Secondary Bridge Research Articles

Experimental study on the design method of lost circulation materials for induced fractures

Owing to the influence of fluctuating wellbore pressure, the fracture width in formations with induced fractures changes dynamically. However, the traditional design method for fracture plugging materials is based on a static fracture width, which leads to the easy destruction of the plugging layer established underground and a high risk of secondary loss. Until now, the treatment of lost circulation in formations with induced fractures still faces significant challenges. Therefore, a dynamic fracture plugging experimental device was developed in this study to investigate the bridging–plugging process of lost circulation materials (LCMs) within induced fractures, as well as the design criteria for LCMs for induced fractures. Experimental results show that through adjusting the mass ratio and total concentration of the three-level bridging material, the plugging position of the bridging material can be changed, and the fracture reopen pressure can be increased. When the mass ratio of the three-level bridging material satisfies primary bridge particle: secondary bridge particle: tertiary bridge particle = 1:1:2 and the total concentration is greater than 5%, the plugging material compounded with the three-level bridging material is prone to retention in the induced fractures, exhibiting short bridging time, low permeability of the formed plugging layer, and high fracture initiation pressure. It can effectively prevent the opening of fractures or the generation of new induced fractures, thereby reducing the risk of secondary loss. The research results can provide a scientific theoretical basis for the loss control of induced fractures.

Phase-Shift Control With Unified PWM/PFM for Improved Transient Response in a Bidirectional Dual-Active-Bridge DC/DC Converter

Determining how to efficiently obtain superior transient response under both unidirectional power-changing and power-reversing operations in a bidirectional dual-active-bridge (DAB) dc/dc converter is a challenging problem. The traditional direct phase-shifting scheme would induce a transient dc current bias in the high-frequency link of the DAB, and therefore lead to some adverse issues, such as magnetic saturation and increased current stress. In addition, the ac transient can propagate to the dc terminates and give rise to a worse transient response in a closed-loop control system. In this study, a fast phase-shift control is proposed which can execute all the possible power changes in a unified manner. By properly operating the primary bridge with pulsewidth modulation (PWM) and the secondary bridge with pulse frequency modulation (PFM), the DAB converter can complete the phase-shifting operation fast without a dc current bias in the ac link. A closed-loop control based on the hybrid PWM/PFM is further designed to regulate the primary dc current with improved transient performance. Since both PWM and PFM are standard, the whole control algorithm can be implemented efficiently in practical applications. Experimental results are provided to show that the power of the DAB converter can be governed bidirectionally with the proposed phase-shift control. The dc terminal current can be changed to both polarities with fast transient and no apparent overshoot or oscillation.

A Three-Level Resonant DAB Converter Featuring Minimized Circulating Losses for EV Battery Charging

A three-level modified series-parallel bidirectional isolated dc <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> dc resonant converter (TL-MSPBRC) is proposed for EV battery charging. The converter's performance is enhanced for wide load conditions as the modified series-parallel resonant tank is formed by considering the parasitics in the transformer. The first-harmonic approximation (FHA) equivalent circuit model is employed to analyze the converter characteristics for the frequency modulation technique. This converter has high conversion efficiency in charging and discharging operations because of the soft-switching capability of the power switches in the primary and secondary bridges. In addition, low on-state resistance switches in the three-level primary bridge minimize the conduction losses. A 3.3-kW converter prototype with a battery voltage range of 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 300-V is developed to validate the design method and the simulation results. The proposed converter has minimized circulating losses, good short-circuit protection, and excellent efficiency of 97.7% at the rated power level.

