Transient Response Research Articles

Improving the robustness of distributed secondary control in autonomous microgrids to mitigate the effects of communication delays

Distributed control has been employed in autonomous microgrids (MGs) to attain secondary control goals. However, the reliance of MG’s distributed secondary control on communication makes it vulnerable to degraded performance and the risk of instability due to communication delays. This paper enhances the flexibility of the MG control framework, with each distributed generator incorporating supplementary local feedback signals. This added flexibility strengthens the MG’s ability to counteract disturbances caused by delays and enhances its dynamic performance. The introduction of extra feedback signals has a direct impact on the dynamic response of the MG, leaving its steady-state condition unaffected. In comparison to the methods found in existing literature, the increased flexibility relaxes the inherent trade-off between the objectives of improved transient response and the system’s ability to mitigate disturbances caused by delays. To model the MG, a set of delay differential–algebraic equations (DDAEs) is used. The small-signal linearized model is derived and employed to evaluate the stability of the MG as well as fine-tune the control parameters. The effectiveness of this proposed control structure is demonstrated using the MATLAB/Simulink environment and a controller in the loop (CIL) setup, tested against both fixed universal and asynchronous delays, as well as time-varying delays.

High-Performance Airflow Sensors Based on Suspended Ultralong Carbon Nanotube Crossed Networks.

Airflow sensors are in huge demand in many fields such as the aerospace industry, weather forecasting, environmental monitoring, chemical and biological engineering, health monitoring, wearable smart devices, etc. However, traditional airflow sensors can hardly meet the requirements of these applications in the aspects of sensitivity, response speed, detection threshold, detection range, and power consumption. Herein, this work reports high-performance airflow sensors based on suspended ultralong carbon nanotube (CNT) crossed networks (SCNT-CNs). The unique topologies of SCNT-CNs with abundant X junctions can fully exhibit the extraordinary intrinsic properties of ultralong CNTs and significantly improve the sensing performance and robustness of SCNT-CNs-based airflow sensors, which simultaneously achieved high sensitivity, fast response speed, low detection threshold, and wide detection range. Moreover, the capability for encapsulation also guaranteed the practicality of SCNT-CNs, enabling their applications in respiratory monitoring, flow rate display and transient response analysis. Simulations were used to unveil the sensing mechanisms of SCNT-CNs, showing that the piezoresistive responses were mainly attributed to the variation of junction resistances. This work shows that SCNT-CNs have many superiorities in the fabrication of advanced airflow sensors as well as other related applications.

Numerical study of transient absorption saturation in single-layer graphene for optical nanoscopy applications

Transient absorption, or pump–probe microscopy is an absorption-based technique that can explore samples ultrafast dynamic properties and provide fluorescence-free contrast mechanisms. When applied to graphene and its derivatives, this technique exploits the graphene transient response caused by the ultrafast interband transition as the imaging contrast mechanism. The saturation of this transition is fundamental to allow for super-resolution optical far-field imaging, following the reversible saturable optical fluorescence transitions (RESOLFT) concept, although not involving fluorescence. With this aim, we propose a model to numerically compute the temporal evolution under saturation conditions of the single-layer graphene molecular states, which are involved in the transient absorption. Exploiting an algorithm based on the fourth order Runge–Kutta (RK4) method, and the density matrix approach, we numerically demonstrate that the transient absorption signal of single-layer graphene varies linearly as a function of excitation intensity until it reaches saturation. We experimentally verify this model using a custom pump–probe super-resolution microscope. The results define the intensities necessary to achieve super-resolution in a pump–probe nanoscope while studying graphene-based materials and open the possibility of predicting such a saturation process in other light-matter interactions that undergo the same transition.

