Switching Time Research Articles

Model predictive control for single-phase cascaded H-bridge photovoltaic inverter system considering common-mode voltage suppression

In this article, a model predictive control (MPC) with common-mode voltage (CMV) suppression is proposed for single-phase cascaded H-bridge (CHB) inverters, which can also simultaneously achieve control objectives of grid-connected current tracking, voltages balancing of different H-bridge submodules on the DC-side and switching frequency reduction. To suppress high-frequency components of the common-mode voltage without additional switching devices, the algorithm proposed designs the predicted and reference values of the CMV and incorporates them in the cost function. At the same time, the capacitor voltages balancing control is integrated in the calculation of the optimal modulation function of the H-bridge, which reduces the complexity of control effectively. Besides, switching times of the MOSFETs are compared in two cycles. The cost function is constructed to represent comprehensive effect of the control. Finally, an experiment is performed on the hardware-in-the-loop experimental platform. The experimental results show that the proposed algorithm can offer a better voltage THD and reduce the times of switch action by nearly half while maintaining high-precision current tracking and maximum power point of photovoltaic modules, which alleviate the potential electromagnetic interference and cabling problem.

Particle manipulation based on the controllable light field of graphene nano-butterfly structures

In this Letter, we have proposed a nano-optical convey belt consisting of three sets of graphene nano-butterfly structures (GNBS) with different lengths arranged in a periodic pattern to trap, transport, and sort particles depending on controlling the Fermi level of graphene. The graphene nano-butterfly structure, based on a couple of trapezoids, can form a potential well to capture particles by localized surface plasmon resonance under the excitation of an incident laser. There are three adjustable geometric parameters containing width (W1, W2) and length (L) that make the GNBS have a high degree of design flexibility. Graphene can support surface plasmons in the mid-infrared region, and at the same time, it possesses a more flexible tuning mechanism compared to metals. When the incident light power is 1 mW/μm2 and the resonance wavelength is 10.6 μm, the depth of the potential well is greater than 10KbT for 50 nm particles. Moreover, the sorting of particles with different diameters has also been validated under appropriate power and switching time. Based on the capabilities of capture and sorting verified by numerical analysis, our design offers a new scheme for on-chip optofluidic applications.

Switching Frequency Improvement of a High Speed on/off Valve Based on Pre-excitation Control Algorithm

The high-speed on/off valve (HSV) serves as the fundamental component responsible for generating discrete fluids within digital hydraulic systems. As the switching frequency of the HSV increases, the properties of the generated discrete fluid approach those of continuous fluids. Therefore, a higher frequency response characteristic of HSV is the key to ensure the control accuracy of digital hydraulic systems. However, the current research mainly focuses on its dynamic performance, but neglect its FRC. This paper presents a theoretical analysis demonstrating that the FRC of the HSV can be enhanced by minimizing its switching time. The maximum switching frequency (MSF) is mainly determined by opening dynamic performance when HSV operates with low switching duty ratio (SDR), whereas the closing dynamic performance limits the MSF when HSV operates with high SDR. Building upon these findings, the pre-excitation control algorithm (PECA) is proposed to reduce the switching time of the HSV, and consequently enhance its FRC. Experimental results demonstrate that PECA shortens the opening delay time of HSV by 1.12 ms, the closing delay time by 2.54 ms, and the closing moving time by 0.47 ms in comparison to the existing advanced control algorithms. As a result, a larger MSF of 417 Hz and a wider controllable SDR range from 20% to 70% were achieved at a switching frequency of 250 Hz. Thus, the proposed PFCA in this paper has been verified as an effective and promising approach for enhancing the control performance of digital hydraulic systems.