Multiple Open-Circuit Fault Detection and Isolation Using Universal Low-Cost Diagnosis Circuits for Reconfigurable Dual-Active-Bridge Converters

Compared with single-switch open-circuit faults (SOCFs), multiple switches open-circuit faults (MOCFs) of power electronic devices (PEDs) due to high voltage or current stress, false triggering, and manufacturing tolerance have become more challenging. To address this issue, a reconfigurable dual-active-bridge (R-DAB) converter is presented with a fast, accurate, robust, and low-cost fault detection (FD) and fault isolation (FI) scheme to accommodate both SOCFs and MOCFs. Compared with the standard dual active bridge (DAB) topology, the proposed R-DAB will utilize a center-tapped high-frequency transformer and two symmetrical auxiliary inductors, where inherent half-bridge conduction branches are capable of maintaining uninterrupted operations. The proposed FD and FI scheme is straightforward and universal since only the center-tap current in the primary and secondary bridge is monitored as the universal fault signature. Moreover, a simple and low-cost fault diagnostic circuit was designed, which can detect and isolate various open circuit faults (OCFs) of PEDs under varying input and output conditions, without using expensive voltage and current sensors. This sensorless fault diagnosis technique can achieve the fastest fault detection and isolation speed reported so far, which is within a couple of \boldmath <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu s$</tex-math></inline-formula> for various OCFs. Experimental results were acquired from an R-DAB prototype under various OCFs to validate the effectiveness of the proposed technique.

Three-Phase Single-Stage Bidirectional CCM Soft-Switching AC–DC Converter With Minimum Switch Count

In this article, a three-phase single-stage bidirectional ac–dc converter with low component count is proposed. The single-stage structure is configured by integrating a three-phase ac–dc converter and a three-phase dual active bridge converter. The power factor correction and bidirectional power control are performed by adjusting the modulation index of sinusoidal pulse width modulation (SPWM) and phase-shift angle between the primary and secondary bridges. The low-frequency components generated by SPWM are absorbed by fundamental blocking capacitors connected in series with transformer windings, resulting in true high-frequency isolation. The proposed converter can achieve soft-switching of all switching devices even in continuous conduction mode. A 110 Vac, 3 kW, 100 kHz prototype is implemented to validate the proposed concept and demonstrated 95.34% peak efficiency.

High-Gain Bidirectional LCLC Resonant Converter With Reconfigurable Capability

A reconfigurable gain circuit is proposed for an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCLC</i> resonant converter with bidirectional capability considering wide varying redox flow battery source. A suitable hybrid control scheme for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCLC</i> resonant converter with secondary synchronous rectifier is proposed in this work. The proposed reconfigurable circuit enables to configure secondary bridge as an active voltage doubler, full-bridge circuit during forward power transfer mode and reverse power transfer mode, respectively. The reconfigurability helps significantly to design a transformer with lower secondary turns and achieve desired high gain. The reduced transformer secondary turns result in reduced transformer parasitics. The presence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCLC</i> resonant tank helps to provide the additional gain; the hybrid control scheme ensures zero-voltage switching turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> for the primary, and secondary synchronous <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfets</small> throughout the operating range. The proposed converter is analysed using fundamental harmonic approximation. The proposed reconfigurable gain circuit and hybrid control scheme is verified experimentally for an 800 V/1 kW hardware prototype fed from 24 to 54 V input.

1 kV, 10-kW SiC-Based Quadruple Active Bridge DCX Stage in a DC to Three-Phase AC Module for Medium-Voltage Grid Integration

Interfacing low voltage dc to medium voltage three-phase ac grid is often based on series-stackable modular converter architectures. To minimize energy storage requirements, it is advantageous to employ a quadruple active bridge (QAB) stage operating as a “dc transformer” in each stackable module. The QAB stage offers three isolated dc link voltages, which then allow for flexible stacking of three single-phase dc-to-ac inverter stages. Each of the module phases processes a pulsating power having a component at twice the line frequency. This presents a challenge in maintaining zero voltage switching (ZVS) on the secondary sides of the QAB during low-power portions of the line cycle. This article is focused on the design of the QAB stage. A detailed analysis of ZVS switching waveforms is presented, including effects of nonlinear device capacitances. It is shown how ZVS can be achieved at all times using a relatively small circulating current provided by the magnetizing inductance of the high-frequency transformer. Analytical expressions are given for the optimal values of the magnetizing inductance and the dead times of the QAB primary and secondary bridges. The approach is verified by experimental results on a 1 kV, 10-kW SiC-based prototype, demonstrating a relatively flat efficiency curve with a peak efficiency of 97.1% at 75% load.

