High Power Conversion Research Articles

Efficient Charge Transfer in MAPbI3 QDs/TiO2 Heterojunctions for High-Performance Solar Cells

Methylammonium lead iodide (MAPbI3) perovskite quantum dots (QDs) have become one of the most promising materials for optoelectronics. Understanding the dynamics of the charge transfer from MAPbI3 QDs to the charge transport layer (CTL) is critical for improving the performance of MAPbI3 QD photoelectronic devices. However, there is currently less consensus on this. In this study, we used an ultrafast transient absorption (TA) technique to investigate the dynamics of charge transfer from MAPbI3 QDs to CTL titanium dioxide (TiO2), elucidating the dependence of these kinetics on QD size with an injection rate from 1.6 × 1010 to 4.3 × 1010 s-1. A QD solar cell based on MAPbI3/TiO2 junctions with a high-power conversion efficiency (PCE) of 11.03% was fabricated, indicating its great potential for application in high-performance solar cells.

Pre-sizing of a modular high power density DC/DC converter with GaN components

Finding the most appropriate architecture to achieve a function is a major engineering challenge. In the power conversion context, the question that arises is: what is the best trade-off between an architecture based on a single high-power converter and another based on the combination of multiple low-power converters? This article aims to answer this question in the specific case of the isolated interface between the low voltage (28VDC) and high voltage (±270VDC) buses of an aircraft. Towards this goal, the targeted power electronics converter is carefully modeled in order to obtain an accurate and fast computing model. A technological database of the different usable components is then used to feed an optimization algorithm. The execution of the latter achieves an attractive and robust result showing an excellent performance in terms of power-to-weight ratio, which is the key index of this study. The precision and speed of this computer-aided design is based on analytical models that are quick to run and therefore enable exploring almost exhaustively the search space. More specifically, the high-frequency transformer has a large relative mass and generates significant losses that are difficult to assess. A major modeling effort has been undertaken and has been enabled to define a simplified but convincing and accurate model (successfully assessed on a wide bandwidth using an experimental setup). It was used for the first time in this optimization process. According to the targeted aeronautical specifications, the two best solutions would make it possible to achieve a mass power density of 4.5kW/kg, i.e. twice as high as traditional solutions. This result very clearly shows that the appropriate use of the new GaN transistors makes it possible to make a technological breakthrough. Considering the voltage and current ratings of these components, this shows that the combination of multiple partial converters is very promising and will make it possible in the future to achieve a significant increase in the compactness of electrical power conversion functions. This sizing study therefore clearly shows the potential of the standardized design of power electronics converters and the search for the best combinations (series, parallel) to meet any specific specifications. Additionally, the developed approach, based on a modeling effort, especially as far as the high-frequency transformer is concerned, and collection of manufacturer data, also makes it possible to limit the implementations and associated tests.Hence, the main contributions of this article are (i) the assembly of the analytical models of the various components constituting an isolated DC–DC power supply, (ii) the simplification of an analytical model of the planar HF transformer, its experimental validation and its first use in a loop of optimization, (iii) the fact of showing supporting figures that GaN technology enables technological breakthroughs to achieve high power density, which opens the way to modular architectures based on partial converters of electrical power, (iv) the comprehensive description of a powerful pre-study design tool enabling to greatly reduce power converters’ time to market.

Double Dual High Step-Up Power Converter with Reduced Stored Energy

This paper introduces a dual-switchhigh step-up DC-DC power converter. The proposed converter features a high step-up voltage gain, relatively low cumulative stored energy over its inductors, low voltage stress on the active switches, and high efficiency, even at a relatively high duty ratio. An assessment of the proposed converter against conventional boost and a high step-up power converter is presented in terms of steady-state time, voltage gain, stored energy over its inductors, and efficiency. The assessment shows a reduction of 81.25% and 62.5% of stored energy in inductors to comply with the same operational conditions. Simulation and experimental results are provided to validate the benefits of the proposed dual-switch high step-up power converter.

Hybrid Si/SiC Switches: A Review of Control Objectives, Gate Driving Approaches and Packaging Solutions

Hybrid silicon (Si)/silicon carbide (SiC) switches are gaining increased attention for designing high-efficiency and high-power density energy conversion systems. They offer very good conduction and switching power loss performance compared to using only Si insulated gate bipolar transistor (IGBT) or SiC metal–oxide–semiconductor field effect transistor (MOSFET) devices as a result of combining the best properties of both devices. Several Si/SiC gate control strategies, gate driving approaches, and packaging considerations have been proposed in the literature. This article presents a comprehensive review and performance comparison of different Si/SiC gate control strategies, gate driver solutions, and packaging approaches that are already proposed in the literature. In addition, it aims to provide a general guideline for selecting the appropriate Si/SiC gate control approach that is suitable for different applications considering several Si/SiC switch design properties. It also aims to establish a general metrics for evaluating the performance of different Si/SiC gate driver solutions that are proposed in the literature in order to help the designer choose a suitable gate driver solution for different applications. Moreover, it highlights future research and development needs of hybrid Si/SiC switches in terms of gate control techniques, gate driver approaches, and packaging solutions in order to achieve further performance improvements and fully exploit their benefits.

