Wide Operating Range Research Articles

A Hybrid Submodule Three-Phase Multiplexing Arm Modular Multilevel Converter With Wide Operation Range and DC-Fault Blocking Capability

Three-phase multiplexing arm modular multilevel converter (TPMA-MMC) possesses lower cost, smaller volume, and higher efficiency compared with MMC. However, the limited operation range limits its popularity. Hence, in this article, it redefines arm submodule (SM) configuration type, where the conventional arm is configured with full-bridge submodules (FBSMs), and the multiplexing arm is formed by half-bridge submodules (HBSMs). Meanwhile, a new energy balance principle and modulation scheme are proposed to expand TPMA-MMC’s operation range. Furthermore, the DC-fault blocking schemes could be implemented to realize DC-fault tolerance reliably without the multiplexing arm blocking. Compared with hybrid MMC(H-MMC), it could reduce by 33.33% in submodules a least, which leads lower footprint and operation loss. Due to reregulating the energy flowing path of multiplexing arm, and rearranging the chain-link voltage of multiplexing and conventional arm, it could reduce the required SM capacitance and further decrease 65% energy storage requirement, resulting in improving the power density. Finally, the topology control scheme and DC-fault blocking scheme are verified by simulation and scale-down prototype experimental results.

Optical Magnetic Field Microsensors Based on GaN Diode Optopairs Integrated With Magnetic Fluids

In this work, the development of optical magnetic microsensors based on chip-scale GaN-on-sapphire diode optopairs integrated with magnetic fluids is demonstrated. The submillimeter-sized optopairs function as light emitters and detectors and the transparent sapphire substrate as light-guiding media is covered with magnetic fluids using PDMS recesses. The magnetic fluid strength introduces the optical reflection introduces changes in optical reflection at the boundary between the sapphire and the magnetic fluid, thus varying the amount of light received by the photodetector. Verified through experimental measurements, the micro-sensor exhibits a wide detection range of 50-2000 Gs and a fast response time of 0.06 s. The developed magnetic sensor provides remarkable features of rapid response, wide measurement range, high compactness, and simplicity of operation, making it well-suited for use in practical applications.

Structural development of the high-speed free jet test facility

The 2 m×2 m high-speed free jet test facility is a 2 m level intermittent blowdown-ejector ground test facility, which has the ability of tri-sonic operation. The closed test section is replaced with a large test chamber. In the development process of the project, the main focus is the uncertainty influences of the jet pressure pulsation action on the facility, the functional realization of step change test Ma number by adjusting semi-flexible nozzle profile in a wide operating range for 2 m level facility, etc. These difficulties have been solved in various ways, such as theoretical analysis and calculation, adoption of multidisciplinary optimization techniques, a reasonable choice of vibration suppression means, and accumulation of rich experience in the field of wind tunnel design. At present, this facility has been built and debugged, and the integrity of the structure has been verified.

O Splines-Based Fixed-Frequency Integral Sliding-Mode Controller for PFC Rectifier

This paper proposes a fast-response sliding mode controller (SMC) for a semi-bridgeless boost converter under large and quick load fluctuations to ensure tight output voltage regulation and unity power factor correction (PFC) at the line side. In this sense, a novel approach for estimating the reference current profile is presented focusing on the real-time phasor estimation via the O-splines of the discrete-time Taylor-Fourier transform (DTTFT). This method allows for improving the computational efficiency and dynamic performance of the estimations of amplitude, frequency and phase of the network voltage used for the generation of the reference current profile. Several aspects of the controller design are discussed, including the choice of the sliding surface, the existence and stability conditions, and the implementation of an adaptive hysteresis band to fix the switching frequency and reduce zero-crossing distortion. Experimental results of a GaN-based prototype validate the theoretical predictions, exhibiting a PF close to 1 and a total harmonic distortion lower than 3.2% in presence of load changes of up to 50% and changes in the output voltage set point. Several comprehensive experimental comparisons between the proposed framework and the most widely used methods recently reported in the literature are accomplished in terms of transitory and steady-state responses. The robustness of the proposed control approach is experimentally demonstrated under sag conditions and a wide operating range of the input voltage.

