Changes In Power Output Research Articles

Slight power output manipulations around the maximal lactate steady state have a similar impact on fatigue in females and males.

Neuromuscular fatigue (NMF) and exercise performance are affected by exercise intensity and sex differences. However, whether slight changes in power output (PO) below and above the maximal lactate steady state (MLSS) impact NMF and subsequent performance (time to task failure, TTF) is unknown. This study compared NMF and TTF in females and males in response to exercise performed at MLSS, 10 W below (MLSS-10) and above (MLSS+10). Twenty participants (9 females) performed three 30-min constant-PO exercise bouts followed (1-min delay) by a TTF at 80% of the peak-PO. NMF was characterized by isometric maximal voluntary contractions (IMVC) and femoral nerve electrical stimulation of knee extensors [e.g., peak torque of potentiated high-frequency (Db100) and single twitch (TwPt)] before and immediately after the constant-PO and TTF bouts. IMVC declined less after MLSS-10 (-18 ± 10%) compared to MLSS (-26 ± 14%) and MLSS+10 (-31 ± 11%; all P < 0.05), and the Db100 decline was greater after MLSS+10 (-24 ± 14%) compared to the other intensities (MLSS-10: -15 ± 9%; MLSS: -18 ± 11%; all P < 0.05). Females showed smaller reductions, relative to baseline, in IMVC and TwPt compared to males after constant-PO bouts (all P < 0.05), this difference being not dependent on intensity. TTF was negatively impacted by increasing the PO in the constant-PO (P < 0.001), with no differences in end-exercise NMF (P > 0.05). Slight manipulations in PO around MLSS elicited great changes in the reduction of maximal voluntary force and impairments in contractile function. Although NMF was lower in females compared to males, the changes in PO around the MLSS impacted both sexes similarly.NEW & NOTEWORTHY It is unknown whether minimum changes in power output (PO) below and above the maximal lactate steady state (MLSS) affect neuromuscular fatigue (NMF) development in females and males. The present data showed that a decrease or increase of 10 W in PO in relation to MLSS elicited lower and greater impairments in contractile function, respectively. Even though females had less of an overall decline in NMF than males, similar exercise intensity-dependent response occurred independently of sex.

Design and control of hybrid energy microgrid system using renewable energy sources

Decentralized distributed generation technologies based on renewable energy resources like Photo Voltaic (PV) or/and Wind Turbine Generators (WTG) address the above barriers to large extent and are therefore considered as emerging alternate power solutions to telecommunication base stations. Three stand-alone SPV power systems using different storage technologies i.e. PV-Battery system, PV-Fuel Cell (FC) system and SPV-FC-Battery system are optimized, analysed, compared in paper. PV configurations with tracker also included. According simulation results observed that PV-Battery hybrid system with maximum power point tracker most economical solution. Cost and energy sensitivity with solar radiation data also analysed in this paper. Hybrid system modelling, designing of each component of Hybrid system is done in MATLAB sim power. In this paper, the hybrid system modelled is used for the different insulation, noticed the power output change with the insulation input change. Simulation is done for a step change of 1 kW for the PV-FC system. Different Maximum power point tracking algorithms are discussed, from these algorithms P&O method is implemented in MATLAB. Simulation done for one module and compared the result with actual result. This MPPT tracker used in the PV-FC, PV-Battery-FC hybrid systems for extracting the maximum power available from the PV system.

Modelling on Novel Cable Traction Power Supply System and Power Distribution Analysis

Novel cable traction power supply system (NCTPSS) is a kind of long distance co-phase traction power supply system (TPSS), it can effectively solve problems caused by train's passing through electrical phase separation and improve utilization rate of regenerative energy in system, which is an ideal traction power supply mode. However, its structure is relatively complex due to cable power supply pattern, and internal power flow distribution mechanism still needs further study. In order to establish train-network coupling power flow calculation model, in this paper, two-port network model of each system component is established at first, then equivalent solid circuit model of the system is built by external cascade strategy and tearing nodal method. Then, power flow, the change of traction transformer power output and network voltage are analyzed under the condition that trains work in traction and regenerative braking condition, based on actual train operation schedule. The research shows that the proposed model can accurately calculate and detailed reflect electrical characteristics of NCTPSS, traction transformer capacity is effectively decreased compared with that needed in existing TPSS; Regenerative power can feed back to entire cable traction network and be reused by traction trains with high utilization rate inside NCTPSS.

