Low Voltage Level Research Articles

High-Temperature Superconducting Cable Optimization Design Software Based on 2-D Finite Element Model

With the increasing electricity power demand in major cities, the existing conventional power cables is difficult to meet the requirements of high-density and large-capacity power transmission. Compared with conventional power cables, high-temperature superconducting cables can significantly increase transmission capacity, reduce power losses, and save land occupation, which have great potential in future urban high-density power transmission applications. However, the process of designing a complete set of HTS cable is very complex, and many factors need to be considered comprehensively, such as current distribution, AC loss calculation, thermal stability analysis. In this case, a HTS cable design software platform is under development to simplify design process and improve the work efficiency of designers. Based on the software, design schemes of three-phase 10kV/1.5kA HTS cable with two different structures are given. A 2-D AC loss finite element model of HTS cable is established and verified. The simulation results show that at low voltage level, the HTS cable with three-phase coaxial structure has good performance, and can save more land, which is more suitable for the expansion of urban power grid in the future.

Network-Agnostic Adaptive PQ Adjustment Control for Grid Voltage Regulation in PV Systems

The service of grid voltage regulation is required nowadays from inverter-based resources (IBRs) particularly at the lower voltage level. In the transmission network, this is easily managed by leveraging solely the reactive power (Q) capability of the IBR, but in distribution networks that are mix of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$r$</tex-math></inline-formula> the voltage magnitude is coupled with both active (P) and reactive power injection. There are methods in the literature designed for these cases that utilize both P and Q in voltage regulation, but they usually require network and load data, which may not be readily available. Furthermore, they often disregard an apparent nonmonotonic relation between the inverter terminal voltage and the P/Q ratio risking instability. To fill this gap, this article introduces a network-agnostic P–Q adjustment technique for photovoltaic (PV) systems or other IBRs. The proposed technique tracks in a step-like manner the reference voltage set point if it is feasible, or the maximum grid voltage otherwise. This allows identification of the critical P/Q ratio without any prior information at the cost of limited voltage ripple due to a variable step-size strategy implemented. The superior performance of the proposed scheme is validated through simulations in MATLAB-Simulink in a reduced UKGDS 95-bus system and through lab experiments on a scaled down laboratory grade prototype.

Control Strategy for Power Generation from a Capacitive Mixing Cell and Grid Injection

In this work, the possibility of extracting energy from a capacitive mixing cell based on the potential that exists as a result of the salinity gradient between fresh and salt water passing through the electrodes of a deionization cell is studied. For this, a two-stage process is defined. The first step uses a dual buckboost converter for the positive and negative cycles of the input voltage. This topology acts as a current source and is chosen due to its ability to provide high power factor and to work with extremely low voltage levels. The second stage consists of an Hbridge inverter synchronized with the AC grid to feed power into the grid. A hysteresis control system has been designed for the current flowing through the coil. With this, it has been analyzed how the efficiency of the total system (cell + power converter) varies with the changes in the series resistance of the CapMix cell or with the discharge current selected in the power converter. Simulations are carried out to characterize the energy extraction and some experimental results confirm the possibility of using this new renewable energy source.

A Novel Hybrid Method for Short-Term Probabilistic Load Forecasting in Distribution Networks

In recent decades, the evolution of loads and distributed energy resources has added great complexity and uncertainty to distribution networks. In such a context, a reliable characterization of the uncertainty associated with prediction is fundamental to the wide range of the newly emerging applications in the low-voltage level grid. In this regard, this paper proposes a novel method to solve the short-term probabilistic load forecasting (STPLF) problem in distribution networks in which the loads are usually too volatile to be forecasted accurately. The approach developed employs a Dirichlet process mixture model (DPMM) to handle the uncertainty of load patterns, which is inferred by a Markov chain Monte Carlo (MCMC)-based method. Thereafter, the DPMM representation of the load patterns is combined with a tree-based ensemble learning method to address the STPLF by solving a classification problem. The final result is averaged over all MCMC samples. The proposed technique is compared to selected benchmark methods at different aggregation levels using smart meter datasets collected from customers located in Ireland as well as the City of Saskatoon, SK, Canada. The results obtained demonstrate that the proposed approach outperforms the benchmark methods in STPLF at the given aggregation levels.

