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The hydrogen evolution and nitrite reduction reactions are key to producing green hydrogen and ammonia. Antenna–reactor nanoparticles hold promise to improve the performances of these transformations under visible‐light excitation, by combining plasmonic and catalytic materials. However, current materials involve compromising either on the catalytic activity or the plasmonic enhancement and also lack control of reaction selectivity. Here, we demonstrate that ultralow loadings and non‐uniform surface segregation of the catalytic component optimize catalytic activity and selectivity under visible‐light irradiation. Taking Pt−Au as an example we find that fine‐tuning the Pt content produces a 6‐fold increase in the hydrogen evolution compared to commercial Pt/C as well as a 6.5‐fold increase in the nitrite reduction and a 2.5‐fold increase in the selectivity for producing ammonia under visible light excitation relative to dark conditions. Density functional theory suggests that the catalytic reactions are accelerated by the intimate contact between nanoscale Pt‐rich and Au‐rich regions at the surface, which facilitates the formation of electron‐rich hot‐carrier puddles associated with the Pt‐based active sites. The results provide exciting opportunities to design new materials with improved photocatalytic performance for sustainable energy applications. [ABSTRACT FROM AUTHOR]

Summary: In this paper, for standalone and grid‐connected PV systems, a three‐phase simplified split‐source inverter (SSI) is proposed and controlled using a model‐predictive control (MPC). The maximum power point tracking (MPPT) approach used is an incremental conductance method based on a PI controller for both systems. The standalone system is composed of PV modules, a three‐phase SSI, and a bidirectional power DC–DC converter that connects a battery bank and a DC‐side capacitor. The output AC voltages of SSI are controlled using MPC. The bidirectional power DC–DC converter regulates the DC‐link voltage (DCLV). The grid‐connected system consists of PV modules, a three‐phase SSI, and an AC‐side L‐filter. The DC‐link PI controller generates reference currents for the MPC algorithm. The MPC uses these reference currents to adjust and deliver the PV power to the grid while regulating the DCLV. The PI controllers' parameters are selected for both systems using the Harris Hawks optimization method. Both PV systems simulation results show that under various operating conditions, they have succeeded in fixing a DCLV and producing a high‐quality AC output voltage and current at low THD. Experimental results for the three‐phase standalone PV system used to verify the system's performance. [ABSTRACT FROM AUTHOR]

Summary: Bridgeless ac‐dc converters are the optimal choice for many applications, as they offer many advantages such as low distorted supply current, high power factor, and improved efficiency. This paper presents a new topology for a single‐phase bridgeless ac‐dc converter. The proposed hybrid topology is based on integrating the inverting and non‐inverting buck‐boost dc‐dc converters that are connected to the ac supply through an LC filter. To insure sinusoidal supply current, the proposed hybrid bridgeless ac‐dc converter is operated in discontinuous current mode. The proposed converter has many merits, such as a reduced number of components, enhanced efficiency, and soft start‐up capability. The operation modes and design of the proposed converter are presented. In addition, a design method is proposed for the input LC filter to minimize the voltage stress across switches. Moreover, a small signal model for the proposed converter is developed. The proposed converter topology is simulated to evaluate the dynamic behavior and verify the accuracy of the presented small signal model. Furthermore, an 850 W prototype is developed to validate the features of the proposed converter experimentally. Tight voltage regulation, sinusoidal supply current, and near‐to‐unity power factor operation are observed from the results, regardless of supply or load disturbances. [ABSTRACT FROM AUTHOR]

Modular Multilevel Converters (MMCs) are promising candidates for high‐voltage high‐power applications. The main challenge of the MMCs is the zero‐frequency operation. To achieve a successful DC–DC conversion process with balanced capacitors' voltages with limited voltage ripple, this paper suggests the employment of the conventional two‐leg half‐bridge submodule‐based MMC structure in conjunction with a single bidirectional high‐voltage (HV) valve across the low‐voltage side. In the suggested structure, the HV valve is controlled on and off to ensure energy equalization for the MMC arms. In addition, soft‐switching for the HV valve is proposed to reduce the switching losses. Detailed illustration and design of the proposed concept are presented. Simulation and experimentation results are elucidated to show the effectiveness of the proposed DC–DC hybrid MMC. The results showed efficient performance of the suggested converter. [ABSTRACT FROM AUTHOR]