Steady-State and transient kinetic investigations of the oxidation of NO over Pt/SiO2

The reaction mechanism of the oxidation of NO under conditions of high NO concentration over a 2 wt% Pt/SiO2 was studied using both kinetic and transient isotopic tracing experiments. The reaction mechanism was found to involve both NO adsorption and oxygen adsorption, contrary to the situation under low NO concentration where NO reacts from the gas phase. The kinetic rate data could be fitted to the Langmuir-Hinshelwood model permitting the estimation of rate and equilibrium constants of elementary steps. These steps were investigated using transient responses following independent reactant gas isotopic switches for tracing the nitrogen path and the oxygen path during NO oxidation. These transients could be sufficiently described by a microkinetic model based on two pools of NO intermediates, one pool each for the adsorbed molecular oxygen and atomically adsorbed oxygen. Surface atomic oxygen was found to be formed by two different routes: via a direct dissociation of molecularly adsorbed oxygen and also via an assisted pathway that leads to NO2 formation. The latter surface reaction between adsorbed NO and adsorbed molecular oxygen comprised the kinetically relevant step. Insights from the two experimental and model approaches were in good agreement and provided a coherent reaction mechanism for NO oxidation under high NO reactant concentration.

Fault-Tolerant Control for Aircraft with Structural Damage Using Sparse Online Gaussian Process Regression

AbstractThis paper presents the design of data-driven fault-tolerant control using sparse online Gaussian process regression (SOGPR) to stabilize an aircraft with left-wing damage. The structural damage causes changes in mass, moment of inertia, center of gravity, and aerodynamic coefficients. These parameter variations deteriorate the performance of model-based nonlinear control methods. Hence, Gaussian process-based nonlinear dynamic inversion (GP-NDI) is proposed to compensate for uncertainties in situations of structural damage. Unlike parametric adaptive control approaches, Gaussian process regression is a non-parametric method that does not need prior information about uncertainties. And the proposed method implements SOGPR to reduce computational time and memory by incrementally updating the mean and variance. To compensate for the error in the estimated uncertainty, a robust control input is designed. In addition, a weighted delete score is used to improve the transient response. Numerical simulation results are compared with model reference adaptive control (MRAC) and nonlinear disturbance observer (NDO) to analyze a stabilizing and tracking performance in a structural damage situation.

Modified Universal Integral Regulator for Quadrotor UAV in the Presence of External Disturbances

Universal Integral Regulator (UIR) is a widely used control law for control problems, it is based on sliding mode control with the inclusion of a Conditional Integrator (CI). In the original approach of this control law, the main gain is considered a constant. The purpose of this paper is to solve a quadrotor tracking problem using a new nonlinear control law based on the quadrotor tracking problem using a new nonlinear control law based on the UIR, considering the main gain dependent on the tracking error (variable gain), the control law is called in the present work as Modified Universal Integral Regulator (MUIR). It is expected that the MUIR can improve the transient response and reduce the control demand when compared to previous approaches of similar controllers. The adopted Newton-Euler quadrotor model and the controller design are treated separately in two subsystems, attitude and position control loops. The stability of MUIR is demonstrated by the use of a candidate Lyapunov function. Finally, in order to validate the robustness and choice of the proposed controllers, several numerical simulations were developed in the presence of external disturbances. Less error and control activity during transient response were observed when compared to the original Universal Integral Regulator controller.

Transient Stability Improvement on Power Network using Static Synchronous Compensator: A Case of The Nigerian 330 KV Electricity Grid

This study deals with power system transient stability, enhanced via a static synchronous compensator (STATCOM). The system’s steady state and transient responses were modelled with Newton-Raphson-based power flow and modified Euler-based swing equation, respectively. Simulations were performed with and without STATCOM, considering the Nigerian 34-bus power grid. A balanced three-phase fault was used for the transient stability analysis. The voltage magnitudes of Katampe (0.9373), Kaduna (0.9209), Kano (0.9381), Jos (0.8295), and Gombe (0.7795) in the grid violated the statutory voltage limit of 0.95 to 1.05 p.u. before compensation and were improved to 0.9650, 0.9550, 0.9789, 0.9630, and 0.9550 p.u., respectively after STATCOM was applied. The system’s total real line losses before and after compensation were 57.887 and 55.623 MW, respectively. Fault application on bus 20 (Akangba T.S) caused loss of synchronism on generator 14 when the critical fault clearing time (CFCT) exceeded 0.019 s while generators 2 to 13 experienced marginal stability. The STATCOM application restored stability beyond the CFCT of 0.019 s due to compensation provided by the device. Fault introduction on bus 22 drove Egbin, the largest system’s generator corresponding to generator 7 on the swing curve into marginal stability along with generators 3 to 6 and 8 to 14 while generator 2 lost synchronism beyond a fault CFCT of 0.0130 s. However, the STATCOM application restored the system’s stability. STATCOM aided the transient stability improvement of the Nigerian 34-bus power network for effective operation.

