Step Change Research Articles

Grid Forming Converter Control System Synthesis: A Static Output Feedback Approach

This paper proposes an effective control synthesis strategy to stabilize grid forming converters in the presence of disturbances. The conventional control system for a grid forming converter is based on paralleled and cascaded proportional‐integral (PI) controllers, which are widely used in the industry due to their simplicity and reliability. However, the sequential adjustment of PI gains in different control loops, without consideration of dynamic interconnections limits their performance and capability. To address this limitation, the present paper introduces a control design method based on static output feedback theory. The proposed control scheme reduces the dynamic control design problem to an effective gain scheduling problem. In the proposed methodology, without removing the existing practical control structure, its dynamic parts are moved to the open‐loop system, and simultaneous scheduling of all remaining control gains is achieved during one control design process. MATLAB simulations were conducted to evaluate the performance of the designed control system, and compare it with the conventional control one in terms of step response characteristics. The results demonstrate the superiority of the proposed controller, ensuring system stability and exhibiting improved performance. The proposed control framework provides several advantages, including keeping stability in various disturbance conditions, simultaneous tuning of all control parameters, and no need to change the existing simple control structure. © 2024 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Symmetric prism characterisation test to infer heat generation and heat conduction properties of concrete

Performance-based concrete design can accelerate the acceptance of emerging lower carbon concretes to reduce the environmental impact. A semi-adiabatic symmetric concrete prism experimental and analytical approach is proposed as a pathway for concrete thermal characterisation. The prism design promotes 1-D heat flow conditions using a single insulated specimen. The prism dimensions (700 mm ×100 mm ×100 mm) are rationalised to suit usage as a characterisation specimen and mix compositions that replicate those of in-situ concretes can be assessed. The experimental spatial and temporal thermal profiles of a CEM I mix and a high GGBS replacement mix were measured during hydration and through a step change in temperature in the hardened state. Thermocouples and a distributed fibre optic sensor along the central axis of the symmetric prism were used for this purpose. Multi-physics modelling provided a platform to address thermal measurement data uncertainty, extract fundamental concrete thermal parameters and gain insight into the heat generation and heat flow physics in the concrete prism specimens. The complete heat generation and maturity time histories were accurately modelled and ‘concrete thermal footprints’ derived.

Analyzing fishery data and exploring the resource status of Antarctic krill based on its environmental dependence

AbstractAntarctic krill Euphausia superba is a key species in the Southern Ocean ecosystem and has important ecological value. It is also one of the main fishery resources in the Southern Ocean with high economic value. In recent years, with the development of krill fishery and rapid climate change, the conservation and management of krill resources have faced unprecedented challenges. The krill resource is different from the general fishery resources. Due to the krill schooling characteristics, fishery data has some advantages over scientific survey data. Reviewing and analyzing the krill fishery data is necessary. Therefore, in this study, four fishery resource indices (FRIs) were calculated based on Antarctic krill fishery data, and based on the environmental dependence of Antarctic krill, the FRI with the strongest environmental dependence was screened by using the Gradient Forest Model, and the step changes of the FRI with strongest environmental dependence was examined by using the sequential t‐test analyses of regime shifts (STARS). The generalized additive model (GAM) to analyze the correlation between the FRI with the strongest environmental dependence and the main environmental factors, and then explore the resource status of Antarctic krill in the study area. The model results showed that the “FRI_hual” had the strongest environmental dependence and was a better indicator of the status of the Antarctic krill in the study area than the others. In the 2009–2010 year, “FRI_hual” had an obvious regime shift. The interaction of environmental factors “ice_area_2” and “SSH_1” has a great impact on “FRI_hual”. Methods used and results obtained in the study can provide new ideas and a scientific reference for future work, including integrated stock assessment of krill and krill resource monitoring, conservation, and management based on the ecosystem.

