Three-stage Configuration Research Articles

Systematic comparison of commercial devices for temporal characterization of few-cycle laser pulses in the 500-1000 nm spectral range

We compare multiple temporal pulse characterization techniques in three different pulse duration regimes from 15 fs to sub-5 fs, as there are no available standards yet for measuring such ultrashort pulses. To accomplish this, a versatile post-compression platform was developed, where the 100 fs near infrared pulses were post-compressed to the sub-two-cycle regime in a hybrid, three-stage configuration. After each stage, the duration of the compressed pulse was measured with the d-scan, TIPTOE and SRSI techniques and the retrieved temporal intensity profiles, spectrum and spectral phases were compared. Spectral homogeneity was also measured with an imaging spectrometer to understand the input coupling conditions of the temporal measurements. Our findings suggest that the different devices give similar results in terms of temporal intensity profile, however they are extremely sensitive to alignment and to beam quality, especially in the case of the shortest pulses. We address specific steps of measurement procedures, which paves the way towards the standardization of pulse characterization in the near future.

Thermodynamic and Economic Analyses of Zero-Emission Open Loop Offshore Regasification Systems Integrating ORC with Zeotropic Mixtures and LNG Open Power Cycle

The present study provides an energy, exergy and economic analysis of a seawater regasification system (open loop) combining stages of simple organic Rankine cycles (ORCs) arranged in series with an open organic Rankine cycle (OC) in order to exploit the cold energy of liquefied natural gas (LNG). The proposed system, termed ORC-OC, is implemented in a Floating Storage Regasification Unit (FSRU) to achieve the objective of zero greenhouse emissions during the regasification process. Configurations of up to three stages of ORCs and the use of zeotropic mixtures of ethane/propane and n-butane/propane as working fluids are considered in the study of the novel regasification system. Only the two-stage ORC-OC (2ORC-OC) and three-stage (3ORC-OC) configurations accomplish the objective of zero emissions, attaining exergy efficiencies of 61.80% and 62.04%, respectively. The overall cost rate of the latter, however, is 20.85% greater, so the 2ORC-OC results as being more cost-effective. A comparison with conventional regasification systems installed on board shows that the 2ORC-OC yields a lower total cost rate if the LNG price exceeds 8.903 USD/MMBtu. This value could be reduced, however, if the electrical power that exceeds the FSRU’s demand is exported and if compact heat exchangers are implemented.

Air-source hybrid absorption-compression heat pumps with three-stage thermal coupling configuration for temperature lift over 150 °C

Heat pump technology is promising for low-carbon heating supply. However, temperature lift of current technology is still insufficient to meet different industrial demands. Aiming at larger temperature lift, this paper extends the thermal coupling of absorption heat transformer (AHT) and vapor compression heat pump (VCHP) from two-stage configuration to three-stage configuration. Two different three-stage air-source hybrid absorption-compression heat pump cycles are proposed, and analyzed together with a modified two-stage one. Performance optimization, parameter analysis and second law analysis are carried out for the three hybrid heat pump cycles. The three-stage cycle coupling single-stage AHT with double-stage VCHP achieves the best COP of 2.10–1.32 under the temperature lift of 70.0–151.0 °C, while the two-stage one can only achieve COP of 1.10 and temperature lift of 129.0 °C. This enhanced performance is attributed to the less irreversible loss in throttling process. With both better performance and larger temperature lift, the proposed cycle is promising for the industrial application of air-source heat pump.

XPoM-based 8-port photonic interconnection with low polarization sensitivity utilizing S–E–S hybridization

In this paper, we propose a hybrid amplifier-based 8-port Cross-Polarization Modulation (XPoM) interconnection with low polarization sensitivity unlike conventional Semiconductor Optical Amplifier (SOA)-based switching. The three-stage configuration utilizes Erbium-Doped Fiber Amplifier (EDFA) as an intermediate stage to reduce the effects of inherent polarization modulation creating large Transverse Electric – Transverse Magnetic (TE–TM) relative phase shifts. The appreciable error rate of [Formula: see text] and Extinction Ratio (ER) of 14.166 dB have been obtained with 100 GHz of port-spacing at different input powers. The low Polarization-Dependent Loss (PDL) of 1.0045 dB, small variations of azimuth and ellipticity with device angle in S–E–S configuration in contrast to that of SOA, adds to the superiority of the proposed model.