Smoothing control of wind power fluctuations with battery energy storage system of electric vehicles

With the rapid development of wind industry, its integration causes inevitable and rapid power fluctuations in the power grid. To promote the integration of wind power and investigate the energy storage capability of electric vehicles (EVs), a smoothing control strategy is proposed to smooth the wind power fluctuations considering the battery energy storage system of EVs (EESS). Based on a proposed maximum operation area of an individual EV considering its traveling behaviors and traveling comfort level, the response parameters are defined to describe the response characteristics of the EV aggregator (EVA). The EESS can operate as an energy storage system composed of several EVAs with different response parameters. A smoothing control strategy is then developed to smooth the wind power fluctuations with the EESS. Considering the power fluctuation rate and the response capability of the EESS, the required power change of each EVA in the EESS is determined in the smoothing control. Then the required power output change is allocated to individual EVs in the EVA with the developed SOC-adaptive method and the power output limits constrained by the maximum operation area of each EV. Comparative results are provided to validate the effectiveness of the proposed smoothing control strategy. The EESS is able to smooth the wind power fluctuations, and the power output limits and the traveling comfort levels of individual EVs are ensured with the SOC-adaptive method and the constraints from the maximum operation areas.

Positive Correlations between Short-Term and Average Long-Term Fluctuations in Wind Power Output

Wind power has been increasingly deployed in the last decade to decarbonize the electricity sector. Wind power output changes intermittently depending on weather conditions. In electrical power systems with high shares of variable renewable energy sources, such as wind power, system operators aim to respond flexibly to fluctuations in output. Here, we investigated very short-term fluctuations, short-term fluctuations (STFs), and long-term fluctuations (LTFs) in wind power output by analyzing historical output data for two northern and one southern balancing areas in Japan. We found a relationship between STFs and the average LTFs. The percentiles of the STFs in each month are approximated by linear functions of the monthly average LTFs. Furthermore, the absolute value of the slope of this function decreases with wind power capacity in the balancing area. The LTFs reflect the trend in wind power output. The results indicate that the flexibility required for power systems can be estimated based on wind power predictions. This finding could facilitate the design of the balancing market in Japan.

Формування прогнозного балансу електричної енергії України з використанням математичної моделі оптимізації режимів експлуатації генеруючих потужностей

To solve the actual task of assessing additional flexible generation needed to smooth variable renewable energies (VRE) disturbances in the Power Systems worldwide the original method for statistical processing of wind and solar PV generation variability data was proposed in the article. The proposed method allows processing the historical data of VRE day-by-day and hour-to-hour generation and assessing the levels of potential disturbances this type of generation could cause. These disturbances should be smoothened in the Power System by others, usually conventional generators at least to ensure grid stability and electricity quality. Currently, at the stage of the power systems starts transformation, the sources of power system flexibility basically are the power plants whose individual flexibility is characterized by three dimensions: adjustability, ramping and lead time. Lack of flexible generation causes VRE curtailments that negatively affect economic efficiency of such clean generation. From the other hand, the improvement of existing power plants flexibility requires an essential investments and time to retrofit them, and because of that the important question - what is the required level of power system flexibility is needed to smooth current and future VRE generation. The results of statistical data processing for wind and solar PV hour-by-hour power output changes allow accepting the hypothesis about the normal distribution of these data sets. The article presents the key parameters of theoretical normal distributions are calculated for wind and solar PV data sets for 2019 and 2020 as a whole, and also for winter and summer seasons, which allow obtaining a more precise assessment of variability levels for renewables, especially for solar PV hour-by-hour generation changes. The assessments obtained in the article also could be used as the first step for more efficient management of the electricity market, for instance, forecasting the required level of flexible generation or ancillary services market for intraday power system balancing. Keywords: variable renewable energy, power system, flexibility, generation profile, statistical data processing