Event-triggered quasi-time-varying [formula omitted] filtering for switched systems via multiple trigger-dependent Lyapunov functionals

This paper investigates the event-triggered filtering problem for switched systems from the perspective of switched impulsive systems (SISs) by exploiting the characteristics of trigger and impulse behavior. By constructing multiple trigger-dependent Lyapunov functionals (MTDLFs), an event-triggered quasi-time-varying (ET-QTV) H∞ filtering scheme is developed. Since the MTDLFs properly capture the event-induced impulse property of SISs, they release less conservatism. The filtering stability in the scenario of frequent plant switching during an interevent interval is also guaranteed by incorporating the average dwell time switching. The filtering synthesis condition is formulated as a set of QTV matrix inequalities defined over a finite time horizon, based on which a sum of squares-based filter design algorithm is presented further. Additionally, the derivation of a lower bound on interevent intervals is clarified for the event-triggering mechanism (ETM) to exclude the Zeno phenomenon. Finally, the effectiveness and potential practicability of the proposed filtering scheme are validated using a morphing aircraft model.

A Bertalanffy–Richards growth model perturbed by a time-dependent pattern, statistical analysis and applications

We analyze a modification of the Richards growth model by introducing a time-dependent perturbation in the growth rate. This modification becomes effective at a special switching time, which represents the first-crossing-time of the Richards growth curve through a given constant boundary. The relevant features of the modified growth model are studied and compared with those of the original one. A sensitivity analysis on the switching time is also performed. Then, we define two different stochastic processes, i.e. a non-homogeneous linear birth–death process and a lognormal diffusion process, such that their means identify to the growth curve under investigation. For the diffusion process, we address the problem of parameters estimation through the maximum likelihood method. The estimates are obtained via meta-heuristic algorithms (namely, Simulated Annealing and Ant Lion Optimizer). A simulation study to validate the estimation procedure is also presented, together with a real application to oil production in France. Special attention is devoted to the approximation of switching time density, viewed as the first-passage-time density for the lognormal process.

Tilt effect on squeeze-film damping in electrostatic micro-actuators

In this study, we theoretically explore the impact of tilt on the switching dynamics of a MEMS device operated by a pair of electrostatic actuators and subject to pronounced squeeze-film damping in the transition and free molecular flow regimes. Our investigation reveals that inducing tilt, achieved through the application of uneven voltages on the electrodes, introduces additional source terms in the modified Reynolds equation governing the pressure distribution in the squeeze-film gap. These added terms result in an accelerated decay of the squeeze film force, facilitating faster device switching between the initial and target configurations.To analyze the device dynamics, we develop a coupled numerical model and employ evolutionary multi-objective optimization to determine an optimal actuation scheme. This optimization is carried out for scenarios where initially different voltages are applied to the electrodes during a certain pre-defined time interval before transitioning to the steady voltage corresponding to the target gap size at equilibrium. Our findings highlight that the suggested actuation strategy leads to substantial improvements in the switching time of the device. Furthermore, we provide insights into the conditions favoring tilt actuation over parallel-motion actuation where the initially applied voltages are equal.

Robust Switching Time Optimization for Networked Switched Systems via Model Predictive Control.

This article presents a model predictive control (MPC) strategy to find the optimal switching time sequences of networked switched systems with uncertainties. First, based on predicted trajectories under exact discretization, a large-scale MPC problem is formulated; second, a two-level hierarchical optimization structure coupled with a local compensation mechanism is established to solve the formulated MPC problem, where the proposed hierarchical optimization structure is actually a recurrent neural network consisting of a coordination unit (CU) at the upper level and a series of local optimization units (LOUs) related to each subsystem at the lower level. Finally, a real-time switching time optimization algorithm is designed to calculate the optimal switching time sequences.