Systematic generation of a once-through staged reactor design for direct methanation of biogas

With 40 mol% CO2, the energy content of biogas is too low to be used as motor fuel. Motor-grade compressed bio-methane can be produced by direct methanation of biogas with the use of hydrogen. A direct methanation process is considered here as the pre-processing step of separating the biogas is avoided. A systematic staging method is applied to design the process to upgrade biogas to motor-grade bio-methane by maximizing the production of methane with the use of the least possible reaction volume and subject to a quality specification. Here, a once-through process is the target so as to avoid the post-processing separation of the product and recycling. The most promising design is a three-stage configuration with water condensation after each stage. Shell and tube reactors are considered to be less expensive than micro-channel reactors. All three stages are placed in a single shell with boiling water on the shell side. The proposed design is verified by rigorous simulation. The method makes process intensification of chemical reaction systems possible, which is here demonstrated for direct methanation of biogas.

Sparsity-Tuned Elastic Net-Pruned Volterra Equalization for 80 Gb/s PAM4 Transmissions for Optical Inter-Data Centers Interconnects

Volterra equalizations (VE) have delivered significant performance improvement on optical signals, but their extremely high demands on computation complexity severely impede the possibility of large-scale deployment in resource-constrained optical interconnects. In this paper, we propose and experimentally demonstrate a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sparsity tuned elastic net-pruned Volterra equalization (SENVE)</i> technique to remove the redundancy in the structure of conventional VE (baseline VE) to save complexity without degrading system performance. With a three-stage configuration: pretraining, pruning, and retraining, our SENVE scheme can: (1) realize the compressed structure from a larger VE to reduce computation complexity and (2) accomplish budget-conscious and hardware- friendly structured sparsity of VE to efficiently accelerate the VE's evaluation. We experientially demonstrate the proposed scheme on an 80-Gbps four-level pulse-amplitude modulation (PAM4) signal in O-band for 40-km single-mode fiber (SMF) transmission with a 30-GHz externally modulated laser (EML). Under optimal pruning but without retraining scenarios, the experimental results show that, compared with baseline VE at the KP4-FEC limit, the proposed SENVE can achieve up to 68.7% complexity reduction without degrading performance over 40 km transmission at an received optical power (ROP) of −5 dBm. Moreover, we also find our proposed SENVE with retraining can achieve up to 90.8% and 35.8% complexity reduction, with respect to baseline VE and L1-regularization VE, without sacrificing system performance under the same over-pruning scenarios.

A Novel Bandstop Filter Based on Two-Port Coaxial Cavities for the Installation of Metallic Mode Stirrers in Microwave Ovens

Metallic stirrers are commonly used in mode-stirred reverberation chambers but are less common in microwave ovens, because the use of a metallic axis creates a coaxial port in the cavity wall where the axis is introduced, which may result in significant microwave leakage levels. However, due to electromagnetic, mechanical, temperature, or chemical requirements, metallic axes must be used in some cases. In this paper, we present a high power coaxial filter that enables the use of metallic stirrers in microwave applications. The filter employs two-port coaxial cavities that are analyzed to determine their design parameters. These cavities are coupled via coaxial lines to achieve proper attenuation levels. The cavities were designed using commercial electromagnetic (EM) software, and a filter prototype was validated using vector network analyzer (VNA) measurements. The simulated and measured results show that a three-stage configuration can achieve attenuations greater than 70 dB at the 2.45 GHz ISM band, allowing the use and external handling of the metallic axis inserted into microwave ovens with negligible microwave radiation leakage.

Three-Stage Padding Configuration for Sparse Arrays with Larger Continuous Virtual Aperture and Increased Degrees of Freedom

Three-Stage Padding Configuration for Sparse Arrays with Larger Continuous Virtual Aperture and Increased Degrees of Freedom

A Full-Bridge Partial-Power Processing Converter for Three-Stage Small Wind Turbine Systems

&#x0D; In order to process the energy generated by small wind turbines (SWT) in grid-connected systems, three-stage configurations (rectifier, dc-dc converter, and inverter) have been suitable due to low cost of three-phase diode rectifiers, facility to perform the maximum power point tracking in dc-dc converters, and power decoupling between the grid and wind generator. As drawback, the three-stage solutions can present higher losses in relation to two-stage systems due to the additional converter. To reach a better efficiency, partial-power converters (PPC) can be used, in which only a part of the power generated by the SWT is processed by the converter. In this method, topology, power/voltage levels, and the operating range characteristics can impact the power handled by the converter. Since the experimental analysis of PPC applied to SWT systems remains to be investigated in the literature, this paper analyzes the Full-Bridge with Zero-Voltage Switching operating as PPC in SWT systems connected to the single-phase grid. In order to evaluate the performance of the proposed structure, experimental results are verified for a 1.5 kW SWT, in which the FullBridge PPC processes only 70% of the generated power. In relation to the full-power processing, the partial-power processing has reduced the losses in 35.9%.&#x0D;

