Changes In Power Level Research Articles

Gain scheduled internal model control based on the dynamic sliding mode method for the water level of nuclear steam generators

Abstract The Steam Generator (SG) is a crucial component of a nuclear power plant. Proper water level control in a nuclear steam generator is of great importance to ensure a sufficient cooling source for the nuclear reactor and to prevent damage to turbine blades. The water level control problem of steam generators has been a leading cause of unexpected shutdowns in nuclear power plants, which must be addressed for plant safety and availability. The control problem is challenging, particularly at low power levels due to shrink and swell phenomena and flow measurement errors. Furthermore, the dynamics of the steam generator vary as the power level changes. Therefore, there is a need to enhance the water level control system of the SG. In this paper, a Gain Scheduled Internal Model Control (IMC) based on the Dynamic Sliding Mode (DSMC) method is developed for the level control problem. The proposed method exhibits the desired dynamic properties throughout the entire output tracking process, independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed controller in terms of performance, robustness, and stability. The simulation results confirm the improvement in transient response achieved by using the proposed controller.

Deposition and Optical Characterization of Sputter Deposited p-Type Delafossite CuGaO2 Thin Films Using Cu2O and Ga2O3 Targets.

CuGaO2 thin films were deposited using the RF magnetron sputtering technique using Cu2O and Ga2O3 targets. The films were deposited at room temperature onto a quartz slide. The sputtering power of Cu2O remained constant at 50 W, while the sputtering power of Ga2O3 was systematically varied from 150 W to 200 W. The films were subsequently subjected to annealing at temperatures of 850 °C and 900 °C in a nitrogen atmosphere for a duration of 5 h. XRD analysis on films deposited with a Ga2O3 sputtering power of 175 W annealed at 900 °C revealed the development of nearly single-phase delafossite CuGaO2 thin films. SEM images of films annealed at 900 °C showed an increasing trend in grain size with a change in sputtering power level. Optical studies performed on the film revealed a transmission of 84.97% and indicated a band gap of approximately 3.27 eV. The film exhibited a refractive index of 2.5 within the wavelength range of 300 to 450 nm.

Microwave Frequency Doubler with Improved Stabilization of Output Power

The passive multipliers based on semiconductor diodes, most frequently a Schottky type, should be driven by a certain value of input power, where the conversion losses are optimal. This means that the variation in the input power level causes the change in the output power level. A solution to this issue is the integration of an output power amplifier, which in the state of saturation provides quasi-stabilization of the output power. Practically, this approach gives an unsatisfactory performance: weak stabilization or narrow input power range. This paper comprises a concept of an active frequency multiplier with the use of one FET transistor and a special adaptive bias circuit in order to obtain a very wide input power range when the output power is stable. The principle of the operation, design guidelines, and measurement results have been presented for an example circuit of the frequency doubler. The results show the possibility to obtain up to 10 dB input power range for a 1 dB change in output power level without the use of additional amplifiers.

THERMAL-HYDRAULIC ANALYSIS OF A HIGH-TEMPERATURE HELIUM-GAS-COOLED REACTOR UNDER VARIOUS STEADY-STATE OPERATING CONDITIONS

This paper focuses on thermal-hydraulic analysis, which plays a critical role in system efficiency and the selection of the optimal design of nuclear reactors. The analysis is done based on a one-dimensional computer code called MIGHT that performs a subchannel thermal-hydraulic analysis of a typical gas-cooled fast breeder reactor (GCFBR) cooled by helium (He). In steady-state operation, two typical channels, the hot and average channels, with the same flow rate and pressure drop were tested. Temperature distribution profiles and the heat flux were computed and compared for different types of power distribution. The effects of coolant mass flow rate and power level on the thermal-hydraulic performance of the tested GCFBR were investigated for cosine power profile. The results demonstrate that the lowest flow rate for the tested reactor to continue operation in the safe mode at the nominal operating power (2530 MWt) is 80% of the nominal flow rate (10 × 10<sup>6</sup> kg/h). The maximum cladding temperature stays within the suggested design limit of GCFRs (700-750°C) when the power is increased by 10% and 15%. The results revealed that temperature is more sensitive to changes in power level than mass flow rate. Data of GCFBR typical reactor were used as input data and for code validation. Good agreement between tested reactor data and MIGHT code calculation concerning the reactor proves the reliability of the methodology of analysis from a thermal-hydraulic perspective. The minor discrepancies could be explained by differences in the relevant physical parameters used in each method of calculation.