A minimized electron cyclotron resonance ion thruster for China’s space-borne gravitational wave detection missions

Space-borne gravitational wave (GW) detection spacecraft works in the state of drag free for which a disturbance reduction system is utilized to offset the non-conservative force. The key actuator of drag-free control loop is a micro-thruster with the performance of a high precision thrust and wide-range operations. Ion thruster, such as electron cyclotron resonance ion thruster (ECRIT), is one of the options because its thrust can be controlled precisely by the method of beam current feedback. However, there is still a barrier for the conventional ECRIT to achieve the low thrust of 1 μN as required in space-borne GWs detection missions due to its radial structure. In this work, a minimized ECR ion thruster (mini-ECRIT) is designed by a new idea that it employs an axial ring-cusped field to exploit the low-pressure adaptability of resonance heating. The mini-ECRIT is tested and results in a dynamic thrust range of 1–100 μN, a resolution of 0.1 μN, a thrust noise of 0.1 μN/Hz1/2, and a response time of about 10 ms. In addition, the specific impulse of this thruster can reach as high as 510 s at low thrust 5 μN, being higher than that of previous ion thrusters by a factor of about 5, which may significantly reduce the propellant consumption. This minimized ECR ion thruster may support China’s space-borne GW detection missions such as TianQin.

Guided Linear Upsampling

Guided upsampling is an effective approach for accelerating high-resolution image processing. In this paper, we propose a simple yet effective guided upsampling method. Each pixel in the high-resolution image is represented as a linear interpolation of two low-resolution pixels, whose indices and weights are optimized to minimize the upsampling error. The downsampling can be jointly optimized in order to prevent missing small isolated regions. Our method can be derived from the color line model and local color transformations. Compared to previous methods, our method can better preserve detail effects while suppressing artifacts such as bleeding and blurring. It is efficient, easy to implement, and free of sensitive parameters. We evaluate the proposed method with a wide range of image operators, and show its advantages through quantitative and qualitative analysis. We demonstrate the advantages of our method for both interactive image editing and real-time high-resolution video processing. In particular, for interactive editing, the joint optimization can be precomputed, thus allowing for instant feedback without hardware acceleration.

UniTune: Text-Driven Image Editing by Fine Tuning a Diffusion Model on a Single Image

Text-driven image generation methods have shown impressive results recently, allowing casual users to generate high quality images by providing textual descriptions. However, similar capabilities for editing existing images are still out of reach. Text-driven image editing methods usually need edit masks, struggle with edits that require significant visual changes and cannot easily keep specific details of the edited portion. In this paper we make the observation that image-generation models can be converted to image-editing models simply by fine-tuning them on a single image. We also show that initializing the stochastic sampler with a noised version of the base image before the sampling and interpolating relevant details from the base image after sampling further increase the quality of the edit operation. Combining these observations, we propose UniTune, a novel image editing method. UniTune gets as input an arbitrary image and a textual edit description, and carries out the edit while maintaining high fidelity to the input image. UniTune does not require additional inputs, like masks or sketches, and can perform multiple edits on the same image without retraining. We test our method using the Imagen model in a range of different use cases. We demonstrate that it is broadly applicable and can perform a surprisingly wide range of expressive editing operations, including those requiring significant visual changes that were previously impossible.

Characterization and performance evaluation of fully biocompatible gelatin-based humidity sensor for health and environmental monitoring

Biomaterials will have far reaching effects on solving the ever-rising environmental problems caused by the presently used toxic materials. Disposal of hazardous materials based electronic devices is causing a huge environmental problem in the form of electronic wastes (E-wastes). This study is an effort to contribute in the reduction of E-wastes by presenting the design, fabrication, and performance evaluation of a fully biocompatible humidity sensor with gelatin as the active layer. Gelatin is an excellent choice for humidity sensing because it is a hygroscopic material with the natural ability to attract and absorb water molecules, allowing for an effective detection and measurement of humidity levels in its surrounding environment. We patterned highly conductive (2.05 μΩ-cm) gold (Au) interdigitated electrode (IDE) (50 nm thickness) structure on a glass substrate by using thermal vacuum evaporation followed by the deposition of gelatin thin film by using cost effective technique of spin coating (at 1,500 rpm for 15 s). The device size was 25 mm × 22 mm with a line spacing of 1.50 mm between IDEs. Electrical characterisation was carried out to determine necessary performance parameters of the fully biocompatible humidity sensor and the obtained results exhibited a fast response/recovery time (4/6.30 s), wide operating range (15 %RH to 86 %RH), highly repeatable behaviour of 3 different samples and long lifetime (1 month). Wide variation in the resistance of sensor was observed at extreme humidity sensors ranging from 2.45 MΩ (15 %RH) to 0.12 MΩ (86 %RH). The fabricated sensor was used for the practical applications of health monitoring, touch less sensing, and environment monitoring. Moisture content of multiple commercially available moisturizers was determined by using gelatin based fully biocompatible humidity sensor and the obtained results showed that moisturizing cream had highest moisture content of 87 %RH (0.1 MΩ), followed by 80 %RH (0.30 MΩ) of rose water, and 72 %RH (0.67 MΩ) of baby oil.