Experimental Assessment of Predictive Current Control Applied to Induction Machine Drive Systems Operating Under Single-Phase Open-Circuit Fault


 Predictive Current Control (PCC) has been widely applied in several applications. However, the literature has not discussed its use as a fault tolerance control algorithm in induction drive systems. In this way, this paper discusses the PCC method in two faulttolerant squirrel-cage induction machine drive systems operating under single-phase open-circuit faults. PCC’s postfault performance is compared to Field Oriented Control (FOC) for different steady- and transient-state scenarios, analyzing harmonic distortion, torque ripple, and the transition from healthy to postfault operation. Also, experiments tested the robustness of postfault PCC to low-speed operation, parametric variation, and a step change in reference rotor speed, showing that PCC also presents fault-tolerant operation under these conditions.

A cloud-by-cloud approach for studying aerosol–cloud interaction in satellite observations

Abstract. The effective radiative forcing (ERF) due to aerosol–cloud interactions (ACIs) and rapid adjustments (ERFaci) still causes the largest uncertainty in the assessment of climate change. It is understood only with medium confidence and is studied primarily for warm clouds. Here, we present a novel cloud-by-cloud (C×C) approach for studying ACI in satellite observations that combines the concentration of cloud condensation nuclei (nCCN) and ice nucleating particles (nINP) from polar-orbiting lidar measurements with the development of the properties of individual clouds by tracking them in geostationary observations. We present a step-by-step description for obtaining matched aerosol–cloud cases. The application to satellite observations over central Europe and northern Africa during 2014, together with rigorous quality assurance, leads to 399 liquid-only clouds and 95 ice-containing clouds that can be matched to surrounding nCCN and nINP respectively at cloud level. We use this initial data set for assessing the impact of changes in cloud-relevant aerosol concentrations on the cloud droplet number concentration (Nd) and effective radius (reff) of liquid clouds and the phase of clouds in the regime of heterogeneous ice formation. We find a Δln⁡Nd/Δln⁡nCCN of 0.13 to 0.30, which is at the lower end of commonly inferred values of 0.3 to 0.8. The Δln⁡reff/Δln⁡nCCN between −0.09 and −0.21 suggests that reff decreases by −0.81 to −3.78 nm per increase in nCCN of 1 cm−3. We also find a tendency towards more cloud ice and more fully glaciated clouds with increasing nINP that cannot be explained by the increasingly lower cloud top temperature of supercooled-liquid, mixed-phase, and fully glaciated clouds alone. Applied to a larger number of observations, the C×C approach has the potential to enable the systematic investigation of warm and cold clouds. This marks a step change in the quantification of ERFaci from space.

Visual cue spatial context affects performance of anticipatory postural adjustments

Past research indicates that anticipatory postural adjustment (APA) errors may be due to the incorrect selection of responses to visual stimuli. In the current study we used the Simon task as a methodological tool to challenge the response selection stage of processing by presenting visual cues with conflicting spatial context; in this case generating a step response to a left pointing arrow which appears to the participant's right side or vice versa. We expected greater mediolateral APA errors, delayed APA and step onset times, and greater lateral CoP displacement prior to stepping for visual cues with incongruent spatial contexts compared to cues with congruent. Thirteen healthy young adults completed step initiation trials (n = 40) from a force platform while whole-body kinematic motion was tracked. Participants were presented with arrows pointing to the left or right, indicating to step with the left or right limb, respectively. These arrows were presented on the same side as the desired step direction (congruent) or the opposite side (incongruent). Results revealed that incongruent trials resulted in significantly more incidences of mediolateral APA errors and greater mediolateral CoP deviations during the APA compared to congruent visual cue context trials. No effects were observed for the temporal outcomes, suggesting that young adults can maintain temporal execution of steps despite these motor control errors. This study demonstrates that the spatial context of visual information significantly impacts the success of response selection processes during step initiation, furthering our knowledge of how humans integrate visual information to initiate whole body movement.

Quantitative Comparative Study on the Performance of a Valve-Controlled Actuator and Electro-Hydrostatic Actuator

The development of the electrification of aircraft has prompted aviation hydraulic systems to shift from traditional centralized valve actuators (CVAs) to electro-hydrostatic actuators (EHAs). In this paper, aiming at the demand for a quantitative comparison of performance between CVAs and EHAs, CVA and EHA prototypes with the same power level and test platform were developed. Then, based on the power flow and dynamic models of the CVA and EHA, simulation and experimental comparative tests were conducted using different load spectrum test conditions and step response test conditions. The comparative test results showed that the efficiency of the EHA was better than that of the CVA, and the dynamic response of the CVA was better than that of the EHA. Finally, a power loss quantification and parameter sensitivity analysis were performed to reveal the impact of different parameters on the different power losses and to provide suggestions for improving the performance of CVAs and EHAs.