Application of Static Synchronous Compensator for Improvement of Power System Transient Stability

Transient stability is the power system’s ability to maintain synchronism when exposed to severe disturbances such as loss of generation, rapid load changes, transmission lines tripping, switching operations and faults. Transient instability causes cascading outages, system collapse and economical losses. This study employed static synchronous compensator (STATCOM) for power system transient stability improvement. The system’s steady state and transient responses were respectively modelled with Newton-Raphson power flow and modified-Euler linearized swing equations. A balanced three-phased short circuit fault was introduced on selected buses for transient stability analysis. The steady state and transient responses of the system were simulated with and without STATCOM. The critical fault clearing time (CFCT) was obtained from the generators’ swing curves. The IEEE 9-bus and 14-bus power networks were used as test cases. The voltage magnitudes of all buses in both networks fell within the specified 0.95 to 1.1 p.u. voltage limit with and without compensation. The total active line loss on IEEE 9-bus and 14-bus networks which were 4.641 and 13.514 MW without compensation reduced to 4.600 and 13.014 MW, respectively with STATCOM’s application. The total reactive line losses of both networks which were 92.160 and 31.393 MVAr without compensation decreased to 90.160 and 30.693 MVAr, respectively with STATCOM’ utilization. The CFCT for fault on bus 8 of the IEEE 9-bus system without compensation were 0.2100 and 0.2700 s for generators 2 and 3, respectively. The system’s stability was, however, extended beyond 0.2700 s due to compensation from STATCOM. In the case of IEEE 14-bus system, the CFCT for fault on bus 6 was 0.36364 s for generators 2, 3, 4 and 5, respectively without compensation. The STATCOM inclusion, however, enhanced the system’s stability beyond 0.36366 s where all the four had lost synchronism. This work established that the use of STATCOM on the considered networks appropriately extended the CFCT such that the stability of the systems was not lost in the event of fault application via robust compensation of reactive power.

Diagnosis of Li-ion battery degradation based on resistive and diffusion-related transient voltage changes at early stage of discharge

Lithium-ion batteries degradation can be classified into capacity reduction and increase of the internal resistance. Accurate estimation of the degradation is important to determine the economic value and the remaining useful life of the battery. This paper proposes a method which analyzes the transient voltage response at the early stage of discharge, starting from the fully charged state. An equivalent circuit composed by a series resistance and a Warburg element is adopted to fit the transient voltage. The Warburg element is modeled as a transmission line composed by a ladder of resistances and capacitances. The method is validated with data obtained before and after aging cycles performed at 1.4 C charge and 2.0 C discharge rates, at 25 °C, 10 °C and −5 °C. The loss of cyclable lithium is deemed to be the main reason behind the battery degradation at all the tested temperatures. The dependency of the Warburg parameter to the remaining cell capacity is the same regardless of the aging temperature, suggesting that estimation of the Warburg parameter provides information about the state of health of the cell. On the other hand, the relationship between the capacity reduction and the increase of resistance has a temperature-dependent slope with low increase at lower temperatures where lithium plating is likely to occur. Accordingly, a relatively low resistance increase is deemed to be the sign of lithium plating.

CD4+ CAR T-cell exhaustion associated with early relapse of multiple myeloma after BCMA CAR T-cell therapy

AbstractMultiple myeloma is characterized by frequent clinical relapses after conventional therapy. Recently, chimeric antigen receptor (CAR) T cells targeting B-cell maturation antigen (BCMA) has been established as a treatment option for patients with relapsed or refractory disease. However, although >70% of patients initially respond to this treatment, clinical relapse and disease progression occur in most cases. Recent studies showed persistent expression of BCMA at the time of relapse, indicating that immune-intrinsic mechanisms may contribute to this resistance. Although there were no preexisting T-cell features associated with clinical outcomes, we found that patients with a durable response to CAR T-cell treatment had greater persistence of their CAR T cells than patients with transient clinical responses. They also possessed a significantly higher proportion of CD8+ T effector memory cells. In contrast, patients with short-lived responses to treatment have increased frequencies of cytotoxic CD4+ CAR T cells. These cells expand in vivo early after infusion but express exhaustion markers (Hepatitis A virus cellular receptor 2 [HAVCR2] and T cell immunoglobulin and mucin domain-containing-3 [TIGIT]) and remain polyclonal. Finally, we demonstrate that nonclassical monocytes are enriched in the myeloma niche and may induce CAR T-cell dysfunction through mechanisms that include transforming growth factor β. These findings shed new light on the role of cytotoxic CD4+ T cells in disease progression after CAR T-cell therapy.