Due to the growing attention for the environmental impacts and power loss minimization, distributed generators (DGs) have been introduced widely into the electric power system. One of the challenges of integrating with the power system is to determine their optimal placement and sizing, which, when not respected, adversely affects the performance of the electrical network. In this paper, three multi‐objective algorithms of particle swarm optimization (PSO), variable constants (VCPSO) and genetic algorithm (GA) are adopted and implemented. The main objectives are to detect the optimum size and location of multiple DGs aiming to reduce the active power loss and improve bus voltage deviations in the distribution networks. The paper conducts a comprehensive review of the optimal size and location of the DG via systematic procedures, including definition, classifications, technologies of DGs. Then, the performances evaluation of the three optimization methods are presented and compared with other methods. The presented optimization methods are tested on the IEEE‐33 bus, 32‐line radial distribution network. Four different scenario‐based studies including base case and different number of DGs are performed to examine the accuracy of the presented algorithms. The obtained results prove that all the three algorithms are suitable for this multi‐objective optimization and VCPSO offers the best solution in terms of convergence and, and it has lowest average computation time. The performance and accuracy of the presented approaches and their improvements in the power loss and bus voltage profile are discussed and presented in detail. The obtained results show that more than 65% of active power loss reduction has been attained with the proper sizing and placement of DG systems. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

BACKGROUND: Zucchini yellow mosaic virus (ZYMV) infects cucurbits and has been identified as a major limiting factor in their production. The purpose of this study was to create copper oxide nanostructures (CONS) to control ZYMV in squash plants. Protection of squash against ZYMV was assessed in terms of virus severity, ZYMV concentration, transcription of pathogenesis‐related genes and growth enhancement of treated squash. RESULTS: The findings revealed that squash plants treated with CONS had a significant reduction in disease severity when compared with untreated plants. In squash plants treated with CONS, defense genes associated with the salicylic acid signaling pathway were strongly expressed compared with untreated plants. The structural characteristics of CONS, such as their small size and appropriate shape, added to their excellent anti‐ZYMV efficacy. CONS‐treated squash plants show significantly improved growth traits compared with untreated plants. CONCLUSION: Based on the results of this study, CONS may be a new strategy for the control of ZYMV in squash. This represents an unconventional solution to control this virus, particularly as no chemical pesticides can control viral diseases. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

In this work, a novel three‐phase unidirectional off‐board Electric Vehicles (EVs) fast charger is proposed. Each phase of the proposed converter consists of a two‐stage converter. The first stage is an AC–DC front‐end converter with power factor correction (PFC) control. The front‐end AC–DC converter is based on an isolated boost converter, which has a boosting capability and provides galvanic isolation. In this stage, parallel‐in parallel‐out isolated boost converter modules are employed in each phase. This enables sharing the current among modules to avoid implementing one module with a high current rating to meet the fast‐charging requirements. The multimodule option provides fault‐ride through capability for the proposed charger. The DC outputs of involved phases, that is, three isolated DC voltages, are fed to three cascaded DC–DC unidirectional buck converters. The charging terminals are used to charge the EV battery through a filter inductor with a charging current controller's aid. A detailed illustration of the suggested closed‐loop controllers is presented to ensure a successful operation for the proposed architecture. A simulation case study for a 25‐kW charger is presented. Finally, a 1‐kW prototype is implemented for experimental validation. [ABSTRACT FROM AUTHOR]

