Variable Speed Wind Research Articles

Mosquito swarms shear harden

Recently Cavagna et al. (Sci Rep 13(1): 8745, 2023) documented the swarming behaviors of laboratory-based Anopheles gambiae mosquitoes. Here key observations from this 3D-video tracking study are reproduced by a minimally structured (maximum entropy) stochastic trajectory model. The modelling shows that in contrast with midge swarms which are a form of collective behavior, unperturbed mosquito swarms are more like collections of individuals that independently circulate around a fixed location. The modelling predicts the observed response Anopheles gambiae mosquitoes in wild swarms to varying wind speeds (Butail et al. in J Med Entomol 50(3): 552–559, 2013). It is shown that this response can be attributed to shear hardening. This is because mosquitoes are found to be attracted to the centre of the swarm by an effective force that increases with increasing flight speed. Mosquitoes can therefore better resist the influence of environmental disturbances by increasing their flight speeds. This contrasts with other emergent mechanical-like properties of swarming which arise accidentally without a change in an individual’s behavior. The new results add to the growing realization that perturbations can drive swarms into more robust states.

The Mathematical Modeling and Performance of Sky Radiative Coolers

Sky radiative cooling is a kind of passive cooling technology that uses the “atmospheric window” to emit the object’s own heat to the low temperature of outer space; this technology has low energy consumption, no pollution, and other useful characteristics, so in recent years it has attracted widespread attention. The cooling effect of the sky radiative cooler is mainly affected by the constantly changing outdoor ambient temperature. In addition, the structure of the radiative cooler itself also means that its radiative cooling power undergoes obvious changes. Here, we utilized COMSOL simulation software to establish a numerical heat transfer model for radiative cooling, aimed at investigating the influencing factors on the sky radiative cooler and methods to enhance the structure of the radiative cooling. This study discusses outdoor ambient wind speed, the inlet flow rate of the cooler, installation angle of the cooler, and different cooler structures. Based on simulation results, it is observed that, for varying wind speeds, when the ambient radiation temperature is higher than the surface temperature of the cooler, a larger ambient wind speed leads to a poorer refrigeration effect. The maximum temperature difference in surface temperature at wind speeds of 0 m/s and 4 m/s is 0.59 °C. When the ambient temperature is lower than the surface temperature of the cooler, a smaller wind speed results in a greater net refrigeration power. The maximum temperature difference in this scenario is 0.32 °C. The net refrigeration power of the radiative cooler increases with an increase in water flow rate. As the water flow rate increases from 0 L/min to 5 L/min, the net refrigeration power increases from 25 W/m2 to 200 W/m2 and gradually stabilizes. Considering the radiative impact of the cooler on the surrounding environment, as the installation angle increases from 0° to 90°, the surface temperature of the cooler first increases and then decreases, reaching its highest temperature of 29.26 °C at 45°. The surface temperature of the cooler varies with the thickness of the air sandwich, increasing from 1 cm to 12 cm, and then decreasing. The lowest temperature of 23.4 °C is achieved at a thickness of 8 cm. The increase in the fin structure on the surface of the radiative cooler leads to a decrease in its refrigeration performance, and the difference between the inlet and outlet temperatures of the radiative cooler with a flat plate structure is always greater than that of the finned plate, and the difference in the average radiance is 23.52 W/m2. Finally, the energy-saving effect of the sky radiative cooling composite system is analyzed. Taking a typical small office building as an example, an energy consumption analysis model is set up, and the energy consumption of the composite system is simulated in four cities with different climates, using EnergyPlus software (version 8.6); the system’s power consumption is the largest in hot and humid climates. Compared with the traditional vapor-compression refrigeration system, the composite system reduces air conditioning power consumption by 25.7%, 32.5%, 37.1%, and 44.8% in Guangzhou, Shanghai, Jinan, and Shenyang, respectively. The main innovations of this paper include analyzing and studying the influence of the tilt angle change of the radiative plate on the refrigeration performance of the cooler and the relationship between the surrounding buildings, adding air sandwiches and ribs to the radiative cooler to analyze the influence of convective heat transfer on the refrigeration effect, which plays a guiding role in the design and research of the sky radiative cooler.

