Load Adjustment Research Articles

Power coefficient measurements of a novel vertical axis wind turbine

AbstractWind tunnel experiments were performed to evaluate the power coefficients of three vertical axis wind turbines (VAWTs), namely, (a) conventional VAWT (two‐bladed troposkien shape), (b) novel 50% shifted troposkien shape‐vertical axis wind turbine (50% STS‐VAWT), and (c) novel 100% STS‐VAWT. All turbines had the same height, swept area, and NACA0015 airfoil with the same chord length. During the power coefficient measurements for each one of the turbines, the wind tunnel velocity was varied while the turbine rotation was kept constant through rheostatic load adjustment. Two different turbine rotations were used (600 rpm and 700 rpm). The resulting tip speed ratios (TSRs) ranged from approximately 2 to 6 in the current investigation. Both the power coefficients and the tip speed ratios were corrected against wind tunnel blockage effects. The 50% STS‐VAWT model showed an overall better aerodynamic performance (both corrected and uncorrected power coefficients) when compared against the other two configurations, likely due to a combination of (a) power generation increased due to blade‐wake interaction (BWI) reductions and (b) power generation capacity related to the blade length of each turbine.

The Development of the Physiological Adjustment of Physical Loads and Its Impact on the Circulatory System and the Skills of Football Players

Summary This research was focused on the important question, what is the effect of the development of physiological adjustment of the physical load on the respiratory system and the performance of the skills of football players. In addition we tried to comfirm the relationship between the physical qualities and the performance of the skills. We have applied the experimental approach which best suits to this type of question. Proposing a program based on the physiological adjustment of the respiratory system, we applied the approach to a sample of twenty players (table 3), which were a deliberate sample divided into experimental and control, during the general physical preparation. The results confirmed that there are statistically significant differences between the pre-test and post-test of the experimental sample in both the respiratory system tests and the functional performance tests, in addition to statistical differences between the control and experimental groupe in the post-test.

Analysis of the Day-ahead Deviation Plan and Research on the Real-time Scheduling of Photovoltaic Greenhouses Based on Exergy Theory

For the correction problem of day-ahead plan deviation caused by energy prediction deviation in day-ahead scheduling stage of photovoltaic greenhouses, an exergy analysis method is used to propose the deviation model of heat required for photovoltaic greenhouses. Based on the deviation model, a real-time optimization scheduling model is established. The deviation model not only considers the non-negligible exergy loss during heating process of pipes, but also considers the difference between heat and thermal exergy affected by the actual indoor temperature. The goal of the real-time scheduling model is to minimize the absolute value of the difference between the energy supply and demand prediction deviation to be corrected and the adjustment of multi-form energy storage and electric loads, so that develop the real-time adjustment plan of energy storage and electric loads. The analysis results of the actual photovoltaic greenhouse show that of the heat required by a greenhouse based on the exergy theory calculation, the exergy loss of the heating process accounts for about 10%–20% of the total thermal exergy required and it cannot be ignored, so the calculation results can reflect the actual heat required more accurately and the greenhouse temperature is more suitable for plant growth. Moreover, the proposed real-time scheduling model can correct the deviation of the day-ahead plan and improve local consumption. The promotion ratio can reach 7%. Finally, the farmers’ electricity purchases cost is reduced. Thereby the effectiveness of the proposed heat deviation model and real-time scheduling model is verified.

Operation Optimization of Multi-District Integrated Energy System Considering Flexible Demand Response of Electric and Thermal Loads

Multi-district integrated energy system (IES) can make full use of the complementary characteristics of district power and thermal system, and loads in different districts. It can improve the flexibility and economy of system operation, which has a good development prospect. Firstly, based on the general energy transfer model of the district heating network (DHN), the DHN system is described by the basic equations of the heating network and nodes considering the characteristics of the transmission time delay and heat loss in pipelines. A coupling model of DHN and multi-district IES is established. Secondly, the flexible demand response (FDR) model of electric and thermal loads is established. The load characteristics of each district in IES are studied. A shiftable load model based on the electric quantity balance is constructed. Considering the flexibility of the heat demand, a thermal load adjustment model based on the comfort constraint is constructed to make the thermal load elastic and controllable in time and space. Finally, a mixed integer linear programming (MILP) model for operation optimization of multi-district IES with the DHN considering the FDR of electric and thermal loads is established based on the supply and demand sides. The result shows that the proposed model makes full use of the complementary characteristics of electric and thermal loads in different districts. It realizes the coordinated distribution of thermal energy among different districts and improves the efficiency of thermal energy utilization through the DHN. FDR effectively reduces the peak-valley difference of loads. It further reduces the total operating cost by the coordinated operation of the DHN and multi-district IES.

