Multiple Windings Research Articles

Adsorption and retention of fracturing fluid and its impact on gas transport in tight sandstone with different clay minerals

To elucidate the adsorption characteristics and retention mechanisms of fracturing fluids in diverse clay minerals, we conducted on-line nuclear magnetic resonance (NMR) and atomic force microscopy (AFM) experiments. The depth and extent of solid phase damage are determined by the ratio between the size of fine fractions in fracturing fluid residue and the pore-throat size in experiments. Poor physical properties (K < 0.5 mD) result in a more preferential flow pathway effect during flowback, and the stepwise incremental pressure differential proves to be more effective for the discharge of fracturing fluid in submicron pore throats. The permeability is significantly influenced by the differential distribution of retained fracturing fluid, as supported by direct experimental evidence. The presence of good physical properties (K > 0.5 mD) combined with a scattered distribution of retained fracturing fluid is associated with high gas phase recovery permeability, whereas a continuous sheet-like distribution results in low recovery permeability. The expansive surface area and presence of filamentous illite minerals facilitate the multiple winding and adsorption of fracturing fluids, demonstrating strong hydrogen-bonding, multi-layering and multiple adsorption properties. The geological characteristics of the main gas formations exhibit significant variation, and the severity of damage caused by fracturing fluids occurs in diverse sequences. To address this issue, a differentiated strategy for optimizing fracturing fluids has been proposed.

Design and Analysis of Receiver Coils with Multiple In-Series Windings for Inductive Eddy Current Angle Position Sensors Based on Coupling of Coils on Printed Circuit Boards.

We present a method for improving the amplitude and angular error of inductive position sensors, by advancing the design of receiver coil systems with multiple windings on two layers of a printed circuit board. Multiple phase-shifted windings are connected in series, resulting in an increased amplitude of the induced voltage while decreasing the angular error of the sensor. The amplitude increase for a specific number of windings can be predicted in closed form. Windings are placed electrically in series by means of a differential connection structure, without adversely affecting the signal quality while requiring a minimal amount of space in the layout. Further, we introduce a receiver coil centerline function which specifically enables dense, space-constrained designs. It allows for maximization of the number of possible coil windings while minimizing the impact on angular error. This compromise can be fine-tuned freely with a shape parameter. The application to a typical rotary encoder design for motor control applications with five periods is presented as an example and analyzed in detail by 3D finite-element simulation of 18 different variants, varying both the number of windings and the type of centerline functions. The best peak-to-peak angular error achieved in the examples is smaller than 0.1° electrically (0.02° mechanically, periodicity 5) under nominal tolerance conditions, in addition to an amplitude increase of more than 170% compared to a conventional design which exhibits more than twice the angular error. Amplitude gains of more than 270% are achieved at the expense of increased angular error.

Multiple Brillouin Zone Winding of Topological Chiral Edge States for Slow Light Applications.

Photonic Chern insulators are known for their topological chiral edge states (CESs), whose absolute existence is determined by the bulk band topology, but concrete dispersion can be engineered to exhibit various properties. For example, the previous theory suggested that the edge dispersion can wind many times around the Brillouin zone to slow down light, which can potentially overcome fundamental limitations in conventional slow-light devices: narrow bandwidth and keen sensitivity to fabrication imperfection. Here, we report the first experimental demonstration of this idea, achieved by coupling CESs with resonance-induced nearly flat bands. We show that the backscattering-immune hybridized CESs are significantly slowed down over a relatively broad bandwidth. Our work thus paves an avenue to broadband topological slow-light devices.

A Novel Modularization Method for Voltage Equalization of Ultracapacitor Bank Using Coupled Inductor

The voltage equalization of ultracapacitors (UCs) in a UC bank using coupled inductors is superior due to their advantages of simple control, fast energy transfer capabilities, etc. However, as the number of UCs connected in series or parallel in a UC bank increases, the number of windings on a single core required for balancing also increases. This causes severe mismatches between the inductance of the multiple winding in a single core, making the implementation more complex. Therefore, a novel modularization method is proposed in this paper for a matrix-connected UC bank. The proposed method achieves cell balancing, module balancing, and demagnetization with less number of components. Moreover, the proposed method uses a single pair of complementary pulse width modulation (PWM) signals with a 50% duty ratio for all switches. The energy is transferred from the higher voltage cell to the lower voltage cell simultaneously through the coupled inductors, which increases the balancing speed. The balancing performance of the proposed modularization is validated experimentally.

