Device Power Conversion Research Articles

Bipolar Organic Material Assisted Surface and Boundary Defects Passivation for Highly Efficient MAPbI3‐Based Inverted Perovskite Solar Cells

At the device operating conditions, defects such as interstitials, vacancies, and impurities at the grain boundary and surface of photoactive layer have great impact on the power conversion efficiency (PCE) and device stability. To better passivate the surface and boundary defects, and further enhance the PCE and device stability, herein, a bipolar organic material termed 1,4‐bis(perfluorophenyl)‐2,5‐di(pyridin‐4‐yl)‐1,4‐dihydropyrrolo [3,2‐b] pyrrole (PFPPY) is introduced as modifier in antisolvent. The effects of PFPPY on perovskite film quality, photovoltaic performance, and charge transfer properties are systematically investigated. Under the optimized conditions, the PFPPY‐treated device shows an impressive PCE of 19.62%, which is 12% higher than the reference device (17.59%), and greatly enhanced stability, maintaining 95% of its initial efficiency under room temperature (RT) and relative humidity (RH) 30% condition for 650 h without encapsulation.

전기추진선박의 제어전원 및 보조장치 전원공급용 DC/AC 인버터의 입력전압변동 시험평가 및 분석

The main power supply of electric vehicles and ships is generally composed of a battery, a generator and a fuel cell, and a propulsion motor and inverter are used as a driving device. In addition to the main power supply for electric power-driven driving, additional auxiliary power supply for control system and auxiliary system is required, and power conversion devices (inverters and converters) are used for this purpose. Power conversion devices for auxiliary power supply receives power from main power supply such as battery, generator and fuel cell and performs the AC or DC power conversion. The voltage variation of main power supply depends on the usage conditions of electric propulsion system. The power conversion devices for auxiliary power supply shall not cause output stop even if the voltage of main power supply suddenly changes to the allowable voltage range. The output of the power conversion devices for auxiliary power supply shall have an operating capability to produce a stable output within the permitted voltage range. This paper deals with the test evaluation and analysis for the input voltage fluctuation of the DC/AC inverter(power conversion devices) in auxiliary power supply of electric ship..

Tuning the A-Site Cation Deficiency of La0.8Sr0.2FeO3−δ Perovskite Oxides for High-Efficiency Triiodide Reduction Reaction in Dye-Sensitized Solar Cells

Due to the low material cost, simple preparation process, and no pollution to the environment, dye-sensitized solar cells (DSSCs) have become one of the important power conversion devices. The counter electrode (CE, also called cathode), an important part of DSSCs, plays a critical role in the photovoltaic performance of DSSCs. Platinum (Pt) with high electrocatalytic activity is the most commonly used CE material in DSSCs, which suffers from the problems of high price and poor stability, highlighting the importance of developing novel low-cost, active, and stable Pt-free CEs. In this work, a series of A-site deficient (La0.8Sr0.2)1–xFeO3-δ (x = 0, 0.02, 0.05, 0.1) perovskite oxides are designed to serve as CEs in DSSCs. Through investigating the influence of the A-site deficiency on the power conversion efficiency (PCE), it is found that the introduction of an appropriate deficiency in perovskite oxides is beneficial for catalytic activity of triiodide (I3–) reduction reaction (IRR) of the CE, thus improving the photovoltaic performance of DSSCs. Consequently, the (La0.8Sr0.2)0.98FeO3−δ/multiwalled carbon nanotubes (MWCNTs) CE-based device exhibits the highest PCE of 8.22%, while the Pt-based device only yields a PCE of 7.21%. The significantly enhanced efficiency of DSSCs is mainly attributed to the synergistic effect between the high oxygen vacancy concentration and the appropriate amount of Fe4+ as well as reduced particle size, which enhances the charge transfer capability and the I3– diffusion capability simultaneously. Furthermore, the decent IRR durability of (La0.8Sr0.2)0.98FeO3−δ/MWCNTs composites confers the corresponding DSSCs an excellent long-term stability. This work provides a facile way to design active and durable Pt-free perovskite oxide-based CEs in DSSCs, which may lay the foundation for the commercialization of DSSC technology.