Based on the comparison and analysis of the economic characteristics of transformers in an operating substation

The technical parameters of transformer are the basic data for analyzing and calculating the comparative analysis of transformer economic characteristics, The comparative analysis of transformer economic characteristics is to seek for reducing transformer active power and improving its operating efficiency, That is to reduce the transformer loss rate, And reduce the reactive power loss of the transformer. The active power loss, reactive power loss and integrated power loss of transformer are calculated. The quantitative calculation formula of economic operation mode of transformer in substation is obtained through analysis, The economic operation mode arrangement and load adjustment can be carried out for the transformer of a certain substation, The purpose of economic operation of transformer and reduction of network loss can be achieved.

Improving the accuracy of calculations of electrical loads for industrial enterprises

Nowadays many enterprises of the mineral resource complex install modern and energy-efficient equipment. By the way nobody takes into account that it influences the correctness of the electrical loads calculation. The aim of this study is to determine the necessity of adjustment of the electrical loads of the calculation method in order to avoid an unjustified overestimation of power consumption, which affects the reliability of the whole system. Conducted analysis of the difference between reference and actual values of electrical loads calculation shows a discrepancy of more than 25%. This suggests that reliable determination of power consumption at the initial design stages allows one to create an efficient power supply system.

Research and Implementation of Generator Unit’s Load Drop Under Over-frequency

In the case of power interconnection faults such as power lockout, the large-scale power transfer will have a great impact on the stability of the the sending end and receiving end power grid. According to the load regulation demand under the large-scale power gap of the power grid, combined with the adjustment capacity of the thermal power unit, the load target value and the load adjustment rate of the unit are real-time dynamically adjusted with the amplitude change of the grid frequency. The frequency difference is used to reduce the peak frequency of the grid and avoid the occurrence of high-frequency generator-shedding.

Data‐driven control for combustion process of circulating fluidised bed boiler

Owing to the advantages of burning low-quality coal (coal slime and coal gangue), furnace desulfurisation, low N O x emission and deep load adjustment, the circulating fluidised bed (CFB) combustion technology becomes one of the few fossil fuel utilisation technologies funded continuously by the Chinese government. However, compared with the pulverised coal boiler, the combustion process of CFB boiler is more complicated because of the larger time delay, significant uncertainty and more coupled variables. In this study, a data-driven proportional–integral-derivative (DD-PID) control strategy is presented for the combustion control of CFB boiler to improve the operating performance under full operating conditions. By analysing the running mechanism of combustion process, an inverse decoupler is introduced to transfer the combustion object to the generalised controlled object, which has relatively independent input–output relationship. After that, a normative procedure of DD-PID, including PID-parameter database establishment, information-vector neighbourhood selection, active PID-parameter determination, database update, and redundant vector deletion, is given. Finally, a series of case study, including numerical tests applied to the proposed combustion model and application test employed on 330 MW CFB simulation platform proves the feasibility of DD-PID control strategy.

Predicting cognitive load in acquisition of programming abilities

In this paper, we propose a method to predict cognitive load and its factors affecting the learning efficiency in programming learning from the learning behavior of learners. Generally, since the concepts of programming are difficult for learners, some of them suffer inappropriate cognitive load to understand them. Although teachers must keep cognitive load of such learners appropriate, it is difficult for them to find learners who has inappropriate cognitive load from a large number of learners. To find learners with inappropriate cognitive load, we construct models with the random forest algorithm, using learning behavior collected from learners solving fill-in-the-blank tests. An experiment shows the models can detect cognitive load for IL and GL along with their factors. Teachers must address adjustment of cognitive load of learners. This result clarifies the learning factors affecting cognitive load of learners, which enables teachers to address the adjustment with small burdens.