Winding Characteristics and Magnetization State Regulations of Variable Flux Memory Machines With Segregated Distributed Windings

The variable flux memory (VFM) machine with segregated multiple three-phase windings is investigated, with particular reference to its winding characteristics and magnetization state (MS) regulations. The overlapped distributed windings are separated into multiple three-phase winding sets with each set non-overlapped, which contributes to the independent relationship between the winding set and corresponding permanent magnet (PM) pole-pairs. Consequently, the single winding set can independently complete the MS regulation, and thus the overall current requirement is reduced. Moreover, it is revealed that the amplitude of de/re-magnetizing magneto-motive force (MMF) with single winding set operation is actually higher than those with multiple winding sets operation thanks to the asymmetric winding layout, resulting in the enhanced de/re-magnetizations and thus the further reduced de/re-magnetizing currents. The winding function, MMF distribution, inductance, and torque of the machine are analyzed, and intentional MS regulations with different methods are compared. A prototype machine is fabricated and tested for experimental validations.

Using Multiple Stator Windings and Multi-Level Converters for Frequency Matching in Microturbine Generators

Using Multiple Stator Windings and Multi-Level Converters for Frequency Matching in Microturbine Generators

A Centralized Battery Energy Storage-Based Medium-Voltage Multiwinding DVC for Balance and Unbalance Operations

This paper proposes a centralized battery energy storage based medium-voltage multi-winding dynamic voltage compensator (DVC) for balance and unbalance operations. In this topology, the compensation voltage is added to the grid side through the transformer, and the primary side of the transformer is shunted by multiple windings to support the voltage sag on the medium-voltage distribution systems. According to the symmetrical and asymmetrical grid-side voltage sags, the positive and negative sequence mathematical models of DVC as well as their voltage-current double closed-loop control strategies are developed. As for the DC bias caused by circulating current between the primary windings of each phase of the multi-winding transformer, circulating current suppression algorithm is added to the positive and negative sequence inner current loops. Simulation and experiments results are performed to verify the effectiveness and superiority of the proposed methodology on voltage support.

A Modular Magnetic Linked Converter Station for Offshore Power Transfer Through HVDC Link

This paper proposes a modular magnetic linked converter station (CS) for offshore power transfer through a high voltage dc (HVDC) link. The proposed converter station can collect medium voltage ac and dc power simultaneously and transform the power to HVDC suitable for offshore power transmission. The proposed CS adopts multiple half-bridge (HB) converters to form a front-end interface that can collect both medium voltage ac and dc power. Moreover, several high-frequency magnetic linked multiport converters (MLMCs) are employed in the CS to isolate and step up the voltage. The MLMC is operated at a unity step-up voltage ratio which matches the turn ratio in multiple windings shared by a common magnetic link. This condition facilitates minimum current stress on the switches and inherent soft-switching operation. In the proposed CS, the hard switching operation of the front-end HB converters does not affect the switching condition of the MLMCs. Furthermore, the application of the switched capacitor-based HVDC converter enables discretized dc-link capacitor arrangement to limit high inrush current under dc fault. A controller structure is also proposed for the CS to balance the electrical parameters. The results from a simulation study of the proposed CS, both in steady-state and dynamic conditions, show that the proposed CS performs satisfactorily with the proposed controller, which is validated by the laboratory scale experiment.

A Turn-Ratio-Changing Half-Bridge CLLC DC–DC Bidirectional Battery Charger Using a GaN HEMT