Diamond-Like Carbon Film Deposited via Electrochemical Route for Antireflection Applications in Photovoltaic

Diamond-like carbon (DLC) is widely studied for various applications such as optoelectronics, energy, aerospace, and medicine. It’s hard, chemically inert, and optically transparent. Due to its superior antireflection properties, DLC films are more suited for photovoltaic technology. Here in this work, we report a facile, high speed, and low-cost method of DLC film development from an aqueous solution via electrodeposition. The effect of applied voltage and solution concentration on the properties of DLC film was analyzed. The morphology, shape, and uniformity of the DLCs were analyzed with optical and electron microscopies. The presence of C-H, C-C, and C=C bonds in the DLC films was confirmed from FTIR and Raman spectroscopies. Whereas the optical behavior was analyzed with a UV-Vis-NIR spectrophotometer. The DLC films were deposited at 2.7 V, 4V, 6V, 8V, and 10V, and it was shown that for a fixed electrolyte concentration and electrode spacing, the applied voltage can be adjusted to obtain varying deposition rates. Likewise, the solution concentration was varied in the 2 vol.% to 10 vol.%, and it was demonstrated that by increasing the solution concentration the deposition rate increases. The increase in the deposition rate was evidenced by an increase in the deposition current as well as the roughness of the films. It was noticed that smaller-sized, well-defined, and more uniform DLC films were obtained at lower concentrations and low voltage levels. The band gap was varied between 2.91ev to 3.39ev. It was clearly shown that reflection reduced remarkably after depositing DLC film on the substrate surface. This work demonstrates that DLC film has a potential to utilized as an antireflection layer in photovoltaic application.

Fully Differential Current-Mode Configuration for the Realization of First-Order Filters with Ease of Cascadability

It is well known that fully differential signal processing is more advantageous than single-ended signal processing in a noisy environment, and is widely used in audio, video and other signal processing applications. This paper introduces a new fully differential configuration that contains a first-order low-pass (LP) filter, high-pass (HP) filter, and all-pass (AP) filter, all present within the same circuit design. The proposed fully differential configuration is simple and employs only one multiple-output current differencing transconductance amplifier and one grounded capacitor. The circuit has a wide operating frequency range (up to 73 MHz). The additional features offered by the proposed circuit include use of the lowest number of active and passive components, suitability of the integrated circuit chip, support of cascadability, electronic tunability, no passive component-matching restrictions, availability of all first-order responses, i.e., LP, HP, and AP, and low-level operating supply voltages. Non-ideal and parasitic analyses are investigated for the proposed circuit, and PSPICE simulation results are presented to verify the proposed theory. Additionally, the proposed fully differential LP filter circuit is experimentally verified using off-the-shelf ICs. Moreover, the cascading feasibility is demonstrated by realizing a fully differential nth-order LP filter.

Prosumers Flexibility as Support for Ancillary Services in Low Voltage Level

The prosumers flexibility procurement has increased due to the current penetration of distributed and variable renewable energy sources. The prosumers flexibility is often able to quickly adjust the power consumption, making it well suited as a primary and secondary reserve for ancillary services. In the era of smart grids, the role of the aggregator has been increasingly exploited and considered as a player that can facilitate small prosumers' participation in electricity markets. This paper proposes an approach based on the use of prosumers flexibility by an aggregator to support ancillary services at a low voltage level. An asymmetric pool market approach is considered for flexibility negotiation between prosumers and the local marker operator (aggregator). From the achieved results it is possible to conclude that the use of flexibility can bring technical and economic benefits for network operators.

