Feedback Coefficients Research Articles

Robust Bumpless Transfer Control for Switched Systems with Unmatched Uncertainties Based on the Common Robust Integral Sliding Mode Under Arbitrary Switching Rules

In this paper, a robust bumpless transfer control scheme for tracking control is proposed to avoid large jumps in the control signals for a switched system (SS) with unmatched uncertainty and disturbance. The robust bumpless controller comprises a robust linear feedback control (RLFC) and a continuous sliding mode control (CSMC) based on the given robust integral sliding mode (RISM). The RLFC meets the requirement of bumpless indices, and the CSMC suppresses the unmatched uncertainty and disturbance. First, the RLFC design is proposed, and the linear feedback coefficients satisfy the bumpless indices, despite the uncertainty and disturbance. Then, a RISM surface design is proposed, in which the uncertain SS satisfies the given H-infinity robust performance index, and can resist the unmatched uncertainty. Consequently, the CSMC ensures that the RISM surface can be reached in finite time from the initial time instant. By composing the CSMC with the RLFC, the control scheme achieves the robust trajectory tracking and the suppression of the control signal bumps during switching. Finally, the proposed robust bumpless transfer control scheme was applied to the different examples, and the simulation results verified its effectiveness.

Closing the nuclear fuel cycle: Strategic approaches for NuScale-like reactor

The present study proposes the potential implementation of eight different closed fuel cycle strategies for a NuScale-like reactor core using its own spent fuel as a reusable source of fissile material for energy production. For that, the spent fuel composition after three burnup cycles of approximately 12 MWd/kgU of NuScale-like initial core and five years of cooling in a spent fuel pool was theoretically reprocessed by GANEX or UREX+ methods. After reprocessing, these two new fuel compositions were spiked in a mixture of thorium (Th) or depleted uranium (DpU), and afterwards inserted into specific batch positions of the core. Therefore, the proposed NuScale-like core configurations contain fuel assemblies loaded with conventional uranium-based fuel and others loaded with reprocessed fuel, resulting in the following combinations: UO2 and GANEX spiked with Th, UO2 and GANEX spiked with DpU, UO2 and UREX+ spiked with Th, UO2 and UREX+ spiked with DpU. The main idea is to comprehend the advantages of adopting the closed nuclear fuel cycle for a NuScale-like reactor by comparing the reference case and the cases containing reprocessed fuel. The results exhibited that all instances in which the core was simulated with reprocessed fuel improved the feedback coefficient, maximum excess of reactivity varying the boron concentration in the coolant, and power peak factor (PPF). Furthermore, the closed nuclear fuel strategies also demonstrated savings of about 17.50% in terms of separating work units (SWU) due to plutonium and uranium recycling, and a potential burnup extension of approximately 43%. The Serpent code version 2.1.32 developed by VTT and ENDF/B-VII.0 nuclear data library has been used to perform the simulations.

Finite-Time Synchronization Criteria for Caputo Fractional-Order Uncertain Memristive Neural Networks with Fuzzy Operators and Transmission Delay Under Communication Feedback

Unlike existing memristive neural networks or fuzzy neural networks, this article investigates a class of Caputo fractional-order uncertain memristive neural networks (CFUMNNs) with fuzzy operators and transmission delay to realistically model complex environments. Especially, the fuzzy symbol AND and the fuzzy symbol OR as well as nonlinear activation behaviors are all concerned in the generalized master-slave networks. Based on the characteristics of the neural networks being studied, we have designed distinctive information feedback control protocols including three different functional sub-modules. Combining comparative theorems, inequality techniques, and stability theory, novel delay-independent conditions can be derived to ensure the finite-time synchronization (FTS) of fuzzy CFUMNNs. Besides, the upper bound of the settling time can be effectively evaluated based on feedback coefficients and control parameters, which makes the achievements of this study more practical for engineering applications such as signal encryption and secure communications. Ultimately, simulation experiments show the feasibility of the derived results.

Numerical investigation of steering synchronization dynamics of laterally coupled laser array with monolithically-integrated external cold cavity.