Analysis of heat transfer characteristics of sandwich cylindrical shell with an aerogel-metal-rubber composite core

Metal-rubber sandwich cylindrical shell displays a broad range of potential applications in the field of thermal insulation due to its advantages of lightweight, high-temperature stability, and superior high-temperature thermal insulation properties. To optimize the thermal insulation performance of a sandwich cylindrical shell with a metal-rubber core, this study proposes the idea of filling the pores of the metal-rubber with aerogel, thereby forming a composite structure of aerogel and metal-rubber (AMR). Through finite element analysis, the law of internal temperature changes in the AMR composite structure and the distribution laws of the velocity field, viscosity field, and pressure field of the sandwich cylindrical shell under varying wind speeds are investigated. These findings are further verified through heat transfer and forced convection tests. The results reveal that the thermal conductivity of the AMR composite structure at the same density is lower than that of the metal-rubber, and the thermal insulation performance of the AMR composite structure is directly proportional to its density. Meanwhile, through the analysis of forced convection heat transfer in the cylindrical shell, it is found that wind speed has a direct relationship with the pressure field, velocity field, and viscosity field. In addition, there is a relatively high viscosity and a low flow rate near the wall of the cylindrical shell, with a higher flow rate at the axis of the cylindrical shell. At the same wind speed, the temperature rise of the sandwich cylindrical shell shows a positive correlation with an increase in density, and the maximum stable temperature also increases correspondingly. Moreover, at the same density, the thermal conductivity demonstrates a negative correlation with increasing temperature.

Fuzzy Logic Energy Management Based on Wind Turbine for Standalone Application

Wind turbines (WT) offer valuable environmentally friendly energy solutions, particularly for electricity generation, owing to their renewable nature. These renewable energy systems (RESs) present an indispensable solution for sites that are not associated with the electrical grid. However, their intermittent power generation, which can be more or less than that required by the load, due to variable wind patterns, poses a challenge. To overcome these weaknesses, the integration of robustly controlled storage systems is a good proposal as it enhances the stability of standalone applications in terms of voltages and powers. In this paper, an intelligent supervisory power control system is developed to manage the different components of the renewable energy generator (REG). A fuzzy logic proportional–integral PI controller is also introduced, in the permanent magnet synchronous generator (PMSG) and the batteries, to better regulate energy, compared to a conventional PI controller. The main objective of this study is to introduce a new control strategy to satisfy the energy requirement of the load. The configuration of the suggested control methodology consists of a fuzzy logic supervisor (FLS) elaborated to manage energy flows, ensuring equilibrium between production and consumption amidst weather and load changes. The presented control method was applied to an autonomous wind battery station, showcasing its ability to maintain energy supply, minimize fluctuations, and enhance stability. Simulation results, executed in MATLAB/Simulink, confirm the effectiveness of the proposed system under various scenarios of wind speed variability and storage system state of charge.

Spatial contrasts in mid-Holocene dune activities in deserts of northern China: Results from PMIP4 simulations in comparison with geological data

Numerous studies have explored paleoenvironmental conditions in China's dune fields around the mid-Holocene (MH), ∼6000 calendar years ago, often based on individual paleosol-aeolian sand depositional sequences and local-scale landscape dynamics. So far, continent-scale modeling studies have only indirectly assessed dune activation and stabilization processes via changes in simulated precipitation, net precipitation (precipitation minus evaporation), and effective moisture (precipitation divided by evaporation). Here we conducted a comprehensive study using gridded data on potential evapotranspiration, precipitation, and surface wind velocity from 13 climate models participating in the Paleoclimate Modeling Intercomparison Project phases 4 (PMIP4) and compared the model results with geological records. Our evaluation of spatial patterns of dune activity in northern China around the MH reveals that the intensity of annual MH dune activity exhibited significant differences between the eastern and western parts of Chinese deserts compared to those of the preindustrial period (PI). Dune activity was significantly weaker in the eastern region, while in the western part, it was considerably stronger. The key drivers of this disparity were the distinct spatial variations in near-surface wind speed and effective moisture between the two regions. Compared with the optically stimulated luminescence ages of the paleosol-aeolian sand sedimentary sequences derived from a compilation of geological records from 88 sites across northern China, the model results suggest that the weakening of dune activity and the process of dune stabilization in eastern China around the MH were mainly attributed to a significant increase in effective moisture and a concurrent decrease in near-surface wind speed due to the intensified East Asian summer monsoon. Additionally, the weakening of westerlies in western China resulted in reduced effective moisture, contributing to increased sand availability for dune development and subsequent desert expansion.