Dusty weather is a most important disturbance for photovoltaic (PV) systems, that may result in PV panels exposure to partial shading conditions where the PV panel characteristics show several maximum power points. Moreover, dusty weather conditions may lead to rapid changes in solar radiations. Thus, conventional power system tracking algorithms are not being capable to track the global maximum power point (GMPP). This paper provides an advanced maximum power point tracker for partial shading and dusty weather conditions. In the presented technique, scanning and power lock conditions are added to the conventional perturbations and observation technique in photovoltaic system under partial shading or dusty weather conditions. This tracking method scans the PV characteristic in steps and stores all the maximum power points in order to get the GMPP. The proposed tracker is capable to identify the uniform weather conditions to save it from having unnecessary scanning. In addition, this tracker permits dynamic tracking of the GMPP under dusty weather conditions with less fluctuations and stable operation compared to the conventional methods. Accurate and fast conversion to the GMPP during various weather conditions is accomplished using the proposed technique. The proposed modified perturb and observe technique is validated using simulation and practical results. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Medium‐/High Voltage DC grids are interesting for the integration of renewable energy sources. DC‐DC conversion systems are highly needed for the development of DC grids. Recently, Modular Multilevel Converter (MMC) is the most promising technology for medium‐/high‐voltage applications, but employing the conventional MMC with DC output voltage leads to diversion in the Submodule (SM) capacitor voltages, that is energy drift. This paper proposes a modified modular multilevel DC‐DC converter with self‐energy equalization, which ensures successful DC‐DC conversion with balanced capacitors voltages. In the modified topology, clamping Insulated Gate Bipolar Transistors (IGBTs) are employed in each arm to enable parallel‐connection of the capacitors in the same arm. During the operation (equalization period), the parallel‐connected upper capacitors are connected to the parallel‐connected lower capacitors in each leg through a small limiting inductor to transfer energy between the arms to ensure balanced capacitor voltages. The proposed configuration, along with the operational concepts, mathematical analysis, and design, are presented. Finally, simulation and experimental results are presented for validation. [ABSTRACT FROM AUTHOR]

The most common two challenges in high-voltage direct current (HVDC) multi-terminal transmission are the DC fault isolation and the DC voltage stepping up/down. Additionally, interconnecting voltage source converter (VSC)- and line commutated converter (LCC)-based HVDC network topologies has been challenging. This study introduces a new DC–DC converter topology concept connecting both LCC- and VSC-based HVDC networks with bidirectional power flow without operation stoppage. The proposed topology is formed of two front-to-front connected bridges with an AC-link formed of a capacitor and an inductor (which can be replaced by a transformer for voltage step-up/step-down). The LCC-HVDC network bridge is formed of insulated gate commutated thyristors while the VSC-HVDC network bridge is formed of insulated gate bipolar transistors. Therefore, ON/OFF switching of both bridges and bi-directional power flow are possible. Moreover, the reactive power transfer is nullified at rated active power exchange between the proposed converter bridges. The proposed concept's detailed analysis and control equations are introduced. Different operation scenarios are simulated in addition to scaled-down experimentation to test the applicability of power transfer scenarios without operation stoppage in normal operation. [ABSTRACT FROM AUTHOR]

Conventional modular multilevel converters (MMCs) are promising converters for high-voltage high-power applications. Unlike DC-AC conversion, DC-DC conversion of MMCs suffers from unbalanced capacitor voltages due to the energy drift problem. In this study, a new modular DC-DC converter is proposed, which consists of front-end half-bridge MMC with half-bridge submodules followed by full-bridge MMC with full-bridge submodules. The proposed modular multilevel DC-DC converter can be used effectively for connecting two different DC voltage levels in high-/medium-voltage DC grids. The proposed architecture provides successful DC-DC conversion with balanced capacitor voltages throughout the arm interchange concept. It also provides a high conversion ratio, bidirectional power flow, low losses, low current stresses, reduced number of submodules, and DC fault blocking capability. Detailed illustration, operational concept, and design of the proposed architecture with the arm interchange concept are presented. Simulation results for a high-voltage high-power DC-DC converter with the suggested approach are presented to demonstrate the system performance during different normal as well as abnormal operating conditions. Finally, a scaled-down prototype has been implemented for validation. The extracted simulation and experimental results elucidate the presented claims. [ABSTRACT FROM AUTHOR]