Day-ahead Scheduling of Islanding Microgrids Based on Wind Power Forecast

Wind power, as the main energy source of the island microgrid, has uncertain output. Reasonable setting of TOU price can improve adaptability to changes in wind power output. Based on the time series characteristics of wind speed, the EWMA is used to predict the wind speed day-ahead. Then through the method of distribution superposition fitting and roulette, the day-ahead forecast data of wind power considering power fitting error is obtained. As a reference, a new TOU price division method based on wind power output is proposed. At the same time, P2G and energy storage devices were introduced into the cogeneration system to achieve Gas-electric transformation functions. Combined with the heating and electric demand response of the user side, comprehensively considering the mutual conversion relationship between multiple energies. On the premise of considering economy and environmental protection, the Gurobi solver is called by Yalmip to get the start-stop status of the powerside unit and the user-side unit.

Investigating Small Modular Reactor's Design Limits for Its Flexible Operation With Photovoltaic Generation in Microcommunities

Abstract Use of flexible and dispatchable generation from the small modular reactors (SMRs) in combination with the nondispatchable generation from renewable energy systems (RES) can be an effective alternative to pursue the mandate of replacing the fossil-fuel based electricity with the carbon-neutral energy systems in the remote microcommunities. This paper evaluates the feasibility of SMRs' flexible operations in microcommunities with the photovoltaic (PV) generation as a case study. Considering the design limits of SMRs for (a) the range of net change in electrical power output and (b) the ramp rates of net change in turbine power, a power system study is conducted to cover the three aspects of flexible operations, namely: (1) Planned load-following, (2) Unplanned load-following, and (3) Frequency regulation. A generic governor model in power system simulator for engineering (PSS/E), a power system transmission and planning software, is adapted to incorporate the operating limits of the reactor for the dynamic simulation. The multitimescale approach, combining (a) steady-state time-series power flow analysis and (b) dynamic simulations with high-resolution solar irradiation datasets, is proposed to assess the implications of SMR's design limits. The results obtained on an existing remote feeder with three sets of operating limits—namely, the conventional, advanced and extreme limits of ramp rates juxtapose the SMRs' performance, given the challenging operating conditions with PV generation in remote locations. The results indicate that the SMR under study can accommodate the highest permissible PV penetration obtained by the hosting capacity analysis of the feeder under the clear sky conditions. However, dynamic simulations with the extreme PV variabilities show that the PV penetration level should be further limited so that the maximum deviations in SMR power levels stay within 40% of its rated capacity. SMR provides adequate frequency support for the PV penetration of up to 50% of the feeder maximum demand in this study.

Stochastic Drift Counteraction Optimal Control of a Fuel Cell-Powered Small Unmanned Aerial Vehicle

This paper investigates optimal power management of a fuel cell hybrid small unmanned aerial vehicle (sUAV) from the perspective of endurance (time of flight) maximization in a stochastic environment. Stochastic drift counteraction optimal control is exploited to obtain an optimal policy for power management that coordinates the operation of the fuel cell and battery to maximize the expected flight time while accounting for the limits on the rate of change of fuel cell power output and the orientation dependence of fuel cell efficiency. The proposed power management strategy accounts for known statistics in transitions of propeller power and climb angle during the mission, but does not require the exact preview of their time histories. The optimal control policy is generated offline using value iterations implemented in Cython, demonstrating an order of magnitude speedup as compared to MATLAB. It is also shown that the value iterations can be further sped up using a discount factor, but at the cost of decreased performance. Simulation results for a 1.5 kg sUAV are reported that illustrate the optimal coordination between the fuel cell and the battery during aircraft maneuvers, including a turnpike in the battery state of charge (SOC) trajectory. As the fuel cell is not able to support fast changes in power output, the optimal policy is shown to charge the battery to the turnpike value if starting from a low initial SOC value. If starting from a high SOC value, the battery energy is used till a turnpike value of the SOC is reached with further discharge delayed to later in the flight. For the specific scenarios and simulated sUAV parameters considered, the results indicate the capability of up to 2.7 h of flight time.

