Enhanced Power Factor Research Articles

Aqueous-Solution Synthesized p-Type Cu2Se0.96Te0.04-xIx/Cu2O Composite and Thermoelectric Performance of TEG Made of 6 Pairs of p-Leg Cu2Se0.96Te0.02I0.02/Cu2O Composite and n-Leg InSb0.94Bi0.06.

Cu2Se-based thermoelectric materials exhibit high dimensionless figure of merit (zT) values at elevated temperatures (900-1000 K) but relatively lower zT values at intermediate temperatures, approximately 500 K. We synthesized a series of polycrystalline Cu2Se0.96Te0.04-xIx/Cu2O composites (where x = 0.00, 0.01, 0.02, and 0.03) using an energy-efficient synthesis method conducted at room temperature, followed by heat treatment at 923 K for 6 h. X-ray diffraction (XRD) analysis confirmed the monoclinic crystal structure of the α phase. The introduction of iodine doping at Te sites introduced electron carriers to p-type Cu2Se0.96Te0.04, reducing the hole carrier concentration. Consequently, the electrical resistivity increased, and the thermopower exhibited a significant increase. The incorporation of electron carriers into the p-type Cu2Se0.96Te0.04/Cu2O composites resulted in an enhanced power factor within the medium-temperature range. Specifically, at 500 K, the Cu2Se0.96Te0.02I0.02/Cu2O (x = 0.02) composites demonstrated the highest power factor among the series of Cu2Se0.96Te0.04-xIx/Cu2O composites, measuring 9.1 μW cm-1 K-2. According to the weighted mobility analysis, it is clear that the x = 0.02 composite possesses the optimal carrier concentration, which accounts for its superior power factor compared to the other composites in the series. Furthermore, the Cu2Se0.96Te0.02I0.02/Cu2O composites and Cu2Se0.96Te0.04/Cu2O composites displayed zT values of 0.49 and 0.33, respectively, at 550 K. Additionally, iodine doping led to an enhancement in the average zT values between 450 and 550 K. Therefore, electron doping in p-type materials presents itself as a viable strategy for shifting the operating temperature of a thermoelectric device from high to medium temperature. We successfully fabricated a thermoelectric generator comprising 6 pairs of p-leg Cu2Se0.96Te0.02I0.02/Cu2O composites and n-leg InSb0.94Bi0.06. This TEG achieved impressive results, including a maximum output voltage, power output, power density, and efficiency of 0.115 V, 10.6 μW, 35.1 μW cm-2, and 1.74% at a temperature difference (ΔT) of 120 K.

Experimental test performance for a comparative evaluation of a voltage source inverter: Dual voltage source inverter

Abstract This article proposes an adaptive Kernel-Hebbian least mean square (KHLMS) controller for a dual voltage source inverter (VSI). The recommended topology consists of a distributed energy resource (DER) supported VSI called main VSI (MVSI) and split capacitor supported VSI termed as auxiliary VSI (AVSI). Both the MVSI and AVSI are used to serve the shunt compensation when DER is not integrated with MVSI. The DER scenario is considered to suppress the active power flow shortage in the utility grid. Here, optimal active power flow control (OAPFC) is managed by MVSI and shunt compensation is achieved by AVSI during DER operated mode. Hence, a dual VSI based distribution static compensator (DSTATCOM) facilitates the configuration merits such as reduction in system downtime cost, filter rating switching stress etc. Supremacy of both the neural network (NN) based controller and topology is presented by comparing VSI (called AVSI) in the context of harmonic reduction in source side, voltage balancing, power factor (PF) enhancement, better voltage regulation and OAPFC. The experimental results are obtained through field programmable gate array (FPGA) based hardware units which exhibit radical improvement in the power quality (PQ) conferring as per the international standard grid code (IEEE-519-2017).