A system identification-based MPPT algorithm for solar photovoltaic pumping system under partial shading conditions

ABSTRACT This paper presents a Maximum Power Point Tracking (MPPT) algorithm using system identification (SI) for solar photovoltaic (PV) pumping system under partial shading (PS) conditions. The measurement of the PV panel current was not required for the proposed MPPT algorithm. The MPPT algorithm was developed for an electric motor with a nonlinear pump load. In this study, a high-efficiency synchronous reluctance motor (SynRM) was designed as a 4-inch submersible pump motor. The system aimed to the small-scale solar photovoltaic water pumping systems. The SynRM was designed and optimized to use at low voltage levels such as solar PV panels without requiring a boost converter. Thus, the motor could be connected directly with any low voltage leveled power supply. The motor was produced 0.55 kW power with an efficiency of 86.5%. Eight PS patterns were generated to obtain four different scenarios for analyzing of the proposed algorithm. The Maximum Power Point (MPP) was determined with high accuracy for global maximum for all PS conditions using the proposed algorithm. Thus, the motor was operated at the MPP in all conditions thanks to the developed algorithm. The overall system efficiency was obtained between 72% and 82% under these conditions.

Investigating peer-to-peer power transactions for reducing EV induced network congestion

Current electricity pricing models take into account costs of generation, transmission, emissions and a fixed cost of distribution based on time of day and type of primary source. However, the authors postulate that increasing fast charging for EVs will lead to increased overloading and voltage drops observed in networks at the low voltage level. To this end, the authors propose a novel method that encourages reactive power injection to minimize voltage drops and active power injection to minimize cable loading by using a centralized, double-sided optimized algorithm. This model allows for peer-to-peer power delivery, incentivized using pricing factors, encouraging local optimization-based solutions to network overloading as well as increased islanding in the network as a means of improving grid resilience and allowing optimal EV charging and discharging. Incentivized peer-to-peer transactions are then recorded in a centralized blockchain, with instantaneous power serving as the transactional commodity for both fixed consumers and generators (houses) and mobile consumers and generators (EVs). The mathematical model, as well as the impact of such a decentralized network compared to a business-as-usual network shows the potential of decongestion of 5–10% in terms of a reduction in voltage drops and cable loading with even a low EV penetration level (<5% of available transportation) by using existing resources as V2G and voltage stability resources.

Strategic integration of battery energy storage and photovoltaic at low voltage level considering multiobjective cost-benefit

Renewable energy sources, such as solar photovoltaic (PV) systems and battery energy storage systems (BESS), help reduce greenhouse gas emissions while fulfilling the world?s growing energy demand. The inclusion of BESS reduces the peak hour demand, and control of charging and discharging of BESS can be economical for distributors facing time-based energy pricing. This paper discusses a novel multiobjective Horse herd optimisation algorithm (MOHHOA) approach, which is inspired by the social behaviour of horses in herds for PV and BESS optimal allocation in the radial distribution system. The proposed algorithm combines multiple benefits like benefits from economic gain per day, reduction in CO2 emission per day, and reduction in energy loss per day. IEEE 69-bus radial distribution system (RDS) is used for testing the suggested approach. The case studies and simulation results show that the suggested model effectively accommodated PV power generation in IEEE 69-bus RDS without violating any system constraints. Results indicate improvement in node voltage profiles, security margins and energy losses, and peak energy savings, and system characteristics as a whole, and there were significantly improved techno-economic performance of the distribution system.