ANALYSIS OF MODELS OF AN AUTOMATIC POWER CONTROL SYSTEM FOR A PRESSURIZED WATER REACTOR IN DYNAMIC MODE WITH A CHANGE IN THE STATIC CONTROL PROGRAM

The process of decarbonization of the industry was intensified by the decision to include nuclear energy in the EU Green Taxonomy. The increase in the capacity of nuclear power plants and the attractiveness of this industry for a long time causes interest in the use of nuclear power plants for electricity dispatching. Thus, the development of an automatic control system for changing the power of nuclear power plants in dynamic modes becomes relevant. The energy release along the height of the reactor core under the action of xenon fluctuations is one of the problems in ensuring the safe operation and stability of the NPP power unit when the power level changes. Violation of the energy release safety criteria occurs when non-stationary transient xenon processes with positive feedback occur in the core. Within the framework of the automatic control theory, the modeling of the system and the control object is compiled on the basis of the use of physical and mathematical models. Transfer functions, structure and parameters of the control system are determined. As an alternative, it is proposed to use an approximation model of the process in the core. The model is presented on the basis of transformations in such a way that the results of the calculation on a certain interval coincide or are close to the results of the calculation when using the analytical model. Such a model can approximate a process that depends on two parameters: time and degree of load change. The results of changing the regulation of technological parameters by the automated power control system of nuclear power unit in dynamic mode, the model of which is based on an approximation or physical and mathematical model, were analyzed. The results of changing the parameters are obtained by comparing the results during the transition of control from one static program to another. Switching between static control programs was studied for such process parameters as coolant temperature at the entrance to the reactor core, average coolant temperature and steam pressure in the secondary circuit. The studies were carried out under the condition that the reactor power was reduced to 80 % during the operation of one control program and increased to 100% of the power when another static program was used in reverse.

Transient analysis of a direct cycle nuclear heated gas turbine plant with nitrogen coolant

This paper investigates the thermodynamic cycle compatibility of combining a modified commercial gas turbine with a prismatic High Temperature Gas Reactor (HTGR) with a nitrogen coolant. In-addition the paper investigates the transient response of the combined reactor and turbine combination against operational power transients for a variety of control methodologies. The analysis methodology utilises turbine gas dynamics, lumped thermal mass and a point reactor kinetic model built within the Matlab and Simulink modelling environment. Design point data from commercial gas turbine data sheets provide the key turbine gas dynamic parameters enabling transient performance estimates of output power coolant mass flow and heat transfer properties of the direct cycle reactor plant. The methods permit simple assessment of a variety of currently available gas turbine products for use within a nitrogen cooled direct cycle prismatic HTGR. The combination of a Siemens SGT 600 gas turbine with a ∼ 45MWth prismatic HTGR is illustrated and considered to have potential as an overall plant combination. The transient analysis explored a novel control approach where characteristics of both inventory and turbine bypass control features were combined, delivering both fast and proportional power control within a single control system, whilst maintaining high part load system efficiency. Furthermore, when combined with passive reactivity control based on the core negative temperature coefficient, the control method was shown to reduce overall core thermal transients experienced during power level changes. The proposed design illustrates the potential for minimising development risk associated with the direct cycle HTGR through direct use of current commercial gas turbine products, whilst using negative temperature coefficients for reactivity control and maintaining a simple turbine control system design.