Electrically Programmed Doping Gradients Optimize the Thermoelectric Power Factor of a Conjugated Polymer

AbstractFunctionally graded materials (FGMs) are widely explored in the context of inorganic thermoelectrics, but not yet in organic thermoelectrics. Here, the impact of doping gradients on the thermoelectric properties of a chemically doped conjugated polymer is studied. The in‐plane drift of counterions in moderate electric fields is used to create lateral doping gradients in films composed of a polythiophene with oligoether side chains, doped with 2,3,5,6‐tetrafluoro‐tetracyanoquinodimethane (F4TCNQ). Raman microscopy reveals that a bias voltage of as little as 5 V across a 50 µm wide channel is sufficient to trigger counterion drift, resulting in doping gradients. The effective electrical conductivity of the graded channel decreases with bias voltage, while an overall increase in Seebeck coefficient is observed, yielding an up to eight‐fold enhancement in power factor. Kinetic Monte Carlo simulations of graded films explain the increase in power factor in terms of a roll‐off of the Seebeck coefficient at high electrical conductivities in combination with a mobility decay due to increased Coulomb scattering at high dopant concentrations. Therefore, the FGM concept is found to be a way to improve the thermoelectric performance of not yet optimally doped organic semiconductors, which may ease the screening of new materials as well as the fabrication of devices.

High Thermoelectric Performance in Solution-Processed Semicrystalline PEDOT:PSS Films by Strong Acid-Base Treatment: Limitations and Potential.

Thermoelectric (TE) generation with solution-processable conducting polymers offers substantial potential in low-temperature energy harvesting based on high tunability in materials, processes, and form-factors. However, manipulating the TE and charge transport properties accompanies structural and energetic disorders, restricting the enhancement of thermoelectric power factor (PF). Here, solution-based strong acid-base treatment techniques are introduced to modulate the doping level of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films with preserving its molecular orientation, enabling to achieve a remarkably high PF of 534.5µWm-1 K-2 . Interestingly, theoretical modeling suggested that further de-doping can increase the PF beyond the experimental value. However, it is impossible to reach thisvalue experimentally, even without any degradation of PEDOT crystallinity. Uncovering the underlying reason for the limitation, an analysis of the relationship among the microstructure-thermoelectric performance-charge transport property revealed that inter-domain connectivity via tie-chains and the resultant percolation for transport are crucial factors in achieving high TE performance, as in charge transport. It is believed that the methods and fundamental understandings in this work would contribute to the exploitation of conducting polymer-based low-temperature energy harvesting.

Anomalous enhancement of thermoelectric power factor in multiple two-dimensional electron gas system.

Toward drastic enhancement of thermoelectric power factor, quantum confinement effect proposed by Hicks and Dresselhaus has intrigued a lot of researchers. There has been much effort to increase power factor using step-like density-of-states in two-dimensional electron gas (2DEG) system. Here, we pay attention to another effect caused by confining electrons spatially along one-dimensional direction: multiplied 2DEG effect, where multiple discrete subbands contribute to electrical conduction, resulting in high Seebeck coefficient. The power factor of multiple 2DEG in GaAs reaches the ultrahigh value of ~100 μWcm-1 K-2 at 300 K. We evaluate the enhancement rate defined as power factor of 2DEG divided by that of three-dimensional bulk. The experimental enhancement rate relative to the theoretical one of conventional 2DEG reaches anomalously high (~4) in multiple 2DEG compared with those in various conventional 2DEG systems (~1). This proposed methodology for power factor enhancement opens the next era of thermoelectric research.

All-Scale Hierarchical Structuring, Optimized Carrier Concentration, and Band Manipulation Lead to Ultra-High Thermoelectric Performance in Eco-Friendly MnTe.

MnTe emerges as an enormous potential for medium-temperature thermoelectric applications due to its lead-free nature, high content of Mn in the earth's crust, and superior mechanical properties. Here, it is demonstrate that multiple valence band convergence can be realized through Pb and Ag incorporations, producing large Seebeck coefficient. Furthermore, the carrier concentration can be obviously enhance by Pb and Ag codoping, contributing to significant enhancement of power factor. Moreover, microstructural characterizations reveal that PbTe nanorods can be introduced into MnTe matrix by alloying Pb. This can modify the microstructure into all-scale hierarchical architectures (including PbTe nanorods, enhances point-defect scattering, dense dislocations and stacking faults), strongly lowering lattice thermal conductivity to a record low value of 0.376W m-1 K-1 in MnTe system. As a result, an ultra-high ZT of 1.5 can be achieved in MnTe thermoelectric through all-scale hierarchical structuring, optimized carrier concentration, and valence band convergence, outperforming most of MnTe-based thermoelectric materials.