Tuning the optoelectronic properties of Subphthalocyanine (SubPc) derivatives for photovoltaic applications

Abstract In the quest of enhanced power conversion efficiency (PCE) and device performance of small molecule based organic solar cells, four new acceptor-donor-acceptor (A-D-A) type novel chromophores (Y1-Y4) have been designed with subphthalocyanine (SubPc) as a common donor and different benzene bridged end-capped 2-methylenemalononitrile (A1), 6-methylene-2-thioxo-1,3-thiazinan-4-one (A2), 2-(2-methylene-3-oxo-2,3-dihydro-1H-inden-1ylidene) malononitrile (A3) and 5-methylene-2-thioxothiazolidin-4-one (A4) acceptor groups. Photovoltaic and quantum chemical parameters of Y1-Y4 were computed through DFT and TD-SCF using selected B3LYP hybrid functional. Next, the parameters affecting chemical reactivity, opto-electronic properties, charge mobility and exciton dynamics of Y1-Y4 were characterized through calculations of frontier molecular orbitals, absorption profiles, density of states (DOS) and transition density matrix (TDM) respectively. The results imply that the designed candidates (Y1-Y4) proved more proficient in executing the afore-said parameters compared to R (reference). Amongst all, Y3 surpassed in exhibiting the best efficiency with highest absorption value (667 nm) and lowest band gap (2.12 eV). Moreover, low reorganization energies, high dipole moment and comparable values of open circuit voltage (Voc) make these molecules a useful tactic for use in small molecule based organic solar devices.

Effect of CaCu3Ti4O12 dopant on the magnetic and dielectric properties of high-frequency MnZn power ferrites

To obtain miniaturized, lightweight, and integrated power conversion devices, the core material must be suitable for operation at higher frequencies (in the megahertz range) and must exhibit excellent performance, specifically, low core losses. In this study, MnZn power ferrites, a common core material, were doped with calcium copper titanate (CCTO) using a solid-state reaction method. The effects of CCTO doping (0.0–0.5 wt%) on the structural, magnetic, and dielectric properties of the MnZn ferrites were studied. The addition of 0.2 wt% CCTO to the MnZn ferrites improved the grain uniformity and decreased the porosity; thus, the material exhibited a fine microstructure. In addition, the saturation induction, initial permeability, and resistivity of the MnZn ferrites were increased, and the high-frequency core losses were suppressed. The core losses of the 0.2 wt% CCTO sample were only 495 kW/m3 at 3 MHz, 30 mT, and 25 °C. The lower core losses resulted mainly from reductions in the hysteresis loss and eddy current loss. The real permittivity of two representative MnZn ferrite samples was also investigated. The application of state-of-the-art MnZn ferrites with superior electromagnetic properties in high-frequency power conversion devices is anticipated. This study demonstrates that adding a dielectric material improves the electromagnetic properties of MnZn power ferrites.

Condition Monitoring of DC-Link Electrolytic Capacitors in PWM Power Converters Using OBL Method

Since the lifespan of an electrolytic capacitor is relatively short compared to other power semiconductor devices, the failure rate accounts for 60% and, thus, it is the most vulnerable component of the power conversion device. Therefore, the accurate measurement of the lifetime of an electrolytic capacitor is very important in ensuring the reliability of the entire system, including the capacitor. In this paper, an online failure detection method for a DC-link electrolytic capacitor in a back-to-back Pulse width Modulation (PWM) converter using the opposition-based learning particle swarm optimization-based Support Vector Regression (OPSO-SVR) technique is proposed. In this method, the capacitance and the DC-link capacitor power have been used in offline mode for SVR training and testing. During the offline mode, the SVR parameters have been optimized with the OPSO algorithm to use online to estimate the real value of the DC-link capacitor. The experimental results prove the superiority of the proposed technique over the SVR.

Understanding the Performance of Organic Photovoltaics under Indoor and Outdoor Conditions: Effects of Chlorination of Donor Polymers.

