Medium Power Levels Research Articles

Optimal Design of High-Power Density Medium-Voltage Direct Current Bipolar Power Cables for Lunar Power Transmission

Power systems on the lunar surface require power lines of varying lengths and capacities to connect generation, storage, and load facilities. These lines must be designed to perform efficiently in the harsh lunar environment, considering factors such as weight, volume, safety, cost-effectiveness, and reliability. Traditional power transmission methods face challenges in this environment due to temperature fluctuations, micrometeoroid impacts, and ionizing radiation. Underground deployment, although generally safer, faces challenges due to low soil thermal conductivity. At a depth of 30 cm, the lunar temperature of −23.15 °C can be advantageous for managing waste heat. This study presents a novel approach, developed using COMSOL Multiphysics, for designing bipolar MVDC cables for lunar subsurface power transmission. Kapton® MT+ is chosen as the insulating material for its exceptional properties, including high thermal conductivity and superior dielectric strength. The cables are designed for voltages of ±10 kV and ±5 kV and capacities of 200 kW (low power), 1 MW (medium power), and 2 MW (high power). Our findings indicate that aluminum conductors offer superior performance compared to copper at medium and high power levels. Additionally, elevated voltage levels (±10 kV) enhance cable design and power transfer efficiency. These specially designed cables are well-suited for efficient operation in the challenging lunar environment.

Comparison between contact diode laser with 980 nm and 1470 nm wavelengths for posterior laryngofissure in pigs

To compare two different wavelengths of the surgical contact diode laser (CDL) for producing a posterior laryngofissure in in-vivo pigs. Anesthetized pigs underwent a tracheostomy and an anterior laryngofissure through a cervicotomy. They were randomly selected for the CDL wavelength and Power, according to the peak of Power set at device (980nm wavelength: Ppeak power of 10 W, 15 W, and 20 W, or 1470 nm wavelength: Ppeak 3 W, 5 W, 7 W, 10 W). At the end of the experiment, the laryngotracheal specimen was extracted and sent for histology and morphometry measurements (incision size, depth, area, and lateral thermal damage). Hemodynamic data and arterial blood gases were recorded during the incisions. Statistical analysis of the comparisons between the parameters and groups had a level of significance of p < 0.05. Twenty-six pigs were divided into CDL 980 nm (n = 11) and 1470 nm (n = 15). There was a greater incision area at the thyroid level in the 980 nm CDL and a wider incision at the trachea level, with a larger distance between mucosa borders. There were no significant differences in the area of lateral thermal damage between the two groups and neither difference among the power levels tested. Both wavelengths tested showed similar results in the various combinations of power levels without significant differences in the lateral thermal damage. The posterior laryngofissure incision can be performed by either of the wavelengths at low and medium power levels without great difference on lateral thermal damage.

Impact of microwave heating on product safety and quality in meatballs

The effects of microwave heating at different processing time and power levels (360 W, 600 W and 900 W) on Salmonella Typhimurium, Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus in Turkish type meatballs were evaluated. Besides, the changes in the textural and sensorial properties of meatballs were determined to reveal the cooking time and temperatures that would make the product safety without affecting the consumer preferences. In this direction, the experimentally contaminated meatballs were subjected to microwave heating at low, medium and high power levels for different processing times and analysed for the survival of the relevant pathogenic bacteria. The total aerobic bacteria count in meatballs could be reduced approximately 3–4 log CFU/g by medium and high microwave powers, whereas 5–7 log CFU/g inhibition was obtained in meatballs inoculated with pathogens. The increase in power level together with the increasing process time resulted in a decrease in the counts of bacteria and an undesirable effect on the textural and sensorial qualities of meatballs. Microwave heating at medium and high power levels as from 3 min, caused excessive drying and blackening of the product, making it difficult to consume due to crust formation. Consequently, to achieve optimal acceptability of the product by consumers, meatballs should be heated with a microwave power of 600 W and 900 W for 3 min.