Grid interface control of wind–solar generator in Hail region of Saudi Arabia using FOPI controller

This study investigates the performance of a wind–solar generator (WSG) in the Hail region of Kingdom of Saudi Arabia (KSA) with a fractional order PI controller (FOPI) applied to the grid connection line. The proposed hybrid generator consists of a wind turbine with a PMSM machine and a PV panel connected to a secondary distribution grid by a DC link, three-phase inverter, and an RL filter. The line currents injected into the grid and/or loads are controlled by calculating the output reference voltage of an inverter and by the reference active and reactive requested powers. For this purpose, control loops around the RL filter were developed with fractional-order proportional-integral (FOPI) controllers, and a comparison with classic PI controllers was made. The system was simulated using the MATLAB/Simulink software. The results showed that the generator satisfied the power demand under the climatic conditions of the Hail region. They also demonstrated the good performance of the proposed controllers, which had good tracking accuracy and robustness to variations in wind speed and power demanded by loads in a very short time. The FOPI controller exhibited faster dynamic response and less overshoot than the classic PI controller.

Optimal external opportunistic maintenance for wind turbines considering wind speed

ABSTRACT A novel optimal opportunistic maintenance strategy for wind turbines considering wind speed as a stochastic process is proposed in this paper. Under this strategy, periodic preventive maintenance is conducted to reduce the probability of downtime due to failure, whereas external opportunities are leveraged to reduce the cost of preventive maintenance. This combined maintenance approach can also reduce costs associated with the wind turbine lifecycle. The formulated expected costs per unit time considered two scenarios, i.e. regular operation and energy generation interruption, to obtain the optimal solution via a genetic algorithm. Furthermore, we illustrated the economic advantages of the proposed strategy by comparing various maintenance strategies, as well as a sensitivity analysis to determine the effects of the different parameters in the proposed model. Experimental results demonstrate that the proposed opportunistic maintenance strategy is more cost-effective for wind turbines than comparable methods, with an optimal solution that varies according to variations in wind speed.

Smoothing Intermittent Output Power in Grid-Connected Doubly Fed Induction Generator Wind Turbines with Li-Ion Batteries

Wind energy is an increasingly important renewable resource in today’s global energy landscape. However, it faces challenges due to the unpredictable nature of wind speeds, resulting in intermittent power generation. This intermittency can disrupt power grid stability when integrating doubly fed induction generators (DFIGs). To address this challenge, we propose integrating a Li-ion battery energy storage system (BESS) with the direct current (DC) link of grid-connected DFIGs to mitigate power fluctuations caused by variable wind speed conditions. Our approach entails meticulous battery modeling, sizing, and control methods, all tailored to match the required output power of DFIG wind turbines. To demonstrate how well our Li-ion battery solution works, we have developed a MATLAB/Simulink R2022a version model. This model enables us to compare situations with and without the Li-ion battery in various operating conditions, including steady-state and dynamic transient scenarios. We also designed a buck–boost bidirectional DC-DC converter controlled by a proportional integral controller for battery charging and discharging. The battery actively monitors the DC-link voltage of the DFIG wind turbine and dynamically adjusts its stored energy in response to the voltage level. Thus, DFIG wind turbines consistently generate 1.5 MW of active power, operating with a highly efficient power factor of 1.0, indicating there is no reactive power produced. Our simulation results confirm that Li-ion batteries effectively mitigate power fluctuations in grid-connected DFIG wind turbines. As a result, Li-ion batteries enhance grid power stability and quality by absorbing or releasing power to compensate for variations in wind energy production.

