Transformer Coupling Research Articles

Dual-Frequency Programmed Harmonics Modulation-based Simultaneous Wireless Information and Power Transfer System via a Common Resonance Link

Most simultaneous wireless information and power transmission (SWIPT) systems currently operate at a single frequency, where the power and information transmission affect the resonance state of each other. This paper proposes a structure using dual-frequency programmed harmonics modulation (DFPHM). The primary-side inverter outputs a dual-frequency (DF) wave containing the power transmission and information transmission frequencies, while the DF wave is coupled to the secondary side through a common inductive link. After the power and information are transmitted to the secondary side, they are demodulated in different branches. Wave trappers are designed on each branch to reduce the interference of information transmission on power transmission. There is no tight coupling transformer in the system to inject information, so the system order is not high. Experiments verified that the proposed structure based on DFPHM is effective.

A map of the amine-carboxylic acid coupling system.

Chemical transformations determine the structure of a product, and therefore its properties, which in turn affect complex macroscopic functions such as the metabolic stability of pharmaceuticals or the volatility of perfumes. Therefore, reaction selection can influence the success or failure of a candidate molecule to meet a functional objective. The coupling of an amine with a carboxylic acid to form an amide bond is the most popular chemical reaction used for drug discovery1. However, there are many other ways to connect these two common functional groupstogether. Here we show computationally that amines and acids can couple via hundreds of hypothetical yet plausible transformations, and we demonstrate experimentally the application of a dozen such reactions. To investigate the contribution of chemical transformations to properties, we developed a string-based notation and used an enumerative combinatorics approach to produce a map of conceivable amine-acid coupling transformations, which can be charted using chemoinformatic techniques. We find that critical physicochemical parameters of the products, such as partition coefficient and polar surface area, vary considerably depending on the transformation chosen. Data mining the amine-acid coupling system produced here should enable reaction discovery, which we demonstrate by developing an esterification reaction found within the mapped space. Complex molecules with distinct property profiles can also be discovered within the amine-acid coupling system, as we show here via the late-stage diversification of drugs and natural products.

Dynamic Direct Voltage Controller (D2VC) for grids with intermittent sources

This work proposes a voltage regulator to solve quality issues at the point of common coupling (PCC) of distribution grids affected by the intermittency of renewable energy sources. The proposed solution is a voltage compensator based on single-phase voltage source converter (VSC) units, called Dynamic Direct Voltage Controller (D2VC). The three-phase D2VC topology comprises three single-phase VSC back-to-back units. For each unit, one converter is connected in series with the grid at the PCC and the other converter is connected in shunt similar to an UPFC (Unified Power Flow Controller). To avoid coupling transformer, the series converter is directly connected in series to the existing distribution transformer thus no extra transformer is necessary. The D2VC can regulate the three-phase voltage profile at the PCC and balance all phases independently. The control strategy for each series converter is based on the estimation of the instantaneous symmetrical components of the voltage. Simulation results using PSCAD/EMTDC and an experimental platform of the D2VC are shown to confirm all the D2VC advantages in grids with resistive lines (R >> X). The proposed solution is much lighter and effective than the conventional indirect voltage control (reactive power control) and more robust than on load tap changer transformer.

High-Gain High-Efficiency IPOS LLC Converter With Coupled Transformer and Current Sharing Capability

In this paper, an input-parallel output-series (IPOS) LLC resonant converter with a coupled transformer and current sharing capability is proposed for high-gain high-efficiency applications such as the renewable energy grid connection. The coupled transformer is utilized to reduce the core size and core loss by implementing the magnetic flux cancellation method, which achieves a natural balance of output voltage simultaneously. The current sharing between the converter modules is achieved by a bridge wire that interconnects the resonant tanks of different modules. Furthermore, the current sharing inside a module is also achieved by the proposed compensation current based on the coordination of compensation inductor and delay control. A 200 kHz 100 V/1.2 kV 3.6 kW two-module IPOS LLC resonant converter prototype is built to verify the proposed method. The peak efficiency can reach as high as 97.5%, and the current sharing between modules and inside a module are well presented.

