A three-phase four-wire unified power quality conditioner without series transformers

This work presents a topology for a Unified Power Quality Conditioner (UPQC), without series transformers, connected to a three-phase four-wire electrical grid. Based on the proposed power topology, the UPQC is able to compensate unbalanced-and harmonic-components, power factor and short-duration voltage variations (voltage sag/swell). In other words this UPQC consists in a universal solution capable to mitigate most power quality problems in an electrical installation. The applied control algorithms are based on instantaneous power definitions (active and non-active currents), together with a robust synchronizing circuit (PLL), to detect the phase angle of the fundamental positive-sequence component of the system voltage. A trustworthy model of the proposed UPQC was investigated in order to verify its performance under power quality problems observed at the load currents and system voltages

Pre- and Post-Activity Stretching Practices of Collegiate Soccer Coaches in the United States

International Journal of Exercise Science 13(6): 260-272, 2020. Current pre- and post-activity stretching guidelines are designed to optimize performance and reduce injury risk. However, it is unclear whether soccer coaches adhere to these recommendations. The purpose of this study was to determine if collegiate soccer coaches’ perceptions and practices align with current scientific recommendations. A total of 781 questionnaires were electronically distributed to soccer coaches from NCAA Division I and III universities.The questionnaire obtained demographic, professional, and educational information, as well as stretching practices. Statistical analysis consisted of computing frequency counts and means where applicable. Pearson\u27s Chi-square tests were performed to assess the potential differences in stretching perceptions and practices among the cohort of soccer coaches. Results suggest that soccer coaches are choosing some forms of stretching more frequently than other coaches (χ2= 342.7, p\u3c 0.001). Further analysis failed to determine significant associations between stretching type and coaching certification, level, sex, years of experience, and age. Of the 209 respondents, 84.9% believed pre-activity stretching to be of greater than average importance on a seven-point Likert scale. Dynamic stretching (68.7%) or a combination of static and ballistic stretching (18.0%) prior to athletic events was the most typical stretching prescribed. Current post-activity practices demonstrate that most coaches (95.4%) are using some form of a general cool-down following practice or competition. This study is an important assessment of the extent to which collegiate coaches administer appropriate stretching techniques. Most coaches adhere to current recommendations; however, they should continue to evaluate their practices against ongoing research and the practices of their peers

Internet of Things in Water Management and Treatment

The goal of the water security IoT chapter is to present a comprehensive and integrated IoT based approach to environmental quality and monitoring by generating new knowledge and innovative approaches that focus on sustainable resource management. Mainly, this chapter focuses on IoT applications in wastewater and stormwater, and the human and environmental consequences of water contaminants and their treatment. The IoT applications using sensors for sewer and stormwater monitoring across networked landscapes, water quality assessment, treatment, and sustainable management are introduced. The studies of rate limitations in biophysical and geochemical processes that support the ecosystem services related to water quality are presented. The applications of IoT solutions based on these discoveries are also discussed

Improvements on the Incremental Conductance MPPT Method Applied to a PV String with Single-Phase to Three-Phase Converter for Rural Grid Applications

A power electronic interface that integrates a photovoltaic string with a single-phase grid to feed a three-phase induction motor, while driving a fan-type load, is presented. The interface is composed of a single-phase active rectifier and a three-phase inverter with output transformer, wherein the Photovoltaic (PV) string is straightly connected to the DC-link, avoiding the use of additional converter for maximum power point tracking, commonly seen in previous works. However, in this system configuration, disturbances at the DC-link may occur due to increments and decrements of load active power, with consequent low-frequency oscillations at the AC grid side of the active rectifier. Therefore, a modified Incremental Conductance based algorithm is proposed, with which low-frequency oscillations around the maximum power point are minimized even under disturbances at the DC-link. Moreover, the overall system energy management, composed of control algorithms, that integrates maximum power point identification , DC-link voltage regulation, motor speed controller and power quality at the input AC mains, is also proposed. Simulation results are provided to evaluate the system effectiveness under AC mains with voltage sag occurrence, load transient and steady-state conditions at different solar irradiance levels