Large scale study on influence of biopolymer to mitigate wind induced sand erosion with durability analysis

The desertification is a serious threat that affects the sustainable agriculture, ecosystem, and economic progress of society. There is an urgent need for an environment friendly, cost-effective, durable, and practical approach to mitigate wind induced erosion. The present study introduces a novel approach through large scale testing using biopolymer, including durability analysis. The research investigates the influence of biopolymer namely Acacia gum (AG) to mitigate wind induced sand erosion. For the experimental setup, rectangular trays (180 cm × 60 cm × 15 cm) containing 11 erosion pins (three rows along the length, in a staggered way at equal spacing) have been filled with desert sand. Solutions have been prepared using biopolymer concentrations (1%, 2%, and 3%) mixed with water. The prepared solution was sprayed onto specimens and the treated samples were then left for air drying (7 and 28 days curing period). The study has been performed on summer days with an average temperature of 40 °C. After biotreatment, the specimens were examined in a wind tunnel at variable wind speeds of 6, 10, and 15 m/s to measure sand loss rate (SLR) for different wind intervals (i.e., 1, 2, 3, 4, and 5 min). Surface strengths were assessed using a pocket penetrometer. To check the durability of biotreated sand samples, 28 days curing period samples, with all biopolymer percentages have gone through 5 wetting and drying cycles (WDC). After the last WDC, samples were left again for 28 days and then experienced all tests. The minimum and maximum SLR for desert sand ranged from 17 kg/m² at 6 m/s and 1 min duration to 123 kg/m² at 15 m/s and 5 min duration respectively. Instead biotreated sand samples presented negligible SLR. Surface strength increased with increasing biopolymer concentration and a curing period. The maximum surface strength was 334.47 kPa recorded at 3% concentration during the curing period of 28 days. Further analysis involving SEM, EDX, and PXRD, confirmed sand particle bonding. For surface strength, 3% biopolymer concentration consistently produced positive outcomes, even after undergoing 5 WDC.

Fuzzy assisted optimal tilt control approach for LFC of renewable dominated micro-grid: A step towards grid decarbonization

Grid decarbonization is very crucial for the energy transition. The massive penetration of renewables in conventional power networks is the essential step for decarbonization but at the cost of complex control architecture. Due to the stochastic behaviour of renewables, load frequency control (LFC) is a very tedious task. This paper addresses the LFC issue in a standalone micro-grid (S-μG) via wild horse optimizer (WHO) assisted intelligent fuzzy tilt integral derivative with filter – one plus integral (FTIDF-(1 + I)) controller. The proposed S-μG consists of a solar photovoltaic (PV), wind turbine (WT) generator (WTG), and diesel engine generator (DEG) as power generating units and a flywheel as the energy storage unit (ESU). A nonlinear WTG model is used to extract the power from varying wind speeds, and a variable step size incremental conductance (V-InC) maximum power point (MPP) tracking (MPPT) technique is considered to harvest the optimal power from PV. To replicate the practical scenarios, nonlinearities of the governor, turbine, and flywheel are also considered in this work. The proposed intelligent WHO-FTIDF-(1 + I) controller can handle huge uncertainties and nonlinearities of the considered μG. FTIDF-(1 + I) controller prominence has been established over TIDF and FTIDF controllers. The effectiveness of WHO has been demonstrated over particle swarm optimization (PSO) and grey wolf optimization (GWO). From the obtained results, it is perceived that the reduction in maximum frequency deviation Δf with the proposed controller as compared to WHO-TIDF, WHO-FTIDF, PSO-FTIDF-(1 + I), and GWO-FTIDF-(1 + I) are 99.75%, 97.71%, 94.87% and 33.34% respectively. Finally, detailed robustness analysis, stability evaluation and real-power system validation via the IEEE 39 bus system of the proposed controller are also performed.