Understanding the effects of the chemical structures of donor polymers on the photovoltaic properties of their corresponding organic photovoltaic (OPV) devices under various light-intensity conditions is important for improving the performance of these devices. We synthesized a series of copolymers based on poly[(2,6-(4,8-bis(5-(2-thioethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))] (PBDB-TS) and studied the effects of chlorine substitution of its thiophene-substituted benzodithiophene (BDT-Th) unit on its photovoltaic properties. Chlorination of the polymer resulted in a bulk heterojunction (BHJ) morphology optimized for efficient charge transport with suppressed leakage current and an increased open-circuit voltage of the OPV device; this optimization led to a remarkable enhancement of the OPV device's power conversion efficiency (PCE) not only under the condition of 1 sun illumination but also under a low light intensity mimicking indoor light; the PCE increased from 8.7% for PBDB-TS to ∼13% for the chlorinated polymers, PBDB-TS-3Cl, and PBDB-TS-4Cl under the 1 sun illumination condition and from 5.3% for PBDB-TS to 21.7% for PBDB-TS-4Cl under 500 lx fluorescence illuminance. Interestingly, although the OPV PCEs under 1 sun illumination were independent of the position of chlorine substitution onto the polymer, PBDB-TS-4Cl exhibited better performance under simulated indoor light than its derivative PBDB-TS-3Cl. Our results demonstrate that efficient light absorption and charge-carrier generation play key roles in achieving high OPV efficiency under low-light-intensity conditions.

Enhanced Methanol Electro‐Oxidation Activity of Pt/rGO Electrocatalyst Promoted by NbC/Mo2C Phases

AbstractDirect methanol fuel cells are attractive power conversion devices for portable and stationary applications. Many electrocatalysts have been explored for fuel cell applications but there is scope to design newer and more efficient electrocatalytic materials. For this purpose we have synthesized Mo2C and bimetallic NbC‐Mo2C carbide phases by carbothermic reduction process. The carbide catalysts are characterized by various analytical techniques. The carbide samples are higly porous and their surface areas are of the order of 630 m2 g−1. Usually Pt is the state‐of‐the‐art anode catalyst in direct methanol fuel cells. Here, Nb‐Mo2C and 10 wt% Pt nanoparticles are deposited on reduced graphene oxide support to obtain Pt/Nb‐Mo2C‐rGO. This material shows highest mass activity of 836.4 mA mgPt−1 when compared to 10 wt% Pt/Mo2C‐rGO and bare 20 wt% Pt/rGO catalysts. Notably, electrochemical tests show that the 10 wt% Pt/Nb‐Mo2C‐rGO catalyst exhibits lower onset potential, large electrochemical surface area, higher activity, and stability for methanol electro‐oxidation in acidic solution compared to the Pt/Mo2C‐rGO and Pt/rGO catalysts. The activty enhancement is atributed to the defective nature of the interface between Pt, Nb‐Mo2C and rGO. It is found that Nb‐Mo2C not only alleviates CO poisoning of Pt nanoparticles, but also generates oxygen containing species at lower potentials. This process helps scavenging the intermediate species such as COads on Pt surfaces and regenerates the active Pt sites for routine alcohol oxidation reaction. The chronopotentiometry and chronoamperometry studies also show that Pt/Nb‐Mo2C‐rGO exhibits lower alcohol oxidation overpotential and longer polarization time/stability compared to Pt/Mo2C‐rGO and bare Pt/rGO catalysts.

Silver sulphide nano-particles enhanced photo-current in polymer solar cells

Silver sulphide nano-particles (NPs) have been employed as light trapping mechanism in the solar absorber layer of thin film inverted organic solar cell. The synthesized nano-particle has been characterized using high-resolution scanning and transmission electron microscopy (HRSEM and HRTEM), X-Ray diffraction (XRD). The effects of $$\hbox {Ag}_{2}\hbox {S}$$ NPs in the newly fabricated inverted polymer solar cell with architecture ITO/ZnO/P3HT:$$\hbox {PC}_{61}\hbox {BM}$$-$$\hbox {Ag}_{2}\hbox {S}$$ /$$\hbox {MoO}_3/\hbox {AL}$$ were characterized using optical and electrical properties of the solar absorber film. The optimized NPs in the photoactive layers are designed to improve photons harvesting, charge transport and reduced charge recombination, which resulted in the collection of high short circuit current density, as large as $$16.50\hbox { mAcm}^{-2}$$. The measured high photocurrent and better device rectification has lead to improved power conversion efficiencies (PCEs) and device stability. The best power conversion efficiency recorded in this investigations was 5.15 % at the concentration of 1 % $$\hbox {Ag}_{2}\hbox {S}$$ by weight. Furthermore, the solar cells exhibited extraordinary environmental stability stored in ambient environment which is attributed to the inverted device architecture.