Advanced Modulation Scheme of a Dual-Active-Bridge Series Resonant Converter (DABSRC) for Enhanced Performance

This paper proposes a two-degree-of-freedom (2-DoF) modulation technique for the efficient optimization of an open-loop three-phase dual-active-bridge series resonant converter (3P-DABSRC). The efficiency and performance of an conventional dual-active-bridge (DAB) converter decrease when it is operated over a wide range of voltage gain. The efficiency and performance of a DAB converter depend upon the switching and conduction losses. Circulating current is the main cause of conduction loss, and hard switching of active switches adds a switching loss. To increase the performance of DAB converters, the first objective is to minimize the conduction loss, and the second objective is to reduce the switching loss. Still, unfortunately, it is not easy to achieve these two objectives simultaneously. Circulating current helps us to reduce the switching loss, but the unbridled amount of circulating current will increase the root-mean-square inductor tank current, and as a result, the conduction loss will be increased. This paper presents an advanced modulation scheme for a 3P-DABSRC that can be used not only in low-power applications, but also in high-power applications. The DABSRC consists of a series LC resonant tank, isolated high-frequency transformer, and dual active bridge connected with the primary and secondary sides of the transformer. The proposed 2-DoF modulation technique not only minimizes the circulating current, but also eliminates the switching loss. Keeping the minimum phase shift between the primary and secondary bridges reduces the circulating current, and thus, all switches can be operated with zero-voltage switching (ZVS) for the entire power range. The power is controlled by changing the switching frequency from 45 to 63 kHz. To confirm the proposed topology and modulation scheme, a 1500 W DABSRC, which interfaces a 300 V DC bus with a 75 V DC bus, is simulated. A loss model of the proposed topology is also made to verify the results. The simulation results are used to confirm the proper operation of the 3P-DABSRC.

Universal Sensorless Open-Circuit Fault Detection and Isolation Method of Dual-Active-Bridge Converters With Low-Cost Diagnostic Circuit

As one of the promising power interfaces between the energy storage components and the dc link, dual active bridge (DAB) converters have gained extensive researches. Its reliability and healthy operation under one or even multiple unexpected open-circuit faulty conditions have become one of the main design challenges. Conventional fault detection (FD) and fault isolation (FI) methods exhibit obvious limitations in terms of detection speed, number of FD signatures, universality, accuracy, computational burden, and implementation cost due to the added sensors. To fill in this gap, this article presents a robust, fast, accurate, and low-cost FD and FI method for DAB converters, which is applicable under various operational conditions. The proposed method will adopt the differential switch node voltage between the primary and secondary bridge of DAB converters as the universal fault signature for complete FD and FI. The corresponding fault diagnostic circuit is simple, compact, low cost, and easy in implementation. This sensorless fault diagnostic technique can detect the switch open-circuit fault within a quarter of a switching cycle and realize the fault isolation accurately. A DAB prototype with a fault diagnostic circuit was designed, and main experimental results under various faulty conditions were provided to validate the advantages of the proposed method.