Influence of seasonal air density fluctuations on wind speed distribution in complex terrains in the context of energy yield

Given the variable nature of wind speed and the importance of accurately determining the energy that can be generated at a given site, understanding the wind speed at different time scales is crucial. In addition to differences within a very short period (i.e., hourly and daily), these changes are also pronounced throughout the seasons. They are affected by the atmospheric conditions and the terrain's complexity. Therefore, this study investigates the seasonal wind speed variability and its impact on the potential energy generation in a representative study case of Koznica, the mountainous region in Kosovo. The wind speed measurements campaign started in May 2019 and ended in April 2020; the measurements were made at a 10 min time scale. Ground measurements show that the wind direction is mainly northwest and southeast. Then, the wind speed and potential energy generation variability analysis were conducted for three different measurement heights. The results show that winter and spring have the highest potential wind energy capacity with an average speed of 6.7 m/s. In comparison, the average wind speed is 6.12 m/s. Potential energy generation for each season (i.e., spring, summer, autumn, and winter is as follows: 64,396.7, 22,040.3, 42,539.3, and 46,417.2 MWh/year, respectively, while the average capacity factor is 25%. Solution-oriented findings from this study might provide valuable insights to policymakers and investors regarding wind power energy exploration in Kosovo and other places with similar geo-climatic conditions.

Climate, trends and variability of extreme winds along the southwest coast of India

AbstractThe extreme wind climate and its trends and variability of the southwest coast of India, particularly the Kerala coast, are investigated using hourly reanalysis wind speeds for the period 1979–2021. The observed maximum wind speed and 99th percentile wind speed off Kerala coast are 21.0 and 11.3 m·s−1, respectively. The predominant direction of high wind speeds is in the SW–WNW sector, which accounts for 93.5% of the total high winds. Extreme wind speeds in this region are not due to tropical cyclones alone, but also due to seasonal high winds. Seasonally, the premonsoon and SW monsoon extreme winds are predominantly in the WSW–WNW directional sector, while postmonsoon strong winds are present in all directional sectors, but predominantly in the SSW–WNW sector, followed by the E–SSE sector. The 99th percentile wind speeds during premonsoon, SW monsoon and postmonsoon are 8.8, 12.3 and 8.9 m·s−1, respectively. A significant decreasing trend is observed in the 99th percentile wind speeds during 1979–2021, ranging from 3 to 6 cm·s−1·year−1 off Kerala coast. This is in contrast with global increasing extreme wind speeds, and it can be attributed to regional variability as well as weakening of the land–sea thermal gradients associated with rising surface temperature in the Arabian Sea in the light of global warming. In addition to the long‐term declining trend and monthly as well as seasonal features, distinct interannual variations are also noticed in the 99th percentile wind speeds. Analysis shows that the atmospheric teleconnections associated with El Niño–La Niña events and Indian Ocean Dipole have an important role in the variability of extreme wind speeds. The co‐occurrence of positive (negative) IOD with El Niño (La Niña) results in a sharp decline (increase) in extreme wind speeds. Significant decadal variations are also noticed in the 99th percentile wind speeds.

Impacts of land use on climate in the Taihu Basin based on WRF model

The impacts of land use on the climate in the Taihu Basin were quantitatively simulated using the mesoscale climate model named Weather Research and Forecasting (WRF) model. Results showed that (1) cities with large or increasing areas of construction land had considerably higher temperature increases than other regions; (2) coastal cities to the east of the Taihu Basin, such as Shanghai, Suzhou, Jiaxing, and Taizhou had the highest wind speeds, while cities far from the coast to the west, such as Nanjing, Hangzhou, and Huzhou, experienced reduced wind speeds; The main wind direction over the Taihu Lake was southeast, with an increase in wind speed variation, but wind speeds decreased in 2019; (3) Areas near water or with large water areas had lower temperatures, while areas near forests or construction sites had higher temperatures. Although the area of construction land increased as cities developed, the increase in temperature was not significant; (4) As urbanization accelerated, temperature differences in some areas gradually decreased, and overall temperatures increased. As urban development reached a certain level, the impact of increased construction land on temperature gradually decreased, but the region exhibited an overall high temperature, leading to a reduction in the urban heat island effect.