Synergistic Benefits of Cesium‐Doped Aqueous Precursor in Air‐Processed Inverted Perovskite Solar Cells

Air‐processed perovskite solar cells (PSCs) allay the need for costly fabrication in a controlled atmosphere but currently suffer from disadvantages in power conversion efficiency (PCE) and device stability. Herein, the systematic investigation into CH3NH3PbI3–xClx prepared with an antisolvent‐assisted process in a relative humidity of 40 ± 5% is reported, using cesium‐containing aqueous solutions of various strengths. Diffractometry and microscopy reveal how grain sizes vary among the samples, suggesting an optimum concentration for grain size. Those films are fabricated in air into solar cells, and their electrochemical impedance and current–voltage characteristics under light are measured. The films demonstrating optimum strength achieve PCEs of up to 16.6%, compared with the maximum of 14.4% achieved by untreated films. The air‐processed films also exhibit mitigated hysteresis, with indices decreasing to 0.021. Photoluminescence characterization reveals reduced defect densities in Cs‐doped materials and, together with photoelectron spectroscopy, suggests an upward shift in energy bands. Such changes explain the improvement in photovoltaic performance. Stability tests on unencapsulated cells over 14 days show that those made from the perovskite with optimum Cs‐doping degrade slowest, with their conversion efficiencies falling by <10% every 100 h. Our findings may contribute to the low‐cost commercialization of PSCs.

Versatile power and energy conversion of magnetoelectric composite materials with high efficiency via electromechanical resonance

A better understanding of magnetoelectric (ME) energy materials with superior properties stimulates exploration of next generation of versatile energy devices with a high efficiency. Although a number of investigations have focused on developing multiferroic composite materials because of their potential in cutting-edge multifunctional devices, advances in basic research have not yet been translated into benefits for practical applications. In the present investigation, we introduce a two-phase magnetoelectric composite made of nanocrystalline FeBSi metallic ribbons (Metglas) and Mn3+,2+ acceptor doped Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PMN-PZT) single crystal, and great enhancements in ME coupling coefficient (αME~12500 V/Oe cm) with a tunable resonance frequency, current-to-voltage (I–V) conversion ratio (~15090 V/I), as well as power conversion efficiency (η ~95%) are found at the fundamental electromechanical resonance, which represent the highest values ever reported. This study also provides a fundamental understanding of the role of a figure of merit (FOM), kij,eff× Qm,eff, on ME coupling performances in ferromagnetic and ferroelectric two-phase ME composite. The enhanced performances are attributed to the laser heat treatment induced Nano crystallization in Metglas, lower magnetic and dielectric loss (tan δ), and also higher mechanical quality factor (Qm,eff) in ME composite. This research opens up the possibilities of developing ME composite materials for next-generation versatile energy and power conversion devices.

Ultra-low core losses at high frequencies and temperatures in MnZn ferrites with nano-BaTiO3 additives

The miniaturization and integration of power conversion devices and components, such as converters and switching power supplies, require ferrite cores with high operating frequencies and temperatures. Hence, the frequency and temperature dependence of core losses is a bottleneck restricting the development of power conversion devices. Herein, nanoparticles of a dielectric material—barium titanate (BTO)—are adopted to suppress high-frequency and high-temperature core losses in MnZn ferrites. Using a loss separation method, the effects of BTO on core losses and their temperature dependence are investigated. Residual loss at 25 °C and eddy current loss at high temperatures were significantly suppressed by the addition of BTO. Remarkably, adding 0.04 wt% BTO nanoparticles resulted in MnZn ferrites with ultra-low core losses of 302 kW/m3 (25 °C) and 890 kW/m3 (100 °C) at 3 MHz and 30 mT. These superior MnZn ferrites with ultra-low core losses have potential applications in power conversion devices with high operating frequencies and temperatures. This study also provides a novel approach for suppressing core losses.

