DC Type Research Articles

Techniques for Analyzing and Reducing Voltage Conversion Ratio Transition Losses of Capacitive DC–DC Converters for Fast-DVS-Enabled Systems

Switched-capacitor (SC) converters have numerous advantages in supplying fast and fine-grained voltages to microprocessors. However, the losses associated with the voltage conversion ratio (VCR) transition, which has not been investigated in detail, may cause a significant efficiency drop. This letter presents a simple and accurate model for estimating energy losses during the VCR transition of many-ratio SC dc–dc converters. The loss model begins with the assumption that the charge redistribution among flying and load capacitors is the leading cause for the VCR transition losses. The analysis of different types of many-ratio SC dc–dc converters shows that the model is consistent with the simulated results. For more verification, a test chip containing a converter with an algorithmic voltage-feed-in topology was fabricated in a 0.18-μm CMOS process, with the measured results also in good agreement with the model outcomes. Furthermore, to mitigate the VCR transition loss, several techniques are discussed and analyzed based on the presented model. In particular, the SC converter with flying capacitor reordering method shows 28.9% conversion efficiency improvement over the conventional SC converter with negligible circuit overhead.

Minimization of Network Power Losses in the AC-DC Hybrid Distribution Network through Network Reconfiguration Using Soft Open Point

The Alternating Current-Direct Current (AC-DC) hybrid distribution network has received attention in recent years. Due to advancement in technologies such as the integration of renewable energy resources of DC–type output and usage of DC loads in the distribution network, the modern distribution system can meet the increasing energy demand with improved efficiency. In this paper, a new AC-DC hybrid distribution network architecture is analyzed that considers distributed energy resources (DER) in the network. A network reconfiguration scheme is proposed that uses the AC soft open point (AC-SOP) and the DC soft open point (DC-SOP) along with an SOP selection algorithm for minimizing the network power losses. Subsequently, the real-time data for DER and load/demand variation are considered for a day-a-head scenario for the verification of the effectiveness of the network reconfiguration scheme. The results show that the proposed network reconfiguration scheme using AC-SOP and DC-SOP can successfully minimize the network power losses by modifying the network configuration. Finally, the effectiveness of the proposed scheme in minimizing the network power losses by the upgraded network configuration is verified by constructing an AC-DC hybrid distribution network by combining two IEEE 33-bus distribution networks.

RANCANG BANGUN SEPEDA DENGAN MOTOR DC 350 W

Teknologi sekarang tidak bisa lepas dari sumber energi yang digunakan. Contohnya hampir semua kendaraan bermotor di negara-negara maju ataupun berkembang menggunakan energi bahan bakar minyak (BBM). Saat ini, sumber bahan bakar minyak semakin hari semakin menipis, maka di butuhkanlah energi lain sebagai energi alternatif baru untuk mengurangi krisis energi yang bertujuan untuk membuat energi minyak di bumi ini bisa bertahan lama dan tidak habis. Maka dari itu untuk mengurangi pemakaian BBM dibutuhkan alternatif lain untuk mengurangi pemakaian BBM ataupun minyak bumi tersebut. Alternatif nya ialah sepeda dengan menggunakan listik ataupun disebut sepeda listrik. Sepeda listrik adalah kendaraan tanpa bahan bakar minyak yang digerakkan oleh dinamo dan akumulator, yang terbagi dalam dua jenis arus, yaitu DC maupun AC. Namun di dalam penggunaan secara massal di Indonesia, motor listrik yang beredar bertipe arus DC. Sepeda listrik bisa di bilang sebagai alat tranportasi alternatif yang sangat efesien, di Indonesia sepeda listrik sangat cocok karena di Indonesia beriklim tropis, sangat cocok sebagai sarana olahraga. Sepeda listrik juga tidak menimbulkan polusi, tidak berisik, tidak memerlukan izin khusus, tidak memerlukan lahan parkir yang luas dan biaya perawatannya juga lebih rendah dari pada kendaraan bermotor atau alat transportasi lainnya.