Synchronization Strategy Based on Resonant Current Detection for Bidirectional Wireless Charging System

Bidirectional wireless power transfer (BWPT) greatly improves the reliability of power supply. However, wireless communication between the primary and pickup controllers is usually required to transmit load information, which has time delay and is easily interfered by electromagnetic fields. Existing solutions to avoid the use of communication can be divided into three categories: additional DC/DC circuit, primary side bridge control and secondary side bridge control. Compared with the other two methods, the secondary side bridge control has low loss and good robustness. But it usually requires Phase-Locked Loop (PLL) to eliminate the frequency error between primary and secondary side bridges, which increases the complexity. In this paper, a constant current control strategy without communication is proposed. It is based on the secondary side bridge control and the switching sequence of the secondary side bridge is periodically synchronized according to the phase of the resonant current. It works robustly without the need for additional hardware such as PLL or Multiplier. The harmonic sensitivity analysis, parameter optimization design and stability analysis are carried out to improve the control efficiency. Experimental results based on a 1kW prototype with dual LCC resonant network are presented to verify the effectiveness of the proposed control strategy.

Innovative Design of Novel Main and Secondary Arch Collaborative Y-Shaped Arch Bridge and Research on Shear Lag Effect of Its Unconventional Thin-Walled Steel Box Arch Ribs

The first main and secondary collaborative Y-shaped steel box arch bridge under construction in China is a rarely seen innovative practice among bridges already built at home and abroad, which is an attractive engineering research topic in the field of advanced bridge design and construction, and the investigation of this bridge has made a groundbreaking contribution. The structure of unconventional thin-walled steel box arch ribs is very novel, abandoning the traditional two-dimensional arch rib structure form and adopting the new structural mode of single–double combination and joint working of main and secondary arches. However, for this innovative design, many technical difficulties including innovative design details, mechanical behavior of thin-walled structures and construction methods still need to be pioneeringly explored and thoroughly researched. In this paper, the innovative design concept of unconventional thin-walled arch ribs for spatial Y-shaped steel box arch bridges is described, and a comparative analysis with the corresponding conventional single arch rib structure is carried out. Due to the limitations of the common conventional arch bridge research methods, a combined global and local finite element method is used to analyze the static and dynamic properties of the structure, and the shear lag effect of the thin-walled steel box arch ribs is studied in a pioneering and exploratory approach. In addition, the stress distribution of the bifurcated section of the arch ribs and the configuration of the diaphragm are analyzed in detail to verify the reasonableness, advantage and applicability of the innovative design. The results show that the main and secondary arch collaboration Y-shaped steel box arch bridge has reasonable structure and superior mechanical properties and has a greater value for promotion The design concept and analysis method are worthy of use as a reference for the aesthetical and mechanical design of similar spatial Y-shaped arch bridges in the future.

Common High-Frequency Bus-Based Cascaded Multilevel Solid-State Transformer With Ripple and Unbalance Power Decoupling Channel

A novel three-port cascaded multilevel solid-state transformer (CM-SST) is proposed in this article, which is based on modular multilevel converter submodules (SM) interconnected by high-frequency link (HFL), forming a decoupling channel to SMs and a low-voltage dc port. The common high-frequency bus in HFL helps to reduce the numbers of secondary full bridges in the form of multiplexing. The decoupling channel achieves the automatic balancing of capacitors voltage and natural elimination of SM ripple power, so the arms second-order circulating current can be eliminated from the root cause. Therefore, the CM-SST can simultaneously realize the switches decreasing, capacitance size reducing, arms circulating current elimination, and control simplification. In this article, the topology, equivalent model, HFL design, ripple-power decoupling, power loss, and control scheme are analyzed in detail. In addition, an evaluation of CM-SST compared with the traditional methods is provided, including sizing, components count, control, and efficiency. Finally, the correctness and effectiveness of the proposed scheme are verified by the simulation and experiment.

Bridge-to-Bridge Independent Control Method for Dual-Active-Bridge Interlinking Converter

In dual-active-bridge (DAB) converters, the driving-synchronization signal is supposed to be required to be transmitted across the primary bridge and the secondary bridge to realize a phase shift for power flow. In this letter, a novel bridge-to-bridge independent (B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I) control method is proposed. In this control method, cross-bridge transmission of sampling/driving signals is not required. Thus, full modularity of each side in the DAB converter was realized. B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control is suitable for high-voltage series low-voltage parallel (HSLP) modular DAB interlinking converter in medium-voltage dc applications because: first, the bridge-level modularity of B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control benefits electromagnetic compatibility and insulation design with the HSLP connection; second, B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control features series-side voltage sharing; and third, B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control can adapt for various operation modes of microgrids.