Analysis on short-term decay heat after shutdown during load-follow operation with seasonal and daily scenarios

For the future energy-mix policy for carbon neutrality, demand for the capability of load-follow operation has emerged in nuclear power plants in order to accommodate the intermittency of renewable energy. The short-term decay heat analysis is also required to evaluate the decay heat level varied by the power level change during the load-follow operation, which is a very important parameter in terms of short-term decay heat removal during a grace time. In this study, the short-term decay heat level for 10 days after the shutdown was evaluated for both seasonal and daily load-follow cases. Additionally, the nuclide-wise contribution to the accumulated decay heat for 10 days was analyzed for further understanding of the short-term decay heat behavior. The result showed that in the seasonal case, the decay heat level was mainly determined by the power level right before the shutdown and the amount of each nuclide was varied with the power variation due to the long variation interval of 90 days. Whereas, in the daily case, the decay heat level was strongly impacted by the average power level during operation and meaningful mass variations for those nuclides were not observed due to the short variation interval of 0.5 days.

Transient Modulation for the Step-Load-Change Process in a Dual-Bridge Series Resonant Converter

A phase-shifted dual-bridge series resonant DC-DC converter (DBSRC) is a competitive candidate for applications of an energy storage system. At the request of a step-load-change command such as the start-up and power-level change, the converter may suffer from large-amplitude transient oscillations due to improper transient modulation. Furthermore, the DC bias current and overshoot current/voltage in the resonant tank and transformer caused by oscillations may result in transformer saturation and poor dynamic performance. To solve these problems, two fast transient modulation (FTM) methods are proposed in this paper. First, based on the steady-state analysis of the converter with phase-shift control, the current and voltage trajectory of the resonant capacitor can be obtained. Then, the detailed principles of two FTM methods are explained for achieving a smooth transition. Through the adjustment of the durations of the adjacent switching intervals temporarily, the transient trajectory can be predicted and is expected to match the destination trajectory within one switching period. Consequently, the proposed FTM methods enable the converter to move from one steady state to another instantly and the step-load-change transition can be an overshoot-free procedure. Finally, both simulation and experimental tests prove that the two modulation methods can effectively eliminate DC bias current and overshoot current/voltage in the DBSRC transient process and obtain a fast transient response.

A Comprehensive Review on Wireless Capacitive Power Transfer Technology: Fundamentals and Applications

Capacitive power transfer (CPT) technology is becoming increasingly popular in various application areas. Due to its limitations, such as low frequency, low coupling capacitance, and the high voltage stress on metal plates, the studies on high power CPT applications fell behind previously. Therefore, the wideband gap (WBG) semiconductor devices and the compensation topologies are further adopted to tackle these limitations. The main purpose of the paper is to review CPT applications in terms of performance parameters, advantages, disadvantages, and also challenges. Initially, the basic principles of CPT technology are examined, which cover compensation topologies, coupler structures, transfer distance, power electronic components, and system control methods. Then, CPT applications are evaluated for performance parameters (i.e., power level, operation frequency, system efficiency, transfer distance) along with compensation types, inverter types, and coupler types. The applications are categorized into six main groups according to industrial topics as safety, consumer electronics, transport, electric machines, biomedical, and miscellaneous. Herein, power level changes from <inline-formula> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> to kW ranges, the operation frequency varies from 100s of kHz to 10s of MHz ranges as well. The maximum system efficiency is recorded as 97.1 &#x0025;. The transfer distance varies from <inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> range to 100s of mm ranges. The full-bridge inverter topology and four-plate coupler structure are noticeable in CPT applications. Finally, advantages, disadvantages, and challenges of CPT applications are evaluated in detail. This review is expected to serve as a reference for researchers who study on CPT systems and their applications.