Different Effects of Reversible Electroporation-Mediated Fe3O4@AuNPs Delivery as Radiosensitizing Agents on Cancer Cells versus Normal Cells

Aim: In the present study, we sought to enhance the efficacy of radiotherapy via increasing the cellular uptake of Fe3O4@AuNPs as radiosensitizing agents using reversible electroporation, attaining a higher sensitivity for cancer cells to therapy-induced damage. Methods: The KB human nasopharyngeal carcinoma cell line was treated with different concentrations of gold-coated magnetic nanoparticles. The cells then received electroporation (750[Formula: see text]V/cm, 8 pulses for a duration 100[Formula: see text][Formula: see text]s with 100[Formula: see text]ms intervals) and radiotherapy (6MV X-ray, 2[Formula: see text]Gy). Control groups were carefully considered to assess the pure effect of both single and combinational therapeutic protocols. The MTT test and flow cytometry assay using Annexin V-PI kit were performed to evaluate potential effects on cell survival rate and to determine the induced level of apoptosis. Additionally, cellular uptake of nanoparticles was assessed and quantified using ICP-OES analysis. Results: Our study showed that nanoparticles and the applied procedure of electroporation had no considerable effects when utilized separately, but their combined application induced significant cell death ([Formula: see text]45%) and apoptosis ([Formula: see text]17%). Besides, the application of Fe3O4@AuNPs in the presence of electric field, 24[Formula: see text]h before the radiotherapy of tumor cells enhanced the cancer cell death ([Formula: see text]53%) as well as apoptosis rate ([Formula: see text]33%). The same scenario was also observed with normal HGF human gingival fibroblasts, confirmed by significantly lower levels of cell death and apoptosis. Conclusion: It can be concluded that electric fields at low voltage levels may significantly and selectively enhance the entry of nanoparticles into cancer cells, thereby accentuating the sensitivity of these cells to nanoparticle-mediated radiation therapy.

Experimental Study of Transient Dose Rate Effects of Two Level-Shifting Transceivers and Simulations on Their ESD Circuits

This article investigates the transient dose rate effect (TDRE) of two types of level-shifting transceivers. Experimental results show that both transceivers have a high latch-up threshold. One uncommon phenomenon is found that there are photocurrents generated at the input ports for both transceivers when exposed to transient <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> radiation. Moreover, the polarity and amplitude of the photocurrents are related to the input voltage level. A hypothesis is proposed that this uncommon phenomenon is caused by the electrostatic discharge (ESD) circuits at the input ports and then it is successfully verified by TCAD simulations. The simulation results show that the vertical parasitic p-n-p transistor in pMOS of the ESD circuit could turn on under transient <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> radiation, and generate a positive photocurrent when the input port is configured to high-level voltage. On the contrary, when the input port is configured to low-level voltage, its lateral parasitic p-n-p transistor in pMOS could turn on and generate a negative photocurrent. The amplitude of the positive photocurrent is obviously larger than the negative photocurrent due to different gains of the parasitic transistors. Simulation results also show the number of pMOSs in n-well has significant impacts on the amplitude of photocurrents.

A Mixed-integer Linear Programming Model for the Plug-in Electric Vehicle Charging Problem in Unbalanced Low Voltage Electrical Distribution Systems Considering Neutral Conductor

The increasing penetration of plug-in hybrid electric vehicles (PHEVs) imposes new challenges in low voltage distribution networks (LVDNs), due to worsening load imbalance, power losses, and increased probability of blackouts because of the overloads. To overcome these issues, PHEV charging must be performed in a coordinated fashion. In this context, there are several coordinated charging methods in the literature, none of which considers modeling neutral conductors of LVDN.This paper aims to present a mixed-integer linear programming model (MILP) for the PHEV charging problem in unbalanced LVDNs, considering the neutral conductor. In this regard, the main parameters of unbalanced LVDN, such as voltage profile and power loss, are examined with and without modeling the neutral conductor. The results indicate that it is required to consider the neutral conductor to achieve realistic values of the LVDN's parameters. The proposed model is applied to a 449-nodes smart distribution grid consisting of 31 nodes at a medium voltage (MV) level and 418 nodes at a low voltage (LV) level. To verify the performance of the proposed model, it is compared with two uncoordinated charging methods. The results show the effectiveness of the proposed strategy.

