Overview of condition monitoring and operation control of electric power conversion systems in direct-drive wind turbines under faults

Electric power conversion system （EPCS）, which consists of a generator and power converter, is one of the most important subsystems in a direct-drive wind turbine （DD-WT）. However, this component accounts for the most failures （approximately 60% of the total number） in the entire DD-WT system according to statistical data. To improve the reliability of EPCSs and reduce the operation and maintenance cost of DD-WTs, numerous researchers have studied condition monitoring （CM） and fault diagnostics （FD）. Numerous CM and FD techniques, which have respective advantages and disadvantages, have emerged. This paper provides an overview of the CM, FD, and operation control of EPCSs in DD-WTs under faults. After introducing the functional principle and structure of EPCS, this survey discusses the common failures in wind generators and power converters; briefly reviewed CM and FD methods and operation control of these generators and power converters under faults; and discussed the grid voltage faults related to EPCSs in DD-WTs. These theories and their related technical concepts are systematically discussed. Finally, predicted development trends are presented. The paper provides a valuable reference for developing service quality evaluation methods and fault operation control systems to achieve high-performance and high-intelligence DD-WTs.

Adaptive Power Control Based on Double-layer Q-learning Algorithm for Multi-parallel Power Conversion Systems in Energy Storage Station

An energy storage station(ESS)usually includes multiple battery systems under parallel operation.In each battery system,a power conversion system(PCS)is used to connect the power system with the battery pack.When allocating the ESS power to multi-parallel PCSs in situations with fluctuating operation,the existing power control methods for parallel PCSs have difficulty in achieving the optimal efficiency during a long-term time period.In addition,existing Q-learning algorithms for adaptive power allocation suffer from the curse of dimensionality.To overcome these challenges,an adaptive power control method based on the double-layer Q-learning algorithm for n parallel PCSs of the ESS is proposed in this paper.First,a selection method for the power allocation coefficient is developed to avoid repeated actions.Then,the outer action space is divided into n+1 power allocation modes according to the power allocation characteristics of the optimal operation efficiency.The inner layer uses an actor neural network to determine the optimal action strategy of power allocations in the non-steady state.Compared with existing power control methods,the proposed method achieves better performance for both static and dynamic operation efficiency optimization.The proposed method optimizes the overall operation efficiency of PCSs effectively under the fluctuating power outputs of the ESS.

Optimizing the power conversion processes in diluted donor/acceptor heterojunctions towards 19.4%efficiency all-polymer solar cells

All polymer solar cells(all-PSCs)promise mechanically-flexible and morphologically-stable organic photovoltaics and have aroused increased interests very recently.However,due to their disorderly conformation structures within the photoactive film,inefficient charge generation and carrier transport are observed which lead to inferior photovoltaic performance compared to smaller molecular acceptor-based photovoltaics.Here,by diluting PM6 with a cutting-edge polymeric acceptor PY-IT and diluting PY-IT with PM6 or D18,donor-dominating or acceptor-dominating heterojunctions were prepared.Synchrotron X-ray and multiple spectrometer techniques reveal that the diluted heterojunctions receive increased structural order,translating to enhanced carrier mobility,improved exciton diffusion length,and suppressed non-radiative recombination loss during the power conversion.As the results,the corresponding PM6+1%PY-IT/PY-IT+1%D18 and PM6+1%PY-IT/PY-IT+1%PM6 devices fabricated by layer-by-layer deposition received superior power conversion efficiency(PCE)of 19.4%and 18.8%respectively,along with enhanced operational lifetimes in air,outperforming the PCE of 17.5%in the PM6/PY-IT reference device.