Water level control of nuclear steam generators using intelligent hierarchical autonomous controller

The challenge of water level control in steam generators, particularly at low power levels, has always been a critical aspect of nuclear power plant operation. To address this issue, this paper introduces an IHA controller. This controller employs a CPI controller as the primary controller for direct water level control, coupled with an agent-based controller optimized through a DRL algorithm. The agent dynamically optimizes the parameters of the CPI controller in real-time based on the system’s state, resulting in improved control performance. Firstly, a new observer information is obtained to get the accurate state of the system, and a new reward function is constructed to evaluate the status of the system and guide the agent’s learning process. Secondly, a deep ResNet with good generalization performance is used as the approximator of action value function and policy function. Then, the DDPG algorithm is used to train the agent-based controller, and an advanced controller with good performance is obtained after training. Finally, the popular UTSG model is used to verify the effectiveness of the algorithm. The results demonstrate that the proposed method achieves rise times of 73.9 s, 13.6 s, and 16.4 s at low, medium, and high power levels, respectively. Particularly, at low power levels, the IHA controller can restore the water level to its normal state within 200 s. These performances surpass those of the comparative methods, indicating that the proposed method excels not only in water level tracking but also in anti-interference capabilities. In essence, the IHA controller can autonomously learn the control strategy and reduce its reliance on the expert system, achieving true autonomous control and delivering excellent control performance.

Microwave–osmotic–vacuum combination drying of mango cubes with maltodextrin moderated sucrose solution

A microwave–osmotic–vacuum combination drying technique was used to evaluate the effect of processing factors such as temperature and concentration with 15% inclusion of maltodetrin (dextrose equivalent, DE 10) during the microwave osmotic drying under continuous medium spray flow (MWODS) and power level during finish microwave vacuum drying (MVD). Moisture loss (ML), solids gain (SG), ML/SG ratio, weight reduction (WR), bulk density (BD), rehydration capacity (RC), drying times, and quality parameters, total color difference (ΔE), texture (hardness and chewiness) were evaluated during the process to assess the product quality. Drying conditions were optimized to maximize ML, ML/SG, WR, BD, RC and minimize ΔE, hardness, chewiness, and drying times. Optimum levels were found at 58.5 °C temperature, 50.0% concentration, and 30 min contact time during MWODS and 20% initial power up to 50% moisture content and 10% final power level to the final moisture content of 20% (32 min). In addition to MVD, freeze drying, vacuum and air drying were also used for comparison for finish drying. Overall, the MWODS with maltodextrin moderated sucrose as solute and MVD for finished drying resulted in better product quality and remained closest to the freeze dried samples.

Robust Class E2 Wireless Power Transfer System Based on Parity–Time Symmetry

Thanks to the superiority of zero-voltage switching (ZVS), the Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> topology has become a promising candidate in wireless power transfer (WPT) at medium and small power levels. However, in practical applications, it is a challenging and significant issue to maintain robust WPT under varying transfer distances, especially for the highly sensitive Class E power amplifier (PA). To solve this issue, the parity–time (PT) theory is initially developed into the Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> WPT system. A general design procedure for the PT-symmetry-based Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> WPT system is proposed, including the parameters of the Class E PA, resonant tank, and Class E rectifier. The power losses and efficiencies of the above-mentioned components are analytically derived as well. The ZVS operation is quantitatively described for the PT-symmetry-based Class E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> WPT system, demonstrating that the maximum phase variation with coupling coefficient is rather small and independent of the natural resonant frequency, thereby achieving robust and highly efficient power transfer. Finally, the prototype with current feedback control to guarantee the PT mechanism and ZVS is built. The experimental results illustrate that under various coupling coefficients, robust and efficient power transfer is realized by a 165-W prototype with about 92.6% efficiency.

Output Current Ripple and Efficiency Optimal Control Method for Multi-Phase Interleaved LLC Resonant Converter

The interleaving technique is required for LLC resonant converters to achieve high power levels, handle higher input/output currents, and reduce output current ripple. However, the high system efficiency and the low output current ripple for the multi-phase LLC resonant converter cannot be achieved at the same time at low and medium power levels. Most methods try to keep the multi-phase LLC resonant converter in load-sharing mode regardless of the power level, which will result in low system efficiency at low and medium power levels. In this paper, an output current ripple and efficiency optimal control method with finite load distribution schemes is proposed for the multi-phase LLC resonant converter to balance the efficiency and output current ripple. The optimal control method improves the efficiency as much as possible while keeping output current ripple low. According to the calculation of output current ripple and efficiency, the optimal load distribution scheme is selected. The pulse-frequency modulation (PFM) and phase-shift modulation (PSM) hybrid control is applied to regulate the load of each phase. An analysis is provided, and a 540-W three-phase interleaved LLC resonant converter is built to verify the superiority.

Comparison of Microleakage of Mineral Trioxide Aggregate Apical Plug Applied by the Manual Technique and Indirect Use of Ultrasonic with Different Powers.