Dividing‐wall column for separating wide boiling mixture: Optimal design and servo control strategy

AbstractThe dividing‐wall column (DWC) stands as an energy‐efficient distillation technology designed to efficiently separate ternary systems into their pure components within a single column. Despite its efficiency, integrating two towers into a DWC poses challenges in controllability. Published studies have focused on developing controllers for disturbance rejection but have not addressed the issue of servo control. Addressing this, our study proposes a servo controller problem and a methodical approach to strategically select controlled variables that undergo consecutive set point step changes, aiming to track the purity of key products obtained from the DWC. To achieve this goal, we developed a dynamic model specifically tailored to the DWC. Determining the design parameters involved employing a genetic algorithm optimization technique, minimizing the total annual cost. Subsequently, we implemented three servo parallel proportional‐integral (PI) feedback controllers for three distinct product streams. The fine‐tuning of their controller gain and reset time is carried out by minimizing the integrated square error while adhering to valve opening constraints. Our investigation revealed a limitation: the introduction of simultaneous step changes in all three controlled variables proved unfeasible with the three active PI controllers. As an alternative, our findings recommend prioritizing two variables: the lightest (distillate) and heaviest (bottom) key components, alongside the middle component (side stream) and either the lightest or heaviest key component. This research underscores the complexities of implementing step changes in multiple controlled variables within a DWC, offering insights into optimal control strategies for enhancing the efficiency of this innovative distillation technology.

Physiological and perceptual responses to temperature step changes between cold and hot environments

Objectives. This study explores the effects of temperature steps on thermal responses to understand abrupt temperature shifts faced by heat-exposed workers during winter. Methods. Three temperature step changes with three phases (S20: 20–40–20 °C, S30: 10–40–10 °C, S40: 0–40–0 °C) were conducted. Phase 1 took 30 min, phase 2 took 60 min and phase 3 took 40 min. Eleven participants remained sedentary throughout the experiment, and physiological responses, thermal perception and self-reported health symptoms were recorded. Results. In temperature up steps, steady skin temperature and sweating onset were delayed, and heart rate dropped by 10 bpm from S20 to S40. In temperature down steps to cold conditions, individuals transitioned from thermal comfort to discomfort and eventually cold strain. Blood pressure increased in temperature down steps, correlating with temperature step magnitudes. Thermal responses to temperature steps of equal magnitude but opposite directions were asymmetries, which weakened as step magnitude increased. Thermal perceptions responded faster than physiological changes after temperature steps, while self-reported health symptoms lagged behind physiological responses. Conclusions. These findings contribute to expanding basic data to understand the effects of temperature step magnitude and direction.

Thermal Management of Proton‐Exchange Membrane Fuel Cells with Enhanced Fuzzy Control via an Improved Whale Optimization Algorithm

Proton exchange membrane fuel cells (PEMFCs) require an appropriate operating temperature to achieve high performance and longevity. In addressing the critical need for effective thermal management in PEMFCs for vehicle propulsion systems, this study has developed and introduced a novel thermal management system model equipped with dual‐cooling loops. Addressing the issues of slow response and poor dynamic performance inherent in traditional control strategies, as well as the computational complexity that hinders the practical application of existing advanced control strategies, this research proposes a fuzzy proportional‐integral‐derivative (PID) controller optimizing the improved whale optimization algorithm (IWOA‐FPID) aimed at enhancing fan side control. By simulating step changes in current load and designing dynamic operating conditions based on the most basic and simple energy management system, the performance of IWOA‐FPID in temperature control is validated. The final results indicate that the IWOA‐FPID strategy significantly outperforms existing control methods, notably reducing adjustment time and minimizing temperature overshoot to ≈0.5 K. The proposed framework achieves efficient temperature control, highlighting its potential for broader application in vehicular fuel cells and offering a promising solution to the challenges of PEMFC thermal management.