Effect of uniaxial compressive strain on the thermoelectric properties of two-dimensional HfNF

Two-dimensional transition metal nitride halides have shown promise in thermoelectric applications due to their low dimensionality, excellent electron transfer properties, and quantum confinement of carriers. This study focuses on investigating the impact of uniaxial compressive strain on the stability, electronic and thermoelectric properties of monolayer HfNF through first-principles calculations. The research findings reveal that the semiconductor properties of monolayer HfNF remain unchanged under various strain conditions. Furthermore, the thermoelectric properties of monolayer HfNF materials are examined using Slack model and the Boltzmann transport theory under different strain conditions. The findings indicate that applying uniaxial compressive strains at temperatures of 500 K, 700 K, and 900 K increase the Seebeck coefficients of n-type and p-type HfNF, resulting in an enhanced power factor for the material. Specifically, the power factor of p-type HfNF under uniaxial compressive strain increased by 83%, with the ZT value reaching 2.01 at 900 K, which is approximately 40% higher than the ZT value without strain. These results suggest that strain can be utilized as a modulation method to enhance the thermoelectric properties of materials. Moreover, the study suggests that two-dimensional HfNF holds great promise for thermoelectric applications when subjected to uniaxial compressive strain.

ANN based smart sensing of short-term voltage stability assessment of modern power system

This study addresses the critical challenge of Short-term Voltage Stability (STVS) in the contemporary electric grid system, characterized by diverse static loads, induction motors, electronic loads, electric vehicle charging stations, and renewable energy sources. High-power sensing elements are identified for power system stability and transient measurements, and the existing system is explored for fault measurement and stability maintenance. The analysis employs an IEEE 14-bus dynamic model with two distinct load configurations. In the first configuration, the static load at bus 14 is replaced with a composite load, encompassing static loads, induction motors, electronic loads, and EV charging stations. For the second novel configuration at bus 14, the static load is substituted with a composite load and a solar photovoltaic (PV) generator operating in reactive power compensation mode. This addition of the PV generator compensates for elevated reactive power demand in the 14-bus system. The study conducts voltage stability analysis in two phases, evaluating the voltage profile and transmission line load ability in both scenarios during the first phase. In the second phase, STVS is simulated by briefly opening the circuit breaker in bus 2. The results reveal notable improvements in the voltage profile of all buses, a 6 % enhancement in power factor at bus 14 in the dynamic model with the novel configuration, and a 3 % increase in the loading factor of the IEEE Bus 14 system. The dynamic model incorporating a PV generator and composite load in bus 14 demonstrates superior STVS performance compared to the setup with only a composite load. The abstract concludes by highlighting the development of real-time voltage profile assessment using Artificial Neural Network (ANN) topology, leveraging results from the Continuous Power Flow (CPF) analysis of the novel model with a PV generator and composite load in the far end bus. This restructuring ensures a logical and clear organization, encompassing an introduction to the problem, a description of methods employed, presentation of results, and a succinct conclusion summarizing the key findings.

Enhancing the thermopower of single-molecule junctions by edge substitution effects.

Heteroatom substitution and anchoring groups have an important impact on the thermoelectric properties of single-molecule junctions. Herein, thermoelectric properties of several anthracene derivative based single-molecule junctions are studied by means of first-principles calculations. In particular, we pay great attention to the edge substitution effects and find that edge substitution with nitrogen can induce a transmission peak near the Fermi energy, leading to large transmission coefficients and electrical conductance at the Fermi energy. Additionally, the steep shape of the transmission function gives rise to a high Seebeck coefficient. Therefore, an enhanced power factor can be expected. The robustness of this edge substitution effect has been examined by altering the electrode distance and introducing heteroatoms at different positions. The enhancement of the power factor due to edge substitution makes the studied single-molecule junction a promising candidate for efficient thermoelectric devices.

Enhanced power factor and suppressed lattice thermal conductivity of CoSb3 skutterudite via Ni substitution and nanostructuring for high thermoelectric performance

Ni substitution reduced the grain size and enhanced the carrier concentration of CoSb3, which resulted in high power factor and low thermal conductivity and thereby enhanced the zT of the material.