Analysis and optimization of frequency modulation strategy for hydropower units

Analysis the deficiencies of typical control strategies for AGC regulation and primary frequency regulation on conventional hydropower units. The logical relationship between primary frequency regulation and AGC is optimized. A new regulation method is proposed and applied in a hydropower plant. Practice shows that the method can avoid contradiction between AGC load adjustment and primary frequency modulation, and improve the frequency modulation performance of the unit. The optimization finally satisfy the requirements of power grid assessment.

Studies of thermal deformation and shape control of a space planar phased array antenna

Large planar phased array antenna in space will inevitably occur deformation due to the space thermal environment, which could severely influence the pointing accuracy of the antenna. This paper focuses on the studies of thermal load and shape adjustment method of a planar phased array antenna structure. The finite element method is adopted both to develop the structural model and to obtain the steady temperature field of the antenna structure, based on which a novel shape adjustment method that utilizes cables as actuators is proposed. This method transforms the control problem into the optimization problem of the actuators placement. The optimal placements of actuators and the corresponding control forces are determined by using discrete PSO method and quadratic optimization method. A 100 meter scale antenna structure is presented as example to validate the effectiveness of the proposed method numerically. Simulation results indicate that this method could successfully control the thermally induced deformation of the structure and maintain antenna's shape accuracy.

Study on reduction mechanism of Fe2O3 by NH3 under SNCR condition

Amino compounds were injected into a boiler at high-temperature area usually to realized De-NOx. However, amino compounds were highly corrosive. The metal tube skin of stage III superheater in a medium temperature separation circulating fluidized bed boiler (MTS-CFBB) was investigated to verify the corrosion effect of amino compounds on the boiler tube wall. The sodium salt which was found in the inner layer of the metal tube skin indicated that large area cracking occurred at the metal tube during the operation process; and further indicated that the corrosion rate of the tube wall was speedy. Meanwhile, the tube furnace experimental system and the reaction equations module in HSC Chemistry 6.0 were used to obtain the reduction properties of NH3 on Fe2O3 at high temperature. The weight loss rate of Fe2O3 under N2-NH3 atmosphere increased from 3.3 wt% to 5.5 wt%, when the temperature rose from 600 °C to 900 °C, and the weight loss rate of samples did not increase any more with the temperature rising to 1000 °C. The injected NH3 reduced the Fe3O4 to form FeO quickly at 810 °C. With the thermal stress caused by the boiler load adjustment and start up or shut down, the looser FeO formed at the interior of tubes, and then, the different expansion coefficient of Fe based compounds led to the extensive cracking. In summary, NH3 generated by SNCR was the main reason for corrosion happened on the tubes at high-temperature.

The Novel Rotor Flux Estimation Scheme Based on the Induction Motor Mathematical Model Including Rotor Deep-Bar Effect

During torque transients, rotor electromagnetic parameters of an induction motor (IM) vary due to the rotor deep-bar effect. The accurate representation of rotor electromagnetic parameter variability by an adopted IM mathematical model is crucial for a precise estimation of the rotor flux space vector. An imprecise estimation of the rotor flux phase angle leads to incorrect decoupling of electromagnetic torque control and rotor flux amplitude regulation which in turn, causes deterioration in field-oriented control of IM drives. Variability of rotor electromagnetic parameters resulting from the rotor deep-bar effect can be modeled by the IM mathematical model with rotor multi-loop representation. This paper presents a study leading to define the unique rotor flux space vector on the basis of the IM mathematical model with rotor two-terminal network representation. The novel rotor flux estimation scheme was validated with the laboratory test bench employing the IM of type Sg 132S-4 with two variants of rotor construction: a squirrel-cage rotor and a solid rotor manufactured from magnetic material S235JR. The accuracy verification of the rotor flux estimation was performed in a slip frequency range corresponding to the IM load adjustment range up to 1.30 of the stator rated current. This study proved the correct operation of the developed rotor flux estimation scheme and its robustness against electromagnetic parameter variability resulting from the rotor deep-bar effect in the considered slip frequency range.