System-level modeling, analysis and coordinated control design for the pressurized water reactor nuclear power system

A flexible operation of the nuclear power system (NPS) over a large operating range is emphasized when it is used as marine power. The current study exposes two bottlenecks in this field: (1) lack of the system-level high-quality dynamic model whose structure is simple enough for control design limits the implementation of the model-based controller; (2) nonlinearity problem due to the large load variation poses challenges for NPS to maintain its performance over a wide operating range. For these reasons, a first-hand simplified nonlinear model is developed and validated for the pressurized water reactor nuclear power system (PWRNPS) through mixed modeling methods of mechanism analysis and data identification. An optimal 50% full-power compromise steady-state operation scheme is first proposed for PWRNPS to balance its primary coolant temperature and secondary steam pressure. Using the simplified nonlinear model as the predictive model, a novel nonlinear model predictive controller (NMPC) is designed to realize the wide-range flexible operation of PWRNPS. Especially, an integrating tracking error is innovatively added to the cost function of NMPC to achieve offset-free control. Two groups of simulations on a complex PWRNPS process developed on the MATLAB/SIMULINK platform demonstrate the effectiveness of the proposed methods.

Preparation and Characterization of Polysulfone Composite Membrane Blended with Kenaf Cellulose Fibrils

Polysulfone (PSF) is widely used material for ultrafiltration (UF) membranes, which has outstanding mechanical properties, great chemical resistance, good thermal stability and wide pH operation range. The hydrophobic property of the PSF membrane seriously limits its application. Hence, blending with hydrophilic material as additives such as cellulose have been intensively studied to improve the hydrophilicity of membranes. Cellulose fibrils are composed of nano-sized elements, which have high hydrophilicity, strength, and biodegradation. A composite membrane was prepared by the phase inversion induced by an immersion process. The characteristics of the composite membrane were investigated with Fourier transform infrared spectroscopy (FTIR) and Scanning Electron Microscopic (SEM). The pure water flux of the composite membrane increased dramatically with the increase of cellulose fibrils. Mean pore size and porosity were significantly increased. Both mechanical properties and hydrophilicity were enhanced due to the addition of the cellulose fibrils.

The Similarity Law of Cavitation Number on Cavitation Instability in Liquid Rocket Inducer

Abstract The influence of inducer rotation speed on the propagation characteristics of rotating cavitation and on the unsteady characteristics of cavitation in rotating cavitation and cavitation surge were examined using a three-bladed inducer, which is named THK inducer, to develop the rocket engine turbopump that can operate stably over a wide operating range. The novel point of the paper is focusing on the cavitation itself, which is the cause of cavitation instabilities. The paper conducted two types of experiments using an inducer and single hydrofoils, and the dimensional and nondimensional unsteady characteristic, which is the frequency of unsteady cavitation and the Strouhal number, were evaluated. Three types of rotating cavitation and cavitation surge were observed in the inducer. For a given cavitation number, the Strouhal number of rotating cavitation and the frequency of unsteady cavitation in cavitation surge are independent of the inducer rotation speed, respectively. The characteristic of rotating cavitation corresponds to that of cavitations arising in hydrofoils, but its characteristic of cavitation surge does not correspond. The dynamic characteristic of cavitation compliance in cavitation surge is similar to that of several rocket engine turbopumps. Therefore, it was proved that rotating cavitation is a cavity oscillation and cavitation surge is a system oscillation. Additionally, in a flow field with the same flow coefficient and different impeller rotation speed, the unsteady characteristics of cavitation instabilities are equal if the cavitation number is equal, which is named the “similarity law of cavitation number on cavitation instability.”

Fluorescent detection of tartrazine based on the supramolecular self-assembly of cationic perylene diimide.