Enhanced thermoelectric performance of a wide-bandgap twisted heterostructure of graphene and boron nitride.

The manipulation of the relative twist angle between consecutive layers in two-dimensional (2D) materials dramatically modulates their electronic characteristics. Twisted bilayer graphene (tblg) and twisted boron nitride (tBN) exhibit Moiré patterns that have the potential to revolutionize various fields, from electronics to quantum materials. Here, the electronic and thermoelectric properties of 21.8° tblg and 21.8° tBN and a 21.8° twisted graphene/boron nitride (Gr/BN) heterostructure were investigated using density functional theory and Boltzmann transport theory. The twisted Gr/BN heterostructure possesses a wide band gap of 1.95 eV, which overcomes the limitations of the absence of a band gap of graphene and boron nitride's extremely wide band gap. A significant increase in thermoelectric power factor was obtained for the heterostructure compared to its parent materials, 21.8° tblg and 21.8° tBN. It has a thermal conductivity of 5.88 W m-1 K-1 at 300 K, which is much lower than those of 21.8° tblg and 21.8° tBN. It is observed that graphene plays an important role in electron transport or power factor enhancement, whereas BN helps in reducing the thermal conductivity in twisted Gr/BN systems. A strong role of boundary scattering in thermal transport compared to electrical transport was observed. A high figure of merit (ZT) of 1.28 for the twisted Gr/BN heterostructure at a ribbon width of L = 10 nm and T = 900 K was obtained. This suggests its suitability as an effective material for thermoelectric applications.

Weak electron-phonon coupling contributing to enhanced thermoelectric performance in n-type TiCoSb half-Heusler alloys

n-type TiCoSb half-Heusler (HH) alloys show lower thermoelectric performance may be notably owing to the low valley degeneracy of the conduction band. Here, we show that this drawback can be counterbalanced by a decrease in the deformation potential coefficient and hence, weak electron-phonon coupling strength driven by the substitution of Nb for Ti in the n-type alloys Ti1-xNbxCoSb0.96Bi0.04. The combined substitutions of Nb and Bi yield a reduction of ∼86% in the deformation potential of the conduction band minimum, with the lowest value of ∼5 eV at 300 K achieved in Ti0.85Nb0.15CoSb0.96Bi0.04. This effect leads to enhanced power factor from ∼0.018 mW m−1 K−2 for x = 0 to ∼1.69 mW m−1 K−2 for x = 0.15 at RT due to the resulting strong increase in electron mobility by one order of magnitude. Both the isovalent Bi and aliovalent Nb substitutions further contribute to decrease the lattice thermal conductivity owing to enhanced mass and strain field fluctuations. The beneficial combined effects of weaker electron-phonon coupling and enhanced point-defect phonon scattering results in a higher dimensionless thermoelectric figure of merit ZT, with a peak value ∼ 0.37 at 870 K in Ti0.85Nb0.15CoSb0.96Bi0.04, representing a ∼ 375% improvement with respect to pristine TiCoSb.

A bridgeless configured asymmetrical alternating current–direct current converter‐based isolated single‐stage electric vehicle battery charger with supply side power factor enhancement