Treatment seeking for gambling disorder in nationwide register data - observations around a major shift in legislation.

Treatment seeking for gambling disorder is known to be low and there has been a lack of longitudinal research regarding treatment opportunities. The present study aimed to assess possible changes in treatment uptake after a formal introduction of gambling disorder in social services and health care legislations, by using register data, including patient characteristics with respect to socio-demographics and comorbidities. Nationwide register data were collected for the years 2005-2019, describing diagnoses in specialized out-patient health care and in in-patient hospital care. Numbers and characteristics of patients with gambling disorder were followed longitudinally. Also, a new legislation for treatment by public institutions was introduced in 2018, and data were compared for the years before and after the shift in legislation, both nationally, for each of the three major urban regions, and for the rest of the country. Comparisons were made with respect to concurrent mental health comorbidities, age and gender. The number of out-patient gambling disorder diagnoses increased over time, but without any significant step changes around the shift in legislation. Over time, patients were younger, became more likely to have gambling disorder as their primary diagnosis, and less likely to have mental health comorbidities, whereas gender distribution did not change. Among the smaller group of patients diagnosed in in-patient settings, mental health comorbidity increased over time. Despite gradual changes over time, no changes in demographics were seen around the actual shift in legislation, although the psychiatric comorbidity appeared to increase after this change. After the introduction of gambling disorder in the responsibility of social services and health care settings in Sweden, the number of patients diagnosed with gambling disorder increased only modestly. Likely, further implementation of gambling disorder treatment is required in the health care services. Also, longer longitudinal studies are needed in order to understand to what extent patients not seeking health care treatment are received by municipal social services or remain outside the treatment system.

Direct Visualization of Chemical Transport in Solid-State Chemical Reactions by Time-of-Flight Secondary Ion Mass Spectrometry.

Systematic control and design of solid-state chemical reactions are required for modifying materials properties and in novel synthesis. Understanding chemical dynamics at the nanoscale is therefore essential to revealing the key reactive pathways. Herein, we combine focused ion beam-scanning electron microscopy (FIB-SEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to track the migration of sodium from a borate coating to the oxide scale during in situ hot corrosion testing. We map the changing distribution of chemical elements and compounds from 50 to 850 °C to reveal how sodium diffusion induces corrosion. The results are validated by in situ X-ray diffraction and post-mortem TOF-SIMS. We additionally retrieve the through-solid sodium diffusion rate by fitting measurements to a Fickian diffusion model. This study presents a step change in analyzing microscopic diffusion mechanics with high chemical sensitivity and selectivity, a widespread analytical challenge that underpins the defining rates and mechanisms of solid-state reactions.

Estimating maximum initial wave amplitude of subaerial landslide tsunamis: A three-dimensional modelling approach

Landslide tsunamis, responsible for thousands of deaths and significant damage in recent years, necessitate the allocation of sufficient time and resources for studying these extreme natural hazards. This study offers a step change in the field by conducting a large number of three-dimensional numerical experiments, validated by physical tests, to develop a predictive equation for the maximum initial amplitude of tsunamis generated by subaerial landslides. We first conducted a few 3D physical experiments in a wave basin which were then applied for the validation of a 3D numerical model based on the Flow3D-HYDRO package. Consequently, we delivered 100 simulations using the validated model by varying parameters such as landslide volume, water depth, slope angle and travel distance. This large database was subsequently employed to develop a predictive equation for the maximum initial tsunami amplitude. For the first time, we considered travel distance as an independent parameter for developing the predictive equation, which can significantly improve the predication accuracy. The predictive equation was tested for the case of the 2018 Anak Krakatau subaerial landslide tsunami and produced satisfactory results.

Research on the Driving and Control of an Intelligent Book Robot

Based on the theoretical foundation provided by kinematic simulations under various parameter conditions using Adams for robots' control, this paper designs a dual-closed-loop drive control system for the robot. It constructs the drive speed control hardware circuit and simulates the step response of positional PID, incremental PID, and fuzzy PID in Simulink. Positional PID is selected as the velocity control algorithm due to its fast response characteristics and ease of implementation. The drive circuit and control algorithm are jointly simulated using Proteus to verify the speed control effect of the robot's drive.