A High Step-Up Interleaved Current-Fed Resonant Converter for High-Voltage Applications

A current-fed LLC resonant converter is proposed for high-voltage and high-power applications. Here, a two-phase interleaved structure is used in the input stage under the continuous conduction mode (CCM) to effectively reduce the input current and output voltage ripple values and the input filter and the output capacitors volumes. Due to the expandable structure and high voltage gain, the proposed configuration is suitable for high voltage applications since low voltage stresses are applied across its components. In fact, voltage stresses across the power semiconductors, i.e., MOSFETs and output diodes, along with the output capacitors, are almost one-third of the output voltage in the implemented three-stage configuration of the proposed converter. Here, the switching frequency is chosen close to, but less than, the converter series resonant frequency to reduce its different components’ current stresses and perform soft-switching operation for all power devices under wide input voltage and output power variations. Therefore, conduction and switching losses, and EMI noises are effectively reduced. Consequently, efficiency is improved and high-frequency operation is possible, which reduces the volume of passive components to achieve high-power density. The given topology is thoroughly analyzed mathematically. Also, a 1 kW prototype converter has been implemented to validate the given simulations and analyses. Here, wide input voltage (100 V-200 V) and output power (100 W-1000 W) variations are applied, and an asymmetric pulse width modulation (APWM) technique is used at 143 kHz switching frequency to regulate the output voltage at 1 kV. The obtained maximum efficiency value is 95.3%.

An advancement in CO2 utilization through novel gas switching dry reforming

This study is the first experimental demonstration of CO2 capture and utilization for dry methane reforming using a novel chemical looping concept, “Gas Switching Dry Reforming” (GSDR) to produce syngas. The new reactor concept utilizes a single fluidized bed reactor to complete redox (reactions) cycles by alternating air and gaseous fuel feeds, generating heat and near pure CO2 for usage in a consecutive dry reforming stage. Autothermal operation of GSDR was achieved using NiO/Al2O3 oxygen carrier, in a three-stage configuration where pure CO is used in the reduction stage while CH4 and CO2 are fed simultaneously in the reforming stage. Most of the heat duties of the process is generated by the exothermic oxidation reaction. The reforming stage is very sensitive to temperature with very good CH4 and CO2 conversion achieved at 850 °C but dropped rapidly at lower temperatures. Carbon deposition is a major issue affecting the performance of GSDR process although this is found to be minimized by a combination of high operating temperature and larger CO2/CH4 ratio, but also led to low H2/CO molar ratio driven by the reversed water gas shift reaction. Reducing the utilization of the oxygen carrier by 50% also proves to decrease carbon deposition by 62% due to the presence of latent oxygen on the oxygen carrier. However, CH4 and CO2 conversion are affected negatively resulting in a drop of ∼22%. An excellent opportunity for maximizing the energy efficiency of the GSDR is by integration with a Gas-To-Liquid (GTL) Fisher Tropsch to use outlet gas stream from the reforming as feedstock to GTL while the unconverted hot gasses from GTL process is fed to the reduction stage of GSDR.

A frequency-based LCL filter design and control considerations for three-phase converters for solid-state transformer applications

This paper presents a design methodology of a LCL filter for its application on the interconnection with the grid of a three-phase solid-state transformer, which is based on a three-stage configuration. The filter operates without damping resistors, and the design methodology proposed is based on the direct location of resonance frequencies, taking into consideration the effect of the grid impedance. The developed methodology can be applied to different power levels. In addition, control tuning considerations are proposed in order to avoid resonance points, evaluating the overall performance through the current total harmonic distortion in the point of common coupling. Furthermore, the used dq0 reference control frame achieves the objectives without the need to increase the number of sensors, neither the use of observers. The design methodology is validated by testing the operating system at 10 kW, 100 kW and 1 MW. For 1 MW, it is also implemented on a real-time simulator.