IMPLEMENTASI PLTMH UNTUK MENDUKUNG GREEN TECHNOLOGY DI DUSUN PETAPAN KLUNGKUNG

The area of Petapan Hamlet is an upstream area where there are still many water sources as the main flow for downstream irrigation. There is one secondary stream with a fairly large channel size (2 m wide and 1 m deep). The flow velocity of this channel averages 1.6 m / sec with an average water depth in the dry season of 40 cm. The relatively large size of the channel results in a water flow of 1.26 liters / second. There is one place where the dimension of the channel shrinks for the distribution of irrigation to a width of 1 meter so that the correlation with a steady flow rate will increase. The people of Petapan Hamlet have built a tourism area based on green tourism with educational tourism as the main point. This tourism area is traversed by the subak water channel which will later be used as a place to play and educational tours about the subak irrigation system for tourists visiting this place. There is no supporting infrastructure in developing this tourism, both facilities and supporting facilities for the convenience of tourists in carrying out their activities The energy source that will be used to support the development of educational tourism is obtained from PLN sources. Lack of knowledge of the tourism community based on green tourism green technology (environment-based energy) which can be used as educational tourism In 2019, a micro hydro generator in the form of a waterwheel has been built with an output power of 7000 kg / cm2. This power is obtained from the encouragement of water flow when it touches the blade of the wheel. This power is relatively large if it can be transmitted to generators. Problems that arise related to large power are small rotations. From the mill, the maximum rotation produced is 15 rpm. Making the rotation conversion by means of pulley reduction and gearbox resulting in a rotation of 1500 rpm. This obstacle is overcome by utilizing a DC type generator to lighten rotation and losses due to friction with 500 watts of power.

A novel role for local immune suppression in chronic q fever infected abdominal aortic aneurysms?

Abstract Background Chronic Q fever (QCF) is the persistence of C. Burnettii after an acute infection. Atheromas in the abdominal aorta are a preferential location of this bacterial persistence and may result in accelerated abdominal aorta aneurysm (AAA) formation or even rupture. CQF is characterized by a poor response to antibiotic therapy with high mortality. The localization of the bacteria in the acidic lysosomes is thought to be the main cause of poor antibiotic efficacy. Purpose A potent immune system is mandatory for successful antibiotic therapy. PBMC simulation assays have shown potent immune activation on stimulation with C. Burnettii. Here we assess whether this holds true in situ by combining 3 six-marker panels with phenotypical markers describing the adaptive and innate immune system and looking at key check-points in immune regulation. Methods (Tissue) PCR-positive CQF infected AAAs (n=10) are compared to atherosclerotic AAAs (n=13) and normal abdominal aortas from kidney transplant donors (n=3). We combine DAPI and elastin autofluorescence with 3 distinct panels of 6 markers in an 8-color IHC technique (Vectra 3, Perkin Elmer, MA) to describe the local immune landscape. The panels focus on 1) adaptive immune response, 2) innate immune response and 3) checkpoint inhibitors. Cells were phenotyped and quantified using an automated quantitative analysis method. Results In contrast to normal abdominal aortas, both atherosclerotic AAAs and CQF AAAs show impressive lymphocyte recruitment and proliferation with the formulation of very large tertiary lymphoid structures. CQF AAAs show a 2-fold increase in regulatory T cell numbers compared to atherosclerotic AAAs. These regulatory cells are both surrounding germinal centers and are seen throughout the tissue. Additionally, CQF AAAs show more positive cells and a higher expression of PD-L1, which is a key immunosuppressive mediator. Conclusion The immune landscape within the aortic wall shows far greater immune suppression than previously found in in vitro and peripheral blood studies. We show that CQF infections are associated with severely increased numbers of regulatory T cells, even compared to the low-grade and chronic inflammation present in atherosclerosis. Subsequently, a look at the immune checkpoint PD-L1 shows an increased expression in CQF aortas, elucidating a possible underlying mechanism and treatment target. Figure 1. Representative microscopy images of normal (left) atherosclerotic AAA (middle) and CQF AAA (right), full thickness overview (top row) and magnified region off interest (bottom row). Vast increase in regulatory T cells (FoxP3+), recognisable by the yellow nucleus, surrounding germinal centres in only the CQF aorta. Furthermore, DAPI in blue, B cells in green, helper T cells in red, cytotoxic T cells in cyan, classic DC type 2 in magenta. Funding Acknowledgement Type of funding source: Public grant(s) – EU funding. Main funding source(s): ERC starting grant (ERC-2014-StG-336454-CoNQUeST); TTW-NWO open technology grant (STW-14716)