Effects of electro-mechanical uncouplers, hormonal stimulation and pacing rate on the stability and function of cultured rabbit myocardial slices.

Introduction: Recent advances have enabled organotypic culture of beating human myocardial slices that are stable for weeks. However, human myocardial samples are rare, exhibit high variability and frequently originate from diseased hearts. Thus, there is a need to adapt long-term slice culture for animal myocardium. When applied to animal cardiac slices, studies in healthy or genetically modified myocardium will be possible. We present the culture of slices from rabbit hearts, which resemble the human heart in microstructure, electrophysiology and excitation-contraction coupling. Methods: Left ventricular myocardium from New Zealand White rabbits was cut using a vibratome and cultured in biomimetic chambers for up to 7days (d). Electro-mechanical uncoupling agents 2,3-butanedione monoxime (BDM) and cytochalasin D (CytoD) were added during initiation of culture and effects on myocyte survival were quantified. We investigated pacing rates (0.5Hz, 1Hz, and 2Hz) and hormonal supplements (cortisol, T3, catecholamines) at physiological plasma concentrations. T3 was buffered using BSA. Contractile force was recorded continuously. Glucose consumption and lactate production were measured. Whole-slice Ca2+ transients and action potentials were recorded. Effects of culture on microstructure were investigated with confocal microscopy and image analysis. Results: Protocols for human myocardial culture resulted in sustained contracture and myocyte death in rabbit slices within 24h, which could be prevented by transient application of a combination of BDM and CytoD. Cortisol stabilized contraction amplitude and kinetics in culture. T3 and catecholaminergic stimulation did not further improve stability. T3 and higher pacing rates increased metabolic rate and lactate production. T3 stabilized the response to β-adrenergic stimulation over 7d. Pacing rates above 1Hz resulted in progredient decline in contraction force. Image analysis revealed no changes in volume fractions of cardiomyocytes or measures of fibrosis over 7d. Ca2+ transient amplitudes and responsiveness to isoprenaline were comparable after 1d and 7d, while Ca2+ transient duration was prolonged after 7d in culture. Conclusions: A workflow for rabbit myocardial culture has been established, preserving function for up to 7d. This research underscores the importance of glucocorticoid signaling in maintaining tissue function and extending culture duration. Furthermore, BDM and CytoD appear to protect from tissue damage during the initiation phase of tissue culture.

Tailored Polymeric Carbon Nitride Coupled with Bi2O3 for Constructing Z‐Scheme Heterojunction with Enhanced Photocatalytic Activity

The great demand for visible‐light‐induced catalysts with high photocatalytic performance has stimulated extensive interest in constructing g‐C3N4‐based Z‐scheme heterojunctions. In this research work, we constructed the g‐C3N4/Bi2O3 Z‐scheme heterojunction by precipitation‐hydrothermal method, and confirmed the close contact interface between g‐C3N4 and Bi2O3 to form the heterojunction by various characterization techniques, which facilitates the efficient separation of photogenerated electrons‐holes. Compared to pure g‐C3N4 and Bi2O3, the g‐C3N4/Bi2O3‐1 composite exhibited a transient photocurrent response approximately 7 and 5 times higher than that of g‐C3N4 and Bi2O3, respectively, with stronger visible photocatalytic activity and degraded 99.8% methylene blue within 75 min. Ion trapping experiments showed that •OH free radical had the greatest effect on the degradation of methylene blue, while •O2‐ and h+ had less effect. According to the experimental test results, the possible photocatalytic degradation mechanism of g‐C3N4/Bi2O3‐1 catalyst was proposed. This study provides a new avenue for the development of novel g‐C3N4‐based Z heterojunction materials with application value.