Highly Efficient Power Conversion from Salinity Gradients with Ion-Selective Polymeric Nanopores

A polymeric nanopore membrane with selective ionic transport has been proposed as a potential device to convert the chemical potential energy in salinity gradients to electrical power. However, its energy conversion efficiency and power density are often limited due to the challenge in reliably controlling the size of the nanopores with the conventional chemical etching method. Here we report that without chemical etching, polyimide （PI） membranes irradiated with GeV heavy ions have negatively charged nanopores, showing nearly perfect selectivity for cations over anions, and they can generate electrical power from salinity gradients. We further demonstrate that the power generation efficiency of the PI membrane approaches the theoretical limit, and the maximum power density reaches 130m W/m2 with a modified etching method, outperforming the previous energy conversion device that was made of polymeric nanopore membranes.

Regulation of Power Conversion in Fuel Cells

Here we report a regulation about power conversion in fuel cells. This regulation is expressed as that total power produced by fuel cells is always proportional to the square of the potential difference between the \{equilibrium\} potential and work potential. With this regulation we deduced fuel cell performance equation which can describe the potential vs.the current performance curves, namely, polarization curves of fuel cells with three power source parameters: equilibrium potential E_0; internal resistance R; and power conversion coefficient K. The concept of the power conversion coefficient is a new criterion to evaluate and compare the characteristics and capacity of different fuel cells. The calculated values obtained with this equation agree with practical performance of different types of fuel cells.

Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays

The maximum power conversion efficiencies of the top-emitting,oxide-confined,two-dimensional integrated 2×2 and4×4 vertical-cavity surface-emitting laser（VCSEL） arrays with the oxide-apertures of 6 μm,16 μm,19 μm,26 μm,29 μm,36 μm,39 μm,and 46 urn are fabricated and characterized,respectively.The maximum power conversion efficiencies increase rapidly with the augment of oxide-aperture at the beginning and then decrease slowly.A maximum value of27.91%at an oxide-aperture of 18.6 μm is achieved by simulation.The experimental data are well consistent with the simulation results,which are analyzed by utilizing an empirical model.

Study on Purchasing Power Conversion Coefficient at Par

The basic theory of the purchasing power at par refers to the rate of one country＇s currency to U.S. dollar while purchasing ＂a basket＂ goods and services in the same quantity and quality respectively in this country and U.S.A. This paper gives out calculation method of purchasing power conversion coefficient at par and how to calculate the non-base year purchasing power at par.

Application of Single-to-Single Phase Matrix Conversion in Conventional Rectifier-Inverter

The principle of single to single phase matrix electric power conversioin is further studied and the conversioin switch function is introduced into conventional rectifier inverter, thus a general character of the two conversion techniques is discovered. It is characteristic of the switch functiion to follow mains voltage distortion and mains frequency drift. By utilizing the merit, unidirectional switch duty rations of the inverter follow the variation of DC link voltage automatically, thus the size of DC link electrolytic capacitor can be reduced considerably, bringing about improved mains side power factor. Corresponding topologies and theoretical and theoretical derivations are given, and so are the simulation results, based on which it is confirmed that the single to single phase matrix conversion technique is potentially useful in large scale production, and the introduction of switch function can yield good economic returns.

Layered-stacking of titania films for solar energy conversion:Toward tailored optical,electronic and photovoltaic performance

Nanostructured TiO2 with differentiate morphologies has attracted tremendous attention due to its wide band-gap nature as well as outstanding optical and electric properties for solar-driven light-toelectricity conversion application. Layered-stacking TiO2 film such as double-layer, tri-layer, quadrupleor quintuplicate-layer, is highly desirable to the design of high-performance semiconductor material photoanodes and the development of advanced photovoltaic devices. In this minireview, we will summarize the recent progress and achievements on proof-of-concept of layered-stacking TiO2 films（LTFs） for solar cells with emphasis on the tailored properties and synergistic functionalization of LTFs, such as optimized sensitizer adsorption, broadened light confinement as well as facilitated electron transport characteristics.Various demonstrations of LTFs photovoltaic systems provide lots of possibilities and flexibilities for more efficient solar energy utilization that a wide variety of TiO2 with distinguished morphologies can be integrated into differently structured photoanodes with synergistic and complementary advantages. This key structure engineering technology will also pave the way for the development of next generation state-ofthe-art electronics and optoelectronics. Finally, from our point of view, we conclude the future research interest and efforts for constructing more efficient LTFs as photoelectrode, which will be highly warranted to advance the solar energy conversion process.