This study numerically explores the synchronization dynamics of a one-dimension edge-emitting laser array monolithically-integrated with an external cold cavity comprehensively, aiming to achieve an in-phase mode optical field. By employing the optical feedback rate equation, the impact of mutual feedback coefficient and coupling coefficient on the synchronization process are investigated thoroughly. The proposed external cold cavity, designed according to the Talbot effect, could significantly diminish the reflectivity of front facet through separated electrode structure, therefore facilitating the phase-locking process. Consequently, the study uncovers the effective regime for establishing in-phase mode operation. Additionally, the numerical analysis also reveals the vivid synchronization dynamic from a chaotic state to partially-phase-locked, then completely-phase-locked, and ultimately periodic oscillation. Furthermore, the impact of practical fabrication tolerances on the synchronization process are explored as well. Based on the simulation results, our work could offer valuable insights for steering the on-chip optical field and developing novel laser arrays with high beam quality.

Preliminary study of transuranic transmutation in a small modular chloride salt fast reactor

The management of radioactive waste poses a significant challenge to the sustainable development of nuclear energy. Efficient transmutation of nuclear wastes is crucial to minimize their accumulation. A small modular chloride salt fast reactor (sm-MCFR) capable of transmuting transuranic elements (TRU) is proposed in this paper, combining the advantages of the small modular reactor (SMR) and the molten salt reactor (MSR). The sm-MCFR is characterized by a high fuel loading and a compact core structure that can be quickly deployed around large commercial reactors to achieve TRU transmutation. To evaluate the TRU burnup capability of the sm-MCFR, several fuel salts and reprocessing modes were analyzed using the internally developed TRITON MODEC Coupled Burnup Code (TMCBurnup) tool. NaCl-MgCl3 with 98 % enrichment in 37Cl is chosen as carrier salt for the sm-MCFR, which can achieve 76.7 % TRU transmutation rate in average and 355 kg·GW−1·a−1 TRU transmutation quality at a continuous reprocessing rate of 10 L/d for 50 operation years. The optimized sm-MCFR reduced the radioactive toxicity of TRU by 84 %, thereby simplifying waste reprocessing. In addition, the sm-MCFR has a negative temperature feedback coefficient of −7.195 pcm/K, favoring safe reactor operation.

Extended development of the Monte Carlo code MCNP for effective delayed neutron fraction calculation in molten salt reactors

In this study the Monte Carlo code MCNP is extended to account for the fuel circulation effect in molten salt reactors. An algorithm is created to track delayed neutron precursors and the effective delayed neutron fraction is calculated using predicted fuel velocity fields from the computational fluid dynamics solver. Delayed neutron precursors are monitored throughout various sections of a closed fuel loop in a molten salt reactor. The Moten Salt Fast Reactor is chosen as the benchmark for the extended code, with the calculated multiplication factor and reactivity feedback coefficients agreeing well with referenced results. Dependence of the effective delayed neutron fraction on the fuel flow rate is studied. Validation of the extended code is performed using the Molten Salt Reactor Experiment, showing a good agreement between the calculated delayed neutron fraction loss and the experimental data. These results demonstrate that the extended MCNP code can be reliably used for delayed neutron fraction calculations in both fast and thermal spectrum molten salt reactors.

A Gap Nonlinearity Compensation Strategy for Non-Direct-Drive Servo Systems

In this paper, a gap nonlinear compensation strategy is proposed for the full closed-loop control structure of non-direct-drive servo motor systems. Firstly, an improved deadband model containing the initial value of the gap is proposed, and two gap amplitude identification methods, namely, incremental torque and velocity difference integral, are compared. Then, for the full closed-loop structure, based on the describing function and the stability theory of the nonlinear system, the limit-loop oscillating frequency and the influencing factors are predicted, which are related to the system control stiffness and independent of the gap amplitude; finally, the state-feedback control is proposed, and the feedback coefficients are designed by using the pole configuration, making the system a pseudo-linear system. Simulation and experimental verification show that the method can suppress the limit loop oscillation, attenuate the system shock, and have a certain robustness.

Observer-based adaptive memory event-triggered consensus tracking control for high-speed train under DoS attacks

This paper focuses on the event-triggered consensus tracking of high-speed trains under denial-of-service (DoS) attacks. A novel anti-disturbance control strategy is proposed, based on an adaptive memory state observer and a disturbance observer. A memory is introduced to buffer system output information which enhancing the precision of the state observer, and the gust disturbance during the high-speed train operation is estimated by the disturbance observer. The Linear Matrix inequality technique is used to obtain the observer feedback coefficient and the controller gain, and the Lyapunov theory is employed to demonstrate the controller’s consistency tracking performance. Applying the memory to the event-triggered mechanism, a new adaptive memory event-triggered scheme is designed to better ensure system performance and effectively prevent the occurrence of Zeno behavior. To achieve precise identification of DoS attacks in the event-triggered environment, a new detection algorithm is proposed. Finally, simulation examples are used to validate the effectiveness and practicality of the proposed scheme.