Response to cyclophosphamide and rituximab therapy in idiopathic inflammatory myopathies: A single center experience

Aim of the workTo evaluate the clinical response to cyclophosphamide (CYC), and rituximab (RTX) following CYC regarding muscle power and creatine kinase (CK) level changes, and the ability to manage cardiac and bulbar affection in dermatomyositis (DM) and polymyositis (PM) patients. Patients and methodsTwenty two idiopathic inflammatory myopathies (IIM) patients: 14 (63.6%) DM and 8 (36.4%) PM were categorized into CYC group (n = 17) received only CYC, and RTX group received RTX following refractory CYC (n = 5). History taking and clinical examination were done, and Medical Research Council Sum Score (MRC-SS) and CK were evaluated at baseline visit, by end of monthly CYC, and 18 months after CYC or RTX. Improvement of cardiac affection or bulbar manifestations was checked. ResultsPatients were 16 females and 6 males (F:M 2.7:1) and mean age was 34.9 ± 14.9 years. The patients were followed up for 7.7 ± 4.3 years. MRC–SS increased in (CYC group) and in (RTX group) (p < 0.001, and p = 0.018 respectively). CK levels decreased significantly in CYC group (p < 0.001) but not in RTX group. MRC-SS changes in males, females, DM, PM patients were (p = 0.007, p < 0.001, p < 0.001, p = 0.006 respectively), and CK changes (p = 0.17, p < 0.001, p < 0.001, p = 0.006 respectively). The two DM cardiac patients and the three PM patients with bulbar manifestations in (RTX group) showed improvement in their extra-muscular manifestations. ConclusionCYC can be an effective drug in the treatment of IIM muscle affection. RTX may be promising for refractory myositis, cardiac and bulbar manifestations, so these patients should be a target for its early administration.

Analysis of Sound Power Level Changes Caused by Wheel with Flat Spot Using Numerical and Physical Experiment

Damage to the running surfaces of wheels on railways poses a threat to road safety. They can lead to accidents and disasters. Wheels with a flat spot are the biggest threat. The paper reviews problems that arise when wheels with a flat spot come into contact with a rail, and the methods of their detection and diagnosis. However, the known methods for their determination are still very complex and not precise enough. The research presented is based on previous theoretical studies, during which a simplified mathematical model of the normal force arising from the contact of a wheel with a flat spot with a rail, assuming that as a result of this, a change in sound power is caused was developed and theoretical calculations were performed. It theoretically determined wheel damage during rolling caused by wheel-induced changes in associated sound power, i.e., preliminary values of diagnostic parameters and applied methods. Although initial theoretical research already exists, there was a lack of physical experiments to support the validity of the results of the theoretical model. This work presents the original plan and methodology of the physical experiment performed. A physical experiment performed with the ATLAS LG system and sound pressure measuring equipment showed the suitability and applicability of the theoretical model for the determination of wheel damage.

Integrated neuromuscular fatigue analysis system for soldiers' load carriage trial using DWT

This research work addresses neuromuscular fatigue of soldiers using wearable sensors during load carriage trial. Ten healthy male soldiers participated in the experiment. EMG was recorded bilaterally from selected lower extremity muscles and EEG was recorded on the frontal cortex of the brain. Each subject was asked to run and/or march on the treadmill with and without load at 6.4 kmh−1 with inclination increased at every five minutes, until volitional exhaustion was reached. Feature extraction was performed using discrete wavelet transform on both signals. Results demonstrated significant changes in power levels at lower and middle frequency bands for EMG in most muscles during both unloaded and loaded conditions. However for EEG signals, significant changes of power distribution were observed at the frontal cortex during unloaded conditions only. Furthermore, through data visualisation, fatigue was detected at the muscle level first, before enforcing to send signals to the brain for decision making in order to stop the exercise.