High‐Gain Logic Inverters based on Multiple Screen‐Printed Organic Electrochemical Transistors

AbstractOrganic electronic circuits based on organic electrochemical transistors (OECTs) are attracting great attention due to their printability, flexibility, and low voltage operation. Inverters are the building blocks of digital logic circuits (e.g., NAND gates) and analog circuits (e.g., amplifiers). However, utilizing OECTs in electronic logic circuits is challenging due to the resulting low voltage gain and low output voltage levels. Hence, inverters capable of operating at relatively low supply voltages, yet offering high voltage gain and larger output voltage windows than the respective input voltage window are desired. Herein, inverters realized from poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate‐based OECTs are designed and explored, resulting in logic inverters exhibiting high voltage gains, enlarged output voltage windows, and tunable switching points. The inverter designs are based on multiple screen‐printed OECTs and a resistor ladder, where one OECT is the driving transistor while one or two additional OECTs are used as variable resistors in the resistor ladder. The inverters’ performances are investigated in terms of voltage gain, output voltage levels, and switching point. Inverters, operating at +/−2.5 V supply voltage and an input voltage window of 1 V, that can achieve an output voltage window with ∼110% increment and a voltage gain up to 42 are demonstrated.

Gate Driver Circuit Based on Depletion-Mode Indium-Gallium-Zinc Oxide Thin-Film Transistors Using Capacitive Coupling Effect

This article proposes a highly reliable gate driver circuit based on amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs). The proposed circuit adopted an additional boosted-down structure to maintain the control node (Q-node) of the output TFTs at a low voltage level using the capacitive coupling effect instead of the TFT structure. Consequently, the proposed circuit exhibited stable operation for depletion-mode TFTs with a threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> ) of −3 V. The boosted-down structure improved the operation reliability because it reduced the current flow from Q-node to low-level voltage node by removing the continuously degraded TFTs. The drain–source voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> ) stress on the TFTs connected to the Q-node was reduced by separating these TFTs from the Q-node during bootstrapping. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {DS}}$ </tex-math></inline-formula> value during Q-node bootstrapping was reduced from 44.3 to 27.3 V. A pull-down TFT was designed to operate with a 50% duty ratio to ensure reliability against the bias stress. The output node was discharged by the Q-node discharging TFTs in the next stage during the remaining 50% period. Therefore, the output node was discharged with a total duty ratio of 100%. The proposed circuit operated stably as a shift register with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> varying from −3 to 9 V. Consequently, using capacitive coupling effect, the proposed circuit exhibited reliable operation with depletion- and enhancement-mode a-IGZO TFTs.

Transformerless Grid Connected Control of Wind Turbine Based on H-MMC

A high-power wind turbine has low rotational speed and a relatively low terminal voltage level. Thus, the wind energy conversion system (WECS) is commonly connected to the grid by an isolated boost transformer, which increases costs and room greatly. In this article, the hexagonal modular multilevel converter (H-MMC) is applied so that the high-power wind turbine can be directly connected to the medium-voltage ac grid. It has the advantages of transformerless grid connection and low ripples of capacitor voltages. As the bridge arm voltage of H-MMC contains both the low-frequency component induced by a wind turbine and the power frequency component induced by the grid, the voltage ripples of submodules (SMs) are reduced. Due to the large differences in the voltage level between the wind turbine and the grid, the low-amplitude-modulation voltage of the wind turbine side is easily obliterated by the high-amplitude-modulation voltage of the grid side, which will cause distortion of the bridge arm current. Therefore, auxiliary SMs with variable reference voltage are adopted to improve the tracking accuracy. The MATLAB/Simulink simulation and the RT-LAB hardware-in-the-loop experimental results verify the feasibility of the proposed topology and the effectiveness of the control strategy.