Preliminary experiment and performance evaluation of a terrestrial solar thermoelectric generators under fluctuant solar radiation

The solar thermoelectric generator (STEG) is a promising alternative terrestrial solar power generation device due to its ability to utilize almost full solar spectrum. Many researches have been carried out to improve its efficiency. Some improved STEG has achieved remarkable efficiency in the laboratory. However, its performance in practical situations has been few studied, which limits its practical applications. In this work, the experimental investigation and performance evaluation of the terrestrial STEG system in typical days in East China are presented. Detailed changes in efficiencies and output power of the system are revealed. The results show that the performance of the system changes with the environment. The system can obtain the highest one-day electrical efficiency of 3.22% at 12:00 in the noon and thermal efficiency of 53% at 15:00 in the afternoon. The influences of solar irradiance, cooling water temperature and water cooling quality are discussed. The optimization methods of the system running in real environment are discussed and optimized to improve the average efficiency in the long run. The performances of this system and pure solar water heating system without TE modules are compared and the details are presented. The hybrid system has a higher comprehensive performance and lower thermal performance than the pure solar water heating system. This work provides a valuable reference for the design and optimization of STEG running in real environment.

Probability box theory-based uncertain power flow calculation for power system with wind power

Abstract The uncertainty of wind speed may lead to the deviation and change of wind power output, which influences the stability of wind farm. Therefore, in this paper, a probability box (p-box) based uncertain power flow model for wind power is proposed, which initially introduces p-box to power flow calculation. A probabilistic interval power flow model with both probability and interval is established. Firstly, the drift interval of wind speed is obtained and its p-box model is established by analyzing the distribution of wind speed. Secondly, the wind power output p-box is derived from the wind speed p-box based on the relationship between wind power output and wind speed, then the p-box of wind power output is discretized and introduced into the power flow equation to obtain the power flow p-box model. Finally, Newton–Raphson method is used to solve the power flow p-box model. Experiments on data collected from a wind farm (running standard IEEE30-bus test system) in Inner Mongolia demonstrate that our method is more effective and accurate than the traditional Monte Carlo simulation (MCS) and classical interval power flow (IPF) method.

Numerical simulation of the effect of chimney configuration on the performance of a solar chimney power plant

Previous studies have shown that the crosswind reduces the output power of a SCPP (solar chimney power plant) with the deflection of the plume at the exit and separation of wind flow there at the downstream. The present numerical investigation was focused on the effect of the stack configuration on the performance of a SCPP. In this paper, the SCPP of the prototype in Manzanares was simulated, where the Boussinesq approximation was used for solving the continuity, Navier–Stokes and energy equations by the standard k-epsilon turbulence model in finite volume method. Governing parameters are taken as oblique angles from 27° to 45° and wind velocity from 0 to 10 m s−1. Investigation revealed that by changing the stack configuration, the performance of the SCPP could be improved. Numerical simulation of the conventional chimney was compared with the simulation data of the proposed altered chimney geometry (outlet bevel cutting) and observed that the throttling effect on the outlet of the chimney could be reduced. It was noticed that by changing the chimney oblique angle from 27° to 45°, the efficiency of the power plant was dropped. Further, the results illustrated that the oblique angle relies on the wind velocity and it needs to increase with the increase in the wind velocity to obtain a reasonable change in power output. The present investigation was further enhanced to incorporate a comparison of solar chimney power output in two cities (Kuala Lumpur and Kerman) for a better understanding of the effect of environment on constructing the solar tower power plant. The result shows that Kuala Lumpur is appropriated for the installation of SCPP although, the Kerman is suitable too, but the wind velocity in that city is higher than that in Kuala Lumpur.

Research on the Influence of Yaw Control on Wind Turbine Performance under Wake Effect

The wake effect causes power loss and severely reduces the power generation capacity of the wind farm. In order to reduce the impact of wakes, the current main method is to optimize the layout of wind farms, which is unrealistic for the completed wind farms. In contrast, yaw control is used to offset the wake, which minimizes the impact of wakes between WTs (Wind Turbines), thereby increasing the generating capacity of the WTs. In this paper, fluent software is used to simulate the effect of wake on the output power of the downwind WT in two tandem WTs, when the upstream WT yaws at different angles. By analyzing the change of the total output power after yaw, it is concluded that the total output power reaches the maximum when the upstream WT yaws 25°.