Integrated neuromuscular fatigue analysis system for soldiers' load carriage trial using DWT

This research work addresses neuromuscular fatigue of soldiers using wearable sensors during load carriage trial. Ten healthy male soldiers participated in the experiment. EMG was recorded bilaterally from selected lower extremity muscles and EEG was recorded on the frontal cortex of the brain. Each subject was asked to run and/or march on the treadmill with and without load at 6.4 kmh−1 with inclination increased at every five minutes, until volitional exhaustion was reached. Feature extraction was performed using discrete wavelet transform on both signals. Results demonstrated significant changes in power levels at lower and middle frequency bands for EMG in most muscles during both unloaded and loaded conditions. However for EEG signals, significant changes of power distribution were observed at the frontal cortex during unloaded conditions only. Furthermore, through data visualisation, fatigue was detected at the muscle level first, before enforcing to send signals to the brain for decision making in order to stop the exercise.

Non-Intrusive Load Monitoring (NILM) for Energy Disaggregation Using Soft Computing Techniques

Non-intrusive load monitoring (NILM) has become an important subject of study, since it provides benefits to both consumers and utility companies. The analysis of smart meter signals is useful for identifying consumption patterns and user behaviors, in order to make predictions and optimizations to anticipate the use of electrical appliances at home. However, the problem with this kind of analysis rests in how to isolate individual appliances from an aggregated consumption signal. In this work, we propose an unsupervised disaggregation method based on a controlled dataset obtained using smart meters in a standard household. By using soft computing techniques, the proposed methodology can identify the behavior of each of the devices from aggregated consumption records. In the approach developed in this work, it is possible to detect changes in power levels and to build a box model, consisting of a sequence of rectangles of different heights (power) and widths (time), which is highly adaptable to the real-life working conditions of household appliances. The system was developed and tested using data collected at households in France and the UK (UK-domestic appliance-level electricity (DALE) dataset). The proposed analysis method serves as a basis to be applied to large amounts of data collected by distribution companies with smart meters.

Design and Analysis of Active Metamaterial Modulated by RF Power Level

In this paper, a radio frequency (RF)-power-modulated active metamaterial loaded with a nonlinear Schottky diode is presented. Its operating mode is a function of the incident power level. It is switched by a change in the operating state (i.e., on/off) of the Schottky diode, which is directly triggered by a change in the incident power level. For instance, when a low-power RF radiation is incident on the proposed metamaterial, the Schottky diode is turned off, and the metamaterial passes a 2 GHz signal in the pass-band mode. By contrast, when a high RF power is incident, the diode is turned on, and the metamaterial reflects all frequencies in the reflection mode. The proposed active metamaterial was analysed by performing numerical simulations for both low- and high-power modes, and the proposed concept was successfully demonstrated by circuit analysis, full-wave simulation, and experimental results.

Analysis and Design of a Resonant Power Converter With a Wide Input Voltage Range for AC/DC Applications

Resonant converter topologies have the ability to eliminate switching losses through zero-voltage switching (ZVS), making them well-suited for switching operation in the MHz frequency range. However, these types of converters are traditionally very sensitive to changes in input voltage and power level, making them unsuitable as power factor correcting ac–dc converters. This article presents a thorough analysis of the operation of a class DE converter in order to derive a set of conditions under which it can achieve a constant input impedance over a wide input-voltage range (60–325 Vdc) with a constant output voltage (450 Vdc) and, thus, be operated as a power factor correctional (PFC) converter, while maintaining ZVS across the full range. The operation is experimentally verified under dc–dc operation for different power levels at a series of input voltages within the specified range. The implemented prototype achieves conversion efficiencies of up to 94% and handles up to 105-W power at a switching frequency of 2 MHz and above, while achieving constant input impedance over the full input-voltage range, enabling its use as a power factor correcting converter.

Vortex Induced Aerodynamic Noise Generation from Wind Turbine Blades

An important aerodynamic noise source from lifting surface occurs from trailing edge of an aerofoil as found in wind turbine blades. In this work, semi-empirical method proposed by Brookes, Pope, Marcolini is applied to evaluate trailing edge bluntness vortex shedding noise source. For low Mach number flows (0.1884) and moderate to high chord Reynolds number, 4.73 × 105 - 3.35 × 106, change in sound power level was assessed for trailing edge thicknesses in terms of 0.1%, 0.5% and 1% chord lengths at wind speeds of 8 m/s, 10 m/s. For overall change of trailing edge thickness from 0.1% to 1% chord, an increase in noise levels up to 50 dB was found at low frequencies, while a decrease up to 30 dB was found between mid-band to high frequencies of spectra.