AbstractAn approach is presented to employ two different types of converters in bridgeless configuration for supply side power factor enhancement of the system. The isolated single‐stage electric vehicle battery charger uses two different converters in a bridgeless configuration to extract the advantages of both converters for supply‐side power factor enhancement. For the negative and positive semi‐cycles of the supply voltage, the power factor‐enhanced asymmetrical alternating current–direct current converter utilises a fourth order single‐ended primary‐inductor converter and a second order buck‐boost converter, respectively. The use of single‐ended primary‐inductor converter and buck‐boost converter in bridgeless configuration reduces the net order of the system with respect to conventional bridgeless‐single‐ended primary‐inductor converter schemes. The buck‐boost converter also needs the supply‐side filter to eradicate the unwanted harmonics in the supply current which increases the order of the system. The usage of both converters presents many benefits like input inductance of the single‐ended primary‐inductor converter can be utilised as a filtering element with a capacitor for the buck‐boost converter. The anti‐parallel diode conduction operation of both switches facilitates the elimination of extra reverse feed diodes (generally used in bridgeless schemes). The single‐stage charger itself comes with the benefit of elimination of extra stages and thus the losses associated with it. The presented charger also witnesses the elimination of the rectifier due to usage of bridgeless configuration. The isolated single‐stage electric vehicle battery charger is also garnished with electrical isolation which adds to the safety standard of the system. To attain power factor enhancement, the asymmetrical alternating current–direct current converter functions in discontinuous current conduction mode in the present work. The elimination of extra‐stages (with respect to two stage charger), a filter, a rectifier, two extra reverse‐feeding diodes, one voltage sensor, one current sensor (with respect to continuous current conduction mode), and electrical isolation not only makes the system compact and safer but also makes the system cheaper. Elaborated mathematical modelling and stability analysis of the presented alternating current–direct current converter using a pole‐zero map and bode plot have been included in the article. The prototype and MATLAB/Simulink model of isolated single‐stage electric vehicle battery charger system with discontinuous current conduction mode control has been built and results of both prototype and MATLAB/Simulink are deployed to verify isolated single‐stage electric vehicle battery charger system's performance during dynamic and steady‐state conditions.

Enhancing Power Factor on LED Light Driver with Boost and Fly Back Converter Integration

Enhancing Power Factor on LED Light Driver with Boost and Fly Back Converter Integration

Analysis of Converter-Fed Rotor Based Induction Machine

Abstract: This paper presents the analysis of an induction-machine with a concept of the rotor-fed by a converter. Statorwinding configured in star and connected to the input-side of the three-phase voltage-source, whereas rotor-windings are fed by back-to-back converter by means of DC-link capacitor. For this, the Induction-machine is modelled in MATLAB/Simulink and simulated with and without a converter. The rotor circuit is magnetized with the help of back-to-back converter which in turns supply the variable-reactive power by setting the different phase-shift angle between the converters. The results depict the enhancement of Power-factor and also presents the dynamic performance of the machine includes the loading and de-loading as well as the starting condition of the machine. Fundamental-frequency variations of the converter enhance capability of machine to operate at a constant-speed with variable-load operation. Impact of variation in phase-shift angles between the converters on the power-factor, reactive-power, stator and rotor-current are also presented.

Electron-hole dichotomy and enhancement of the thermoelectric power factor by electron-hole-asymmetric relaxation time: A model study on a two-valley system with strong intervalley scattering

Electron-hole dichotomy and enhancement of the thermoelectric power factor by electron-hole-asymmetric relaxation time: A model study on a two-valley system with strong intervalley scattering

Enhanced power factor and thermoelectric efficiency in Cu2Sn1-xYxSe3 system: A low-temperature study

In the present study, we report the effect of Y doping at the Sn-site on structural, electrical, and low-temperature (10–350 K) thermoelectric properties of the Cu2SnSe3 system. The bulk polycrystalline samples of Cu2Sn1-xYxSe3 (0 ≤ x ≤ 0.12) are synthesized by the conventional solid-state reaction route method. Rietveld analysis of room temperature XRD data confirmed that the studied samples possess cubic crystal structure with F4‾3m space group. Temperature-dependent electrical resistivity of the samples with x ≤ 0.04 shows that they exhibit semiconducting behavior; while samples with x > 0.04 exhibit metallic behavior. In the studied temperature range, the Seebeck coefficient for all the samples is found to be positive, indicating that the majority of charge carriers are holes. A significant reduction in the electrical resistivity leads to an enhancement in the power factor, attaining a value of ∼253 μW/mK2 for the sample with x = 0.12 at 350 K. At high temperatures, the thermal conductivity of the samples decreases with temperature which is attributed to the phonon-phonon scattering. The systematic evolution of thermoelectric properties with Y incorporation over the range (0 ≤ x ≤ 0.12) shows the highest ZT of 0.024 at 350 K for the sample with x = 0.10, which is about six times higher than that of the pristine Cu2SnSe3. The results demonstrate that Y-doped compounds Cu2Sn1−xYxSe3 are potential candidates for thermoelectric applications.