This paper presents a 250 kHz bidirectional battery charger circuit using a GaN HEMT. The charger is subjected to a high-/low-side constant voltage at 200 V/20 V. The charger circuit is a hybrid of the LLC and flyback circuit topologies. Both the power output analysis and efficiency control of this circuit are simplified when the magnetization current is minimized using the low-resistance GaN HEMT. The switching frequency is controlled to match the series resonance in a way that is analogous to conventional LLC circuit controls, while the duty ratio that determines the power output and the dead time, which determines the zero voltage switching, is controlled in an analogous manner to the flyback circuit control. The charging and discharging modes were altered by applying a double-throw relay that changes the transformer turn ratio, which is different from conventional LLC designs using the switching frequency adjustment. A nominal turn ratio with Np = 35 and Ns = 3.5 for a 200 V/20 V converter can only produce an internal series resonance with no current flowing in any charging direction. The proposed circuit using a transformer with multiple windings (Np = 35, Ns,F = 4, and Ns,R = 3) was fabricated to deliver 125 W output power from the power grid battery to the vehicle battery in the forward (charging) mode and 90 W in the reverse (discharging) mode. The conversion efficiency was calculated to be as high as 97% in the forward mode and 95% in the reverse mode. The high conversion efficiency is due to the characteristics of the GaN HEMT, including low resistive and switching losses. The equations derived in this paper associate these losses with the series resonant frequency and power conversion rate, which highlight the advantages of using a GaN HEMT in this CLLC design.

Eddy Current and Loss of Graded-Resistance No-Insulation Coils in HTS Synchronous Machines of Electrical Aircraft

The No-insulation (NI) high temperature superconductor (HTS) machine is a promising propulsion technique for future large-scale electrical aircraft because of its high power density and enhanced thermal stability. However, in the machine environment, the ripple magnetic fields can induce significant eddy currents and losses on the NI coil. A grading turn-to-turn resistivity technique has been proposed to solve this problem, in which higher turn-to-turn resistivity is applied on the outermost turns of the NI coil, and lower turn-to-turn resistivity is kept on middle turns. The purpose of this research is to study the effects of grading turn-to-turn resistivity technique on the eddy current and loss of both single and multiple NI HTS coils exposed to ripple fields. To investigate the electromagnetic behavior and loss mechanism of NI HTS coils, a simulation model is proposed that couples the equivalent circuit model and finite element model. Results show that the grading turn-to-turn resistivity can effectively reduce the induced eddy current and lead to a uniform distribution of eddy current among turns of both single and multiple windings. It reduces magnetization loss in superconducting layers but increases the turn-to-turn loss on the radial contacts. These results are useful for the development of NI HTS machines with high thermal stability.

Reconfigurable topology of electric vehicle wireless power transfer system to achieve constant-current and constant-voltage charging based on multiple windings

In the wireless charging system of electric vehicles, different charging stages have different charging requirements, namely constant-current (CC) charging mode and constant-voltage (CV) charging mode. The purpose of this paper is to provide a multi-winding wireless charging system with a reconfigurable topology to realize CC and CV charging with different optimal load resistances so that high efficiency can be achieved over a large load resistance range. The designed system can form different compensation topologies by switching on and off relays, such as the series–series topology and the inductor–capacitor–capacitor-series topology. Different topologies have different optimal load resistances, therefore, it can realize efficient transmission in a large load resistance range. In addition, the half-bridge scheme and the full-bridge scheme are the other two functioning modes for each topology. At the same time, the efficiency of the system can reach up to 94.34% and 95.13% in the half-bridge as well as full-bridge schemes under the CC mode. The highest transmission efficiency can reach 93.37% and 90.78% for the half-bridge as well as full-bridge schemes under the CC mode, respectively. Experiment results have validated the proposed method.

Equivalent Circuit Based Modeling of Multiple Winding Transformers

Developing suitable equivalent circuit models for multiple winding transformers provides great convenience in obtaining system equations. In general, circuits models are available for two-winding transformers. The paper proposes an equivalent circuit model based on ideal transformer representations consisting of dependent sources for multiple winding transformers. The use of equivalent circuit simplifies analysis and makes solutions more understandable. Since the model has a systematic structure, the increase in the number of windings does not affect the obtaining of the system equations. To validate the proposed equivalent circuit model, an application example, whose theoretical results can be easily seen, has been added to the study.