Multiscale Spatio‐Temporal Variations of Suspended Sediment Fronts in the Semi‐Enclosed Bohai Sea, China

AbstractSuspended sediment fronts (SSFs) significantly affect water quality, ecology, and geomorphological evolution of estuarine and coastal waters. Based on 10‐year suspended sediment concentration data derived from satellite images, the multiscale spatio‐temporal variability of SSFs in the Bohai Sea was studied. Frontal probability (FP) was used to quantify the intensity of frontal activity. The 10‐year averaged FP was higher near the coast and decreased with increasing offshore distance. The arc‐shaped distributions of FP near the Yellow River Estuary revealed two tidal shear frontal zones. In the eastern Bohai Sea, 13 finger‐shaped high‐FP areas reflected the spatial pattern and fine structures of tidal sand ridges. The complex topography and strong tidal dynamics provided the essential conditions for frontogenesis. The seasonality of frontal activity was dominantly regulated by the change in wind waves associated with monsoons and stratification. The direct or indirect effects of sediment discharges from the Yellow River and Liaohe River on seasonal and annual variations of frontal activity only existed within close proximity to the estuaries. Frontal activity generally showed an interannual weakening trend, especially in the Laizhou Bay (−0.27%/yr), while an opposite trend was identified in the Liaodong Bay (0.10%/yr). This phenomenon was related to the interannual variations of wind speeds. Meanwhile, wind speed anomalies caused by El Niño‐Southern Oscillation events could explain the significant interannual fluctuations in frontal activity such that, frontal activity was significantly enhanced (suppressed) when El Niño (La Niña) events occurred, especially during 2015–2016 (2017–2018).

Analysis of the effect of parametric uncertainty on dynamic performances of doubly fed induction generator-based wind energy conversion system

The wind, stochastic in nature, is one of the fastest-growing and most promising renewable energy resources in the entire world. Thus, this paper investigates the influence of parameter uncertainties upon a dynamic performance of a grid-tied Doubly-Fed Induction Generator (DFIG)-based Wind Energy Conversion System (WECS). The main uncertain parameters found in the study are mutual and rotor winding reactances which occurred due to the variation of the angular positions of the rotor caused by varying wind speeds. The variation in the wind speed caused the generator rotor speed to deviate between 25% and 150%. Consequently, the rotor winding reactance of DFIG changes from its nominal value of 1.31 mΩ to between 0.983 and −0.655 mΩ; and the mutual reactance from its nominal value of 0.941 Ω to between 0.758 and −0.4708 Ω. As a result, the stator and rotor winding voltages and currents of the DFIG are uncertain.

Optimal control of the electro-hydraulic actuator for variable pitch variable speed wind turbine: Performance enrichment

The wind energy generation system is complex because of varying wind speeds and its control systems to improve its ability of energy harvesting. This paper considers a hydraulic actuator-based variable-pitch angle control of a 1.5 MW wind turbine. The existing control systems of the pitch mechanism of the wind turbines are complex and bulky size. This study applied Genetic Algorithm based Proportional Integral Derivative Controller (GA-PID), Fractional Order Proportional Integral Derivative (FOPID), and Genetic Algorithm based Fractional Order Proportional Integral Derivative (GA-FOPID) controllers to adjust the pitch angle of the wind turbine blade. The performance of GA-FOPID, FOPID, and GA-PID controlled pitch angle is compared by considering different wind speeds. The GA-FOPID controller reduced the variation in mechanical power to 0.08% concerning the rated value and the variation in mechanical torque to 1.51% in comparison to the rated value. Therefore, the GA-FOPID controller shows better performance than the conventional PID.

Lyapunov based Control Strategy for DFIG based Wind Turbines to Enhance stability and Power

The Doubly Fed Induction Generators (DFIG) based wind turbine is fed with maximum power point tracking is presented in this paper in proposed technique the proportional coefficient tuned adaptively as per wind changes and compare with traditional approaches. This novel method uses three control laws to adjust the proportional gain adaptively to wind speed variations. The intended electrical torque is determined via feedback linearization in the first control law, which makes the assumption that the power capture coefficient and target rotor speed are instantly determined. The second control law uses a Lyapunov-based analysis to determine the power capture coefficient as per changes in wind speed, and the third control law establishes the required rotor speed. As a result of these control principles, the operating point of the turbine shifts in a direction that increases the power capture coefficient, leading the rotor speed to adaptively adjust in the direction of the desired speed. The proposed maximum power tracking method differentiates itself from the perturb-and-observe strategy by removing the need to include a dither or perturbation signal and reliably slipstram the trajectory of maximum power points even in the circumstance of a sudden change in wind velocity, which can cause the perturb-and-observe practice to fail.