Improving Performance of Solar Array Fed BLDC Drive Using Firefly Algorithm Based High Gain Converter

The improved transient response of PID controller for improved Luo converter supplied Brushless DC (BLDC) motor using solar energy source is extensively investigated. The BLDC drive uses a hybrid PV system and battery-based power generation as a power source to assure continuous power supply to pump water regardless of solar insolation. The PV system serves as the main energy source, and the battery providing as a backup source that discharged its power only during inclement weather or at night if the photovoltaic panel is insufficient to operate the centrifugal pump. The solar panel feeds power into the battery, whenever water to the field is not required, thus there is no need for an extra power source to charge the batteries. The high output voltage gain DC-DC converter does not make any discomfit to the system performance in regards to irradiance variation, switching loss, or power loss by converter or motor side respectively. Moreover, current sensor, voltage sensor, and control circuits are completed excluded which enhance performance and the cost of the system get reduced effectively. A bidirectional charging control allows a bi-directional converter to alter the battery operation mode automatically. The overall system performance is validated using simulation and experimental setup.

PI Current Controller Design for DC Drive System using 4- Quadrant DC-DC Converter and 3- Phase Rectifier

DC Motors is considered one of the important machines in control systems such as industrial robots, vehicles, and process control. Current control of a DC drive is very desirable because by controlling the current, the torque is controlled. Moreover, current control can be used to prevent large damaging armature currents during start-up. A good current loop is very important when setting up a DC drive. When the control of the current loop is good, the steady state motor current should respond exactly with the reference current, and the transient response to the step change in the reference current should be fast and well-damped. This paper presents two different types of current controller converters that are commonly used in DC motor drives. The first converter is a 4-quadratic switch-mode DC-DC converter, while the second controller is a 3-phase controller rectifier. Both current converters were simulated using Matlab Simulink, where a PI current controller for the inner loop current control DC motor controls these converters. The PI controller was designed based on the Bode plot frequency response method. In this research, the design procedure was based on the small signal model and then, verified using a large signal model. The simulation result showed that the performance using a 4-quadrant DC-DC converter gave better performance than a 3-phase rectifier.

An Improved Perturb and Observe MPPT for Photovoltaic Systems using Fuzzy Step Size

Photovoltaic (PV) systems have emerged as a promising energy resource that caters to the future needs of society, owing to their renewable, inexhaustible, and cost-free nature. The output power of these systems relies on solar cell radiation and temperature. To mitigate the dependence on atmospheric conditions and enhance power tracking, a conventional approach has been improved by integrating various methods. The Maximum Power Point Tracking (MPPT) algorithm is employed to optimize power extraction from PV systems. To overcome limitations such as steady-state voltage oscillations and improve transient response, two traditional MPPT methods, namely Perturb and Observe (P&O) and Fuzzy Logic Controller (FLC), have been modified. This research work aims to simulate and validate the fuzzy step size of the proposed modified P&O and FLC techniques within the MPPT algorithm using Matlab/Simulink™ for efficient power tracking in PV systems.

An on-chip soft-start pseudo-current hysteresis-controlled buck converter for automotive applications

This paper introduces a novel direct current to direct current (DC-DC) buck converter that uses a pseudo-current hysteresis controller and an on-chip soft start circuit for improved transient performance in automotive applications. The proposed converter, implemented with Taiwan semiconductor manufacturing company (TSMC) 0.18 µm complementary metal oxide semiconductor (CMOS) one-poly-six-metal (1P6M) technology, includes a rail-to-rail current detection circuit and an on-chip soft start circuit to handle transient responses and improve efficiency. Transient response analysis shows fast settling times of 28 µs for both load current changes from 100 mA to 1 A and reversals with consistent transient voltages of approximately 190 mV and peak power efficiency of 99.32% at 5 V output voltage and 100 mA load current. Additionally, the converter maintains a constant output voltage of approximately 5 V across the entire load current range with an average accuracy of 90.41%. A comparative analysis with previous work shows superior performance in terms of figure of merit (FOM). Overall, the proposed pseudo-current hysteresis controlled buck converter exhibits remarkable transient response, load regulation and power efficiency, positioning it as a promising solution for demanding applications, particularly in automotive systems where precise voltage regulation is crucial.