This study proposes a new back-to-back (BTB) current source converter (CSC) configuration and presents its application for variable speed wind energy conversion system. The proposed configuration consists of three cascaded ac−dc non-inverting buck-boost converter. The ac side of each converter is connected to an open-end winding of the three-phase permanent magnet synchronous generator and the dc sides are connected in parallel to a current source inverter (CSI) without the need for a dc-side capacitor. Ac−dc converters operate under discontinuous conduction mode, and they draw sinusoidal input currents at the unity power factor from fixed or variable magnitude and frequency supply. In addition, the proposed BTB CSC addresses one of the main drawbacks of the conventional CSI which is the over-voltage experienced by switches during commutation. Moreover, the switching losses of the proposed CSI are eliminated. The ElectroMagnetic Transients including DC (EMTDC)/Power System Computer Aided Design (PSCAD) software is used to assess the feasibility of the proposed topology during normal operating conditions and during low voltage ride through. [ABSTRACT FROM AUTHOR]

This study presents types 1 and 2 hybrid converters with reduced power circuit complexity compared with the mixed cell modular multilevel converter (MC-MMC). The type 1 converter is formed by replacing the director switches of the alternate arm converter by high-voltage (HV) half-bridge (HB) cells rated for half of the dc-link voltage. Also, it resembles special case of MC-MMC, where the entire HB cells of each arm are lumped into a single HV HB cell, with both capacitors of the half- and fullbridge cells are exposed to fundamental current as in the conventional MMC. The upper and lower arms of the type 2 converter resemble a front-to-front connection of two three-phase hybrid cascaded two-level converters, where the cell capacitors of the three-phase two-level converters that act as director switches do not experience fundamental currents. Therefore, the type 2 converter offers compact design compared with type 1 converter and the MC-MMC. The technical viabilities of the proposed hybrid converters are assessed using simulations, with both converters modelled in MATLAB-Simulink using electromagnetic transient simulation approach, considering normal and transient conditions. Experimental results obtained from single-phase type 1 converter confirm the practical viability of the proposed converters. [ABSTRACT FROM AUTHOR]

Although a modular multilevel converter (MMC) is universally accepted as a suitable converter topology for the highvoltage dc transmission systems, its dc fault ride performance requires substantial improvement in order to be used in critical infrastructures such as transnational multi-terminal dc (MTDC) networks. Therefore, this study proposes a modified submodule circuit for MMC that offers an improved dc fault ride through the performance with reduced semiconductor losses and enhanced control flexibility compared to that achievable with full-bridge submodules. The use of the proposed submodules allows MMC to retain its modularity; with semiconductor loss similar to that of the mixed submodules MMC, but higher than that of the halfbridge submodules. Besides dc fault blocking, the proposed submodule offers the possibility of controlling ac current in-feed during pole-to-pole dc short-circuit fault, and this makes such submodule increasingly attractive and useful for continued operation of MTDC networks during dc faults. The aforesaid attributes are validated using simulations performed in MATLAB/ SIMULINK and substantiated experimentally using the proposed submodule topology on a four-level small-scale MMC prototype. [ABSTRACT FROM AUTHOR]

Here, a new bi‐directional hybrid modular non‐isolated DC–DC converter is proposed where it consists of a boost converter (BC) fed from the high‐voltage (HV) side. At the BC output stage, a certain number of half bridge submodules (HB‐SMs) is connected across the BC switch. During the turn‐on period of BC switch, the HB‐SMs are connected sequentially to the low‐voltage (LV) side, which results in charging/discharging their capacitors from/into the LV side. While, during the turn‐off period, the LV side is bypassed and the HB‐SMs capacitors are connected in series across the BC output stage, which results in discharging/charging them into/from the HV side. The power flow is controlled in both directions by controlling the duty cycle. The proposed configuration provides self‐balancing operation thanks to the sequential connection of HB‐SMs capacitors, and it also provides the ability to operate with high conversion ratios. Illustration and analysis of the proposed converter and its closed‐loop controller are presented. A full design of the values and ratings of the involved components are presented. Simulation study for a 2.5 MW (25 kV/10 kV) DC–DC converter is presented. Finally, experimental results for a downscaled prototype are presented for validation. [ABSTRACT FROM AUTHOR]