Resting Cardiac Vagal Tone is Associated with Long-Term Frustration Level of Mental Workload: Ultra-short Term Recording Reliability

Excessive mental workload represent a critical risk factor for workplace accidents. Heart rate variability (HRV) is a non-invasive low cost electrophysiological autonomic biomarker related to emotional and cognitive regulation. Several studies report that mental overload impairs parasympathetic-mediated HRV indices (e.g. rMSSD). However, the influence of resting state HRV as a predictor of long-term mental workload impairments remains unknown. Thirty participants (22 males; 8 females) had their HRV measured (5-min period) before performing the number search task. After the task, the mental load was accessed by the NASA-TLX questionnaire. A simple linear regression model between HRV and NASA-TLX dimensions showed that resting state rMSSD is associated to physical demand (ND-2, R2 = 0.143, p = 0.03) and frustration level (ND-6, R2 = 0.175, p = 0.02) dimensions of mental workload. The comparison between 1 and 5-min epochs suggests that regression models remain reliable even using the ultra-short term HRV (< 1min) recording values (R2 values from 0.11 to 0.15 for ND-2 and R2 values from 0.16 to 0.19 for ND-6). These results suggest that resting state HRV is associated to long-term effects of mental workload on physical and emotional demands. In addition, the ultra-short term HRV indices remains reliable to assess ND-2 and ND-6 dimensions of mental workload when compared to gold-standard time interval (> 5min). The resting state cardiac autonomic tone assessment optimizes the physiological approach with a quick, non-invasive and low-cost assessment that can provide insights about mental load adjustments to prevent work-related accidents.

Research on an EV Dynamic Wireless Charging Control Method Adapting to Speed Change

In order to solve the problem of the electric vehicle (EV) charging amount fluctuation caused by the variation of driving speed during dynamic wireless charging, this paper proposes an EV dynamic wireless charging control method adapting to speed change. Firstly, a dynamic wireless charging model based on a long-track transmitting coil is established, and the expression of the charging power of each load under multi-load situation is obtained. Secondly, the influence of the EV charging number and maximum driving speed on the range of system parameters is studied. Subsequently, the method for determining the load resistance value according to the driving speed under a multi-EV charging condition is further discussed. Afterwards, a charging power control method adapting to the speed variation by load adjustment is proposed. By adjusting the equivalent load of the variable-speed charging EV, its speed variation range can reach 20~60 km/h, while the remaining EVs’ charging power fluctuation range can be kept within 10%~15%. Finally, the experimental prototype is built to verify the above-mentioned control method.

Water stress for a long period before harvest and crop load effects on marketable yield and consumer acceptance of nectarine

Under water shortage growers may need to adjust horticultural practices to optimize yield and fruit quality. This study explores the reduction of crop load as a technique to mitigate water stress considering marketable yield and consumer acceptance as the most relevant traits. Commercial irrigation (CI) and deficit irrigation (DI) for a long period before harvest was applied to a late-maturing nectarine (‘Nectalady’) in 2011 and 2012. In both years, midday stem water potential (midday SWP) in CI trees was around −0.85 MPa while in DI trees the values ranged between −1.50 and −1.80 MPa. In the experiment, CI and DI were combined with three crop loads: low crop load (LCL, 85 fruits/tree) in 2011, and medium crop load (MCL, 150 fruits/tree) and commercial crop load (CCL, 230 fruits/tree) in 2012. Under CCL and MCL conditions, DI reduced marketable yield due to a significant reduction of the number of fruits that can be commercialize (fruit size higher than 65 mm). DI combined with LCL slightly reduced fruit size but not marketable yield. Reducing crop load by 60% (from 230 to 85 fruits/tree) maintained fruit size to the standard of marketable yield despite the water stress. Fruit thinning did not affect consumer acceptance of fruit, but it was slightly increased under DI in the first pick each year. The benefit of DI on consumer acceptance may have been observed because trees did not experienced midday SWP below −1.80 MPa for the extended period of water shortage (35 and 53 days in 2011 and 2012, respectively). For the levels of midday SWP experienced in this study (1.50 to −1.80 MPa), marketable yield was more sensitive to water stress than consumer acceptance. Consequently, growers do not need to worry about fruit quality, but crop load adjustments should be done to maintain marketable yield.