Influence of chalcopyrite nanoplatelets on nematic phases of bend-shaped dimeric molecules: Phase diagram, birefringence, and reorientation transition

We investigated the influence of chalcopyrite (CuFeS2) nanoplatelets on the ordering of uniform and twist-bend nematic phases of achiral bend-shaped dimers, employing polarized optical microscopy, optical and electro-optical measurements. Specifically, aliphatic amine surface-functionalized hydrophobic chalcopyrite nanoplatelets were synthesized and characterized by XRD, TEM, and IR-vis-UV spectroscopy. Nanocomposites of the liquid crystal compound 1”,9”-bis(4-cyanobiphenyl-4'-yl)nonane (CB9CB) with the nanoplatelets were prepared. The study encompasses an assessment of the thermodynamic stability of the nanocomposites, constructing the corresponding phase diagram as a function of temperature and nanoplatelet mass fraction. Large phase temperature shifts were observed for minute mass fractions of NPs. Birefringence measurements were performed to investigate the orientational order parameter and the conical tilt angle's dependence on the mass fraction of the nanoplatelets and the temperature. Additionally, we measured a Fréedericksz-like reorientation transition voltage threshold and switching times as functions of the mass fraction and temperature. A huge increase of the voltage threshold was measured in the twist-bend nematic phase. The dependence of the viscoelastic coefficient ζ on NPls' mass fraction was investigated. The splay elastic constant of the helicoidal structure was estimated, using a coarse grain approximation, to be two orders of magnitude higher than in the uniform nematic phase. Finally, in the twist-bend nematic phase, the impact of temperature and nanoplatelets mass fraction on the hysteresis loop of the reorientation transition was investigated.

Maximizing Reliability in Overlay Radio Networks With Time Switching and Power Splitting Energy Harvesting

Maximizing Reliability in Overlay Radio Networks With Time Switching and Power Splitting Energy Harvesting

Service time thresholds at barrier-operated freeway exit toll booths

This paper discusses service times based on vehicle class at barrier-operated toll booths. Service times were measured using four vehicle classifications: car (C), medium goods vehicle (MGV), trucks & bus (TB), and articulated truck (AT) with two payment options: electronic (ETC) and manual toll collection (MTC). Each toll booth has both payment systems and resulting in mixed toll booth utilization in terms of payment and vehicles. The collected data was utilized to estimate logistic regression, and non-parametric statistical tests were performed. Findings indicate, when vehicle size increases, so does service time for even ETC. Furthermore, logistic regression used to compute threshold service times shifting from ETC to MTC for C, MGV, TB, and AT, which were 5.92, 7.51, 10.00, and 12.80 s, respectively. The transition time for a vehicle switch from ETC to MTC based on the logistic curve is denoted by threshold service time. Below the threshold, ETC is more favorable option and affected by barrier and vehicle class. Overall, the results indicate that operators can benefit from more dynamic operational conditions facilitated by threshold service times, enabling adaptive and efficient toll booth operations. Additionally, these thresholds can serve as valuable measure of service quality for managing freeway exits.

A demultiplexer-based dual-path switching true random number generator

This paper presents a demultiplexer (DEMUX) based dual-path switching true random number generator (TRNG). Unlike the classical single chain TRNG, the proposed TRNG utilizes DEMUXs to separate the cumulative jitter and occurrence of metastability in two paths. It also uses Ring Oscillator (RO) to increase the uncertainty of path switching time. Therefore, two sources of entropy are skilfully combined and no post-processing circuitry is required. The proposed structure is implemented on Xilinx Virtex-7 FPGA development board. The experimental results show that the proposed structure is able to achieve a high throughput of 500 Mbps with 33 Look-up Tables (LUTs) and 4 Flip-Flops (FFs). This effectively improves the throughput with high quality entropy and low hardware overhead.