Statement of the Problem: A mineral trioxide aggregate (MTA) apical plug is commonly applied prior to endodontic treatment of open-apex teeth. However, difficult application and condensation of MTA in the apical region is a drawback of this technique.Purpose: This study aimed to compare the microleakage of MTA apical plug applied by the manual technique and indirect use of ultrasonic with different powers.Materials and Method: In this in vitro, experimental study, divergent open apices were created in 48 single-rooted, single-canal teeth using ProFile. The teeth were randomly divided into four experimental groups (n=10). All groups received 5-mm thick MTA apical plug at the apical region using one of the following methods. In group 1, MTA was manually condensed while in groups 2-4, indirect ultrasonic energy with minimum, medium, and maximum power levels was used for MTA plug condensation. After setting of MTA, the apical microleakage of the MTA plug was quantified using the fluid filtration method. Data were analyzed using the Mann-Whitney and Kruskal-Wallis tests (p< 0.05).Results: Significant differences were noted in microleakage of MTA plug between the manual group and ultrasonic groups with medium (p= 0.043) and maximum (p= 0.029) power levels. No significant difference was noted in microleakage of other groups (p> 0.05).Conclusion: Considering the current results, it seems that application of MTA with indirect ultrasonic energy at medium or high power level would decrease the microleakage of MTA plug in open-apex root canals.

A Simple Two-Stage AC-AC Circuit Topology Employed as High-Frequency Controller for Domestic Induction Heating System

The induction heating process at a domestic level is getting attention nowadays as this power converting topology ensures clean, reliable, flexible, and fast operation. The low input frequency is converted to required regulated high output frequency with indirect and direct power converting approaches. The circuit and control complexity and high conversion losses associated with indirect power converting approaches lower their uses for domestic induction systems. The direct ac-ac power conversion approach is one of the viable solutions for low and medium power level loads, especially for domestic induction heating loads. The circuit complexity, cost, and conversion losses of the direct power converting systems depend on the number of the controlled switching devices as each controlled switch requires one gate driving circuit and one isolated dc supply. Simplified pulse width modulation (PWM) switching control also lower their control effort. Therefore, in this article, a simplified direct ac-ac power converting approach is introduced for a high-frequency domestic induction heating system. Here, the regulation of the high output frequency is achieved by simply cascading the single-phase full-bridge rectifier with a full-bridge inverter with a simple control strategy. The characteristics of the developed topology are validated through simulation results of the Simulink-based platform and practical results of the developed practical setup.

Physicochemical properties of South African prickly pear fruit and peel: Extraction and characterisation of pectin from the peel

Abstract The aim of this study was to determine the physicochemical properties, extract and characterise pectin from green (Morado), purple (Algerian), and orange (Gymno carpo) varieties of South African prickly pear (PP) (Opuntia ficus-indica) fruit peel. Pectin was extracted using sulphuric acid at four different pH levels (1, 2, 3, and 4) and three different microwave power levels (low 300 W, medium 400 W, and high 500 W) at a fixed time of 10 min. Yield of pectin for purple ranged from 2.9 to 13.8%, orange from 1.4 to 9.8%, and from 2.3 to 10.0% for green prickly pear peel (PPP). Maximum yield of 13.8% on purple, 10.0% on green, and 9.8% on orange was obtained at pH 1.0 and medium power level. Ash content of the extracted pectin was significantly high at 25.16, 34.26, and 36.30% for green, orange and purple PPP, respectively. However, pectin showed lower moisture content and equivalent weight. The methoxyl contents were 2.28, 2.38, and 3.86%, for anhydrouronic acid contents were 25.58, 25.93, and 38.84%, and degree of esterification was 49.87, 50.63, and 56.39% across the orange, purple, and green varieties. The PPP pectin spectra exhibited similarities in their absorption pattern to that of commercial citrus pectin.

Predictive energy management of residential buildings while self-reporting flexibility envelope

In recent years, renewable energy resources have been increasingly embedded in the distribution grids, raising new issues such as reverse power flows, and challenging the traditional distribution system operation. In order to mitigate these issues, it has been proposed to operate the distribution system more flexibly. For instance, residential buildings are ideal candidates to offer energy flexibility locally and defer avoidable and expensive system expansions. Due to advances in smart meter technologies and trends towards digitalization, it becomes more and more common that electrical appliances in residential buildings are equipped with remote communication and control capabilities. This paper aims at quantifying a flexibility envelope of actively controlled flexible buildings and at analyzing the sensitivity of flexibility levels with respect to system configuration, control strategy and objective function settings. We consider rooftop photovoltaic units, air-sourced heat pumps for space heating and domestic hot water, thermal energy storage and electric vehicles. The results show that an optimal control aiming at minimizing energy costs while limiting peak power can lead to savings of up to 25% compared to the existing rule-based control. When carbon emissions are considered in the cost function, the optimized controller leads to an emission reduction of up to 21%. The time-dependent quantification of the flexibility envelope further reveals that high and low power levels can only be sustained for a limited period, whereas medium power levels can be sustained the longest.