Performance evaluation of solar PV pumping system for providing irrigation through micro-irrigation techniques using surface water resources in hot arid region of India

Solar PV pumping system for irrigation purpose has been gained importance in recent times considering its environmental friendly characteristics and to reduce the dependency on fossil fuel based energy sources for pumping. In general, 3 HP and 5 HP capacity solar PV pumping systems are used for irrigation purpose in India. However, large capacity pumps are often also used to lift groundwater resources, which may lead to further depletion of ground water table. Keeping in mind these constraints, performance of small sized solar PV pumps of 1 HP capacity was evaluated to lift and irrigate shallow water resources using pressurized irrigation systems. Experimental observations revealed that 1 HP solar PV pumping system either AC or DC type could successfully be used to operate mini-sprinklers, micro-sprinklers and drippers with good irrigation uniformity. Further, a self-sustainable module for sustainable use of water and energy was designed in which both water and energy are harvested and recycled. Life cycle cost analysis showed that 1 HP (DC) solar PV pumping system was slightly cheaper than corresponding AC pumping system. Even, the carbon footprint of 1 HP solar PV pumping systems is quite lower (0.009 kg CO2-eq ha-mm−1) than grid-connected electric pumps (1.214 kg CO2-eq ha-mm−1) and diesel operated pumps (0.382 kg CO2-eq ha-mm−1). Therefore, 1 HP solar PV pumping systems could be a feasible solution for small and marginal farmers in the context of water scarcity situation in near future and to mitigate the climate change effects in agricultural farms.

Single-Phase Bridgeless PFC Topology Derivation and Performance Benchmarking

This article introduces two general ways to derive single-phase bridgeless power factor correction (PFC) topologies and then, 15 accessible bridgeless topologies are derived based on the configuration of different basic types of dc–dc converter cells. Although the majority of the topologies have been previously proposed, other possible research points are reviewed. Besides, a consistent component sizing procedure with electric, thermal, and cost models is applied to conduct the performance benchmarking of these PFC topologies in terms of power loss, volume, and cost. Three boost-type PFC topologies are chosen as examples to demonstrate the procedure and the corresponding benchmarking results with both theoretical analyses and experimental verification. Finally, mission profiles of one specific application are introduced to show the material cost payback period of adopting one modified bridgeless boost topology instead of conventional one in different scenarios.

Performance analysis of DC type variable speed solar pumping system under various pumping heads

This paper proposes a method for the modelling, simulation and analysis of solar PV water pumping system. A submersible type variable speed DC water pump system is considered in this study under different pumping heads (50 m, 60 m and 70 m) and for 8S × 3P PV array configuration. The hourly electrical performance of the PV array was estimated from the maximum power points of the I-V curves, as the maximum power point tracking (MPPT) controller continuously optimizes the output power of the PV array. The performance equation which relates the flow rate of the pump with pump head and power input to the pump is modelled from the manufacturer’s performance curve with curve fitting technique. Using the generated equation and the calculated hourly power output data, the hourly performance of the solar driven water pump system was estimated for of different pump head. The analysis and simulation results show that a lower pump head results in higher flow rate regardless of the variation in solar irradiation level. The obtained result also indicated that an increase in solar radiation intensity resulted in an increasing of the pump flow rate, pump efficiency and system performance.

Climate-Smart Initiatives in Sri Lankan Agriculture Sector: Experience and Perspectives in Solar Powered Water Pumping for Sustainable Crop Production

The availability of low cost and long-lasting water pumping technology is a dream of every farmer. In Sri Lanka, fuel or electricity-powered water pumps are used to irrigate thousands of hectares of field crops, Vegetables, and fruits. Based on the International Water Management Institute (IWMI) survey conducted in the year 2000, there are about 50,000 agro-wells in the dry zone of Sri Lanka. More than 110,000 pumps are used to pump water from those wells. The fuel cost is the biggest burden for the farmers, which results in a high cost of production. The use of solar energy for water pumping is a promising alternative to conventional electricity and fuel-based water pumping systems. Solar-powered water pumping is based on photovoltaic (PV) technology that converts solar energy into electrical energy to run a DC or AC type water pump. This paper presents a comparative analysis of economic and environmental benefits associated with solar water pumping systems against fuel-based water pumping systems. The analyses were based on practical experience over 50 acres of land cultivated for export-oriented Green Cucumber by 100 members of Tempitiya Farmer Organization in Ampara District of Sri Lanka. It concluded that the solar water pumping system is advantageous compared to a fuel-based pump in terms of economic and environmental aspects.