Smart control of BESS in PV integrated EV charging station for reducing transformer overloading and providing battery-to-grid service

Uncontrolled charging demand in an electric vehicle charging station (EVCS) can potentially result in the overloading of the grid coupling transformer that will affect the transformer’s lifetime. This paper proposes a smart coordinated control of photovoltaic (PV) and battery energy storage system (BESS) integrated in an EVCS in order to avoid transformer overloading. BESS is designed to provide the additional EV power demand which is greater than the transformer’s rated capacity and thus reduce transformer overloading. In addition, the smoothing control of PV power output when PV output is lower than a threshold value is incorporated in the control method. Also, BESS which is used to provide grid services i.e battery to grid (B2G) is also incorporated in the designed smart control when the energy selling price is attractive to the BESS operator. Considering a single point connection type, B2G can only be implemented when there is no EV demand. Furthermore, B2G and battery recharging power is maintained within the transformer’s rated capacity to avoid overloading during their particular services. Two different sizes of BESS and transformer capacity are considered to demonstrate the overloading of transformer for a particular time of the day. A small EVCS with integrated PV-BESS in a residential area and food center is simulated to validate the efficacy of the proposed coordinated control technique. Simulation results demonstrate that the integrated BESS with the proposed control method effectively minimizes transformer overloading during all the studied network operating conditions. Moreover, BESS successfully smooths out PV power output, provide grid service and recharge the battery within the defined rated transformer capacity and thus avoids transformer overloading while satisfying design constraints.

Experimental investigation of PV based modified SEPIC converter fed hybrid electric vehicle (PV‐HEV)

SummaryThis paper presents a high gain modified three‐port dual boost single‐ended primary‐inductor converter (SEPIC) converter operated hybrid photovoltaic (PV)/battery electric vehicle to improve the power transfer capability and efficiency of the power conversion stage. The proposed three‐port dual boost high gain SEPIC converter accepts wide voltage range of input then the conventional single stage SEPIC converter. The three‐winding high frequency coupling transformer integrates the two input sources and step‐up the input voltage. The theoretical and experimental analyses are presented to validate the performance of the proposed modified SEPIC converter in boosting the wide range of input voltage. A 6 kW, 12 to 600 V of experimental model has been developed and tested. The efficiency obtained from the designed model is around 94.11%.

Upgrade of the Pulsed Magnetic Field System With Flat-Top at the WHMFC

The 65 T pulsed magnetic field with 10 ms flat-top has been achieved at the Wuhan National High Magnetic Field Center (WHMFC). This is an upgrade based on the 41 T with 6 ms flat-top system. Both the magnet and the coupling transformer were newly designed and fabricated. The magnet circuit and the auxiliary circuit were driven by ten and two 1 MJ capacitor bank modules, respectively. At the voltage of 19.1 kV for the magnet circuit and 8.5 kV for the auxiliary circuit, peak field of 64 T with 10 ms flat-top and 0.3% flatness was obtained. The primary specific heat measurement of sample CeRhln5 was successfully performed.

Modeling, Analysis, and Implementation of Series-Series Compensated Inductive Coupled Power Transfer (ICPT) System for an Electric Vehicle

This paper focuses on the modeling and implementation of an Electric Vehicle (EV) wireless charging system based on inductively coupled power transfer (ICPT) technique where electrical energy can be wirelessly transferred from source to vehicle battery. In fact, the wireless power transfer (WPT) system can solve the fundamental problems of the electric vehicle, which are the short battery life of the EV due to limited battery storage and the user safety by handling high voltage cables. In addition, this paper gives an equivalent electrical circuit of the DC-DC converter for WPT and comprises some basic components, which include the H-bridge inverter, inductive coupling transformer, filter, and rectifier. The input impedance of ICPT with series-series compensation circuit, their phases, and the power factor are calculated and plotted by using Matlab scripts programming for different air gap values between the transmitter coil and receiver coil. The simulation results indicate that it is important to operate the system in the resonance state to transfer the maximum real power from the source to the load. A mathematical expression of optimal equivalent load resistance, corresponding to a maximal transmission efficiency of a wireless charging system, was demonstrated in detail. Finally, a prototype of a wireless charging system has been constructed for using two rectangular coils. The resonant frequency of the designed system with a 500 × 200 mm transmitter coil and a 200 × 100 mm receiver coil is 10 kHz. By carefully adjusting the circuit parameters, the implementation prototype have been successfully transferred a 100 W load power through 10 cm air gap between the coils.