A cationic perylene probe was designed and synthesized for sensitive determination of tartrazine. In the presence of tartrazine, the fluorescence of theperylene probe was quenched by efficient supramolecular self-assembly of theperylene derivate. The quenching iscaused by the synergistic effect of noncovalent interactions including static electricity, π-π stacking, and hydrophobic interaction. Benefiting from these advantages, the probe exhibited excellent sensing performance to tartrazine within 2 min. The detection and quantification limit of tartrazine are as low as 2.42 and 8.07 nmol L-1, respectively, with a wide linear operation range from 15 to 500 nmol L-1. Most importantly, due to the high binding affinity (3.22 × 107 mol L-1) between the perylene probe and tartrazine, the sensing system shows great anti-interference capacity. Subsequently, the visualization application of the approach was evaluated by portable device, and the limits of detection for visual detection for test strip, membrane, and hydrogel were 0.5, 0.5, and 5 μmol L-1, respectively. Theapproach has been applied to monitor tartrazine in various food condiments with recoveries in the range 91.29-108.83%. As far as we know, this is the first report of using perylene-based probe for tartrazine determination, offering a promising strategy for the construction of perylene-based detection system in the field of food safety.

Implementation and reliability analysis of a new non‐isolated quadratic buck–boost converter using improved Markov modelling

AbstractHere, a new buck–boost converter with reliability analysis is proposed. The converter has utilized a new voltage multiplier cell at the input side to boost the output voltage. It has a continuous input current with a wide range of duty cycle operations. The converter achieves unity gain at 26.8% duty cycle and can also operate in continuous and discontinuous conduction modes in buck and boost modes. The detailed reliability analysis of the proposed converter using improved Markov modelling is also presented by considering both open circuit and short circuit faults across the semiconductor devices. The variation of reliability and the mean time to failure (MTTF) with different converter parameters like the duty cycle and the input voltage is also discussed here. The hardware results of the developed prototype converter are also presented here at varying duty ratios. The power loss analysis and comparison of the converter with other newly proposed buck–boost topologies show the advantages of the proposed converter. For checking the stability of the converter, the state space model of the converter is also discussed in detail of the proposed converter.

A Control-Free Series Resonant Converter for Battery Charging With Automatic CC-to-CV Profile and Whole-Process High Efficiency

Constant current (CC) and constant voltage (CV) outputs are required by electric vehicle chargers to comply with the battery profile, which are challenges to the wide operating range, accurate current and voltage control, and high efficiency of the battery chargers. This paper proposes a control-free battery charger based on a series resonant converter (SRC) that features an inherent automatic CC-to-CV profile and whole-process high efficiency. Both the CC and CV modes enjoy identical switching sequences and operating waveforms, and the transition of CC-to-CV depends on the load condition. Automatic and smooth CC-CV transition can also be obtained after the CC charging process, thus avoiding the overvoltage charging risk. Detection of battery state and active control for the charging profile can therefore be eliminated, making the proposed battery charger rugged and reliable. The CC and CV outputs are flexibly configurable by setting the operating frequency and designing the turn ratio of the transformer respectively. Moreover, with an assistive circuit, soft switching can be realized for all switches regardless of the operating conditions to achieve a high efficiency throughout the whole charging process. Finally, a 1 kVA prototype is presented to validate the control-free and automatic CC-to-CV profile. High efficiency up to 98.4% is measured during the whole CC and CV charging periods.

A Single-Stage Three-Mode Reconfigurable Regulating Rectifier for Wireless Power Transfer

This article proposes a reconfigurable regulating rectifier with a wide operational range for wireless power transfer. The proposed 3-mode rectifier achieves a broad range voltage regulation without global loop control to minimize the chip area occupation. Compared with previous work, more working modes and greater voltage gain allow the proposed rectifier to regulate lower input power, which extends the voltage regulation range. A local loop control scheme is proposed for voltage rectification with three modes. It adaptively senses the duty cycle of the mode signal to determine the working mode of the rectifier, and configure the rectifier to the desired mode for voltage regulation. The proposed system was designed and fabricated in a 180-nm BCD technology with an active area of 1.17 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$mm^{2}$</tex-math></inline-formula> . The measurement results show that the proposed system can rectify wide-range input AC power to a regulated output. The achieved voltage conversion ratio (VCR) is between 0.95X and 2.68X, with a peak power conversion efficiency (PCE) at 87.4%.

Recent Mechanistic Understanding of Fischer-Tropsch Synthesis on Fe-Carbide

With an increase in energy consumption globally, Fischer-Tropsch (FT) synthesis is a good alternative for producing fuels and chemicals from coal, natural gas or biomass. Among them, coal to liquids has been put into production in countries that have large coal reserves. In this process, Fe-based catalysts are commonly used due to their earth abundance, comparatively wide operation range and ready availability to handle low H2/CO ratio from coal. Despite their extensive applications, the kinetic and mechanistic understandings of Fe carburization and FT reaction on Fe-carbides are relatively limited due to the complexity of the phase composition of the applied catalysts. This review summarizes the current state of knowledge of FT synthesis on Fe-carbide with an emphasis on the underlying mechanism. Specifically, the employment of a model catalyst, such as Raney Fe, could provide a convenient way to furnish kinetic information regarding Fe carburization and subsequent FT reaction. A major challenge for further understanding catalytic reactions occurring at the Fe-carbide surface is correlating FT activity and selectivity to a specific active site. To address this issue, the advancements of both DFT calculations and surface science techniques are highly demanded.