Progressive carrier density optimization contributes to enhanced thermoelectric performance in Bi(Te, Se) compound

Layered BiTe and BiSe compounds present promising n-type thermoelectric performance, but the intrinsic high carrier density limits ZT value near room temperature. In this work, thermoelectric performance in Bi(Te, Se) compound is significantly improved by progressively optimizing its carrier density. The room-temperature carrier density is reduced from ∼5.5 × 1020 cm−3 in Bi0.99Te to ∼2.21 × 1020 cm−3 in Bi0.92Sn0.07Te0.4Se0.6-2%Cu, which can lead to obvious enhancement of Seebeck coefficient and power factor, and thus the room-temperature power factor increases from ∼4.17 μW cm−1 K−2 in Bi0.99Te to ∼9.78 μW cm−1 K−2 in Bi0.92Sn0.07Te0.4Se0.6-2%Cu. Moreover, the largely suppressed total thermal conductivity in Bi0.92Sn0.07Te0.4Se0.6-2%Cu also benefit from lowered carrier density because of reduced electronic thermal conductivity, as well as intensified phonon scattering caused by imported point defects. Finally, a room-temperature ZT of ∼0.29 and a peak value of ∼0.41 at 373 K in Bi0.92Sn0.07Te0.4Se0.6-2%Cu are achieved successfully, which are ∼6 and ∼3 times higher than that in Bi0.99Te, respectively.

Thermoelectric and mechanical performance of NiTiAl Heusler compound

In the current study, the NiTiAl exhibited the combination of full Heusler (f-Heusler) and Half-Huesler (h-Heusler) phases. The NiTiAl sample was prepared by arc-melting followed and spark plasma sintering at 1073K. The synthesized sample exhibited p-type semiconductor behaviour having a Seebeck coefficient of 50 μV/K at 790K. Further, the resulting power factor is 1.15mWm−1K−2 at 790 K, which is 115% higher than the TiCoSb. The enhancement in power factor is good in agreement with the increased electrical conductivity and measured carrier concentration (nH) ∼ 1020 cm−3. On the other hand, NiTiAl exhibited a hardness value of 7.8 GPa and the estimated fracture toughness (Kc) is 12% higher than the conventional 18 VEC of TiCoSb. Further, the NiTiAl exhibited a low value of κl ∿1.15 Wm−1K−1 at 473K, due to the phonon-phonon scattering of the h-Heusler/f-Heusler interfaces with increasing temperature. However, due to the presence of a larger fraction of metallic f-Heusler phase, the κe is increased significantly and that led to a higher κ, resulting in lower zT∿0.007 at 473 K. Finally, the acquired results of NiTiAl Heusler compound with 17 VEC will open a door for unexplored compounds than the conventional 18 VEC, which could help the thermoelectric community.

Thermoelectric properties of Ga-doped InSb alloys

Internal structure and thermoelectric properties of In1-xGaxSb alloys, prepared by melting synthesis at 1123 K, were systematically studied in this paper. Crystal structure was investigated by XRD analysis. All samples exhibited crystalline structure of single InSb phase. Transport and electrical properties were studied against temperature elevating. Electrical conductivity was determined via the standard four probe method. The thermal behavior of the electrical conductivity over the temperature range between 273 K and 473 K showed semiconducting behavior. Seebeck coefficient measurements were conducted via differential method in the temperature range 273–473 K. The measurements of Seebeck coefficient confirmed the electrical conductivity behavior of the samples. The maximum obtained Seebeck coefficient value |S| of the parent InSb compound was observed at 224 μV/K, obtained at 273 K. The alloy has been doped with Ga in order to enhance thermoelectric properties. Results showed that introducing of Ga into In sites leads to significant increase in the Seebeck coefficient up to 330.4 μV/K. Power factor was estimated from the measurements of the electrical conductivity and the Seebeck coefficient. Interesting enhancement in the thermoelectric power factor was observed with Ga-doping. The maximum power factor was obtained for the most doped sample exhibiting 2.3 μWm−1 K−2 at 273 K. The thermal conductivity was obviously reduced by substituting In with Ga. The dimensionless figure of merit was estimated showing an enhancement with the Ga addition. The maximum recorded ZT was 0.017 observed at 403 K.