Dynamic multicolor electrochromic skin in high-brightness flexible WO3/Au asymmetric Fabry–Perot nanocavity fabricated on Nylon 66 porous substrate

Recently, the Fabry–Perot (F–P) cavity electrochromic devices, which are constructed by combining nano-size inorganic electrochromic material WO3 and reflective metal layers, have attracted considerable attention due to their potentials in the fields of dynamic multicolor displays and active camouflage. However, in the few studies that have been reported, the peak reflectance of flexible F–P cavity multicolor electrochromic devices in the visible wavelength band is generally lower than 30 %, which limits their reflective display and camouflage effects in high-brightness environments. Thus, we have combined multicolor reflective electrochromic electrodes in WO3/Au asymmetric F–P nanocavity constructed by magnetron sputtering on a Nylon 66 porous substrate with a highly transparent UV-cured gel electrolyte and a PET plastic sealing procedure. As a result, a flexible and dynamic multicolor electrochromic skin with high reflectance (Rmax＞50 %) and excellent flexibility (bending radius of 4 mm) has been fabricated. The WO3 electrochromic layer at the top works as the dynamic dielectric layer in the broadband absorption Fabry–Perot cavity, and the inert metal Au layer at the bottom works as the reflective layer. The WO3/Au asymmetric F–P cavity can acutely capture the variation in optical constants of WO3 due to the thickness change and electric-driven effects. This cavity facilitates the selective reflection and absorption of the energy distribution of the spectrum after the induced interferometric resonance. As a result, the cavity exhibits a rich array of structural colors, including ocher, taupe, yellow, orange, green, and violet. The electrochromic skin exhibits a fast switching time and maintains 99.43 % of the optical modulation amplitude (ΔR) after 110 coloring/bleaching cycles. It provides a potential option in the field of flexible high-brightness reflective displays and dynamic camouflage in the future.

Transient at Finite Switching Time: Monitoring by Neural Net

Transient at Finite Switching Time: Monitoring by Neural Net

Study on phase selection control characteristics of fast vacuum circuit breakers suitable for new power systems

Abstract With a high proportion of new energy access to the power system, the user side of the randomness and volatility of distributed photovoltaic large-capacity access to the 10 kV medium-voltage distribution grid operation results in more frequent fluctuations in the system voltage and more frequent switching of reactive compensation of the shunt capacitor bank on the 10 kV side of the conventional substation. Conventional reactive compensation switching circuit breakers adopt a spring mechanism whose mechanical stability is insufficient and the selection of the relevant fit capacitor bank accuracy is not enough. The 12 kV fast vacuum circuit breaker of small mechanical dispersion for selection related to the combination was proposed. First of all, based on the neutral grounded and ungrounded system of the capacitor bank, the strategy of capacitor bank phase selection closing was developed. For the action characteristics of the phase selection of the 12 kV fast vacuum circuit breaker, the variation laws of mechanical dispersion and the influence factors such as ambient temperature, capacitance voltage, capacitance degradation, mechanical wear, and conductive rod deformation were obtained by simulation and experiment. The results showed that the ambient temperature and capacitance voltage had a great influence on the switching time of the fast circuit breaker, while other factors had a small influence. Again, the pre-breakdown characteristics of the 12 kV fast vacuum circuit breaker were obtained by experiments. The results showed that the influence of contact opening distance and pre-breakdown voltage was a linear relationship, and the pre-breakdown slope was 30 kV/mm. According to the pre-breakdown closing characteristic curve, the pre-breakdown time of the fast circuit breaker was 0.45 ms at most. The feedforward compensation mechanism based on a neural network was proposed to compensate for the action characteristics of the fast circuit breaker and aimed to improve the phase selection accuracy. Finally, two rounds of capacitive current switching tests of 12 kV fast vacuum circuit breakers with C2 level were carried out in a third-party test station. The accuracy of phase closing is within the ±0.5 ms closing window, effectively preventing the occurrence of closing inrush current.

Ferroelectric Al0.85Sc0.15N and Hf0.5Zr0.5O2 Domain Switching Dynamics.