Control of self-excited induction generator based wind turbine using current and voltage control approaches

The self-excited induction generator (SEIG) is widely applied in the wind energy conversion system (WECS) to enhance power generation. The power generation from WECS is varied in terms of varying wind speed. Hence, to improve the working of SEIG-based WECS, the multi-stage coati optimized proportional integral (CPI) fractional order proportional integral derivative (FOPID) controller is proposed in this work. The proposed coati optimized proportional integral - fractional order proportional integral derivative controls the SEIG’s grid side converter and generator side converter. The coati optimization algorithm optimizes the controller parameters of a proposed multi-state controller. The proposed CPI-FOPID controls both the voltage at the grid side converter and the current at a generator side converter. Moreover, the pitch angle of the wind turbine (WT) is controlled by the fuzzy-based tilt integral derivative (F-TID) controller. The proposed work will be implemented on the Matlab/Simulink platform, and the THD of 0.63% has proven the efficacy of the proposed methodology.

Multi-objective optimization strategy for parallel tuning of multiple fractional order controllers in a PMSG based WECS

In this paper, a novel multi-objective optimization strategy is proposed for the parallel tuning of six fractional order controllers used in regulation loops of a PMSG based wind energy conversion system connected to the electric grid. The nonlinear nature of the WECS components has made controllers design challenging. To enhance the transient response of system variables, Fractional Order Proportional Integral (FOPI) controllers are considered as they are more suitable for such nonlinear physical systems. The additional parameters introduced by FOPI are normally tuned using a single objective, multi-dimensional particle swarm optimization algorithm. However, the inter-dependence of regulation loops introduces additional complexity that is solved in this work using a multi-objective optimization strategy based on a succession of Single-Objective PSO and Multi-Objective PSO. A simulation study has been conducted in order to demonstrate the higher performance and superior tracking accuracy of the proposed multi-objective optimization strategy in variable wind speed operating conditions.

Stratospherically induced circulation changes under the extreme conditions of the no-Montreal-Protocol scenario

Abstract. The Montreal Protocol and its amendments (MPA) have been a huge success in preserving the stratospheric ozone layer from being destroyed by unabated chlorofluorocarbon (CFC) emissions. The phaseout of CFCs has not only prevented serious impacts on our health and climate, but also avoided strong alterations of atmospheric circulation patterns. With the Earth system model SOCOLv4, we study the dynamical and climatic impacts of a scenario with unabated CFC emissions by 2100, disentangling radiative and chemical (ozone-mediated) effects of CFCs. In the stratosphere, chemical effects of CFCs (i.e., the resulting ozone loss) are the main drivers of circulation changes, weakening wintertime polar vortices and speeding up the Brewer–Dobson circulation. These dynamical impacts during wintertime are due to low-latitude ozone depletion and the resulting reduction in the Equator-to-pole temperature gradient. Westerly winds in the lower stratosphere strengthen, which is for the Southern Hemisphere (SH) similar to the effects of the Antarctic ozone hole over the second half of the 20th century. Furthermore, the winter and spring stratospheric wind variability increases in the SH, whereas it decreases in summer and fall. This seasonal variation in wind speed in the stratosphere has substantial implications for the major modes of variability in the tropospheric circulation in the scenario without the MPA (No-MPA). We find coherent changes in the troposphere, such as patterns that are reminiscent of negative Southern and Northern Annular modes (SAM and NAM) and North Atlantic Oscillation (NAO) anomalies during seasons with a weakened vortex (winter and spring); the opposite occurs during seasons with strengthened westerlies in the lower stratosphere and troposphere (summer). In the troposphere, radiative heating by CFCs prevails throughout the year, shifting the SAM into a positive phase and canceling out the ozone-induced effects on the NAO, whereas the North Pacific sector shows an increase in the meridional sea-level pressure gradient as both CFC heating and ozone-induced effects reinforce each other there. Furthermore, global warming is amplified by 1.7 K with regionally up to a 12 K increase over eastern Canada and the western Arctic. Our study sheds light on the adverse effects of a non-adherence to the MPA on the global atmospheric circulation, uncovering the roles of the underlying physical mechanisms. In so doing, our study emphasizes the importance of the MPA for Earth's climate to avoid regional amplifications of negative climate impacts.