Minimum-Current-Stress Scheme of Three-Level Dual-Active-Bridge DC–DC Converters With the Particle Swarm Optimization

Current stress is essential for the reliability of power switching devices, especially for high-voltage applications, such as three-level NPC-based dual-active-bridge (3LNPC-DAB) converters. With the conventional single phase shift (SPS) control, the current stress of power devices in 3LNPC-DAB converters is high, which not only affects the conversion efficiency for a wide operating range but also endangers the power devices, which is harmful for the healthy operation of 3LNPC-DAB converters. To solve this problem, this article proposes a minimum-current-stress scheme using particle swarm optimization (PSO) strategy with the aim to reduce the current stress and improve the efficiency of 3LNPC-DAB converters. Different from SPS, two phase shift variables are adopted in the proposed algorithm: one is set between the primary and secondary bridges, and the other is set within the same bridge. Thus, not only the control flexibility is expanded, but also main performance indexes, such as the transmission power, the current stress of each switch, and the efficiency for the whole operating range, are improved. Moreover, the PSO strategy requires fewer parameters to adjust, less computational burden, and faster convergence speed, which simplifies the theoretical calculation and the practical implementation. Finally, the main experimental results for various operating conditions are provided to validate the proposed scheme.

Analysis of Unidirectional Secondary Resonant Single Active Bridge DC–DC Converter

A compact and highly efficient unidirectional DC–DC converter is required as a battery charger for electrical vehicles, which will rapidly become widespread in the near future. The single active bridge (SAB) converter is proposed as a simple and high-frequency isolated unidirectional converter, which is comprised of an active H-bridge converter in the primary side, an isolated high frequency transformer, and a rectifying secondary diode bridge output circuit. This paper presents a novel, unidirectional, high-frequency isolated DC–DC converter called a Secondary Resonant Single Active Bridge (SR–SAB) DC–DC converter. The circuit topology of the SR–SAB converter is a resonant capacitor connected to each diode in parallel in order to construct the series resonant circuit in the secondary circuit. As a result, the SR–SAB converter achieves a higher total power factor at the high frequency transformer and a unity voltage conversion ratio under the unity transformer turns ratio. Small and nonsignificant overshoot values of current and voltage waveforms are observed. Soft-switching commutations of the primary H-bridge circuit and the soft recovery of secondary diode bridge are achieved. The operating philosophy and design method of the proposed converter are presented. Output power control using transformer frequency variation is proposed. The effectiveness of the SR–SAB converter was verified by experiments using a 1 kW, 48 VDC, and 20 kHz laboratory prototype.

Bridge Functionalisation of Bicyclo[1.1.1]pentane Derivatives

Abstract“Escaping from flatland”, by increasing the saturation level and three‐dimensionality of drug‐like compounds, can enhance their potency, selectivity and pharmacokinetic profile. One approach that has attracted considerable recent attention is the bioisosteric replacement of aromatic rings, internal alkynes and tert‐butyl groups with bicyclo[1.1.1]pentane (BCP) units. While functionalisation of the tertiary bridgehead positions of BCP derivatives is well‐documented, functionalisation of the three concyclic secondary bridge positions remains an emerging field. The unique properties of the BCP core present considerable synthetic challenges to the development of such transformations. However, the bridge positions provide novel vectors for drug discovery and applications in materials science, providing entry to novel chemical and intellectual property space. This Minireview aims to consolidate the major advances in the field, serving as a useful reference to guide further work that is expected in the coming years.

Bridge Functionalisation of Bicyclo[1.1.1]pentane Derivatives.