The capability to reliably program partial polarization states with nanosecond programming speed and femtojoule energies per bit in ferroelectrics makes them an ideal candidate to realize multibit memory elements for high-density crossbar arrays, which could enable neural network models with a large number of parameters at the edge. However, a thorough understanding of the domain switching dynamics involved in the polarization reversal is required to achieve full control of the multibit capability. Transient current integration measurements are adopted to investigate the domain dynamics in aluminum scandium nitride (Al0.85Sc0.15N) and hafnium zirconium oxide (Hf0.5Zr0.5O2). The switching dynamics are correlated to the crystal structure of the films. The contributions of domain nucleation and domain wall motion are decoupled by analyzing the rate of change of the time-dependent normalized switched polarization. Thermally activated creep domain wall motion characterizes the Al0.85Sc0.15N switching dynamics. The statistics of independently nucleating domains and the domain wall creep motion in Hf0.5Zr0.5O2 are associated with the spatially inhomogeneous distribution of local switching field due to polymorphism, absence of preferential crystallite orientation, as well as defects and charges that can be located at the grain boundaries. The c-axis texture, single-phase nature, and strong likelihood of less fabrication process-induced defects contribute to the homogeneity of the local switching field in Al0.85Sc0.15N. Nonetheless, defects generated and redistributed upon bipolar electric field switching cycling result in Al0.85Sc0.15N domain wall pinning. The wake-up effect in Hf0.5Zr0.5O2 is explained thorough the continuous addition of switchable regions associated with two independent distributions of characteristic switching times.

CMOS-compatible Hf0.5Zr0.5O2-based ferroelectric memory crosspoints fabricated with damascene process

We report the fabrication of Hf0.5Zr0.5O2 (HZO) based ferroelectric memory crosspoints using a complementary metal-oxide-semiconductor-compatible damascene process. In this work, we compared 12 and 56 µm2 crosspoint devices with the 0.02 mm2 round devices commonly used as a benchmark. For all devices, a 9 nm thick ferroelectric thin film was deposited by plasma-enhanced atomic layer deposition on planarized bottom electrodes. The wake-up appeared to be longer for the crosspoint memories compared to 0.02 mm2 benchmark, while all the devices reached a 2Pr value of ∼50 µC cm−2 after 105 cycles with 3 V/10 µs squared pulses. The crosspoints stand out for their superior endurance, which was increased by an order of magnitude. Nucleation limited switching experiments were performed, revealing a switching time <170 ns for our 12 and 56 µm2 devices, while it remained in the µs range for the larger round devices. The downscaled devices demonstrate notable advantages with a rise in endurance and switching speed.

Design of a large energy acceptance beamline using fixed field accelerator optics

Large energy acceptance arcs have been proposed for applications such as cancer therapy, muon accelerators, and recirculating linacs. The efficacy of hadron therapy can be improved by reducing the energy layer switching time, however this is currently limited by the small momentum acceptance of the beam delivery system (&lt;±1%). A “closed-dispersion arc” with a large momentum acceptance has the potential to remove this bottleneck, however such a beamline has not yet been constructed. We have developed a design methodology for large momentum acceptance arcs with Fixed Field Accelerator optics, applying it to a demonstrator beam delivery system for protons at 0.5–3.0 MeV (±42% momentum acceptance) as part of the Technology for Ultra-Rapid Beam Operation project at the University of Melbourne. Using realistic magnetic fields, a beamline has been designed with zero dispersion at either end. An algorithm has been devised for the construction of permanent magnet Halbach arrays for this beamline with multipole error below one part in 104, using commercially available magnets. The sensitivity to errors has been investigated, finding that the delivered beam is robust in realistic conditions. This study demonstrates that a closed-dispersion arc with fixed fields can achieve a large momentum acceptance, and we outline future work required to develop these ideas into a complete proof-of-principle beam delivery system that can be scaled up for a medical facility. Published by the American Physical Society 2024

Adjustable optoelectronic properties of triphenylamine-ethylenedioxythiophene based hybrid electrochromic polymer with different electron-donating substituents