Simulating hydraulic interdependence between bridges along a river corridor under transient flood conditions

Structural alterations to bridges may result in unintended consequences up- or downstream, such as changes in discharge, velocity, stream power, and water levels. This work presents a framework and methodology to analyze interconnected bridge-stream interactions under flood conditions. Such analysis may help prioritize limited resources available for bridge and river rehabilitations, facilitate holistic design of bridges and better-informed cost/benefit analyses, and address stakeholder concerns raised in response to planned bridge and infrastructure alterations. A two-dimensional unsteady HEC-RAS hydraulic model of the Otter Creek between Rutland and Middlebury, VT is used to simulate the impact of individual structures on the bridge-stream network, as well as potential sensitivity to those impacts, during extreme flood events. The presence of a bridge and approach roadway may induce measurable changes in peak discharge throughout the entire 46 miles of modeled river. These may be by as much as 10% at adjacent structures, down to 1% at structures as far as six miles upstream and nine miles downstream. Depending on their characteristics, bridges and roadways may either attenuate or amplify peak flood flows up- and downstream, or have little to no effect at all, suggesting that there is no easily predictable impact, and that hydraulic modeling is necessary for such analysis on rivers. Alterations to structures that develop substantial backwaters may result in the most dramatic impacts to the network, which can be both positive and negative. Affected bridges may or may not be sensitive to these changes in discharge; structures that do not experience relief (e.g., roadway overtopping) may be most sensitive to any distant perturbations.

Changes in the Spectral Characteristics of the Electroencephalogram during Biocontrol of Heart Rate Variability Parameters in Healthy Subjects

Objectives. To assess changes in the spectral characteristics of the electroencephalogram (EEG) in humans during single sessions of biocontrol of hart rate variability parameters using biological feedback (BFB). Materials and Methods. A total of 150 adolescents aged 16–17 years were studied. Adolescents of the BFB group (n = 110) took part in biocontrol sessions to increase vagal influences on heart rate; the control group (n = 40) remained in the state of calm wakefulness. EEG recordings were made with the eyes closed before and after BFB training. EEG characteristics were studied in terms of changes in absolute power levels (μV2) in artifact-free trace segments in each frequency range. Results and conclusions. The ability of human subjects to change the activity of heart rate parameters determines the level of action on the functions of the central autonomic regulatory structures. This biocontrol method promotes improvements in cortical stability, with increases in α and decreases in β EEG activity. Brain activity synchronization processes during biocontrol were more clearly apparent in the right hemisphere, often involving the prefrontal areas.

Changes in connectivity and local synchrony after cognitive stimulation – Intracerebral EEG study

Electroencephalographic studies utilize event-related power decrease/increase in order to analyze changes of neuronal activity in a single EEG channel during cognitive tasks. Other analytical approaches draw on bivariate methods which evaluate connectivity between two EEG channels. Despite the fact that spatial mapping of combined results of power and connectivity analyses may be used to study the dynamics of neuronal activation patterns, they are normally evaluated separately as different phenomena. Here we show the evaluation of dynamic changes in linear correlation after cognitive stimulation together with changes in power levels in the same channel pairs. Our results demonstrate the temporal evolution of synchronization patterns across the whole brain with a focus on the anatomical structure of the hippocampus. We observed a pattern of local and distant synchrony during cognitive processing, occurring 500 ms after stimulus onset in approximately 1% of all channel pairs. We hypothesize that evaluation of changes in connectivity, together with dynamic changes in power levels, can help identify dominant structures in the process of mental activity after a certain type of cognitive task. This can possibly lead to better understanding of synchronization processes at the neuronal and systemic level.