An Autoregulatory Model of Forest Insect Population Dynamics and Forest Stand Damage Dynamics in Different Habitats: An Example of Lymantria dispar L.

This paper addresses the problem of constructing a mathematical model of population density dynamics and the dynamics of forest areas damaged by spongy moth (Lymantria dispar L.) outbreaks in the United States, Europe, Russia, and Japan. The key variable of the model is either the pest population density or the area of forests damaged by spongy moths during a season. This variable can be considered proportional to the total current pest abundance in the study area. For the purposes of modeling, data from a number of different authors was used (see bibliography), as well as data from surveys conducted at the egg or caterpillar stage. The complexity of modeling the dynamics of L. dispar abundance is largely due to the fact that, when studying the dynamics of spongy moth population density, the values of external factors such as parasites, predators, and the amount of available food are often unknown. A simple model was proposed using only two types of data: population density and monthly weather characteristics. Our analysis demonstrated that, even in the absence of knowledge regarding the characteristics of ecosystem components interacting with the spongy moth population (parasites, predators, and the state of forage trees), it is possible to introduce models that characterize the regulatory processes in the population in terms of (i) the presence of negative and positive feedbacks in the system and (ii) the influence of external weather factors. The system under investigation was described as an autoregressive system, whereby the current state of the population is dependent on its state in previous years. The order of autoregression in the system was estimated using the order of the maximum significant partial autocorrelation function. It was found that the regulation of spongy moth population density was characterized by the presence of two feedback loops: positive feedback between the current population density and the population density in the previous season and negative feedback between the current population density and the population density two years ago. To evaluate the model, its stability margin was calculated and found to be directly proportional to the positive feedback coefficient and inversely proportional to the negative feedback coefficient. The model was demonstrated to explain up to 90% of the observed variance of real data. Although the model coefficients for different local populations (North America, Europe, and Asia) differ, the general form of the equation describing both direct data on population densities and indirect data on pest dynamics characterized by areas of stand damage is consistent. Consequently, the form of the ADL model is general, irrespective of the location of the local population.

Research on Fixed-Slope On-Chip Soft-Start Method Applied to Buck DC–DC Converter

A fixed-slope soft-start method applicable to Buck converters for on-chip integration is proposed to address the issue of varying power stresses (device voltage, current stress) during start-up with different output voltages. The main mechanism involves combining feedback coefficient sampling with a fixed-slope reference voltage to achieve a slow rise in the reference voltage by equating the soft-start charging current to a pulse current through the on-chip integration of a small capacitor. This allows for fixed-slope start-ups for different set output voltages. Spike elimination techniques are employed to address charging current spikes caused by pulse periods, enhancing precise control over the soft-start time. By replacing the traditional resistor divider network with a capacitive divider network in the soft-start method, DC power consumption is minimized. Upon completion of the soft start, a smooth transition to a steady-state operation occurs, with the automatic shutdown of the soft-start module reducing static power consumption. A specific circuit design and layout verification based on 0.18 μm high-voltage BCD technology demonstrates that the proposed method maintains a fixed-slope start-up of approximately 5 mV/μs within the chip’s output range of 0.9 V to 4 V, with a slope control accuracy of up to 98%. The soft-start circuit effectively eliminates surge currents generated during start-up under full load conditions of 3 A and no-load conditions of 0 A, reducing the overall surge current by 44% and enabling a stable voltage rise and the smooth transition to a steady-state operation.

Enhancement of quantum entanglement between twin beams via a four-wave mixing process with double feedback

Two-port feedback has been theoretically studied and proved to be effective in enhancing the degree of entanglement of the output beams for a four-wave mixing process. Here, to further consider the loss effects and phase delays, we use a model that is closer to practical implementation. By reasonably tuning the feedback coefficients, we find that a higher degree of entanglement and higher power of the output beams can be achieved, and a loose requirement for phase-locking accuracy can be obtained. This scheme may have promising applications in practical quantum computation and quantum communication.

