Nonlinear backstepping controller design for sharing active and reactive power in three-phase grid-connected photovoltaic systems

In this paper, a nonlinear backstepping controller is designed for three-phase grid-connected solar photovoltaic (PV) systems to share active and reactive power. A cascaded control structure is considered for the purpose of sharing appropriate amount of power. In this cascaded control structure, the dc-link voltage controller is designed for balancing the power flow within the system and the current controller is designed to shape the grid current into a pure sinusoidal waveform. In order to balance the power flow, it is always essential to maintain a constant voltage across the dc-link capacitor for which an incremental conductance (IC) method is used in this paper. This approach also ensures the operation of solar PV arrays at the maximum power point (MPP) under rapidly changing atmospheric conditions. The proposed current controller is designed to guarantee the current injection into the grid in such a way that the system operates at a power factor other than unity which is essential for sharing active and reactive power. The performance of the proposed backstepping approach is verified on a three-phase grid-connected PV system under different atmospheric conditions. Simulation results show the effectiveness of the proposed control scheme in terms of achieving desired control objectives.

A child-centered scale of informal social control for Latino parents of preschool-age children: development and validation

Perceived neighborhood informal social control may determine whether parents allow their young children to be physically active in the neighborhood. We developed and validated a scale of neighborhood child-centered informal social control appropriate for Latino parents of preschool-age children. The scale was administered to 240 Latino parents, mainly mothers, recruited from neighborhoods cross-stratified by objectively measured crime and traffic safety. Participants completed measures of community cohesion, perceived signs of physical and social disorder, traffic safety and hazards, and perceived stranger danger. A subsample was reassessed 1 week later to determine test-retest reliability. Confirmatory factor analyses (CFAs) were conducted to examine the fit of the data to a priori measurement models. Construct validity was assessed by estimating the associations of the scale with the other measures. The scale showed good test-retest reliability, and factorial and construct validity. The scale needs to be cross-validated on other samples and Latino fathers.

Damping capacity of fly ash-based geopolymer

As environmentally-friendly materials, geopolymers have the potential to replace ordinary Portland cement (OPC) for the construction of railway sleepers and multi-flue chimneys, where the vibration control capabilities of the material must be considered. The critical damping value (ξ) is the main parameter in relation to vibration reduction. In this study, the traditional logarithmic decrement technique was used to measure the ξ of geopolymers. Geopolymers were prepared by activating fly ash using alkali solutions with different SiO2/Na2O ratios. The results show that the ξ of the geopolymers is similar to that of the OPC counterpart. Finite element analysis (FEM) based on the Rayleigh damping model was conducted to replicate the test results, and scanning electron microscopy and mercury-intrusion porosimetry were used to study the microstructure of the geopolymers. A discussion of the possible damping mechanisms based on the microstructural investigation and the FEM analysis is presented.

Effects of active video games on body composition: a randomized controlled trial

BACKGROUND: Sedentary activities such as video gaming are independently associated with obesity. Active video games, in which players physically interact with images on screen, may help increase physical activity and improve body composition.

OBJECTIVE: The aim of this study was to evaluate the effect of active video games over a 6-mo period on weight, body composition, physical activity, and physical fitness.

DESIGN: We conducted a 2-arm, parallel, randomized controlled trial in Auckland, New Zealand. A total of 322 overweight and obese children aged 10-14 y, who were current users of sedentary video games, were randomly assigned at a 1:1 ratio to receive either an active video game upgrade package (intervention, n = 160) or to have no change (control group, n = 162). The primary outcome was the change from baseline in body mass index (BMI; in kg/m(2)). Secondary outcomes were changes in percentage body fat, physical activity, cardiorespiratory fitness, video game play, and food snacking.