Characterisation of intra-hourly wind power ramps at the wind farm scale and associated processes

Abstract. One of the main factors contributing to wind power forecast inaccuracies is the occurrence of large changes in wind power output over a short amount of time, also called “ramp events”. In this paper, we assess the behaviour and causality of 1183 ramp events at a large wind farm site located in Victoria (southeast Australia). We address the relative importance of primary engineering and meteorological processes inducing ramps through an automatic ramp categorisation scheme. Ramp features such as ramp amplitude, shape, diurnal cycle and seasonality are further discussed, and several case studies are presented. It is shown that ramps at the study site are mostly associated with frontal activity (46 %) and that wind power fluctuations tend to plateau before and after the ramps. The research further demonstrates the wide range of temporal scales and behaviours inherent to intra-hourly wind power ramps at the wind farm scale.

Performance of PV modules using co-extruded backsheets based on polypropylene

Due to the general price pressure PV modules experienced in the last decade, a variety of alternative polymer materials and new backsheet designs were developed and introduced into the market, amongst others also extruded backsheets based on polypropylene (PP). The production of co-extruded films represents a backward integration of backsheet manufacturers, allowing for easy material and design modifications regarding additive formulation, fillers and geometry. The main objective of this paper was to describe the influence of the special properties of PP-based backsheets on the performance and reliability of PV modules. The higher reflectance of the PP backsheet compared to a reference polyester (PET) based laminate led to an increase in power output between 1.5 and 2.5%. Test modules using PP and PET backsheets were exposed to 3000 h of damp heat testing. No changes in power output for either of the test modules was observed. However, the selective permeation properties of PP backsheets prevent humidity from entering the module (similarly to PET based backsheets) but allow for significantly higher diffusion of acetic acid out of the PV module. Therefore, in contrast to test modules using Ethylene Vinyl Acetate (EVA) encapsulants and PET backsheets, no silver grid corrosion was observed for modules using PP backsheets. Co-extruded backsheets based on PP show great potential to be a valid replacement of standard PET based backsheets in PV modules. On the one hand, the PP backsheet so far proved excellent stability, exhibiting no severe material degradation after extended exposure to temperature, humidity and irradiation. On the other hand, its improved functional properties (optical properties; selective permeability) lead to increased performance and improved long-term stability of the tested PV modules.

Mechanochemical properties of human myosin-1C are modulated by isoform-specific differences in the N-terminal extension

Myosin-1C is a single-headed, short-tailed member of the myosin class I subfamily that supports a variety of actin-based functions in the cytosol and nucleus. In vertebrates, alternative splicing of the MYO1C gene leads to the production of three isoforms, myosin-1C0, myosin-1C16, and myosin-1C35, that carry N-terminal extensions of different lengths. However, it is not clear how these extensions affect the chemomechanical coupling of human myosin-1C isoforms. Here, we report on the motor activity of the different myosin-1C isoforms measuring the unloaded velocities of constructs lacking the C-terminal lipid-binding domain on nitrocellulose-coated glass surfaces and full-length constructs on reconstituted, supported lipid bilayers. The higher yields of purified proteins obtained with constructs lacking the lipid-binding domain allowed a detailed characterization of the individual kinetic steps of human myosin-1C isoforms in their productive interaction with nucleotides and filamentous actin. Isoform-specific differences include 18-fold changes in the maximum power output per myosin-1C motor and 4-fold changes in the velocity and the resistive force at which maximum power output occurs. Our results support a model in which the isoform-specific N-terminal extensions affect chemomechanical coupling by combined steric and allosteric effects, thereby reducing both the length of the working stroke and the rate of ADP release in the absence of external loads by a factor of 2 for myosin-1C35. As the large change in maximum power output shows, the functional differences between the isoforms are further amplified by the presence of external loads.