MIMO Ground-Radiation Antennas Using a Novel Closed-Decoupling-Loop for 5G Applications

This paper investigates the design of a compact multiple-input multiple-output (MIMO) ground-radiation antenna system for 5G terminal devices. Ground-radiation antennas are small loop-type resonators that can excite the ground plane as radiators while having advantages of small size and convenient tunability, but their compact MIMO systems remain as unsolved issues. In this study, a novel and straightforward decoupling technique based on a closed-decoupling-loop is presented for MIMO applications in the first of its kind. The proposed closed-decoupling loop can be viewed as a coupling transformer between two antenna elements by acting as a half-wavelength loop-type resonator and by introducing a current null at its center; in this way, a tremendous isolation improvement is accomplished even though the distance between two antennas is only 1 mm. Therefore, a compact 2 x 2 MIMO ground-radiation antenna system and its 8 × 8 MIMO system are demonstrated for 5G applications. Both simulation and measurement are taken to validate the proposed decoupling technique and the compact MIMO ground-radiation antenna system.

Finite Element Simulation of NiTiNb Shape Memory Alloy Pipe‐Joint Subjected to Coupled Transformation and Plastic Deformation

The assembling process of Ni47Ti44Nb9 alloy pipe joints considering the phase transformation and plasticity was numerically simulated for the first time with a developed constitutive model. The simulated process was based on the experimental material parameters, which were determined with the experimental tensile results of Ni47Ti44Nb9 shape memory alloy (SMA) and steel bars. The results showed that, after assembly, the Mises stress distributed uniformly along the longitudinal direction of the NiTiNb joint, but nonuniformly along the radial direction. The maximum σeq does not appear at the inner wall of the joints due to the coupling effect of the plastic deformation and the recoverable transformation. The contact pressure distributed uniformly along the circumferential direction, but nonuniformly along the longitudinal direction. The sizes of the SMA joint and the pipe should be properly matched to ensure contact during the stage of the rapid reverse phase transformation to obtain stable connection performance. The pull‐out force was also computed, and the results were in good agreement with the experimental results. The results obtained can provide available information for the optimization of the design parameters of the high‐performance SMA pipe‐joint, such as inner diameter and assembly clearance.

Research on the Power Output Characteristics of a Coupling Transformer in D-FACTS

The series coupling distributed flexible AC transmission system (D-FACTS) device couples the secondary side compensating reactance to the primary side based on the principle of transformer, thus realizing the goal of adjusting the transmission line parameters and controlling the distribution network flow. The coupling transformer is the most important power conversion part in the D-FACTS device but has different working principles of mutual inductor. The magnetizing current of the coupling transformer changes within a large range, which makes the traditional power output model of mutual inductor inapplicable. In this paper, the power output model of coupling transformer was constructed by viewing the coupling transformer as a constant current source. Moreover, the corresponding relationship between the output power of the transformer and related parameters, as well as between variations of reactive output power and active loss power with load changes, was analyzed. Some conclusions were drawn: (1) the output power characteristic curve of the coupling transformer was acquired; (2) given a constant line current, the maximum power was achieved when the system’s capacitive reactance and the internal resistance of the transformer matched, and the maximum power was unrelated to the number of turns of the coupling transformer; (3) the output power changed with the variation of the line current, and there was a proportional relationship between the maximum power and the square of the line current. Next, the relationship between the maximum output power and the air gap thickness of the magnetic core was discussed. Finally, these conclusions were proved accurate via experiments.