RESULTS: At 24 wk, the treatment effect on BMI (-0.24; 95% CI: -0.44, -0.05; P = 0.02) favored the intervention group. The change (±SE) in BMI from baseline increased in the control group (0.34 ± 0.08) but remained the same in the intervention group (0.09 ± 0.08). There was also evidence of a reduction in body fat in the intervention group (-0.83%; 95% CI: -1.54%, -0.12%; P = 0.02). The change in daily time spent playing active video games at 24 wk increased (10.03 min; 95% CI: 6.26, 13.81 min; P < 0.0001) with the intervention accompanied by a reduction in the change in daily time spent playing nonactive video games (-9.39 min; 95% CI: -19.38, 0.59 min; P = 0.06).

CONCLUSION: An active video game intervention has a small but definite effect on BMI and body composition in overweight and obese children.

Couch potatoes to jumping beans: a pilot study of the effect of active video games on physical activity in children

The primary objective of this pilot study was to evaluate the effect of active video games on children's physical activity levels.Twenty children (mean +/- SD age = 12 +/- 1.5 years; 40% female) were randomised to receive either an active video game upgrade package or to a control group (no intervention). Effects on physical activity over the 12-week intervention period were measured using objective (Actigraph accelerometer) and subjective (Physical Activity Questionnaire for Children [PAQ-C]) measures. An activity log was used to estimate time spent playing active and non-active video games.Children in the intervention group spent less mean time over the total 12-week intervention period playing all video games compared to those in the control group (54 versus 98 minutes/day [difference = -44 minutes/day, 95% CI [-92, 2]], p = 0.06). Average time spent in all physical activities measured with an accelerometer was higher in the active video game intervention group compared to the control group (difference at 6 weeks = 194 counts/min, p = 0.04, and at 12 weeks = 48 counts/min, p = 0.06).This preliminary study suggests that playing active video games on a regular basis may have positive effects on children's overall physical activity levels. Further research is needed to confirm if playing these games over a longer period of time could also have positive effects on children's body weight and body mass index.

Feasibility of conducting a randomized trial to promote healthy eating, active play and sustainability awareness in early childhood curricula

We sought to evaluate the feasibility of conducting a randomized trial to evaluate the efficacy of a preschool/kindergarten curriculum intervention designed to increase 4-year-old children's knowledge of healthy eating, active play and the sustainability consequences of their food and toy choices. Ninety intervention and 65 control parent/child dyads were recruited. We assessed the study feasibility by examining recruitment and participation, completion of data collection, realization of the intervention and early childhood educators’ experiences of implementing the study protocol; our findings suggest the intervention was feasible to deliver. In addition, children's sustainability awareness of non-compostable and recyclable items increased. Children in the intervention group significantly reduced their sugary drink consumption and increased their vegetable intake at follow-up compared to control. We conclude with recommendations for revisions to the child interview and parent questionnaire delivery to ensure the roll out of the randomized trial is conducted efficiently and rigorously.

Active video games for improving physical performance measures in older people: a meta-analysis.

BACKGROUND AND PURPOSE: Participation in regular physical activity is associated with better physical function in older people (>65 years); however, older people are the least active of all age groups. Exercise-based active video games (AVGs) offer an alternative to traditional exercise programs aimed at maintaining or enhancing physical performance measures in older people. This review systematically evaluated whether AVGs could improve measures of physical performance in older people. Secondary measures of safety, game appeal, and usability were also considered. METHODS: Electronic databases were searched for randomized controlled trials published up to April 2015. Included were trials with 2 or more arms that evaluated the effect of AVGs on outcome measures of physical performance in older people. RESULTS: Eighteen randomized controlled trials (n = 765) were included. Most trials limited inclusion to healthy community-dwelling older people. With the exception of 1 trial, all AVG programs were supervised. Using meta-analyses, AVGs were found to be more effective than conventional exercise (mean difference [MD], 4.33; 95% confidence intervals [CIs], 2.93-5.73) or no intervention (MD, 0.73; 95% CI, 0.17-1.29) for improving Berg Balance scores in community-dwelling older people. Active video games were also more effective than control for improving 30-second sit-to-stand scores (MD, 3.99; 95% CI, 1.92-6.05). No significant differences in Timed Up and Go scores were found when AVGs were compared with no intervention or with conventional exercise. CONCLUSIONS: Active video games can improve measures of mobility and balance in older people when used either on their own or as part of an exercise program. It is not yet clear whether AVGs are equally suitable for older people with significant cognitive impairments or balance or mobility limitations. Given the positive findings to date, consideration could be given to further development of age-appropriate AVGs for use by older people with balance or mobility limitations.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially.