系統連系変換器の高調波共振現象に対する組み合わせ補償制御と補償安定性

This paper presents a theoretical discussion on a combined-compensation control method and its stability on harmonic resonance for grid-connected converters. The interaction between the grid impedance and the grid-connected converter potentially creates harmonic resonance. The compensation control with a combination of a digital filter and a virtual impedance is an effective solution for this problem. The theoretical analysis developed in this study reveals that the proper use of the two control schemes enhances the availability of grid-connected converters. Simulated results obtained from a three-phase high-power converter system verify this analysis.

Corrections to “A Reliable Medium-Voltage High-Power Conversion System for MWs Wind Turbines” [Apr 20 859-867

This addresses errors in [1]. The first author's affiliation information in the footnote is mistyped. The corrected sentence should read:

Benzo[d]thiazole Based Wide Bandgap Donor Polymers Enable 19.54% Efficiency Organic Solar Cells Along with Desirable Batch-to-Batch Reproducibility and General Applicability.

The limited selection pool of high-performance wide bandgap (WBG) polymer donors is a bottleneck problem of the nonfullerene acceptor (NFA) based organic solar cells (OSCs) that impedes the further improvement of their photovoltaic performances. Herein, a series of new WBG polymers, namely PH-BTz, PS-BTz, PF-BTz, and PCl-BTz, are developed by using the bicyclic difluoro-benzo[d]thiazole (BTz) as the acceptor block and benzo[1,2-b:4,5-b']dithiophene (BDT) derivatives as the donor units. By introducing S, F, and Cl atoms to the alkylthienyl sidechains on BDT, the resulting polymers exhibit lowered energy levels and enhanced aggregation properties. The fluorinated PBTz-F not only exhibits a low-lying HOMO level, but also has stronger face-on packing order and results in more uniform fibril-like interpenetrating networks in the related PF-BTz:L8-BO blend. A high-power conversion efficiency (PCE) of 18.57% is achieved. Moreover, PBTz-F also exhibits a good batch-to-batch reproducibility and general applicability. In addition, ternary blend OSCs based on the host PBTz-F:L8-BO blend and PM6 guest donor exhibits a further enhanced PCE of 19.54%, which is among the highest values of OSCs.

Tripodal Triazatruxene Derivative as a Face-On Oriented Hole-Collecting Monolayer for Efficient and Stable Inverted Perovskite Solar Cells.

Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized π-conjugated structures, hole extraction is expected to be more efficient when the π-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration. The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 23.0%.

Vertical GaN-on-GaN pn power diodes with Baliga figure of merit of 27 GW/cm2

High power vertical GaN devices are in great demand recently due to their potential on extremely high-power conversion efficiency. Here, we show vertical GaN p–n power diodes fabricated on bulk GaN substrates with an optimized guard ring structure for electrical field management and high breakdown voltage. By using a low doped (∼1015 cm−3) 28 μm thick drift layer in combination with optimized ohmic contacts, a breakdown voltage (VB) of 4.9 kV and a low specific on-resistance (RON) of 0.9 mΩ cm2 were achieved. In combination with the high breakdown voltage and low specific on-resistance, the device demonstrated a Baliga figure of merit (V2B/RON) of 27 GW/cm2.

High-Power Converters and Challenges in Electric Vehicle Wireless Charging – A Review

This article reviews various inductive and capacitive wireless charging systems to achieve high-power infrastructures. The characteristics of SAE, ICINRP, and IEEE safety standards for wireless charging technology were highlighted. The working of compensation circuits, resonant converters, and challenges in wireless power transfer (WPT) systems was discussed. The mechanism of different compensation circuits used in the WPT was discussed in detail. In addition, the design of the converter circuit topology of inductive and capacitive power transfer systems in electric vehicle (EV) batteries was highlighted. The foreign object detection (FOD) methods that prevent output power variations due to metal/living objects in the charging environment were explored. The foreign object detection (FOD) techniques in terms of impedance variations in the primary side of the charging circuit were explained. This review on EVs would help researchers and industrialists to identify and develop novel charging infrastructure with low cost and charging time.