Co-vacancy induced magneto-structural transformation in Co and Ge bidirectional-regulation MnCoGe systems

Tuning the structural transformation into the temperature region between the Curie temperatures of Hexagonal and Orthorhombic phases can acquire coincident magneto-structural transformation with a large magnetocaloric effect in MnCoGe alloy. However, the investigations about controlling and achieving magneto-structural coupling in MnCoGe-based alloys usually focus on the unidirectional change among the three elements. Here, we report the first-order magneto-structural coupled transformation in Co and Ge bidirectional-regulation MnCoGe alloys. Resultantly, large magnetocaloric effect is obtained around room temperature in both MnCo1-xGe1+x and MnCo1+yGe1-y systems. The uniform origins of magneto-structural coupling in both systems are explored.

Influence of physical and chemical hydrology on bioremediation of a U-contaminated aquifer informed by reactive transport modeling incorporating 238U/235U ratios

Microbially-catalyzed reductive immobilization of aqueous uranium (U) as a solid phase has been proposed as a U remediation technique. Both laboratory and field experiments have demonstrated that this reduction reaction alters the 238U/235U ratio, producing a 238U-enriched U(IV) solid. In contrast, other major U reactive transport processes fractionate these isotopes much less. This suggests the potential to quantify the extent of bioreduction occurring in groundwater containing U using the 238U/235U ratio, which would substantially improve upon current practices largely relying on U concentration measurements alone. Current reactive transport models for uranium dynamics include only concentration measurements, which are strongly influenced by highly coupled reactive transformation and aqueous transport processes. The complex physical and chemical behavior of U potentially compromises such quantitative analysis of U storage and release. Here we report the first numerical reactive transport model which explicitly incorporates variations in the 238U/235U ratio of U and demonstrates improved interpretation of the principal chemical reactions and groundwater transport processes affecting the subsurface mobility and distribution of this widespread contaminant.Recent U bioreduction studies performed in a contaminated aquifer in Rifle, Colorado, USA applied Rayleigh distillation models to interpret U stable isotope fractionation observed as a result of acetate amendment. These simplified models were unable to resolve the spatiotemporal pattern of U isotope fractionation recorded in the aqueous solutes. Here, we employ the multi-component, isotope-enabled CrunchTope reactive transport software to interpret these measured U isotope ratios, and demonstrate accurate reproduction of observed trends in both geochemistry and 238U/235U ratios for two consecutive years of field experiments. Our results indicate that accurately modeling both the U concentration and isotope ratio distributions greatly constrains the parameter space of the model. We find that the transport properties of U in the Rifle aquifer are governed by the presence of low-permeability regions, which the isotopes are uniquely sensitive to. When U reduction is spatially constrained by these low-permeability regions, the shift in the 238U/235U ratio becomes more muted. Accurate modeling of observed U isotope ratios thus provides a powerful means to better understand bioremediation, and the current study serves to advance the application of this novel method.

Assessing the Impact of Harmonics and Interharmonics of Top and Mudpump Variable Frequency Drives in Drilling Rigs

Declining extraction costs and process efficiencies have incented the revival of the oil and gas sector postrecession. The application of drilling rigs has been done more efficiently. These loads are very large, temporary in nature, and mobile. The drilling of each well can be done as quickly as a few hours and typically not more than a few days. These massive loads are complex to own, maintain, and operate, as a result few specialized drillers share the market. Because of the requirements for variable speed and control, drilling rigs are driven by variable frequency drives (VFDs), which are in their clear majority of older technologies such as six-pulse thyristor bridge or SCR-driven motors. These technologies are known to impose steep ramp rates (up and down) as well as rich harmonic content and variable, typically low, power factor. Furthermore, the locations of drilling rigs are typically remote, where distribution systems, if present, are weak, which lead to large background voltage distortions when such loads are present. This paper presents measurements, simulations, and analytical assessments of the characteristics and effects of harmonics and interharmonics (IHs) generated by top-drive and mud-pump VFDs in a large drilling rig operated in Alberta, Canada. Measurement results reveal very high harmonic and IH generation. To further refine the impact assessment of these harmonic emissions, the harmonic attenuation effect of the VFDs is quantified to avoid overestimating the harmonic generation of the loads. The thermal impact of the current harmonics on the coupling transformer is also quantified.