Control strategies for Multi-Microgrids islanding operation through Smart Transformers

Smart Transformers (ST) are power-electronic based apparatuses that bring new opportunities for defining innovative operating strategies for Medium Voltage (MV) and Low Voltage (LV) distribution grids in future scenarios with increased shares of small-scale generation units. A distinctive advantage of ST is the possibility of connecting a storage device in the DC link when considering a three-stage configuration (AC/DC/AC). In this paper, ST is exploited within the context of Multi-Microgrids (MMG) in order to enhance the possibility of islanding operation through the identification of new control functionalities. The identification of robust control strategies to coordinate the flexibility of all the available resources (distributed resources at the LV and MV grids and storage units connected to the ST) is required to guarantee the successful operation of the MMG in the islanded mode. In order to address the need of specific control requirements, two different configurations are considered, being the proposed control strategies properly described: (1) ST with an energy storage unit in the DC link which fully decouples all the control possibilities for the MV and LV grid sides; (2) ST without an energy storage unit, requiring proper coordination between the MV and LV grid levels.

Overview of Three-Stage Power Converter Topologies for Medium Frequency-Based Railway Vehicle Traction Systems

With new developments in power electronics and semiconductor devices, there has been an increasing interest in the adoption of power electronic traction transformer (PETT) topologies in railways, mainly for the purpose of mass and volume reduction against conventional topologies. Apart from traction transformers, examples include isolation circuits for on-board auxiliary power units (APU) and even 750 VDC, 110 VDC and lower voltage (e.g., 72 VDC) battery chargers. Special attention has been given to the more mature technology of three-stage (ac–dc–MFac–dc) configurations with intermediate medium frequency ac (MFac) links. In contrast to conventional architectures, it becomes difficult to select a suitable multistage topology of power electronics for the design of complex traction systems with advanced requirements. The power electronics utilized in different configurations have a significant effect on performance, efficiency, power quality (harmonics and stability), and cost indicators for the whole system, making the selection and design process more complex. The objective of this paper is to provide a clear overview of proposed topologies with special emphasis on the power electronic architectures utilized in three-stage PETT systems particularly for railway traction systems and on-board APUs. With regards to the listed range of possible architectures provided to the reader, key characteristics, such as total semiconductor (switches and diodes) count numbers per module per phase, input/output voltage levels, operating frequencies, and the most commonly used resonant networks, are summarized and discussed.

In brief

PAGE 353 Two methods for Gaussian-tailed zero-memory nonlinearity design in symmetric noise have been advanced by researchers from China. Their Letter describes the use of a derivative-free method to maximise the efficacy and identify an optimal design. Simulations show the design performs almost as well as the locally optimal detector but with the added advantage of good practicability for applications. PAGE 300 Researchers from Queens University Belfast show how two cascaded Rotman lenses feeding a circular array do not require phase shifters to beam steer/shape and perform retrodirective action. The additional flexibility of beamwidth control was demonstrated by switching the interconnections between the cascaded lenses with experimental validation at 9.3 GHz. The efficacy of the objective function. PAGE 350 A team of researchers from China has proposed a reverse blocking insulated-gate bipolar transistor (IGBT) with a partially narrow mesa structure and trench-collectors. An introduced n-cs layer between two trench gates shields a forward blocking state from high electric fields. Numerical simulation results show that the proposed IGBT can use a 38% thinner n-drift region than the conventional counterpart. Circular patch array. PAGE 334 Smart devices, such as TVs and phones, benefit greatly from the integration of LEDs and embedded cameras, with these additions providing the opportunity to establish optical camera communication systems for Internet-of-Things applications. An experimental demonstration of such a system is detailed in a collaborative Letter by researchers from Spain and the Czech Republic. Proposed IGBT cross section. PAGE 333 A pair of researchers from Japan have realised the first E-band thulium-doped fiber amplifier (TDFA). This novel design includes a three-stage configuration fluoride-based TDF and two filters suppressing amplified spontaneous emission in the S-band. The TDFA exhibits a high signal gain achieved at the shortest wavelength in the gain band when compared with TDFA gains without filters. Bit error rate distance dependence. Stimulated emission spectra.

E‐band thulium doped fibre amplifier

The authors realised the first E-band thulium-doped fibre (TDF) amplifier, which includes a three-stage configuration fluoride-based TDF and two filters suppressing amplified spontaneous emission in the S-band.