Analysis of Power Model for Linear Plasma Device

A single cathode linear plasma device has been designed and constructed to investigate the interactions between plasma and materials at the Sichuan University. In order to further investigate the Ohmic power of the device, the output heat load on the specimen and electric potential difference（between cathode and anode） have been tested under different discharge currents. This special power distribution in the radial direction of the plasma discharge channel has also been discussed and described by some improved integral equations in this paper;it can be further simplified as P ∝ α^（-2） in one-parameter. Besides, we have measured the power loss of the channel under different discharge currents by the calorimetric method, calculated the effective power of the device and evaluated the performances of the plasma device through the power efficiency analysis.

An Adaptive Wireless Power Sharing Control for Multiterminal HVDC

Power sharing among multiterminal high voltage direct current terminals(MT-HVDC)is mainly developed based on a priority or sequential manners,which uses to prevent the problem of overloading due to a predefined controller coefficient.Furthermore,fixed power sharing control also suffers from an inability to identify power availability at a rectification station.There is a need for a controller that ensures an efficient power sharing among the MT-HVDC terminals,prevents the possibility of overloading,and utilizes the available power sharing.A new adaptive wireless control for active power sharing among multiterminal(MT-HVDC)systems,including power availability and power management policy,is proposed in this paper.The proposed control strategy solves these issues and,this proposed controller strategy is a generic method that can be applied for unlimited number of converter stations.The rational of this proposed controller is to increase the system reliability by avoiding the necessity of fast communication links.The test system in this paper consists of four converter stations based on three phase-two AC voltage levels.The proposed control strategy for a multiterminal HVDC system is conducted in the power systems computer aided design/electromagnetic transient design and control(PSCAD/EMTDC)simulation environment.The simulation results significantly show the flexibility and usefulness of the proposed power sharing control provided by the new adaptive wireless method.

Enhancing the crystallinity and stability of perovskite solar cells with 4-tert-butylpyridine induction for efficiency exceeding 24%

Perovskite solar cells(PSCs)have emerged as a promising photovoltaic technology because of their high light absorption coefficient,long carrier diffusion distance,and tunable bandgap.However,PSCs face challenges such as hysteresis effects and stability issues.In this study,we introduced a novel approach to improve film crystallization by leveraging 4-tert-butylpyridine(TBP)molecules,thereby enhancing the performance and stability of PSCs.Our findings demonstrate the effective removal of PbI_(2)from the perovskite surface through strong coordination with TBP molecules.Additionally,by carefully adjusting the concentration of the TBP solution,we achieved enhanced film crystallinity without disrupting the perovskite structure.The TBP-treated perovskite films exhibit a low defect density,improved crystallinity,and improved carrier lifetime.As a result,the PSCs manufactured with TBP treatment achieve power conversion efficiency(PCE)exceeding 24%.Moreover,we obtained the PCE of 21.39%for the 12.25 cm^(2)module.

High Efficiency Formamidinium-Cesium Perovskite-Based Radio-Photovoltaic Cells

Radio-photovoltaic cell is a micro nuclear battery for devices operating in extreme environments,which converts the decay energy of a radioisotope into electric energy by using a phosphor and a photovoltaic converter.Many phosphors with high light yield and good environmental stability have been developed,but the performance of radio-photovoltaic cells remains far behind expectations in terms of power density and power conversion efficiency,because of the poor photoelectric conversion efficiency of traditional photovoltaic converters under low-light conditions.This paper reports an radio-photovoltaic cell based on an intrinsically stable formamidinium-cesium perovskite photovoltaic converter exhibiting a wide light wavelength response from 300 to 800 nm,high open-circuit voltage(V_(oc)),and remarkable efficiency at low-light intensity.When a He ions accelerator is adopted as a mimickedαradioisotope source with an equivalent activity of 0.83 mCi cm^(-2),the formamidinium-cesium perovskite radio-photovoltaic cell achieves a V_(oc)of 0.498 V,a short-circuit current(J_(sc))of 423.94 nA cm^(-2),and a remarkable power conversion efficiency of 0.886%,which is 6.6 times that of the Si reference radio-photovoltaic cell,as well as the highest among all radio-photovoltaic cells reported so far.This work provides a theoretical basis for enhancing the performance of radio-photovoltaic cells.