“Escaping from flatland”, by increasing the saturation level and three‐dimensionality of drug‐like compounds, can enhance their potency, selectivity and pharmacokinetic profile. One approach that has attracted considerable recent attention is the bioisosteric replacement of aromatic rings, internal alkynes and tert‐butyl groups with bicyclo[1.1.1]pentane (BCP) units. While functionalisation of the tertiary bridgehead positions of BCP derivatives is well‐documented, functionalisation of the three concyclic secondary bridge positions remains an emerging field. The unique properties of the BCP core present considerable synthetic challenges to the development of such transformations. However, the bridge positions provide novel vectors for drug discovery and applications in materials science, providing entry to novel chemical and intellectual property space. This Minireview aims to consolidate the major advances in the field, serving as a useful reference to guide further work that is expected in the coming years.

Nonequilibrium Structure Diagram of Pendular Suspensions under Large-Amplitude Oscillatory Shear.

For pendular suspensions with particles in contact with immiscible secondary liquid bridges, the shear field significantly influences particle aggregates and networks. In this work, we study the structure of the pendular network and how the structure changes under large-amplitude-oscillatory shear. Using rheology and optical microscopy, we found unique network destruction followed by reconstruction with increasing strain. Two processes show different shear-field dependencies, strain-rate dependency for destruction and strain dependency for reconstruction. A nonequilibrium state diagram is constructed to show the phase behavior, where the critical particle concentration of sol-gel transition is dependent on the shear history and may depend on shear strain nonmonotonically. Two different mechanisms, shear-induced network breakdown at low strain and shear-induced agglomeration at high strain, are suggested to describe the nonmonotonic critical concentration under the upward strain sweep quantitatively.

Transient DC Bias Current Reducing for Bidirectional Dual-Active-Bridge DC–DC Converter by Modifying Modulation

Transient dc bias current will appear in dual-active-bridge (DAB) dc-dc converter when power changes, resulting in transformer core saturation. Traditionally, a transitional period with extra calculation is added in the transient process to keep the voltage-second balance and eliminate the dc bias current for the DAB converter. In this article, the modulation process rather than the phase-shift control is concerned, and the transient dc bias current can be reduced or even eliminated by staggering the load time of the primary bridge and secondary bridge compare values. The modulation scheme with this modification does not need any transitional period or extra calculation, and the time delay in the closed-loop control is constant and smaller than the previous schemes. Besides, as only the load time is modified, the modulation scheme can be implemented in all the phase-shift control methods and the whole operation range. The experimental results verify the theoretical analysis and show the practical feasibility of the modified modulation schemes.

An Interleaved Boost and Dual Active Bridge-Based Single-Stage Three-Port DC–DC–AC Converter With Sine PWM Modulation

In this article, a new three-port converter is proposed that interfaces two dc voltage sources of different magnitudes and an output ac port in a single stage. The proposed converter is primarily based on the dual active bridge topology where the secondary bridge is composed of four quadrant bidirectional switches, which allows it to be directly connected to an ac port. The primary bridge can also be used as an interleaved bidirectional boost converter by connecting two inductors across the transformer primary, which forms an additional input DC port. The power flow between the dc ports to the ac port is based on dual phase-shift modulation where a phase shift is introduced between the two legs of the primary bridge switches and another phase shift between the primary and secondary bridges. This enables the standard sine pulsewidth modulation to be used for synthesizing ac output. For the power flow mode between the two dc ports alone, a parallel boost modulation is proposed that improves the system efficiency by removing any circulating current introduced by traditional interleaving. The proposed converter achieves fully soft switched three-port power conversion with a reduced number of active devices compared to the existing topologies. The modulation scheme is also much simpler and requires no optimization or complex control. A PowerSim-based simulation program is used for validating the proposed converter. A 200-W prototype is built to experimentally verify the theoretical analysis of the proposed converter.