Self-assembled three-dimensional hierarchical CoMoO4 nanosheets on NiCo2O4 for high-performance supercapacitor

Highly regular three-dimensional (3D) NiCo2O4/CoMoO4 hierarchical nanosheets (NSs) were prepared through a simple hydrothermal process. During the hydrothermal process, ethylamine solution is crucial for the morphology of NiCo2O4/CoMoO4 NSs and self-assembled formation of CoMoO4 with porous architecture on NiCo2O4. Such curly porous hierarchical structure with large surface areas is benefit to provide numerous accessible electrochemically active sites for faradaic redox reactions. In addition, the morphologies and the mass loading adjustment of NiCo2O4/CoMoO4 NSs can be easily achieved by controlling growth time. The as-prepared NiCo2O4/CoMoO4 electrode demonstrates superior specific capacitance (1730 F/g at 1 A/g), satisfied rate capability (60%, at 20 A/g), and excellent cycling stability (76.2% capacitance retention at 10 A/g). These good electrochemical performances exhibit that the as-obtained NiCo2O4/CoMoO4 composites are efficient electrode materials for pseudo-capacitors and may provide a useful guidance for obtaining electrode materials with outstanding electrochemical performance.

Safety strategy of power transmission channel coordinated with transfer capability support for power system emergency

The overload endurance capability (OEC) of transmission equipment in power system emergency not only relates to the safety of equipment itself but also affects the security of the power system. The action threshold of the existing backup protection (such as distance protection zone 3) reacting to the overload condition is determined by the static thermal rating. The action time is set according to the sequence coordination of upstream and downstream transmission lines. This strategy ineffectively adapts to the surge overload current after power flow transferring, may cause backup protection false trip and accelerate the cascading trip of power system. The parameters and their influential factors that represent the OEC of transmission equipment were clarified in this study. The dynamic OECs of the switchgear, current transformer, and overhead line on the transmission channel were analyzed. The heavy load warning method of the transmission section based on the predicted continuous overload endurance capability (COEC), and the load adjustment and overload protection strategy based on the short-time overload endurance capability (SOEC) were proposed. Finally, the feasibility and validity of the proposed methods were verified through a case study. The proposed safety strategy can effectively utilize the SOEC to protect the safety of the power equipment and provide transfer capability support for the security of power system in emergency conditions.

Optimized Control of Reversible VSC with Stability Mechanism Study in SMES Based V2G System

The superconducting magnetic energy storage (SMES)-based vehicle-to-grid (V2G) application has the characteristics of dynamic power response, well instantaneous stability and power system quality for smart power grid, and ability to reduce the standby capacity of traditional peak load adjustment and frequency modulation. And the three-phase reversible voltage source converter (VSC) is the key interface to achieve bidirectional power flow between electric vehicle and power grid. The mathematic model of active damping LCL -type VSC-based on multi-state feedback approach under the stationary αβ -coordinate system is proposed for SMES based V2G applications. And the inherent stability mechanism with the optimized control strategy influenced by the fluctuation of system parameters is analyzed. The simulation and experimental results illustrate that the V2G system achieves unity power factor and low harmonic distortion, combining with well transient performance and system robustness.

Optimal power allocation for residential network in islanded microgrid using capacity market demand response approach

This paper proposes a new demand response algorithm for load shedding and direct load control in smart homes with the goal of lowering peak-to-average ratios and enhancing power balance. The suggested algorithm makes use of two-way communication between distribution agents and smart homes (customers) to provide real-time load control, calculate percentage reductions, and produce distributed load consumption factors. An agent-based residential distribution network with four customers who owned smart appliances was modeled in MATLAB/SIMULINK to validate the technique. The findings show that the residential network is capable of reacting swiftly to supply changes and managing the grid's power balance through distributed load reduction, load shifting, and/or load adjustment, avoiding or limiting load shedding in the event of supply shortages.