Подавление дрейфа рабочей точки интегрально-оптических схем на основе ниобата лития

This work is devoted to the study of the drift of the operating point of integrated-optical circuits based on proton-exchange waveguides in lithium niobate crystal with a recovered structure of the near-surface layer. Recovered of the damaged near-surface layer of lithium niobate wafer was carried out using pre-annealing at temperature of 500 °C. Drift of operating point is characterized by a constant change in the optical output power of the integrated-optical circuits when a bias voltage is applied to the electrodes or temperature changes. Recovered of the damaged near-surface layer of lithium niobate wafer leads to a decrease in the short-term and long-term drifts of the operating point of integrated-optical circuits. Crystal structure factor was investigated on the drift of operating point of integrated-optical circuits based on lithium niobate crystal.

Ultra-short-term PV Power Forecasting Based on Cloud Image Modeling

Due to the impact of many local sudden changes in photovoltaic (PV) output power, its ultra-short-term forecasting is facing great challenges. In a time scale of 1 to 2 minutes, the generation, movement, and ablation of clouds in the sky are the main factors that affect the output power. Therefore, a prediction method based on cloud images is proposed for ultra-short-term prediction of PV output power. First, apply image processing technology to extract image features that affect the changes in PV output power, including cloud coverage rate, direct sunlight rate, and image brightness; second, calculate the extraterrestrial irradiation and air mass at each time point; finally, use the above features as input factors, and use PV output power output data, and a long short-term memory network (LSTM) is used to construct a PV power prediction model to achieve ultra-short-term forecasting of PV output power.

Turbulent Flow of Water-Based Optimization Using New Objective Function for Parameter Extraction of Six Photovoltaic Models

With the development of new energy power systems, the estimation of the parameters of photovoltaic (PV) models has become increasingly important. Weather changes are random; therefore, the changes in the PV output power are periodic and nonlinear. Traditional power prediction methods are based on linearity, and relying only on a time series is not feasible. Consequently, metaheuristic algorithms have received considerable attention to extract the parameters of solar cell models and achieve excellent performance. In this study, the Turbulent Flow of Water-based Optimization (TFWO) is used to estimate the parameters of three traditional solar cell models, namely, Single-Diode Solar Cell Model (SDSCM), Double-Diode Solar Cell Model (DDSCM), and Three-Diode Solar Cell Model (TDSCM), in addition to three modified solar cell models, namely, modified SDSCM (MSDSCM), modified DDSCM (MDDSCM), and modified TDSCM (MTDSCM). Moreover, a polynomial equation of five degrees for the sum of squared errors (PE5DSSE) between the measured and calculated currents was used as a new objective function for extracting the parameters of the solar cell models. The proposed objective function delivered improved prediction accuracy than common objective functions. Experimental results revealed the effectiveness of TFWO compared with six counterparts, namely, “Tunicate Swarm Algorithm (TSA), Grey wolf optimizer (GWO), modified particle swarm optimization (MPSO), Cuckoo Search algorithm (CSA), Moth flame optimizer (MFO) and Teaching Learning based optimization algorithm (TLBO),) for all the traditional and modified solar cell models based on the optimal parameters extracted using best PE5DSSE values.

Study of Renewable Energy Penetration on a Benchmark Generation and Transmission System

Significant changes in conventional generator operation and transmission system planning will be required to accommodate increasing solar photovoltaic (PV) penetration. There is a limit to the maximum amount of solar that can be connected in a service area without the need for significant upgrades to the existing generation and transmission infrastructure. This study proposes a framework for analyzing the impact of increasing solar penetration on generation and transmission networks while considering the responses of conventional generators to changes in solar PV output power. Contrary to traditional approaches in which it is assumed that generation can always match demand, this framework employs a detailed minute-to-minute (M-M) dispatch model capable of capturing the impact of renewable intermittency and estimating the over- and under-generation dispatch scenarios due to solar volatility and surplus generation. The impact of high solar PV penetration was evaluated on a modified benchmark model, which includes generators with defined characteristics including unit ramp rates, heat rates, operation cost curves, and minimum and maximum generation limits. The PV hosting capacity, defined as the maximum solar PV penetration the system can support without substantial generation imbalances, transmission bus voltage, or thermal violation was estimated for the example transmission circuit considered. The results of the study indicate that increasing solar penetration may lead to a substantial increase in generation imbalances and the maximum solar PV system that can be connected to a transmission circuit varies based on the point of interconnection, load, and the connected generator specifications and responses.