Microwave filters on cavity resonators

Waveguide and cavity microwave filters continue to be the most important components of high-power radio electronic systems. Cavity microwave filters are of great interest as a separate group of devices of this type. The fields of application of such filters are constantly expanding, and the variety of their design is quite large. In addition, the requirements for their electromagnetic characteristics and reliability are currently increasing. In this regard, it becomes necessary to analyze the already created designs of these devices and study the main trends of their improvement. The objective of the present study is to review the known technical solutions of bandpass filters, made on cavity resonators of the microwave range. An overview of the designs of devices for filtering electromagnetic waves on cavity resonators with coaxial and waveguide coupling elements of various frequency ranges is carried out. It is proposed to use the configuration of basic resonators as the main criterion for the classification of these devices. In accordance with this criterion, five groups of filters are considered: on rectangular, cylindrical, spherical, coaxial resonators, as well as on resonators of complex shape. The review makes it possible to analyze the features of the implementation of different technical solutions for bandpass microwave filters of medium and high power levels and to identify the main trends in the development of this area of research.

Event-Focused Digital Control to Keep High Efficiency in a Wide Power Range in a SiC-Based Synchronous DC/DC Boost Converter

This paper is focused on the design of a control approach, based on the detection of events and changing between two different conduction modes, to reach high efficiency over the entire power range, especially at medium and low power levels. Although the proposed control strategy can be generalized for different topologies and specifications, in this paper, the strategy is validated in a SiC-based synchronous boost DC/DC converter rated for 400 V to 800 V and 10 kW. Evaluation of the power losses and current waveforms of the converter for different conduction modes and loads predicts suitable performance of quasi-square wave mode with zero voltage switching (QSW-ZVS) conduction mode for low and medium power and of continuous conduction Mode with hard switching (CCM-HS) for high power. Consequently, this paper proposes a control strategy, taking advantage of digital control, that allows automatic adjustment of the conduction mode to optimize the performance for different power ranges.

A switch-source cell-based cascaded multilevel inverter topology with minimum number of power electronics components

Multilevel inverters are a new generation of DC–AC converters at medium and high voltage and power levels. In this paper, a new single-phase cascaded multilevel inverter is presented. For this purpose, a new basic cell is presented at first. Then, the new multilevel inverter structure is yielded by series connection of these cells. The proposed new cell is only capable of generating positive voltage levels, and therefore, to produce zero and negative voltage levels, the proposed structure is constructed based on H-bridge module. In order to reduce the maximum blocking voltage especially on H-bridge switches, the cascaded connection of the proposed converter is investigated. A comprehensive comparison is carried out between the proposed multilevel inverter with the classical and recently introduced structures in terms of the number of switching devices, the number of drivers, the total blocking voltage of the switches as well as the loss and efficiency. The accuracy of the proposed inverter’s performance is simulated in MATLAB/Simulink in symmetric and asymmetric topologies for a 17-level and 23-level output voltage respectively, and then evaluated by the laboratory prototype.

Step-continuous phase power control of multi-section resonant inverter

The method of step-continuous phase power control of a multi-section resonant inverter on the basis of parallel connection of half-bridge inverter sections is proposed. Step power change consists of the commutation of synchronized step-controlled sections and continuous power control at power intervals between commutations is realized by the phase shift of pulses of a continuous-controlled section relative to the pulses of step-controlled sections. Such control provides the increase in inverter efficiency at the medium and low power levels, a wide power control range and constant inverter operation frequency.