This study extends a recently proposed dc auto-transformer to a true multi-port converter that can function simultaneously as dc auto-transformer and a dc/ac converter for dc voltage matching and tapping, and power control in highly meshed multi-terminal dc grids. The presented multi-port converter can generate multiple adjustable dc voltages from a fixed or variable input dc voltage, or from an active ac grid. Theoretical discussions and simulations indicate that when the proposed multi-port converter is used as a hybrid dc and ac hub to manage congestions and resolve loop flow issues in a highly meshed multi-terminal dc network, large dc power can be fed to the lower dc terminal, without exposing the switching devices of the lower subconverter to excessive current stress. Its increased control flexibility and response to dc faults at high and low dc terminals are validated using simulations and experiments. [ABSTRACT FROM AUTHOR]

This study proposes a new back-to-back current source converter (BTB-CSC) suitable for medium-voltage high power wind energy conversion systems (WECSs). It employs a dual three-phase permanent magnet synchronous generator and two current source inverters with a phase-shift transformer at the grid side. The proposed BTB-CSC has the following advantages: reduced power circuit and control complexity; low switching losses (zero switching losses at the inverter side); and independent control of active and reactive powers. Power system computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) simulations are used as to assess the steady state and dynamic behaviour of the proposed system under different operating conditions. It is shown that the proposed WECS can ride-through ac faults. Experimental results from scaled prototype of the proposed WECS are used to validate the simulations. [ABSTRACT FROM AUTHOR]

A single‐switch, single‐stage, three‐phase ac–dc buck–boost converter suitable for medium‐voltage applications is proposed. Basic relations that govern steady‐state converter operation are established, confirmed using PSCAD/EMTDC simulations, and substantiated experimentally. Simulation and experimental results establish that the proposed converter has good dynamic performance in buck and boost modes, with near unity input power factor. [ABSTRACT FROM AUTHOR]

The back-to-back (BTB) converter is used in power conversion applications such as machine drives, wind energy conversion systems (WECS), uninterruptible power supplies and high-voltage, direct current transmission systems. Various topologies have evolved around voltage source converters and current source converters (CSCs) in an attempt to meet various design and reliability constraints. This paper proposes a new CSC-based BTB converter suitable for WECS application. The proposed configuration addresses the main drawbacks of the conventional BTB CSCs, such as the over-voltage frequently experienced by switches during commutation. The inverter side converter has zero switching losses. The proposed WECS offers the following advantages: simple and easy control, reduced switching frequency and maximum power point tracking with controllable grid active and reactive power. A low-voltage ride-through (LVRT) solution is also provided in the proposed WECS. PSCAD/EMTDC simulation is used to assess the steady-state and dynamic behaviours of the proposed system under different operating conditions and during LVRT. Experimental results allow steady-state and dynamic behaviour assessment of the proposed system under different operating conditions. [ABSTRACT FROM AUTHOR]

The suitability of a single-stage ac-dc buck-boost converter for low-voltage applications is investigated. In-depth discussion and analysis of the converter's operating principle, basic relationships that govern converter steady-state operation and details of the necessary control structures needed to comply with the grid code are provided. The validity of the proposed system is confirmed using power system computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) simulations, and is substantiated experimentally. The buck-boost converter under investigation has good dynamic performance in both buck and boost modes, and ensures near unity input power factor over the full operating range, whilst having fewer devices and passive elements than other published versions of the buck-boost converter. [ABSTRACT FROM AUTHOR]