A correlation to calculate time constant of thermocouples

A time constant is the dynamic response time of a thermocouple measuring unsteady flow fields. The measured temperature of a thermocouple is the bead temperature, which is determined by the energy conservation of the bead. Heat transfer of the bead includes convective and radiative heat exchange with the flow, heat conduction with the wires, and surface radiation with the environment. These heat transfer modes affect both the bead temperature and its time constant. The novelty of the paper is to derive a correlation for calculating the time constant of a thermocouple based on the bead energy conservation, covering a wide range of conditions and explicitly reflecting the contribution of surface radiation and conduction. The correlation involves the parameter β related to surface radiation and the parameter cl related to conduction. The correlation for β is obtained by fitting the time constant of small beads in the flows with step change parameters using CFD simulations, while the parameter cl is obtained by fitting the time constant of thermocouples under varying flow conditions using CFD simulations. The relative errors between the calculated time constants with the correlation and those of the CFD simulations are less than 19%. The CFD simulations indicate that the time constants considering radiation and conduction are 33–49% of those considering only the effect of convection for the tested cases. The S type and K type thermocouples were used to measure the standard Hencken flames. By applying current loads and then removing them, the dynamic response curves and the time constants of the thermocouples are obtained. The maximum errors between the calculated time constants with the correlation and the experimental values are less than 10%.

A thermoregulation model based on the physical and physiological characteristics of Chinese elderly

Given the increasing aging population and rising living standards in China, developing an accurate and straightforward thermoregulation model for the elderly has become increasingly essential. To address this need, an existing one-segment four-node thermoregulation model for the young was selected as the base model. This study developed the base model considering age-related physical and physiological changes to predict mean skin temperatures of the elderly. Measured data for model optimization were collected from 24 representative healthy Chinese elderly individuals (average age: 67 years). The subjects underwent temperature step changes between neutral and warm conditions with a temperature range of 25–34 °C. The model's demographic representation was first validated by comparing the subjects' physical characteristics with Chinese census data. Secondly, sensitivity analysis was performed to investigate the influences of passive system parameters on skin and core temperatures, and adjustments were implemented using measurement or literature data specific to the Chinese elderly. Thirdly, the active system was modified by resetting the body temperature set points. The active parameters to control thermoregulation activities were further optimized using the TPE (Tree-structured Parzen Estimator) hyperparameter tuning method. The model's accuracy was further verified using independent experimental data for a temperature range of 18–34 °C for Chinese elderly. By comprehensively considering age-induced thermal response changes, the proposed model has potential applications in designing and optimizing thermal management systems in buildings, as well as informing energy-efficient strategies tailored to the specific needs of the Chinese elderly population.

Evaluation by Liquid Crystal Thermography of Transient Surface Temperature Distribution in Radiant Floor Cooling Applications and Assessment of Analytical and Numerical Models

Abstract The purpose of our study is to evaluate the surface temperature distribution on a radiant floor, particularly focusing on space cooling operations, to assess the presence of nonuniformities. In fact, knowing the temperature difference between the average superficial temperature and the coldest spot can be a useful indication for condensation prevention. Primarily, we performed an experimental campaign in test rooms using temperature sensors and liquid crystal thermography. This allowed us to evaluate the floor temperature distribution both on a local scale, influenced by the discontinuous presence of buried water pipes, and on a macroscale, influenced by internal use, objects, and boundary conditions of the surrounding space. Then, the experimental temperature field on the radiant floor surface has been compared with analytical and numerical models in steady-state and transient phases, respectively. The results indicate limited superficial temperature variations that become more significant at larger tube spacings and under transient conditions. In particular, the numerical transient analysis showed that shortly after a step change in the pipe's temperature boundary condition, a larger variation is locally observable on the floor, which then decays to the new steady-state conditions, presenting more uniformity. However, local effects are generally overshadowed by macro-effects, especially for practical scenarios where many objects, furnishings, and different boundary conditions are present. Finally, as a conservative guideline for the cooling system control, we recommend maintaining the average superficial floor temperature at least 1 °C above the dew point, to account for the described nonuniformities.