Novel Measurement Procedure for Switched-Mode Power Supply Modal Impedances

The measurement of modal impedances of switching-mode power supplies (SMPSs) is of paramount importance in electromagnetic compatibility applications, especially when designing electromagnetic interference filters to suppress the conducted and radiated electromagnetic emissions is the target. A novel measurement technique that makes use of an impedance analyzer and a coupling transformer and allows extracting the complex value of common- and differential-mode noise source impedance of an SMPS is proposed. The measurement procedure is first studied from the theoretical point of view, then experimentally validated with passive components, and eventually implemented in a CISPR-25 conducted emission test setup to measure the magnitude and phase of modal impedances of an automotive SMPS under different operation conditions.

Coupling: The program for searching optimal coupling scheme in atomic theory

The Coupling program, which is important not only for the Grasp2018 package but for the atom theory in general, is presented in this paper. This program is designed as a part of the Grasp2018 package. The Coupling performs the transformation of atomic state functions (ASFs) from a LSJ-coupled CSF basis into several other configuration state function (CSF) bases such as jj, LK, JK, JJ, and many others. It allows identification of the energy structure of practically any element in different coupling schemes and also allows selection of the most suitable one. In addition, examples of how to use the Coupling program are given in additional file Example_Calculation.pdf listed in source directory grasp2018/src/appl/Coupling/Sample_Runs. Program summaryProgram Title:CouplingProgram Files doi:http://dx.doi.org/10.17632/7tv9n8g24w.1Licensing provisions: MIT licenseProgramming language: Fortran 95.External routines/libraries used:Grasp2018 modules: jj2lsj_data_1_C, jj2lsj_data_2_C, jj2lsj_data_3_C and Atsp2K module: sqlsf.f.Nature of problem: The Coupling program is designed as a part of the Grasp2018 package for the computation of atomic state function transitions and for identification atomic properties in different coupling schemes.Solution method: Spin-angular coupling transformation of multiconfiguration expansions obtained in LS and jj coupling schemes.Additional comments including restrictions and unusual features: The transformations of the configuration state functions is supported for one, two, and three open shell structures including open s, p, d, and f-shells. For shells with l>3 (i.e. beyond the f-shells), however, a proper transformation of the antisymmetrized shell states can be carried out only for the case of one or two equivalent electrons. The jj⟷LS transformation matrices, which are applied internally by the program, are consistent with the previously published definitions of the reduced coefficients of fractional parentage and jj⟷LS transformation matrices. The transformation from LSJ-coupling to all main coupling schemes is performed by the program Coupling. The number and types of coupling schemes depend on the number of coupled shells in LS-coupling.

Novel Method and Procedure for Evaluating Compliance of Sources With Strong Gradient Magnetic Fields Such as Wireless Power Transfer Systems