Mechanical model and mechanical property analysis of fibre-reinforced hybrid composite pipes

Compared to conventional fibre-reinforced composite pipes, fibre-reinforced hybrid composite pipes are more complex and are characterised by the use of hybrid fibres, hybrid matrices, and multiple fibre winding angles. In this study, based on the mechanical model of conventional fibre-reinforced composite pipes, the cross-section division method, the radial pressure on the adjacent layer by spiral wound rope structures, and the calculation method of axial force in each layer were improved. Furthermore, the von Mises stresses in each layer were calculated to discriminate the failure to establish a mechanical model of fibre-reinforced hybrid composite pipes with any number of reinforced layers under axial tension, internal pressure, and external pressure. Experimental data and the finite element method (FEM) were used to verify the reliability of the established model, with the axial tensile mechanical properties analysed based on the established model. The results showed that the large-angle fibres no longer withstood the axial tensile load when the winding angle of the large-angle fibres was greater than 45°. The matrices yielding was much earlier than the fibre breakage. The matrices hybrid methods have a large influence on the axial tensile properties of fibre-reinforced hybrid composite pipes, and improving the material properties of the inner and outer liners can significantly improve the axial tensile properties of fibre-reinforced hybrid composite pipes.

A Comparative Study on Parasitic Capacitance in Inductors With Series or Parallel Windings

In high-power medium-voltage applications, inductors usually have multiple windings on a single core, due to the high inductance value and high current stress. The multiple coils are electronically connected in either series or parallel, with considerations of windings loss and cost. However, the differences in parasitic capacitance of inductors using parallel and series connections are not discussed. Therefore, this article reveals that in comparison to parallel connections for windings, utilizing series connection for winding can significantly reduce the parasitic capacitance in multiwindings inductors without sacrificing the power density and adding manufacturing complexities. Physics-based models of parasitic capacitance in inductors with round-cable and copper-foil windings are developed for theoretical analysis. According to the theoretical analysis, the equivalent capacitance contributed by the stored electric field energy between two layers can be halved at least. The theoretical analysis is also verified by FEM simulations. Six prototyped inductors are experimentally compared to validate the theory.

A dual harmonic balanced configuration transformer with harmonic multi-port isolation: Design, modeling and analysis

This paper presents a dual harmonic balanced configuration transformer (DHBCT) carefully designed to achieve harmonic multi-port isolation in the regional hub substation. Firstly, the design and implementation of the special configuration are elaborated. Then, the magnetic field coupling characteristics expressed by the coupling inductances in the dual harmonic balanced configuration are derived and demonstrated. On this basis, the filtering mechanism of the DHBCT that can achieve harmonic multi-port isolation is demonstrated. Besides, in view of the difficulties caused by multiple windings and characterization characteristics for simulation, the electromagnetic decoupling model that can reflect the balanced configuration is established. Considering various application scenarios and the convenience of the application, the decoupling model is extended and simplified. Following that, the fault analysis is investigated using the established model. Finally, the correctness and accuracy of the proposed models and fault analysis method are verified by experiments and simulations.

An Expandable High Voltage-Gain Resonant DC-DC Converter With Low Semiconductor Voltage Stress

A high voltage-gain resonant DC-DC converter is proposed in this brief, where a coupled-inductor with multiple windings is adopted. The proposed converter is composed of a boost unit with input-output in series connection and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$z(z &gt; 1)$ </tex-math></inline-formula> expandable units. Each expandable unit includes two secondary windings of the coupled-inductor and two leakage-inductor-resonant-capacitor cells. The secondary windings are helpful to get a high voltage-gain, while the resonant cells are helpful to realize zero-current-switching for all diodes. Moreover, all the semiconductors can be thought as in series connection, leading the voltage stresses much lower than the output voltage, especially that of the switches. A laboratory prototype with two expandable units is built to verify the proposed converter.

Analysis and Design Considerations of a Dual-Rotor Multiple-Winding Machine

In this article, a novel dual-rotor multiple-winding machine (DRMWM) is proposed for the continuous variable transmission (CVT) in hybrid electric vehicles (HEVs). First, a mathematical model of the proposed machine is constructed by using the harmonic modeling method. Then, on the basis of the magnetic field analysis, the operating principle of the DRMWM is deduced. By introducing multiple windings with two different working harmonics, namely the permanent magnet (PM) harmonics, and the magnetic gear harmonics, the proposed DRMWM can cope with various operating conditions of HEVs. To further obtain optimal performance, a finite-element analysis and multiobjective genetic algorithm II combined sequential optimization is carried out for the proposed DRMWM. The proposed optimization method is proven to be more computationally efficient compared to the global optimization method. Finally, a prototype is manufactured and tested in various operating modes. The results validate the simulation and analytical method predictions. Also, it proves that the proposed DRMWM is suitable to work as the CVT in HEVs.