Ternary organic solar cells offer 14% power conversion efficiency

Organic solar cells （OSCs） have advantages like light-weight, flexibility, colorfulness and solution processability [1 ]. The active layer of OSCs generally contains two organic semiconductors： an electron donor and an electron acceptor. The donor and acceptor make nanoscale phase separation to allow efficient exciton dissociation and also form a three-dimensional （3D） passage to rapidly transfer free charge carriers to respective electrodes.

Review of current progress in hole-transporting materials for perovskite solar cells

Recent advancements in perovskites’ application as a solar energy harvester have been astonishing. The power conversion efficiency(PCE) of perovskite solar cells(PSCs) is currently reaching parity(>25 percent), an accomplishment attained over past decades. PSCs are seen as perovskites sandwiched between an electron transporting material(ETM) and a hole transporting material(HTM). As a primary component of PSCs, HTM has been shown to have a considerable effect on solar energy harvesting, carrier extraction and transport, crystallization of perovskite, stability, and price. In PSCs, it is still necessary to use a HTM.While perovskites are capable of conducting holes, they are present in trace amounts, necessitating the use of an HTM layer for efficient charge extraction. In this review, we provide an understanding of the significant forms of HTM accessible(inorganic, polymeric and small molecule-based HTMs), to motivate further research and development of such materials. The identification of additional criteria suggests a significant challenge to high stability and affordability in PSC.

A new perspective to develop regiorandom polymer acceptors with high active layer ductility,excellent device stability,and high efficiency approaching 17%

The recently reported efficient polymerized small-molecule acceptors(PSMAs)usually adopt a regioregular backbone by polymerizing small-molecule acceptors precursors with a low-reactivity 5-brominated 3-(dicyanomethylidene)indan-1-one(IC)end group or its derivatives,leading to low molecular weight,and thus reduce active layer mechanical properties.Herein,a series of newly designed chlorinated PSMAs originating from isomeric IC end groups are developed by adjusting chlorinated positions and copolymerized sites on end groups to achieve high molecular weight,favorable intermolecular interaction,and improved physicochemical properties.Compared with regioregular PY2Se-Cl-o and PY2Se-Cl-m,regiorandom PY2Se-Cl-ran has a similar absorption profile,moderate lowest unoccupied molecular orbital level,and favorable intermolecular packing and crystallization properties.Moreover,the binary PM6:PY2Se-Cl-ran blend achieves better ductility with a crack-onset strain of 17.5% and improved power conversion efficiency(PCE)of 16.23% in all-polymer solar cells(all-PSCs)due to the higher molecular weight of PY2Se-Cl-ran and optimized blend morphology,while the ternary PM6:J71:PY2Se-Cl-ran blend offers an impressive PCE approaching 17% and excellent device stability,which are all crucial for potential practical applications of all-PSCs in wearable electronics.To date,the efficiency of 16.86% is the highest value reported for the regiorandom PSMAs-based all-PSCs and is also one of the best values reported for the all-PSCs.Our work provides a new perspective to develop efficient all-PSCs,with all high active layer ductility,impressive PCE,and excellent device stability,towards practical applications.