Robust control for power sharing in microgrids with low-inertia wind and PV generators

This paper presents a robust control design scheme for a multidistributed energy resource (DER) microgrid for power sharing in both interconnected and islanded modes. The scheme is proposed for micgrogrids consisting of photovoltaic (PV) units and wind turbine driven doubly fed induction generators (DFIGs). A battery is integrated with each of the wind and solar DER units. The control scheme has two levels: 1) one centralized multi-input–multi-output robust controller for regulating the set reference active and reactive powers and 2) local real and reactive power droop con-trollers, one on each DER unit. The robust control scheme utilizes multivariable H1 control to design controllers that are robust to the changes in the network and system nonlinearities. The effectiveness of the proposed controller is demonstrated through large-distur-bance simulations, with complete nonlinear models, on a test micro-grid. It is found that the power sharing controllers provide excellent performance against large disturbances and load variations during islanding transients and interconnected operation.

Design of robust distributed control for interconnected microgrids

Microgrids are currently controlled independently, according to local requirements and aims, often based on local control strategies and without coordination with other microgrids [1], [2]. However, it is anticipated that future sub-transmission and distribution systems will be composed of several interconnected microgrids and form a complex elec-tric network. Interconnecting together multiple microgrids can lead to undesirable dynamic behaviors, which have not been adequately examined so far. In particular, this paper dis-cusses power oscillations arising from multiple interconnected microgrids and proposes a control scheme based on a robust distributed control approach.

More active pre-school children have better motor competence at school starting age: an observational cohort study.

BACKGROUND: Almost half of young children do not achieve minimum recommendations of 60 daily minutes in physical activity. Physical activity is potentially an important determinant of the development of motor competence in children. This study is one of very few longitudinal studies in this area and the first to investigate early childhood physical activity as a predictor of subsequent motor skill competence. METHODS: Children were assessed as part of the Melbourne InFANT Program longitudinal cohort study at 19 months, 3.5 years and 5 years. Moderate-to-vigorous physical activity (MVPA) (accelerometry) was assessed at each time point. At age 5, children were also assessed in actual (Test of Gross Motor Development-2) and perceived motor competence (Pictorial Scale of Perceived Movement Skill Competence). General linear models were performed with all 12 skills (six object control and six locomotor skills), both actual and perceived, at age 5 as the respective outcome variables. Predictor variables alternated between MVPA at 19 months, 3.5 years and 5 years. RESULTS: Based on standardized TGMD-2 scores most children were average or below in their skill level at age 5. MVPA at 19 months was not a predictor of actual or perceived skill at age 5. MVPA at 3.5 years was associated with actual locomotor skill (B = 0.073, p = 0.033) and perceived total skill at 5 years of age (B = 0.059, p = 0.044). MVPA was not a predictor of actual or perceived object control skill at any age. CONCLUSION: Parents and preschool staff should be informed that more time in MVPA as a preschool child contributes to locomotor skill and to perceptions of skill ability in a child of school starting age. Understanding this relationship will assist in intervention development.

Stability enhancement of DFIG wind turbine using LQR pitch control over rated wind speed

A novel pitch control design method is proposed for the doubly fed induction generator (DFIG) wind turbine (WT) using linear quadratic regulator (LQR). A seven-order model represents the DFIG WT which is linearized by truncated Taylor series expansion. A systematic approach is adopted to determine the weighting matrices in LQR design for the optimal solution. Simulations have been carried out to compare the performance of the proposed LQR pitch control method against a PI pitch control for small and large disturbances. It is shown that the proposed control method enhances low-voltage ride-through capability and improves system damping under large disturbances.