An impact of the line resistance on the power flow calculations with installed phase-shifting transformer in different voltage levels power systems

In modern power systems, phase-shifting transformers are installed not only in the extra high voltage lines, but some of these devices can be built for lower voltage levels (e.g., 40 kV). Due to big voltage difference, in the power flow analyses, not only phase-shifting transformer properties, but also line parameters, including resistance, should be considered. For high voltage power systems, the line reactance is much greater than its resistance (the ratio is even greater than 10), while it is smaller in lower voltages. This fact should be taken into account during any calculations of power flows in such systems. This article considers 400 kV, 220 kV, and 70 kV transmission lines with installed asymmetrical phase-shifting transformers to present the line resistance impact on the final power flow calculations. Also, the IEEE 5-bus power system is tested to prove the dependency of line resistance on power flow calculations and bus voltage values. The highest voltage levels calculation results show that the assumption of omitting line resistance is correct (the relative error is equal to 2%), while for the 70 kV system, the same error results even 30%. What is more, the line resistance for medium voltage power systems cannot be omitted. What is more, the resistance effect is intentionally not taken into account in some power flow calculations presented in the literature.

Economic benefit of preventive cable replacement in distribution networks based on the alignment with reinforcement measures

This article investigates the economic benefit of aligning asset maintenance actions with actions resulting from necessary distribution network development. For this, an existing optimisation approach to strategic network planning at low-voltage level based on a genetic algorithm is expanded to include the opportunistic preventive renewal of assets. The renewal of power cables that is expected due to degradation is brought forward in time and carried out at the same time as actions that are necessary to increase the network capacity to host increasing distributed generation. It is shown in theory and with exemplary case studies that overall costs can be reduced, depending on opportunity costs and the relation of direct costs to costs which the maintenance and reinforcement actions share, such as certain parts of construction work. In the two case studies with real low-voltage, networks the cost reduction amounts to 39% at maximum when cable replacement and the laying of new cables are aligned, compared to the separate execution of the necessary construction work. The case studies also reveal that the decision on the technical option for reinforcing a network may change due to the joint optimisation of renewal and reinforcement. In some cases, now traditional network reinforcement is advised, where sole strategic planning would recommend voltage control devices as the optimal choice.

Rapid Demagnetization of New Hybrid Core for Energy Harvesting

This paper presents the results obtained using the rapid demagnetization method in the case of an NdFeB magnet and a new hybrid core. The developed core consists of three basic elements: an NdFeB magnet, Terfenol-D, and a specifically developed metallic alloy prepared by means of a suction casting method. The main goal of proposing a new type of core in the event of rapid demagnetization is to partially replace the permanent magnet with another material to reduce the rare-earth material while keeping the amount of generated electricity at a level that makes it possible to power low-power electrical devices. To “capture” the rapid change of magnetic flux, a small number of coils were made around the core. However, the very low voltage level at very high current required the use of specialized electronic transducers capable of delivering a voltage level appropriate for powering a microprocessor system. To overcome this problem, a circuit designed by the authors that enabled voltage processing from low impedance magnetic circuits was used. The obtained results demonstrated the usefulness of the system at resonant frequencies of up to 1 MHz.

Demand response and dispatchable generation as ancillary services to support the low voltage distribution network operation

The current power systems, namely the low voltage distribution networks, have been suffering considerable changes in recent years. What appeared to be innovation trends nowadays due to technological advances and manufacturing cost reduction has become the new reality in the coming years. Thus, the growing trend of power generation by renewable sources has posed new challenges and new opportunities. Furthermore, the wide installation of “smart meters” and the interest in placing the citizens as core players into the future energy markets and systems operation improves the role of the distribution system operator. In this way, developing new and innovative methodologies to explore the potential mechanisms for providing ancillary services in distribution networks becomes of great importance, namely in low voltage levels. This research paper proposes an innovative methodology to enhance the demand response participation of small consumers and dispatchable distributed renewable energy sources flexibility as ancillary services to mitigate the voltage and congestion issues in low voltage distribution networks. A realistic low voltage distribution network with 236 buses is used to illustrate the application of the proposed model. The results demonstrate a considerable voltage profile and congestion improvements.