Cation engineering on lead iodide perovskites for stable and high-performance photovoltaic applications

Perovskite solar cells （PSCs） based on methylammonium lead iodide （CH3NH3PbI3） have shown unprecedentedly outstanding performance in the recent years. Nevertheless, due to the weak interaction between polar CH3NH3＋ （MA＋） and inorganic PbI3 sublattices, CH3NH3PbI3 dramatically suffers from poor moisture stability, thermal decomposition and device hysteresis. As such, strong electrostatic interactions between cations and anionic frameworks are desired for synergistic improvements of the abovementioned issues. While replacements of I with Br and/or CI evidently widen optical bandgaps of perovskite materials, compositional modifications can solely be applied on cation components in order to preserve the broad absorption of solar spectrum. Herein, we review the current successful practices in achieving efficient, stable and minimally hysteretic PSCs with lead iodide perovskite systems that employ photoactive cesium lead iodide （CsPbI3）, formamidinium lead iodide （HC（NH2）2PbI3, or FAPbI3）, MA1-x y-zFAxCsyRbzPbI3 mixed-cation settings as well as two-dimensional butylammonium （C4H9NH3＋, or BA＋）/MA＋, polymeric ammonium （PEI＋）/MA＋ co-cation layered structures. Fundamental aspects behind the stabilization of perovskite phases α-CsPbi3, α-FAPbI3, mixed-cation MA1-x-y-zFAxCsyRb2PbI3 and crystallographic alignment of （BA）2（MA）3Pb4I13 for effective light absorption and charge transport will be discussed. This review will contribute to the continuous development of photovoltaic technology based on PSCs.

Blade-coating Perovskite Films with Diverse Compositions for Efficient Photovoltaics

In this research highlight,recent significant advances with hot-assisted blade-coating or air knife-assisted blade-coating of different perovskite compositions with bandgaps ranging from 1.3 eV to 1.9 eV(i.e.widebandgap or small-bandgap perovskites with mixed cations and anions,2D/3D perovskites,Pb/Sn binary perovskites,and all-inorganic perovskites)for single-junction or tandem PSCs are discussed,with an emphasis on elucidating the distinct ink formulation engineering strategies,crystal growth mechanisms,crystallization kinetics,and optoelectronic properties of the different perovskite compositions.

Effects of Blade Geometry on Performance of Wells Turbine for Wave Power Conversion

An optimum design of the turbine would need a clear understanding of the influence of blade geometry on a Wells turbine performance. Practically, it is difficult to suggest the optimum geometry for the Wells turbine due to the complex interrelation among important parameters, the solidity, hub-to-tip ratio, aspect ratio, blade sweep of rotor, and so on. In the present study, the effect of blade geometry with the hub-to-tip and aspect ratios of rotor on the turbine performance was investigated with a numerical technique. As a result, the optimum blade geometry is as follows: the hub-to-tip ratio is about 0.7, and the aspect ratio about 0.5 under other constant important parameters, NACA0020 blade with blade sweep ratio of 0.35, and solidity of about 0.67. Furthermore, the detailed flow patterns for blade geometry were also shown and discussed in this paper.

Predicting the device performance of the perovskite solar cells from the experimental parameters through machine learning of existing experimental results

The performance of the metal halide perovskite solar cells(PSCs)highly relies on the experimental parameters,including the fabrication processes and the compositions of the perovskites;tremendous experimental work has been done to optimize these factors.However,predicting the device performance of the PSCs from the fabrication parameters before experiments is still challenging.Herein,we bridge this gap by machine learning(ML)based on a dataset including 1072 devices from peer-reviewed publications.The optimized ML model accurately predicts the PCE from the experimental parameters with a root mean square error of 1.28%and a Pearson coefficientr of 0.768.Moreover,the factors governing the device performance are ranked by shapley additive explanations(SHAP),among which,A-site cation is crucial to getting highly efficient PSCs.Experiments and density functional theory calculations are employed to validate and help explain the predicting results by the ML model.Our work reveals the feasibility of ML in predicting the device performance from the experimental parameters before experiments,which enables the reverse experimental design toward highly efficient PSCs.