Power Management Using One Cycle Control Strategy for Triple Input Single Output Fly Back DC–DC Converter

Traditional multi-input converters have simpler configuration, but they have some disadvantages like multiple primary winding, high voltage stresses across the switches and also transfer of energy to the load occurs only from anyone of the input sources. This article proposes an isolated converter with reduced number of primary winding, and the load can be supplied by the sources either individually or simultaneously. The main objective of this work is to inject power into the grid using a three input single output Fly back DC–DC converter with closed loop control using one cycle controller (OCC) and PI controller. For power management, the inductor current is measured and the duty ratios of respective sources are controlled in such a manner that the average current flowing through the switch is proportional to power delivered by respective sources. In order to maintain the output voltage to be constant, the duty ratio of any one source is to be controlled by using outer voltage controller and inner current controller. Here, the duty ratios of first two sources are controlled by current mode control using OCC and the duty ratio of third source is controlled by using voltage controller with inner OCC current control. Since OCC is a nonlinear technique, only one PI controller is needed by the system. The system has only two sensors, one for measuring the output voltage and one for measuring the inductor current.

A Multilevel Converter Topology for a STATCOM System Based on Four-Leg Two-Level Inverters and Cascaded Scott Transformers

This paper presents a new power electronic topology for a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">STATCOM</i> allowing the generation of multilevel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</i> voltages. This topology is characterized by a modular configuration since it uses two well known four-leg two-level voltage source inverters. A <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Scott</i> transformer with multiple secondary windings connects the two four-leg inverters to the grid. One of the important features of the proposed power topology is the capability to generate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</i> voltages with high number of levels, in spite of using only two four-leg two-level voltage source inverters. To maximize the number of voltage levels a geometric progression ratio of 3 between the windings of the transformers connected in cascade is proposed. However, to reduce the turns-ratio span, alternatively a fractional geometric ratio of 1.5 is also proposed and analyzed. A control strategy adapted to the proposed power converter topology is also presented. Besides the control of the reactive power the regulation of the four-leg inverter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</i> voltage will also be considered. To support the theoretical studies and assumptions, simulations and experiments are presented. Experimental results were obtained using a low power laboratory prototype. The results shown give evidence to the characteristics and features of the proposed power converter topology and control system.

Conceptualization and Analysis of a Next-Generation Ultra-Compact 1.5-kW PCB-Integrated Wide-Input-Voltage-Range 12V-Output Industrial DC/DC Converter Module

The next-generation industrial environment requires power supplies that are compact, efficient, low-cost, and ultra-reliable, even across mains failures, to power mission-critical electrified processes. Hold-up time requirements and the demand for ultra-high power density and minimum production costs, in particular, drive the need for power converters with (i) a wide input voltage range, to reduce the size of the hold-up capacitor, (ii) soft-switching over the full input voltage and load ranges, to achieve low losses that facilitate a compact realization, and (iii) complete PCB-integration for low-cost manufacturing. In this work, we conceptualize, design, model, fabricate, and characterize a 1.5 kW, 12 V-output DC/DC converter for industrial power supplies that is required to operate across a wide 300 V–430 V input voltage range. This module utilizes an LLC-based control scheme for complete soft-switching and a snake-core transformer to divide the output current with a balanced flux among multiple secondary windings. Detailed loss models are derived for every component in the converter. The converter achieves close to 96% peak efficiency with a power density of 337 W in−3 (20.6 kW/dm−3), excellent matching to the derived loss models, and zero-voltage switching even down to zero load. The loss models are used to identify improvements to further boost efficiency, the most important of which is the minimization of delay times in synchronous rectification, and a subsequent improved 1.5 kW hardware module eliminates nearly 25% of converter losses for a peak efficiency of nearly 97% with a power density of 308 W in−3 (18.8 kW dm−3). Two 1.5 kW modules are then paralleled to achieve 3 kW output power at 12 V and 345 W in−3 (21.1 kW dm−3) with ideal current sharing between the secondary outputs and no drop in efficiency from a single module, an important characteristic enabled by the novel snake-core transformer.