UV-Blocking and Transparent Polydimethylsiloxane Film for Improving Stability of Perovskite Photovoltaics

Long-term stability of high-power conversion efficiency (PCE) against UV degradation is imperative to commercialize organometallic halide perovskite solar cells (PSCs). This degradation problem can be solved by blocking UV light, but it leads to a decrease in the PCE due to the decrease in the total amount of absorbed light in the PSC devices. Here, we propose a facile strategy for this challenging problem by attaching textured and UV-blocking bilayer PDMS films with a gradient refractive index onto the glass of PSC devices. We fabricated a gradient-refractive-indexed PDMS film by adopting a two-layer structure─a pure PDMS layer and a UV blocker (2,2′-dihydroxy-4-methoxy benzophenone)-added PDMS layer. The two-layer structure of PDMS films blocked the UV region (>380 nm) and increased the average transmittance by 1.8% at 600–800 nm due to the gradient refractive index. Additionally, the two-layered PDMS films were surface-textured by pattern replication from chemically etched Si surfaces. Surface texturing improved the average transmittance by 4.11% in the visible region as compared to that for the pure-flat PDMS film. The final PDMS film exhibited blocking of light >380 nm and enhanced absorption in the 400–800 nm region. As a result, MAPbI3 PSCs with a surface-textured bilayer PDMS film showed 0.8% higher PCE than did pristine devices. The PCE of the encapsulated device maintained over 90% of its initial performance after 240 h at 55% relative humidity under outdoor conditions and delivered 87% device performance even with additional UV irradiation after 240 h.

Single-Inductor, Multiple-Input, Multiple-Output, DC-DC Converter Based on a New Software Zero-Current Switching (ZCS) Technique

A single-inductor multiple-input multiple-output converter is proposed in this paper that can be used in low-power systems due to low output current and voltage. This converter is implemented discretely, and only one microcontroller is employed to control the system. The unique zero-current switching (ZCS) technique considered in this paper is such that only by reading the inductor’s left-side voltage the optimal value of the inductor discharge duty cycle is determined. This method can be generalized to low-power and high-power converters, whether implemented and designed as discrete or integrated. This converter works in discontinuous conduction mode. It uses pulse width modulation control and the time-multiplexing control method, which makes the system have high efficiency and makes the cross-regulation problem between the converter’s outputs tiny. The control algorithm considered in this converter is digital, which determines the optimal charge and discharge duty cycles. Also, the switching frequency of this converter is constant, relatively low, and equal to 5[Formula: see text]kHz. The efficiency of this converter has reached 91.6% by using the ZCS technique and other mentioned control methods.

Deadbeat Voltage Control for a Grid-Forming Power Converter With LCL Filter

Grid-forming power converters are controlled as voltage sources to regulate the grid voltage and frequency. These converters can increase power system strength if they impose a voltage waveform resilient to grid transients. For this reason, in this paper, we propose a deadbeat control strategy of the capacitor voltage for high power converters with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter. To damp the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> resonant poles, an active damping strategy is developed, based on a modification of the deadbeat control law. With this purpose, a notch filter is applied to the electrical variables allowing to emulate different damping resistances for the fundamental component and the harmonics. As a result, the active damping does not introduce tracking errors of the fundamental frequency component, while it provides damping to the filter resonance. The proposed strategy does not require knowledge of the grid impedance, an interesting feature in grid-connected power converters because the grid impedance is generally unknown. Experimental results validate the proposed strategy.

Solar cell capacitance simulation and experimental photovoltaic performance analysis of perovskite solar cell based on CsGeI3

In this study, the experimental results of the perovskite solar cell with FTO/TiO2/CsGeI3/spiro-OMeTAD/Pt cell architecture are compared with the simulated results obtained using SCAPS-1D. Optimizations have been carried out by changing TiO2 ETL with CdS and Cd0.5Zn0.5S and spiro-OMeTAD HTL with inorganic CuI, Cu2O, CuSCN and NiO, thickness of perovskite, ETL, HTL and the temperature to formulate a high-performance perovskite solar cell. The impact of varying absorber thickness, ETL and temperature exhibit very minimal or no change. However, the simulated device exhibits high power conversion (4.94% to 7.12%) efficiency by replacement of TiO2 with Cd0.5Zn0.5S. Further, the impact of change of inorganic HTLs have also been studied by considering Cd0.5Zn0.5S as ETL. All inorganic HTLs outperformed well with almost similar cell efficiency (∼19.9%); NiO being highest. Therefore, analyzing all the results, we suggest that to draw a high-power conversion efficiency Cd0.5Zn0.5S shall be chosen as ETL possessing 95 nm layer thickness, 10 nm thick NiO as HTL and keep the absorber thickness 795 nm. Thus, the structure of the simulated solar cell device FTO/Cd0.5Zn0.5S/CsGeI3/NiO/Pt having such cell characteristics can be considered in the manufacturing workflow for its mass-scale production.