Research on Parallel Operation Characteristics and Current Sharing Method of High Power IGBT

With the development of power electronics technology, the capacity of power conversion devices is getting larger and larger, and the current level requirements for high-power IGBT are also getting higher and higher. A single device often cannot meet the requirements, and multiple IGBT need to be used in parallel. When IGBT is connected in parallel, due to the differences in device parameters, external circuit parameters and heat dissipation conditions, the current distribution is easily unbalanced, resulting in device performance waste or even damage. Therefore, the current sharing problem is the core problem to be solved in parallel connection of IGBT. In order to solve the problems such as difficulty in analyzing a single factor for coupling of various influencing factors, difficult control of temperature and high cost of circuit, this paper adopts Saber software simulation method to analyze the influence of various internal and external factors on IGBT’s dynamic and static current sharing, thus obtaining the relationship between these factors and corresponding countermeasures, and obtaining an effective IGBT parallel current sharing scheme. Finally, the correctness and effectiveness of this scheme are verified by experiments.

Novel Method for State Space Modeling of Full Bridge Converter

The requirement of converters is increasing with the increase in demand for the power conversion devices. For efficient power conversion, stability and time response of the system must be improved. For improving characteristics a mathematical model of the system must be determined. In this paper, an improvised state space model of full bridge converter is presented which can be used in converter design. This state-space model incorporates the non-idealities of the transformers like discharge time of primary inductance and secondary inductance as well as the wire resistance. The interdependency of the parameters affects the state space model of the converter compared to the ideal modeling. This variation in state space model of the converter has an impact on design of compensator which improves the system efficiency of the converter.

Development and experimental study of a supercritical CO2 axial turbine applied for engine waste heat recovery

CO2-based transcritical power cycle (CTPC) has been proposed as a suitable engine waste heat recovery (E-WHR) technology with the advantage of miniaturization and good recovery capacity. Expander, as the core power conversion device, is of great importance to the overall cycle performances. The main purpose of this paper is to conduct dynamic tests of the proposed turbine expander, with focus on the turbine operational characteristics and performance. In this study, a partial admission axial turbine expander coaxial with a high-speed synchronous generator is designed and manufactured considering the thermodynamic properties of supercritical CO2. The geometry of the turbine is 56 mm rotor diameter, 4 mm blade height, and 39000 rpm of operating speed at the inlet design condition of 10 MPa and 230 °C, outlet condition of 6 MPa and mass flow rate of 0.18 kg/s. The performance of the developed turbine expander and CTPC system with respect to the rotational speed and mass flow rate are investigated experimentally. Based on the experimental data, the maximum rotational speed of the the turbine reaches 41584 rpm and the turbine expander generated maximum power 2.27 kW at 20878 rpm. The power capacity of the turbine increases to the maximum value first and then decreases with the increase of rotational speed as well as the isentropic efficiency. The power generation of the turbine expander is proportional to pressure ratio as well as mass flow rate.

Wind turbine power converter fault diagnosis using DC-link voltage time–frequency analysis

With the developments in power electronic devices, there is increasing use of the insulated gate bipolar transistor devices in power converters. Power converters are more and more gaining attention in the wind energy conversion system. In this article, a grid-connected wind energy conversion system is considered. Wind energy conversion system optimal operation requires a diagnostic method for back-to-back power converter to be addressed in detail in this article. Therefore, an open-circuit switching fault diagnosis method for a back-to-back power converter is developed to improve the system reliability and optimize the produced power and also achieve its real operational cost. In this work, we investigate only the DC-Link voltage signal and we use the time–frequency analysis to achieve the diagnosis purpose. The scheduled diagnosis approach is divided into two tasks: the first one is the fault detection task and the second one is the fault localization task. The main novelty of the proposed diagnosis approach is to localize the appropriate faulty power converter, that is, rotor side power converter or grid side power converter. Also, this approach is able to localize faults when there is a simultaneous fault on both power converters. Simulations are carried out to verify the robustness of the proposed diagnosis approach. The achieved simulation results would help in diagnosing of Back-to-back power converter that would expectedly cancel the traditional diagnosis method.