On the Generalization of Tempered-Hilfer Fractional Calculus in the Space of Pettis-Integrable Functions

We propose here a general framework covering a wide range of fractional operators for vector-valued functions. We indicate to what extent the case in which assumptions are expressed in terms of weak topology is symmetric to the case of norm topology. However, taking advantage of the differences between these cases, we emphasize the possibly less-restrictive growth conditions. In fact, we present a definition and a serious study of generalized Hilfer fractional derivatives. We propose a new version of calculus for generalized Hilfer fractional derivatives for vector-valued functions, which generalizes previously studied cases, including those for real functions. Note that generalized Hilfer fractional differential operators in terms of weak topology are studied here for the first time, so our results are new. Finally, as an application example, we study some n-point boundary value problems with just-introduced general fractional derivatives and with boundary integral conditions expressed in terms of fractional integrals of the same kind, extending all known cases of studies in weak topology.

A novel Lyapunov-based robust controller design for LCL-type shunt active power filters using adaptive sliding-mode backstepping approach

In this paper, a novel hybrid two-loop nonlinear controller is designed for stabilization and robust control of the LCL-type shunt active power filter (SAPF). To cope with the instability issue of the closed-loop system and the inherent resonance of the LCL coupling, backstepping, sliding mode and adaptive controllers are combined. DC link voltage of the grid-connected inverter is regulated in an outer control loop by determining a proper reference value for an inner loop. In addition to DC link voltage control, a major objective of the proposed closed-loop system is to make the grid current in phase with the grid voltage directly. Hence, active power filtering of the grid-connected inverter can be achieved without any current feedback from the local load. To stabilize the LCL-type SAPF in a wide range of changes, all uncertain parameters of the model including the DC link capacitor and equivalent impedances of the LCL coupling network are estimated by employing a proper Lyapunov function. For practical evaluation of the developed approach, the closed-loop system is implemented by using Texas Instruments’ digital signal processor (DSP-TMS28F335). Considering the application of an adaptive-robust nonlinear controller, it is proved that the system enjoys a stable and robust performance over the whole range of utilization, and it doesn't suffer from resonance issues of the LCL-type SAPFs. Moreover, considering the experimental results, it is observed that the steady-state error of the proposed nonlinear controller is zero in a wide range of operations.

Technical design of an IH-type buncher for KoBRA at RAON

To satisfy the beam requirement of the KoBRA experiment (0.5 nsec in 1σ), rebunching is required in the energy range up to 15 A MeV and for particles with an A/q range from 1 to 7. In cooperation with IBS and Hanmac Corporation, BEVATECH proposed a five-gap IH-buncher cavity which has excellent bunching properties from 5 to 15 MeV/u. Main challenges in this project are the wide energy range and CW operation at RF power levels up to 20 kW. The cavity will offer an effective voltage amplitude of up to 1 MV. To provide the required cooling channels and cooling efficiency, the stems and drifttubes of this cavity will be 3D printed. This paper will discuss the technical design approach and give a status on the development of the buncher cavity.

General method for state-space modeling and nonlinear control of single-phase cascaded multilevel inverters with LCL coupling

Due to the nonlinear behavior of grid-connected cascaded multilevel inverters (GCCMI), the use of nonlinear controllers can guarantee system stability over a wide range of operation. Therefore, state-space modeling is required to design nonlinear controllers. In this manuscript, a comprehensive method is proposed for the general state-space modeling of an n-level GCCMI with LCL coupling. To validate the accuracy of obtained state-space model, an experimental setup of a cascaded multilevel inverter including two H-bridges has been implemented. The outputs of the state-space model are compared with the simulation and experimental results of the GCCMI. This shows that the proposed model is compatible with a real closed-loop system. The simulations were performed using EMTDC/PSCAD software. In the following, the designed general model is used to develop a nonlinear controller based on the Lyapunov stability criteria for a multilevel shunt active power filter (SAPF). Results show that the designed controller is stable and robust in a wide range of operating point changes.