth modulation (PWM) strategy is proposed for open-winding flux modulated doubly-salient reluctance motor (FMDRM) drives for switching action minimization and common-mode voltage (CMV) reduction. Conventionally, the open-winding converter topology is utilized to achieve the zero-sequence current flow path and dc-biased sinusoidal current excitation for the FMDRM, where the switching actions of power switches are doubled compared to the conventional modular three-phase converter, leading to higher switching losses. Different from the conventional space vector PWM scheme, the reference voltages of converter legs are directly calculated by the reference phase voltages in the proposed PWM scheme. In addition, a rotor-position-based sector division method is proposed to deal with the sector imbalance caused by the distorted back electromotive force (back EMF). Furthermore, different leg voltage clamping methods are respectively developed in odd and even sectors for switching action minimization, which can achieve voltage stress balance and CMV reduction. With the proposed scheme, the switching actions in each switching cycle can be reduced by half, which effectively increases the system efficiency of the FMDRM drive. Experiments are carried out on a three-phase 12/8 FMDRM prototype to verify the effectiveness of the proposed scheme.

Cooperative Operational Planning Model for Distributed Energy Resources With Soft Open Point in Active Distribution Network

In this paper, optimal cooperative operational planning of distributed energy resources (DER) in an active distribution network (ADN) with soft open points (SOP) has been investigated. To do so, a new two-layer coordinated optimization framework ADN has been proposed considering SOP. In the upper layer, the location and sizing of the DERs and SOPs has been optimised. While inner layer executes simultaneous optimal functioning of volt/var control (VVC) devices, remote controlled switches (RCS), DERs, and SOPs. The main objective of proposed methodology is to reduce total investment cost of DERs and SOPs as well as operating costs of the system over the planning horizon. Besides, objective function considers the cost of energy not served (ENS), the cost of substation-purchased electricity, and the cost of carbon emissions. Meanwhile, a stochastic module has been employed to address high-level uncertainties associated to renewables and load demands. Besides, the effects of distribution network reconfiguration (DNR) and conservation voltage reduction (CVR) have been taken into account. For various instances, the suggested framework was implemented on an IEEE 119-bus distribution system and solved using a proposed hybrid optimization solver. The efficacy of proposed DER with SOP methodology has been validated on various cases and also tested on sudden external disturbances such as under voltage and over voltage problem conditions. When compared to standard planning schemes, the test results show that it is beneficial in boosting system efficiency, increasing reliability, and lowering the carbon footprint of distribution systems.

Analysis and Measurement of Non-Intrinsic Differential-Mode Noise in a SiC Inverter Fed Drive and Its Attenuation Using a Passive Sinusoidal Output EMI Filter

The analysis, measurement, and attenuation of non-intrinsic differential-mode (NDM) and common-mode (CM) noise in an induction motor (IM) drive are discussed in this paper. In a voltage source inverter (VSI) fed drive, the NDM noise is caused by the excitation of the CM capacitance paths by the line to ground voltage. A measurement method at the input side of IM is proposed to separate intrinsic differential-mode (IDM), NDM, and CM noise from the total line current. It is substantiated that the NDM noise constitutes a significant portion of the measured DM noise. Hence, a passive sinusoidal output electromagnetic interference (EMI) filter (PSOEF) is presented to attenuate the NDM and CM noise. PSOEF is designed using line inductor & capacitor with the same resonance frequency to attenuate the NDM and CM noise. PSOEF has an advantage of reduced size and number of CM components as compared to conventional sinusoidal output EMI filter (CSOEF). The designed PSOEF is presented with space vector pulse width modulation (PWM) and CM voltage reduction PWM to analyze the attenuation performance, circulating current, and filter loss. The proposed measurement method and the design of PSOEF are experimentally validated on a SiC VSI switching at 200 kHz.