Transient response mitigation using type-2 fuzzy controller optimized by grey wolf optimizer in converter high voltage direct current

Long high voltage direct current (HVDC) transmission link is commonly used to transmit electrical energy via land or under-sea cable. The long HVDC avoids reactive power losses (RPL) and power stability problems (PSP). On the contrary, the RPL and PSP phenomena occur in long high voltage alternative current-link (HVAC) caused by the high reactive component in the HVAC-link. However, the HVDC produces a high and slow transient current response (TCR) on the high value of the up-ramp rate. Interval type-2 fuzzy (IT2F) control on converter-side HVDC is proposed to mitigate this TCR problem. The IT2F is optimized by grey wolf optimizer (GWO) to adjust input-output IT2F parameters optimally. The performance of IT2F-GWO is assessed by the minimum value of integral time squared error (ITSE), peak overshoot, and settling time of the TCR. The IT2FC-GWO performance is validated by the performance of IT2F control that is optimized by genetic algorithm (IT2F-GA) and proportional integral (PI) controller. Simulation results show that the IT2F-GWO performs better with small ITSE, low peak overshoot, and shorter settling times than competing controllers.

Dynamic responses analysis of submerged floating tunnel under impact load

Submerged floating tunnel (SFT) may be subjected to sudden impact loads such as submarine and shipwreck. Besides the local damage caused by impact, the overall transient dynamic response may also affect its driving safety. Based on the dynamic impact finite element software, the full-length model, and the locally truncated accurate model with solid element of the SFT are established respectively. By applying different spring stiffness constraints on the boundary of the truncated model, its first three modes are consistent with the full-length model, thus their dynamic characteristics are basically the same. The truncated model is further used to simulate the impact of a massive object on the SFT under different impact velocities, impact mass, impact angles and impact positions. The velocity and mass of the impact object have positive influences on the peak contact force, the displacement amplitude of the tube and the length of the damaged area. When the impact angle is perpendicular to the SFT tube, the contact force, displacement amplitude and the damaged area are the largest. The change of the impact position has little effect on the contact force and the damage area, but it will affect the distribution of displacement amplitude.

Fuzzy controlled modified reduced switch converter for switched reluctance motor under dynamic loading

In this paper, modified reduced switch converter topology is used to drive 8/6 pole, 7500 W switched reluctance motor (SRM) with an electric vehicle (EV) load. Fuzzy logic control (FLC) is developed for the modified converter topology and its performance is compared with the proportional integral (PI) controller. Analytical equations, switching pulses and different mode of operation are presented for modified reduced switch converter using double phase magnetization scheme. The converter topology adopts a modified switching sequence i.e., magnetization then freewheeling before demagnetization. It offers lesser torque ripples, reduced phase current and need only four switches for a 4-phase SRM drive. Modified reduced switch converter is simulated in MATLAB-simulation to investigate and compare the steady state waveforms and transient speed response of the PI and FLC. Torque ripple in modified converter is 50% less than the classical converter. Peak overshoot and settling time performance of FLC is superior as compared to PI, when applied to modified converter with EV loading.

Distinct Hippocampal Oscillation Dynamics in Trace Eyeblink Conditioning Task for Retrieval and Consolidation of Associations.

Trace eyeblink conditioning (TEBC) has been widely used to study associative learning in both animals and humans. In this paradigm, conditioned responses (CRs) to conditioned stimuli (CS) serve as a measure for retrieving learned associations between the CS and the unconditioned stimuli (US) within a trial. Memory consolidation, that is, learning over time, can be quantified as an increase in the proportion of CRs across training sessions. However, how hippocampal oscillations differentiate between successful memory retrieval within a session and consolidation across TEBC training sessions remains unknown. To address this question, we recorded local field potentials (LFPs) from the rat dorsal hippocampus during TEBC and investigated hippocampal oscillation dynamics associated with these two functions. We show that transient broadband responses to the CS were correlated with memory consolidation, as indexed by an increase in CRs across TEBC sessions. In contrast, induced alpha (8-10 Hz) and beta (16-20 Hz) band responses were correlated with the successful retrieval of the CS-US association within a session, as indexed by the difference in trials with and without CR.