To date, the development of valid and globally universally accepted recognized methods for the accurate exposure assessment of wireless power transfer (WPT) technologies is lagging behind the rapid emergence of high power systems in the energy and automotive sectors. WPT systems based on inductive and magnetic resonance technologies generate strong but rapidly decaying magnetic fields, which often exceed reference levels (RL) in the immediate vicinity of the WPT coils by up to a factor of $>$ 100. Compliance testing of WPT systems with limits derived for homogeneous exposure can lead to estimations of exposure that exceed by up to 40 dB assessments of the fields induced in the human body, i.e., the basic restrictions (BR) defined by the international safety guidelines. Testing compliance with the BR is impractical for regulatory purposes due to the high costs of resources of determining the maximum exposure conditions. This paper presents a novel compliance testing method that mitigates the overestimation of the exposure while maintaining the simplicity of the testing procedure. This is achieved by using coupling transformation functions to correlate not only the amplitude and frequency but also the gradient of the incident field with the BR. These novel conservative coupling functions have been determined by means of a large scale numerical study in the frequency range 3 kHz–10 MHz supported by a physics-based approximation. The here proposed compliance testing method is still conservative in comparison to the compliance toward BR of localized sources. However, in comparison to today's practice of applying RL directly, the overestimation is strongly reduced for high gradient fields ( $G_n$ $>$ 50 T/m/T), e.g., by more than 3000 times for field gradients of about 200 T/m/T. We have validated the method by numerical analysis of human exposure to actual WPT sources. The adoption of the new method will help to accelerate the introduction of high-power wireless charging devices in the global market.

Design and Evaluation of Band-Pass Matching Coupler for Narrow-Band DC Power Line Communications

In power line communication (PLC), coupling transformers are usually required for coupling, band-pass filtering and impedance matching. However, coupling transformer design involves so many parameters that it is typically an imprecise and experimental procedure. In addition, the cost and size of transformers prevent them from being an economic and compact solution for PLC couplers. This paper first analyzes a simplified, distributed parameter model of the power line, which can be used to calculate power line impedance easily and accurately. Next, a low-cost, band-pass matching coupler with compact architecture is designed to replace the coupling transformer for direct current PLC (DC-PLC), which ensures impedance matching on the basis of an accurate power line impedance instead of using an average value. Finally, simulations as well as laboratory tests are conducted under 95–125[Formula: see text]kHz (CENELEC B-band), which confirm the new coupler’s excellent band-pass filtering and impedance matching performance.

Dehydroxymethylation of Alcohols Enabled by Cerium Photocatalysis.

Dehydroxymethylation, the direct conversion of alcohol feedstocks as alkyl synthons containing one less carbon atom, is an unconventional and underexplored strategy to exploit the ubiquity and robustness of alcohol materials. Under mild and redox-neutral reaction conditions, utilizing inexpensive cerium catalyst, the photocatalytic dehydroxymethylation platform has been furnished. Enabled by ligand-to-metal charge transfer catalysis, an alcohol functionality has been reliably transferred into nucleophilic radicals with the loss of one molecule of formaldehyde. Intriguingly, we found that the dehydroxymethylation process can be significantly promoted by the cerium catalyst, and the stabilization effect of the fragmented radicals also plays a significant role. This operationally simple protocol has enabled the direct utilization of primary alcohols as unconventional alkyl nucleophiles for radical-mediated 1,4-conjugate additions with Michael acceptors. A broad range of alcohols, from simple ethanol to complex nucleosides and steroids, have been successfully applied to this fragment coupling transformation. Furthermore, the modularity of this catalytic system has been demonstrated in diversified radical-mediated transformations including hydrogenation, amination, alkenylation, and oxidation.

A Unified Power Flow Controller Using a Power Electronics Integrated Transformer

This paper presents a Unified Power Flow Controller (UPFC) application of the Custom Power Active Transformer (CPAT); a power electronics integrated transformer which provides services to the grid through its auxiliary windings. The CPAT structure integrates three single-phase transformers into one shunt-series combining transformer. This integration empowers a sub-station with the capability of dynamically regulating the terminal voltage and current of a transformer through isolated power electronics converters. This paper investigates the CPAT's capability to provide UPFC services which includes power flow control, reactive power compensation, voltage regulation, and harmonics elimination. Simulations of the CPAT-UPFC with a stiff grid and a 5-bus power system demonstrates its functionality as an inter-bus coupling transformer that provides the required grid services. Moreover, the impact of the CPAT-UPFC during load perturbations on the power system is investigated to further validate its transient and steady-state response. Furthermore, an experimental prototype reveals the operation of the three-phase CPAT-UPFC confirming its stable operation according to the theoretical expectations.