Removal of pharmaceuticals in pre-denitrifying MBBR – Influence of organic substrate availability in single- and three-stage configurations

Due to the limited efficiency of conventional biological treatment, innovative solutions are being explored to improve the removal of trace organic chemicals in wastewater. Controlling biomass exposure to growth substrate represents an appealing option for process optimization, as substrate availability likely impacts microbial activity, hence organic trace chemical removal. This study investigated the elimination of pharmaceuticals in pre-denitrifying moving bed biofilm reactors (MBBRs), where biofilm exposure to different organic substrate loading and composition was controlled by reactor staging. A three-stage MBBR and a single-stage reference MBBR (with the same operating volume and filling ratio) were operated under continuous-flow conditions (18 months). Two sets of batch experiments (day 100 and 471) were performed to quantify and compare pharmaceutical removal and denitrification kinetics in the different MBBRs. Experimental results revealed the possible influence of retransformation (e.g., from conjugated metabolites) and enantioselectivity on the removal of selected pharmaceuticals. In the second set of experiments, specific trends in denitrification and biotransformation kinetics were observed, with highest and lowest rates/rate constants in the first (S1) and the last (S3) staged sub-reactors, respectively. These observations were confirmed by removal efficiency data obtained during continuous-flow operation, with limited removal (<10%) of recalcitrant pharmaceuticals and highest removal in S1 within the three-stage MBBR. Notably, biotransformation rate constants obtained for non-recalcitrant pharmaceuticals correlated with mean specific denitrification rates, maximum specific growth rates and observed growth yield values. Overall, these findings suggest that: (i) the long-term exposure to tiered substrate accessibility in the three-stage configuration shaped the denitrification and biotransformation capacity of biofilms, with significant reduction under substrate limitation; (ii) biotransformation of pharmaceuticals may have occurred as a result of cometabolism by heterotrophic denitrifying bacteria.

On the optimization of RO (Reverse Osmosis) system arrangements and their operating conditions

A simple approach has been implemented to identify the optimum RO (Reverse Osmosis) system structure and the operating parameters leading to the minimum total cost. Various two-stage and three-stage arrangements of practical functionality have been optimized. All possible operating points and its corresponding cost have been obtained and a linear search is used to find the minimum cost. The minimum overall costs per unit permeate for the single, two and three-stage arrangements are 1.41, 1.00 and 0.91 $/m3 respectively at product rates of 5.5, 11.5 and 17 m3/h.For two-stage systems, parallel arrangement is recommended for production up to 3 m3/h. Series arrangement with feed and retentate bypass is recommended for demands between 3 and 9 m3/h. For higher permeate rates, series arrangement is recommended.Using three-stage configuration, parallel arrangement is recommended for production less than 6 m3/h. Series arrangement with feed bypass is recommended for production up to 15 m3/h while series arrangement would be preferred above 15 m3/h.Design charts have been developed as a convenient tool for selecting system configuration, operating parameters, membrane area and system cost. The use of design charts provides estimations of the system requirements and cost with about 5% accuracy without resorting to difficult computations.

Dual active bridge synchronous chopper control strategy in electronic power transformer

The electronic power transformer (EPT) is a novel transmission and transformation device, which consists of a series connection of two voltage-source H-bridge converters and a DC-DC converter with high-frequency isolation transformer. When applied to microgrids, EPT will not only deliver energy to loads from the utility grid but also inject some amount of excess power into the utility grid. Hence, the capability of bidirectional power flow is important for EPT, which depends on the DC-link stage. The traditional synchronous chopper control for a dual active bridge (DAB) converter has some limitations in the application of bidirectional power flow area. This study proposes a novel synchronous chopper control strategy for the DAB converter to implement bi-direction power flow, details the basic principle and steady-state operation and presents the mathematical derivations. A three-phase three-stage circuit configuration of 10 kV/400 V bi-direction EPT system based on the novel control DAB converter is designed, and corresponding control schemes for the system are discussed. The performance of this EPT system is validated by the MATLAB/Simulink-based simulations and the laboratory prototype experiments.

Closed-Loop Control of DC–DC Dual-Active-Bridge Converters Driving Single-Phase Inverters

A solid-state transformer (SST) is a high-frequency power electronic converter that is used as a distribution power transformer. A common three-stage configuration of an SST consists of ac-dc rectifier, isolated dc-dc dual-active-bridge (DAB) converter, and dc-ac inverter. This study addresses the controller design issue for a dc-dc DAB converter when driving a regulated single-phase dc-ac inverter. Since the switching frequency of the inverter stage is much higher than that of the DAB stage, the single-phase inverter is modeled as a double-line-frequency (e.g., 120 Hz) current sink. The effect of 120-Hz current by the single-phase inverter is studied. The limitation of a PI-controller, low gain at 120 Hz, is investigated. Two methods are proposed to improve the regulation of the output voltage of DAB converters. The first one uses a bandstop filter and feedforward, while the second method uses an additional proportional-resonant controller in the feedback loop. Theoretical analysis, simulation, and experiment results are provided.