Non-fused Polymerized Small-Molecule Acceptors with a Benzothiadiazole Core for All-Polymer Solar Cells.

Polymerized small-molecule acceptors (PSMAs) have made significant progress as the application in all-polymer solar cells (all-PSCs). Most PSMAs are constructed by near-infrared fused-ring electron acceptors via Stille polymerization, such as Y-series acceptors. However, very limited non-fused electron acceptors with simplified synthetic complexity have been used in PSMAs. In this work, two non-fused PSMAs with a benzothiadiazole (BT) core are developed for application in all-PSCs. The S-O non-covalent interaction and the regioregularity have been introduced to improve the crystallinity and charge transport properties. As a result, a high-power conversion efficiency (PCE) of 11.42% with an enhanced photocurrent has been obtained in these regioregular PBTO-γ-based solar cells, representing the highest PCEs based on non-fused PSMAs. The encouraging results will intrigue more design of non-fused PSMAs toward high-performance all-PSCs.

A High-Power Solar PV-fed TISO DC-DC Converter for Electric Vehicle Charging Applications

In this paper, a two-input, single-output (TISO) DC-DC converter for electric vehicle charging applications with solar photovoltaic (PV) as one of the sources is discussed. A novel, simple, and effective control strategy with maximum power point tracking (MPPT) to maximize power from PV while maintaining a constant bus voltage is proposed. A 100 V, 100 W TISO DC-DC converter is designed and comprehensive simulations are conducted under different conditions. The system characteristics are validated by comparing the results with a conventional P&amp;O algorithm and multiple step size P&amp;O algorithm. The proposed control strategy can precisely generate control signals to track MPPT while maintaining the bus voltage by controlling the output of a fixed DC source according to the changes in PV generation. The overall efficiency of the proposed approach is 98.67%, and the average output voltage is 99.09 V under selected conditions. The overall average output voltage ripple is 0.22% with the proposed approach, while it is 2.91% and 1.55% with the conventional P&amp;O and multiple step size P&amp;O MPPT techniques, respectively. Further, a 500 V, 17 kW high-power converter is designed and a simulation is carried out. The high-power converter provides an average output voltage of 496.92 V with an overall efficiency of 98.72%, and the average output voltage ripple is 0.16%. The results obtained from the simulation under the selected conditions lead to the conclusion that the converter has better efficiency and less variation in the output voltage at higher power levels with the proposed control technique.

Design of new bithieno thiophene (BTTI) central core-based small molecules as efficient hole transport materials for perovskite solar cells and donor materials for organic solar cells

This present study focuses on designing five bithienothiophene (BTTI) central core-based small molecules (MPA-BTTI-A1-MPA-BTTI-A5) in exploring the optoelectronic properties to ensure their potentiality as donor candidates for organic solar cells (OSCs) and HTMs. MPA-BTTI-A1 and MPA-BTTI-A3 are tailored by the replacing thiophene-bridge end-capped acceptors on one side terminal of reference (MPA-BTTI-R). Similarly, MPA-BTTI-A2, MPA-BTTI-A4 and MPA-BTTI-A5 have been designed by employing the same strategy on both side terminals. To ascertain stable geometric structures, CAM-B3LYP/6-311G (d,p) is selected and used in all computational simulations. The MPA-BTTI-A1 exhibits the least energy gap of 1.69 eV with greatest λmax at 722 nm in dichloromethane (DCM) and highest dipole moment of 19.59 D in DCM solvent, indicating excellent miscibility as compared to the model/reference. All newly fabricated molecules (MPA-BTTI-A1- MPA-BTTI-A5) suggest excellent operational efficiency due to their higher Voc also relatively high-power conversion efficiency (PCE) in comparison to reference. Also, all fabricated molecules are attributed with a greater estimated PCE of range (20.74–40.3%), than reference (PCE = 16%). The highest electron mobility of 0.0871 eV is observed in MPA-BTTI-A3 andMPA-BTTI-A2 exhibits the highest hole mobility of 0.1334 eV. Hence, the modification scheme is a promising way in designing proficient photovoltaic materials, paving ways for new design and advancement of a small-molecule HTMs for donor contributors for organic solar cells (OSCs) and in PSCs.