Evaluation of Multifrequency Power Electronic Converters: Concept, Architectures, and Realization

There exist two well-known types of power transfer ac or dc. Power transfer at multiple frequencies has not yet gained much attention. This article aims at bringing out such topologies, which are capable of integrating different electrical power sources (ac or dc) irrespective of its frequency of generation, form a multifrequency (MF) bus, transmit power over a single line, and extract/convert them at the load side. This leads to the definition of unified utility/grid concept. For this, this article presents more insight into three possible MF converter topologies with renewable energy sources (RESs)/battery integration. The proposed topologies work on the principle of orthogonal power transfer. Furthermore, power transfer at multiple frequencies shows an effective way of decoupling the individual sources of the system. Finally, the feasibility of transferring power at multiple frequencies is validated experimentally and the results are discussed herein along with its potential benefits.

Analysis of the DC Fault Current Limiting Characteristics of a DC Superconducting Fault Current Limiter Using a Transformer

Recently, a lot of interesting research has been conducted to solve the fault current problem of the DC system. In long-distance transmission, DC transmission is more economical than AC transmission. The connection of power grids with a DC system can also better control the power flow and provide high stability. However, the control of the fault current in a DC system is more difficult to handle than in an AC system because the DC system does not make a zero point, unlike the AC system. In addition, there is a disadvantage, in that an arc occurs when a circuit breaker operates. In this paper, a new type of DC superconducting fault current limiter (SFCL) is proposed. This new type of SFCL is composed of two superconducting elements, a current limiting resistor/reactor (CLR), and a transformer. With the proposed SFCL, the DC fault current limiting experiments were performed and the DC fault current limiting characteristics of this SFCL due to the component of the CLR were analyzed.

Efficient Induction of Cytotoxic T Cells by Viral Vector Vaccination Requires STING-Dependent DC Functions.

Modified Vaccinia virus Ankara (MVA) is an attenuated strain of vaccinia virus and currently under investigation as a promising vaccine vector against infectious diseases and cancer. MVA acquired mutations in host range and immunomodulatory genes, rendering the virus deficient for replication in most mammalian cells. MVA has a high safety profile and induces robust immune responses. However, the role of innate immune triggers for the induction of cytotoxic T cell responses after vaccination is incompletely understood. Stimulator of interferon genes (STING) is an adaptor protein which integrates signaling downstream of several DNA sensors and therefore mediates the induction of type I interferons and other cytokines or chemokines in response to various dsDNA viruses. Since the type I interferon response was entirely STING-dependent during MVA infection, we studied the effect of STING on primary and secondary cytotoxic T cell responses and memory T cell formation after MVA vaccination in STING KO mice. Moreover, we analyzed the impact of STING on the maturation of bone marrow-derived dendritic cells (BMDCs) and their functionality as antigen presenting cells for cytotoxic T cells during MVA infection in vitro. Our results show that STING has an impact on the antigen processing and presentation capacity of conventionel DCs and played a crucial role for DC maturation and type I interferon production. Importantly, STING was required for the induction of efficient cytotoxic T cell responses in vivo, since we observed significantly decreased short-lived effector and effector memory T cell responses after priming in STING KO mice. These findings indicate that STING probably integrates innate immune signaling downstream of different DNA sensors in DCs and shapes the cytotoxic T cell response via the DC maturation phenotype which strongly depends on type I interferons in this infection model. Understanding the detailed functions of innate immune triggers during MVA infection will contribute to the optimized design of MVA-based vaccines.