AP-1000 fuel assembly performance with UO2 and UO2/U3Si2 fuels and silicon carbide cladding from the viewpoint of neutronics

ABSTRACT Accident Tolerate Fuels have been highly researched since the Fukushima disaster. To improve the safety of the AP-1000 fuel assembly, an advanced fuel, UO2/U3Si2, is considered. In addition, the silicon carbide (SiC) cladding that has the capability of reducing oxidation is compared with the baseline Zircaloy for AP-1000 fuel assembly along with the two different fuel cases (UO2 and UO2-U3Si2). The present study focuses on the neutronic performance of the UO2/U3Si2 fuel and thus the main neutronic parameters such as the fuel cycle length, pin power distribution, atom density evolution of main isotopes, and the reactivity feedback coefficients are evaluated. An increase of 6.72% in the criticality period is introduced when 70%UO2-30%U3Si2 fuel with SiC cladding is considered. The pin power peaking factors, fuel temperature coefficients, and moderator temperature coefficients of the proposed fuel result in very few changes. For instance, the maximum pin power distribution difference between 70%UO2-30%U3Si2 and UO2 fuel with SiC cladding is 0.001, which is negligible. Thus, its performance is as good as the traditional UO2 fuel from the neutronic aspects and controlling power distribution.

Periodic Solutions in a Simple Delay Differential Equation

A simple-form scalar differential equation with delay and nonlinear negative periodic feedback is considered. The existence of several types of slowly oscillating periodic solutions is shown with the same and double periods of the feedback coefficient. The periodic solutions are built explicitly in the case with piecewise constant nonlinearities involved. The periodic dynamics are shown to persist under small perturbations of the equation, which make it smooth. The theoretical results are verified through extensive numerical simulations.

A 500 mVpp Input Range First-Order VCO-Based ADC with a Multi-Phase Quantizer for EEG Recording Front Ends

This paper proposes a VCO-based ADC with first-order noise shaping for EEG signal recording front ends. Addressing the challenge of applying analog integrators in advanced processes due to low voltage issues, a multi-phase quantizer structure is introduced based on V-F conversion within the VCO structure, resulting in lower analog power consumption at the same output bit-width. By introducing a form of Gray code encoding, errors caused by circuit metastability are limited to within 1 bit. Considering the effects of motion artifacts and the electrode DC offset, the circuit achieves a wide input range of 500 mVpp by adjusting the feedback coefficients. A prototype ADC is fabricated using 180 nm CMOS technology, operating at a 1.8 V/1 V power supply voltage, with power consumption of 17.1 μW, while achieving a 62.1 dB signal-to-noise and distortion ratio (SNDR) and 55.2 dB dynamic range (DR). The proposed ADC exhibits input noise of 8.64 μVrms within a bandwidth of 0.5 Hz–5 kHz.

Global Stabilization of a Chain of Two Integrators by a Feedback in the Form of Nested Saturators

Stability of a switching system, which comes to existence when stabilizing a chain of two integrators by a feedback in the form of nested saturators, is studied. The use of the feedback in the form of nested saturators makes it possible to take into account boundedness of the control resource and to ensure the fulfillment of the phase constraint on the velocity of approaching the equilibrium state, which is especially important in the case of large initial deviations. A Lyapunov function is constructed by means of which global asymptotic stability of the closed-loop system is proved for any positive feedback coefficients.

Influence of geometry passive Q-switch based on a nanopowder-polymer on the characteristics of an erbium ring fiber laser

The presented work shows an influence of geometry passive Q-switch based on a nanopowder-polymer on the characteristics of an erbium ring fiber laser. The saturable absorber Bi2Te3 was applied to two types of specially prepared samples of thinned sections of optical fiber, and the resulting structures were built into the ring circuit of an erbium fiber laser. In the first case, the surface of the light guide segment was thinned by chemical etching, and in the second, by mechanical grinding. For the first time, the time-domain optical reflectometry technique was used to control the quality of the resulting sample surface and the resulting losses. For a more complete comparison, a set of different optical splitters was used, providing a change in the feedback coefficient in the resonator from 5 to 95 %. A study in the mode of passive Q-switching using polarized light showed that for both types of modulators there are optimal ratios of the amount of energy output from the resonator to obtain the highest values of the average generation power. The d-shape fiber modulator allows mode-locking to be observed without any additional changes to the laser circuit. The pulse duration in this case was 5 ns with a repetition rate of 4 MHz. A Q-switch based on a chemically thinned fiber segment made it possible to obtain narrower pulses in Q-switching mode (up to 700 ns at 38 kHz), a stable peak position in the transmission spectrum, and an average power of 34 mW.