Interfacial Post‐Treatment for Enhancing the Performance of Printable Carbon‐Based Perovskite Solar Cells

The interface between the perovskite layer and carbon electrode is important for printable carbon‐based perovskite solar cells (PSCs) to improve the power conversion efficiency (PCE) and device stability. A series of acetate salts are employed to in situ post‐modify the interface between the perovskite layer and carbon electrode for printable carbon‐based PSCs by the post‐treatment method. Cesium acetate (CsAc) is identified to enhance the average PCE from 12.6% to 15.3%. The stabilized output PCE reaches 15.6%, and the highest open‐circuit voltage (VOC) is 1.1 V, representing a new milestone in increasing the ratio of VOC/Eg (Eg: bandgap of perovskite) to be 0.67 for the printable carbon‐based PSCs without hole transporting materials. Moreover, the device stability in air is also improved by CsAc post‐modification. The improved performance is attributed to the better matching of energy levels of the perovskite layer with a carbon electrode and reduced defect density in the perovskite layer via in situ produced methylammonium acetate and ion replacement. This simple and effective CsAc post‐treatment method opens a new promising direction for developing scalable carbon‐based PSCs.

Temperature characteristics of core losses for HfO2 doped manganese-zinc ferrites

Abstract Core losses in manganese-zinc (MnZn) ferrites is an important factor governing the performances of power conversion devices such as power converters and switching mode power supplies. With the development trend of miniaturization, lightweight, and high frequency for power supply, it is worth emphasizing that the temperature characteristics of ferrite cores are closely related to energy transfer efficiency and reliability of power conversion devices and components. Herein, the effect of high valence ion additive HfO2 on the microstructure and electromagnetic performances of MnZn ferrites was systematically discussed, as well as physical mechanism of temperature dependence of core losses. The variation of hysteresis loss has been correlated with the hysteresis loop area (B-H), and the effect of the ratio of square of average grain size to resistivity D2/ρ on eddy current loss has been taken into consideration. Remarkably, eddy current loss does not monotonically decrease with the increase of HfO2 content via enhancing resistivity ρ, as well with the variation of average grain size D. The state-of-the-art MnZn ferrites with excellent temperature characteristics of core losses exhibits great potential in power conversion devices operating in a wide temperature range.

(Invited) Epitaxial Lift-Off of GaN and Related Materials for Device Applications

The use of epitaxial lift-off with GaN and other III-N based materials offers substantial benefits for devices across a wide range of applications. Examples include devices for power control and conversion, microwave and millimeter-wave transmitters and receivers, sensors, LEDs and detectors, and many others. For these applications, epitaxial lift-off provides a key additional degree of freedom in fabrication processing and integration, offering potential benefits to the electrical, thermal, and optical properties of devices, as well as enhancing the ability of these devices to be heterogeneously integrated with other materials at low cost. We provide here an overview of this technology and its benefits.

On the assessment of incorporation of CNT-TiO2 core-shell structures into nanoparticle TiO2 photoanodes in dye-sensitized solar cells.

Herein, we report dye-sensitized solar cells (DSCs) based on conventional nanocrystalline TiO2 photoanodes decorated with one-dimensional (1D) CNT-TiO2 core-shell structures (CTH). The core-shell nanotubes are synthesized by a simple sol-gel template-assisted method via in situ deposition of TiO2 on the surface of non-covalently functionalized CNTs. The core-shell nanotubes are well characterized by various techniques. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images show that formation of the TiO2 shell on the surface of the CNT core follows a layer or Frank-van der Merwe growth mode, resulting in a highly uniform interface with excellent charge transfer from the TiO2 conduction band into the CNTs. The thickness and crystal structure of the TiO2 shell can be tailored by controlling the processing parameters. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy verify that CNTs have no surface defects and are well preserved using the employed method and the subsequent heat treatment in air, respectively. UV-vis spectroscopy and photoluminescence spectroscopy reveal an extension to visible regions with an increase in overall intensity and a significant reduction in charge recombination due to a shift of the Fermi level toward positive potentials. We find an increase by up to 37% in the DSC device's power conversion efficiency by incorporating the CNT-TiO2 core-shell nanotubes into the nanoparticle TiO2 photoanode due to the charge recombination reduction and electron injection enhancement.