Design of extended Kalman filter for SEPIC converter and comparison to Kalman filter

Single ended primary inductance converter (SEPIC) is a type of DC–DC converter whose industrial applications include maximum power point tracking and Active power factor correction. Owing to present nonlinear circuit components, SEPIC has discontinuous nonlinearity and for the mathematical model determination, state space averaging or more advanced modeling techniques are required. Once the approximated nonlinear model is obtained, the states of the plant can be estimated using a nonlinear state estimator. Nonlinear estimators are preferred mostly when the real trajectory of the states cannot be estimated accurately by a linear state estimator and the deviation from the linear behavior and nonlinear one is above what is tolerable for the applications. Extended Kalman filter (EKF), being such a state estimator is widely employed in control and fault monitoring applications where a complete or an approximated nonlinear model of the plant is available. EKF especially operates well for the plants where the nonlinearity does not cause the assumptions behind EKF to be violated. In this study, first an approximated nonlinear model for SEPIC is determined. Using the model, EKF is designed to estimate the states of the plant. The efficacy of the designed EKF is demonstrated in a series of numerical MATLAB based simulations where the both open loop and closed loop performances are analyzed, and the results are detailed in the paper.

Review on fault‐diagnosis and fault‐tolerance for DC–DC converters

The DC–DC converters operate extensively in a variety of industrial applications such as electric vehicles, renewable energy systems, aerospace applications, consumer electronics (smartphones, laptops, etc.) and energy storage solutions. The reliability of the DC–DC converters is of a greater significance. The research endeavours made in enhancing the reliability of the DC–DC converters are still very limited and dispersed. Due to the rapid growth in semiconductor technology, the DC–DC converters have an endless number of topologies, with various operating principles and functionalities. Enhancement of the reliability of all types of DC–DC converters is still a challenging task. Power switches are the most fragile components in converter circuits, which inherently fall prey to the faults occurring in the system. Hence, there is always a requirement to take appropriate remedial measures to deal with all kinds of faults. Further, in order to detect the occurrence of fault a fast fault-diagnosis and fault-tolerant strategies in the DC–DC converters is mandatory and the same has to be embedded in the converter for safety purpose. In view of the importance of the same, the fault-diagnostic algorithms and fault-tolerant strategies developed in the literature, by various researchers are furnished in a single document after conducting an exhaustive review.

Numerical simulation of weld nugget in resistance spot welding process

The resistance spot welding (RSW) stands different over other welding techniques as the actual weld nugget is shaped internally relative to the surface of the base metal. The weld formed is fundamentally a mix of heat, pressure and time. The welding conditions are precisely controlled to produce sound nuggets. The application of interface pressure allows accurate prediction of interfacial heat and electrical resistance, which plays a dominant role in Joule’s heat generation. In this work, lap welding using resistance spot welding has been numerically investigated for Mild steel (G-3302) and Stainless steel (SS-202) sheets. Spot welding has been completed by utilizing a 35 kVA DC type resistance spot welding machine, constrained by a Programmable Logic Controller unit. For both materials, two spots, three spots and four spots weld were done in order to obtain various comparative results. The weld nugget formation has been simulated using SIMULIA. The 3D model has been created by using GUI of commercial FEA package ABAQUS 6.14. The model employs coupled thermal-electrical-mechanical analysis. Simulation has been performed for pertinent parameters in ABAQUS 6.14. The obtained plots from numerical model are found to be in strong consistency with experimental data.

Transcriptome landscape of myeloid cells in human skin reveals diversity, rare populations and putative DC progenitors

BackgroundThe heterogeneous functions of dermal myeloid cells in antigen presentation, and scavenging pathogens and cell debris places them centrally in cutaneous inflammation. Single cell transcriptomics can provide new understanding of the heterogeneity and function of yet incompletely understood human dermal myeloid cell subsets. ObjectiveInvestigate the transcriptome landscape of myeloid cells in healthy human skin. MethodsSingle cell RNA-sequencing was performed on skin biopsies from ten healthy donors and analyzed to identify myeloid cell populations. ResultsOne LIN− HLA-DR+ cluster with expression of myeloid-specific genes was identified as a cluster of myeloid cells. Upon reanalysis of this cluster, we identified three macrophage subsets, marked by high expression of CCR1, MARCO or TREM2; and six dendritic cell subsets, marked by high expression of CLEC9A, CXorf21, MCOLN2, LAMP3, KIAA0101 and Langerin, representing respectively cDC1, two subsets of cDC2, a novel DC type, a cluster of proliferating DC, and a Langerhans cell subset. GO term analysis indicated specialized functions for the discrete rare populations of myeloid cells: TREM2 Mφ in lipid metabolism and LAMP3 DC as a mature cDC. Proliferating DCs appeared to represent cDC2 progenitors. ConclusionThe transcriptional landscape of myeloid cell populations in human skin indicates several, novel populations with specialized functions, as well as a rare proliferating DC population that likely accounts for local regeneration or expansion of dermal DCs. We provide robust gene expression markers for each of these populations that should permit better understandings of their roles in various homeostatic and pathologic immune processes in the skin.