Conjugate gradient method with regularization in estimating mold surface heat flux during continuous casting

The reconstruction of the boundary heat flux between solidifying steel and water-cooled mold wall using measured temperature data is recognized as an inverse heat conduction problem (IHCP). A Tikhonov spatial regularization approach to enhance the smoothness of the Conjugate Gradient Method (CGMr) was proposed which incorporates three different orders of spatial regularization: zeroth, first, and second order. The optimal regularization parameter was selected using a modified L-curve method. The accuracy of the CGMr is investigated with Case 1: a triangular time-spatial variation heat flux, and Case 2: a step change in the form of rectangular variation heat flux. The effects of measurement noise, grid points and time-step size are investigated. The results show that the minimum relative error (eRMS) of the predicted Case 1 heat flux is 1.98%, 7.64%, and 8.02% for zeroth-, first-, and second-order spatial regularization, respectively. The corresponding values for the predicted Case 2 heat flux are 3.82%, 13.42%, and 14.91%. Subsequently, CGMr algorithm is applied to calculate the heat flux in a mold simulator experiment. By comparing the relationship between heat fluxes reconstructed by CGMr after different iteration numbers, it is observed that the recovered heat flux of 2.14 MW/m2 with zeroth regularization remains highly stable.

Simulation-Based Assessment of Subsurface Drip Irrigation Efficiency for Crops Grown in Raised Beds

This paper considers the application of a scenario simulation technique to assess subsurface drip irrigation system efficiency while using it to irrigate crops grown under raised bed technology. For simulating purposes, we use a model based on the two-dimensional Richards equation stated in terms of water head in a curvilinear domain. Solutions to problems are obtained using a finite-difference scheme with dynamic time step change. Using the data from pressure measurements obtained while growing potatoes on sandy loess soil in production conditions, we performed a calibration of the model using the particle swarm optimization algorithm. Further, the accuracy of the model was tested and average absolute errors in the range from 3.16 to 5.29 kPa were obtained. Having a calibrated model, we performed a series of simulations with different irrigation pipeline placements determining the configuration under which water losses are minimal. The simulated configuration, under which infiltration losses were minimal, was the installation of pipelines under the raised bed at the depth of 10 cm below the soil surface. The results confirm that the applied technique can be used for decision-making support while designing subsurface drip irrigation systems combined with raised bed growing technology.

Design and Simulation of a Multi-Channel Biomass Hot Air Furnace with an Intelligent Temperature Control System

Timely and effective drying of agricultural products is crucial for ensuring the quality and yield of grains. Biomass drying enhances energy utilization and reduces energy pressure. To this end, a novel multi-channel circulating biomass hot air furnace was designed to provide precise control of the heat source for grain drying, thereby improving the efficiency and quality of the drying process. The combustion process utilizes a multi-channel combined air supply to ensure complete combustion of biomass pellet fuel. During the heat exchange process, heat exchange plates isolate hot and cold areas, discharging combustion exhaust, while ensuring a pure air output. Using rapeseed as the drying subject, a temperature controller based on adaptive fuzzy PID was designed, targeting the biomass hot air furnace’s heat exchange system for modeling and verifying the model with the step response method. Model simulations were conducted in Matlab’s Simulink module using both adaptive fuzzy PID and traditional PID controllers, for a given signal. The settling times for the conventional PID and fuzzy PID were 445 s and 364 s, respectively, with overshoots of 20.1% and 6.3%, showing that the fuzzy PID controller performed better in terms of control performance. The validation tests showed that both control methods could maintain the temperature within ±5 °C. Compared to traditional PID control, the adaptive fuzzy PID control achieved a precision of ±3 °C. At the target temperature of 90 °C, the error was reduced to 3.7%, with a stabilization time of 1014 s. The use of fuzzy PID control exhibited better dynamic response characteristics, meeting the drying needs of rapeseed. This study provides a theoretical basis for the structural design and control system design of biomass hot air furnaces.