Bipartite consensus tracking of second-order fractional-order multi-agent systems on directed signed graphs

This paper studies the bipartite consensus tracking problems of fractional-order multi-agent systems on directed signed graphs. Each agent is modelled as a second-order fractional-order dynamics with the order belonging to ( 0 , 1 ] , and the cooperative and competitive interactions between the agents coexist in the systems. Two distributed bipartite consensus tracking protocols are proposed for the systems based on continuous information and sampled information, respectively. Under the assumption that the directed signed graph is structurally balanced, it is shown that the second-order fractional-order multi-agent systems can achieve the bipartite consensus tracking if the feedback coefficients are chosen appropriately. Finally, several simulations are provided to verify the effectiveness of the theoretical results.

Robust maximum expert consensus model with adjustment path under uncertain environment

The maximum expert consensus model (MECM) is a commonly used consensus model in group decision making (GDM). In traditional MECM, the consensus constraints are not fully considered and the adjustment cost of decision maker (DM) is certain. Moreover, directing the DM’s opinion in a visual path is seldom considered in the consensus reaching process (CRP) of MECM. Inspired by these issues, this paper first proposed two MECMs with different types of consensus constraints. Then, this paper incorporated an adjustment path into MECM by using feedback coefficients that can prevent opinions from being overadjusted. Furthermore, the robust MECM (RMECM) is developed to address the uncertainty of unit adjustment cost under three uncertainty sets. Finally, the feasibility of the proposed models is verified by applying them to the allocation of special funds in the Chinese film industry, which is a large-scale group decision making (LSGDM) problem. The sensitivity analysis and comparative analysis are also conducted to show the efficiency of the proposed models.

Стабилизация характеристик регенераторов

The article relates to the field of research of the physics of the transition of the amplifier from the aggregate state of amplification to the aggregate state of generation. The aim of the study is to find the possibility of controlling the process of transition from one state of aggregation to another, to implement a stable retention of the device at a given point. The latter will make it possible to implement the construction of stable regenerators. A theoretical conclusion is obtained about the possibility of stable signal regeneration, for which the stabilization coefficient of negative feedback on a constant, zero component should be greater than the regeneration coefficient or gain in gain due to positive feedback at the maximum gain frequency, and for a resonant amplifier – at a resonant frequency. The information confirming the theoretical conclusions and conditions on the example of some technical solutions and implementations of practical devices is given. The multiple technical advantages of stable regenerators over traditional amplifying devices are demonstrated, including resistance to excitation of parasitic generation in a wide dynamic range and temperature range. This is explained by the fact that a stable regenerator cannot be excited twice, a stable excitation is a normal state of aggregation of the regeneration of the input signal. There is also a significant increase in sensitivity and, accordingly, a decrease in intrinsic noise by 9-10 orders of magnitude, an improvement in the width of the linear dynamic range by 8-9 orders of magnitude. An improvement in the amplified frequency bandwidth is demonstrated, not only in the area of minimization, but also in the region of significant expansion, more than an order of magnitude, relative to the maximum achievable for specific samples of the amplifying element, the transistor. The fact that the dependence of the regeneration coefficient and the quality factor of the LC circuit is a special case, only for LC regenerators, is shown and explained. The presented broadband regenerators use strip valves or broadband transformers without an LC circuit and have a regeneration coefficient, which does not contradict the theory and is useful in practice. Multiple improvements are predicted in the construction of systems and devices for low-power signals, as well as an improvement by several orders of magnitude of the main technical characteristics of communication and location systems, measuring systems and devices.

Generalized time-delay reverse synchronization with error feedback coefficients

To enhance the application of discrete chaotic systems in secure communication, we introduce a novel generalized time-delay inverse synchronization method with error feedback coefficient. This paper outlines the derivation of an inverse master-slave time-delay generalized synchronization system using the Lyapunov theory with error feedback coefficient design, which is proposed for the first time. To verify the efficacy of the synchronization method, we constructed a new 4D discrete hyperchaotic system. The dynamic properties of the novel system, such as the phase diagram and Lyapunov exponents, are investigated. Empirical outcomes reveal that generalized discrete time-delay synchronization can be accomplished under certain conditions for the error feedback coefficient. The study utilizes the chaotic masking technique to encrypt and decrypt messages in the secure communication system. The experimental findings reveal that by integrating the synchronization approach with the time-delay context of secure communication, the applicable design of the synchronization procedure is adaptable and trustworthy, catering to the pertinent requirements of engineering, and has the capacity to attain instantaneous chaotic synchronization requisites.