A Generalized Additional Voltage Pumping Solution for High-Step-Up Converters

This study develops a generalized additional voltage pumping solution (GAVPS) for a series of high-step-up converters, whose topologies can be modeled by a generalized architecture. The newly designed converters can achieve additional voltage pumping by only applying an additional diode and capacitor to the conventional high step-up converter structure. Integrating the proposed solution into the existing high-step-up converters, five typical case studies with corresponding analyses and comparisons are conducted and presented, which verifies the proposed voltage pumping strategy. Additionally, five prototypes are built in this study, and the experimental results further validate the effectiveness of the proposed GAVPS solution. The proposed strategy in theory will work synergistically with all types of dc–dc converters, which demonstrates its unparalleled significance in expanding its applicability in contemporary power converter industries.

Optimal Configuration of Isolated Hybrid AC/DC Microgrids

This paper proposes a model for planning isolated microgrids. The goal of the proposed model is to minimize the investment, operational, and total costs of an isolated microgrid through the full identification of the system configuration. The model designates the optimal type of microgrid, i.e., ac, dc, or hybrid ac/dc, and the optimal sizing of both the distributed energy resources (DERs) and the electronic power converters, if needed. To render this planning approach generic, the model accommodates a wide variety of DERs, including ac and dc generators, capacitors, and energy storage systems. The detailed operational criteria of each power apparatus are taken into account in order to provide reliable operational scenarios. As a means of guaranteeing active and reactive power adequacy in isolated microgrids, the stochastic nature of generation and demand are also considered. The proposed model was developed analytically as a mixed integer nonlinear problem so that obtaining solution optima is thus possible with the use of a deterministic branch-and-bound nonlinear solver. The validity and effectiveness of the new formulation have been demonstrated through several case studies involving varied load topologies.

A New Type of DC Superconducting Fault Current Limiter

A new type of Superconducting Fault Current Limiter (SFCL) for dc applications is proposed. This SFCL consists of a current transmission/limiting coil, an iron-core, and a set of superconductor rings. The superconductor rings are placed between the current transmission/limiting coil and the iron-core. For application, the current transmission/limiting coil is connected in series to a dc transmission line. During normal power transmission, magnetic flux coupling between the current transmission/limiting coil and the iron-core is prevented by the magnetic shielding of the superconductor rings, and the current transmission coil has low impedance. Because of shielding effect of the superconductor rings iron-core has high permeability at the beginning of short circuit, current-limiting coil can effectively limit fault current rise. When the fault current reaches a certain level, the superconductor rings will quench and the shielding effect is greatly reduced. The current-limiting coil strengthens the coupling with the iron core, increases the inductance, and will suppress the further increase of the fault current. A laboratory proof-of-concept prototype was made to demonstrate the feasibility of the idea. Experiments have been carried out with the prototype. In this paper, we will introduce the detailed information of the principle, the prototype, and the experimental results. In addition, a design of the new type of dc SFCL is installed in a ±160 kV high-voltage direct current system.

Integration of DC circuit breaker and fault current limiter based on zero‐voltage resonant switching approach

It is known that most of the renewable energy resources are the DC type. However, DC microgrids do not have zero crossing in current and voltage. This results in serious concerns about the circuit breaking and fault current limiting in the power system. Conventional thyristor-based DC fault current limiters (FCLs) may provide possible solutions for this problem. Unfortunately, a permanent interruption would arise on the system in case of a temporary fault. For this reason, this proposal aims to develop an integration system of the circuit breaker and FCL using a feedback-controlled zero-voltage switching method. In this proposed model, a load current is detected and an appropriate switch signal is thus generated by the controller based on the feedback-control strategy. Once the load current is beyond the predefined value, the switch will be opened to reduce the current immediately for a period of time set by the timer in advance. Then, the switch will be closed again to raise the current continuously until the overload threshold is reached. The switching transition duration is located at the resonant zero voltage, so that no switching power is required. Both simulation and practical performance results confirm that an expected constant load current can be well controlled over an expected range.