Due to the good optoelectronic properties of triphenylamine (TPA) and its derivatives-based organic conjugated polymers, they have been widely used in various organic electronic devices. They are easy to lose electrons to form stable cationic free radicals with color change under electrochemical oxidation conditions. Therefore, TPA derivatives-based electrochromism materials have attracted the widely attentions of researchers. In this work, a series of TPA derivatives were successfully obtained by Stille coupling reactions, and their basic optical and electrical properties were investigated in detail. Their corresponding polymer films (P(TPA-EDOT), P(PhTPA-EDOT), and P(OCH3TPA-EDOT)) were also prepared on transparent ITO glass by electrodeposition method and their electrochromic properties were further studied. Due to the relatively strong electron donating ability of OCH3– group on the TPA unit, the intramolecular charge transfer peak of OCH3TPA-EDOT is obvious red-shifted and its initial oxidation potential is relatively low, which is beneficial for it to get high-quality electrochromic polymers. Electrochemical analysis shows that all these three polymer films show reversible redox reaction with excellent redox stability. Spectroelectrochemistry shows that all of them have good electrochromic properties and show multi-electrochromic behavior with strong color change. The dynamic study show that all these three polymers have relatively fast switching time (as low as 0.8 s), high coloration efficiency (up to 206.2 C−1 cm2) and obvious optical contrast change. Especially in the near infrared region, the optical contrast is relatively high (P(TPA-EDOT) is 45.3 % at 1100 nm, P(PPhTPA-EDOT) is 53.1 % at 1100 nm, and P(OCH3TPA-EDOT) is 57.2 % at 1100 nm). All these results show that the different substituents on the TPA unit have a certain influence on the resultant monomers’ optoelectronic performances, and they also can adjust the optical band gap of the corresponding polymers with different electrochromic properties.

Biomimetic Exploration and Reflection on Switchable Coordination and Narrow-Band Electrofluorochromic Devices.

Electrofluorochromic (EFC) materials and devices with controllable fluorescence properties show great application potential in advanced anticounterfeiting, information storage and display. However, the low color purity caused by the broad emission spectra and underperforming switching time of the existing EFC materials limit their application. Through biomimetic exploration and the study of reversible electrochemical responsive coordination reactions, boron-nitrogen embedded polyaromatics (B,N-PAHs) with narrow-band emission and high color purity have been successfully integrated into EFC systems, which also help to better understand the role of boron in biological activity. The EFC device achieve good performance containing quenching efficiency greater than 90% within short switching time (ton: 0.6s, toff: 2.4s), and nearly no performance change after 200 cycles test. Three primary color (red, green, and blue) EFC devices are successfully prepared. In addition, new phenomena are obtained and discussed in this biomimetic exploration of related boron reactions. The success and harvest of this exploration are expected to provide new ideas for optimizing properties and broadening applications of EFC materials. Moreover, it may provide ideas and reference significance for further exploring and understanding the function of boron compounds in biological systems.

Mode-folded thin-film lithium niobate phase shifter for channel scalable optical interconnect with high switching efficiency.

Paralleled optical interconnection has been widely used in optical transceivers. Reconfigurable photonic integration with scalable channel numbers is thus highly useful in timely adjusting the link capacity to the changing traffic patterns in data centers or high-performance computing (HPC) systems. In this paper, a 1×8 Mach-Zehnder switch (MZS) over thin-film lithium niobate is proposed and experimentally demonstrated for 1-to-8 channel scalable optical interconnects, with high switching efficiency through utilizing the mode-folded phase shifter. The three-mode phase shifter recirculates the light three times, undergoing phase changing with different waveguide modes. Simultaneously, the multimode waveguiding within the phase shifter results in a pronounced enhancement of the optical field confinement, further improving the Pockels effect for all modes. A 3.5-time improvement of the switching efficiency is experimentally demonstrated, exhibiting a low Vπ·L of 0.6 V⋅cm. The proposed MZS also features low channel crosstalk (below -20 dB over 1530-1565 nm) and nanosecond-order switching time, paving the way towards channel scalable and versatile MSA-compatible optical interconnect.