Laser-induced nitrogen-self-doped graphite nanofibers from cyanate ester for on-chip micro-supercapacitors

The fabrication of high-content heteroatoms-doped carbon nanomaterials is crucial for energy storage. Conventional external heteroatoms-doping usually needs complex and time-consuming preparation processes. Here, we report the facile and high-efficient fabrication of high-content (10.3%) nitrogen-self-doped graphite in the form of banyan root hairs-like nanofibers by laser direct writing on nitrogen-enriched cyanate ester. The resulting laser-induced graphite nanofibers (LIGNFs) exhibit high-temperature stability up to 470 °C in air, which outperforms the laser-induced graphene (LIG), laser-sculptured carbide and MXenes. The medium power level of laser can produce high quality and uniform distributed nanofibers, while the high power level could generate root nodule-like and even agglomerated nanofibers with more effective conductive network and higher nitrogen content, leading to relatively low quality but lower sheet resistance (21.50 Ω/square). Benefiting from the reverse surface atom-controlled pseudocapacitive effect, the LIGNFs-based on-chip in-plane micro-supercapacitors (LIGNFs-IMSCs) provide a superior areal capacitance of 57.96 mF/cm2, which is about seven times as high as that of LIG-based IMSCs. Additionally, the LIGNFs-IMSCs present excellent cycling stability and nearly 100% coulombic efficiency after 12,000 cycles. The novel LIGNFs with high-efficient preparation process, high-thermal stability and excellent electrochemical performance may have promising applications for energy storage devices in extreme environments.

Single-Inductor Multiple-Output (SIMO) Buck Hybrid Converter for Simultaneous Wireless and Wired Power Transfer

In this article, a nonisolated single-inductor multiple-output (SIMO) dc–ac buck-derived hybrid converter for simultaneously driving multiple independent ac and dc loads using only a single inductor in the power stage is proposed. Compared with the prior art, the proposed SIMO-based hybrid converter carries the conspicuous advantages of 1) a simple, compact, and low-cost implementation of the power stage; 2) reduced component count; 3) high power density; 4) increased output power, better flexibility, and scalability in realizing any combinations of ac and/or dc loads; and 5) high efficiency. By operating in pseudocontinuous conduction mode (PCCM), this hybrid converter enables wireless and wired power transfer at medium-power level without cross regulation. In practice, this converter can serve as a Qi-compliant hybrid charger with multiple transmitting coils and universal serial bus (USB) charging ports for quick and concurrent multidevice charging. A hardware prototype of a single-inductor four-output (SIFO) buck-derived hybrid converter is constructed. The experimental results show that the SIFO converter produces a rated output power of 20 W and a maximum efficiency of around 88%.

Driving Range of Electric Vehicles Charged by Wireless Power Transfer

Electric vehicles (EVs) are limited by the on-board batteries in terms of driving range and charging duration. In this paper, the driving range of electric vehicles (EVs) charged by wireless power transfer (WPT) systems is investigated. Specifically, a force-based vehicle model is coupled with a simple extended battery model to simulate the impact of wireless charging on the state of charge of the accumulator sub-system. In total, three different scenarios, i.e., urban, highway and combined driving are presented. The trade-off between having a standalone charging option versus combined dynamic and quasi-dynamic wireless charging is outlined and minimum system requirements, such as charging power levels and road coverage, for unlimited range are established. Furthermore, the effect of external factors such as ambient temperature, battery age and wireless transfer efficiency is investigated. It is shown that employing combined charging at medium power levels is sufficient to achieve unlimited range compared to high power requirements for standalone charging. Finally, safety concerns regarding human exposure are addressed with lower charging powers.

Effect of process parameters on the recovery of lactose in an antisolvent acetone/acetone-ethanol mixture: A comparative study based on sonication medium.

Recovery of lactose from the whey using sonocrystallization was studied experimentally. The effect of sonication medium and irradiation power levels was evaluated using three different ultrasonic equipments. Effects of various parameters such as sonication time, pH of the medium, antisolvent (acetone and acetone-ethanol mixture) and concentration of lactose were determined. The optimal parametric conditions were analyzed using differential scanning calorimetry, thermogravimetric analysis, particle size distribution, and zeta potential measurements. Overall, the highest lactose recovery was obtained using a mixture of acetone and ethanol as antisolvent in bath sonication as well as atomization process.

A Family of Y-Impedance-Network Half-Bridge Converters with Additional Voltage Adjustment Function

Half-bridge converters have been widely used in multiple medium power level applications because of the advantages of having less switches and being easy to control. However, their inherent structure leads to low output amplitude and shoot-through problems. In this study, we propose a family of novel half-bridge converters implementing a Y-impedance-network with additional buck-boost voltage adjustment function with the aim of resolving these issues. In order to verify the effectiveness of the proposed topologies, simulations and experiments were conducted, the results which well validate the feasibility of the proposed converters.