Tuning Surface Oxidation States of Nickel Oxide for Efficient Inverted Perovskite Solar Cells

Nickel oxide (NiOx), as an inorganic p-type semiconductor, has been widely adopted as hole-transporting layers in perovskite solar cells. Despite its superior material stability, the poor charge extraction and multi-vacancies greatly restrict the photovoltages and efficiencies. Here, we propose a facile method to tune the surface oxidation states of NiOx films by a lithium salt treatment for photovoltage enhancement. X-ray photoelectron spectroscopy measurement indicates that the lithium treatment only reduces the Ni3+ sites at the top region rather than in the bulk of NiOx films. This graded distribution allows more efficient charge extraction at the NiOx/perovskite interface as revealed by photoluminescence studies. Through a combination of capacitance–voltage and drive-level capacitance profiling measurements, we confirm enhanced built-in potentials and decreased interface defect densities in lithium-modified devices. Further modifying the interface with a self-assembly monolayer, the energy offsets at the interface can be largely reduced. Based on these enhanced properties, the modified devices achieve a high-power conversion efficiency of 22.4% (0.07 cm2) with a 120 mV enhancement in photovoltage in comparison with the untreated devices.

Induction brazing of NdFeB magnet with PVD-deposited AgCu alloy

The NdFeB magnets service in high-power electric-mechanical conversion devices sometimes endure high stress and high-temperature impact, and adhesion of these magnets using glue cannot ensure the reliability. In this study, the NdFeB was induction brazed with physical vapor deposition (PVD)-deposited Ag72Cu28 alloy layer, then the microstructure, mechanical properties and magnetic properties of the brazed joints were characterized, and effects of the filler metal thickness and the induction heating time were analyzed. The results show that the PVD coating can effectively prevent the surface oxidation of the NdFeB. The AgCu filler metal penetrates into the NdFeB and is partly mixed with the liquefied Nd-rich intergranular phase of the NdFeB, forming a good metallurgical bonding. The thickness of the penetration layer increases obviously with increase of the heating time and filler metal thickness. The bonding strength of the NdFeB brazed joint increases firstly and then decreases with increasing heating time, and a peak bending strength of 196.94 MPa was obtained. Fracture of the brazed joint occurs inside the NdFeB substrate close to the penetration layer. After a further annealing, the coercivity of the brazed NdFeB sample is a little higher than that of the un-brazed sample, and the squareness decreases by only a little. Properties of the brazed joints might be further improved by optimizing the amount of filler metal and the induction heating parameters.

Polyaniline/ZnO Hybrid Nanocomposite: Morphology, Spectroscopy and Optimization of ZnO Concentration for Photovoltaic Applications

The appropriate combination of semiconducting polymer-inorganic nanocomposites can enhance the existing performance of polymers-only-based photovoltaic devices. Hence, polyaniline (PANI)/zinc oxide (ZnO) nanocomposites were prepared by combining ZnO nanoparticles with PANI in four distinct ratios to optimize their photovoltaic performance. Using a simple coating method, PANI, ZnO, and its nanocomposite, with varying weight percent (wt%) concentrations of ZnO nanoparticles, i.e., (1 wt%, 2 wt%, 3 wt%, and 4 wt%), were fabricated and utilized as an active layer to evaluate the potential for the high-power conversion efficiency of various concentrations, respectively. PANI/ZnO nanocomposites are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) absorption, energy dispersive X-ray (EDX), and I-V measurement techniques. The XRD analysis showed a distinct, narrow peak, which corresponds to the wurtzite ZnO (101) plane. The SEM analysis verified the production of the PANI/ZnO composite by demonstrating that the crystalline ZnO was integrated into the PANI matrix. The elemental composition was determined by energy dispersive X-ray analysis (EDX), which confirmed the existence of PANI and ZnO without any impurities, respectively. Using Fourier transform infrared (FTIR) spectroscopy, various chemical bonds and stretching vibrations were analyzed and assigned to different peaks. The bandgap narrowing with an increasing PANI/ZnO composition led to exceptional optical improvement. The I-V characterization was utilized to investigate the impact of the nanocomposite on the electrical properties of the PANI/ZnO, and various concentrations of ZnO (1 wt%, 2 wt%, 3 wt%, and 4 wt%) in the PANI matrix were analyzed under both light and dark conditions at an STC of 1.5 AM globally. A high PCE of 4.48% was achieved for the PANI/ZnO (3 wt%), which revealed that the conductivity of the PANI/ZnO nanocomposite thin films improved with the increasing nanocomposite concentration.