This study deals with the analysis and implementation of compensation algorithms applied to a shunt active power filter, which uses three single-phase full-bridge converters sharing the same dc-bus ...voltage. The shunt filter is applied to three-phase four-wire systems, performing harmonic current suppression, reactive power compensation and power factor improvement. In addition, load unbalances compensation is also carried out. Two different control strategies are presented. In the first strategy, which is called independent current control, the currents of the three-phase power source are independently compensated performing harmonic suppression and load reactive power compensation, that is, the three-phase four-wire system is treated as three independent single-phase systems. In the second strategy, in addition to harmonic suppression and load reactive power compensation, the shunt filter also performs load unbalance compensation, resulting in sinusoidal and balanced source currents. The compensating algorithms are evaluated by means of several experimental test conditions, in order to validate the theoretical development and analyse the performance of the shunt filter.
This study presents a single-phase grid-tied photovoltaic (PV) system based on a global maximum power point tracking (MPPT) technique, which is performed by means of the particle swarm optimisation ...(PSO) method. The PSO-based MPPT technique is employed to solve problems related to mismatching phenomena, such as partial shading, in which the PV arrays are commonly submitted. Considering the search of the global maximum power point under partial shading, the effectiveness of the PSO-based MPPT technique is highlighted when compared with the well-known perturb and observe MPPT technique, since both the mentioned MPPT techniques are used to determine the dc-bus voltage reference to ensure a proper grid-tied inverter operation. A current generator algorithm based on a synchronous reference frame is proposed, which operates in conjunction with a dc-bus controller and MPPT algorithms, computing the reference current of the grid-tied inverter. In addition, the current generator controls the energy processed by the PV system to avoid over power rating of the grid-tied inverter, since the active power injection into the grid, reactive power compensation and harmonic currents suppression are carried out simultaneously. The performance and feasibility of the grid-tied PV system are evaluated by means of simulation and experimental results.
This study presents a comparative performance analysis involving single- and double-stage photovoltaic (PV) systems, which are connected to a three-phase four-wire electrical system by means of a ...four-leg inverter topology. The double-stage PV system is composed of a step-up DC/DC converter and a four-leg grid-connected inverter, while in the single-stage PV system the PV array is directly connected to the inverter DC bus. In addition to the active power injection into the grid, both PV systems have two attractive features, described as follows: (i) power quality improvement due to their capability to perform active power-line conditioning, such as load harmonic current suppression, reactive power compensation, and load unbalance compensation; (ii) dynamic improvement in the occurrence of abrupt solar irradiation variations, which is achieved through the implementation of a feed-forward control loop (FFCL) acting directly in the inverter DC-bus voltage control loop, resulting in speeding up of the dynamics of both the DC-bus voltage and the injected grid-inverter currents. The referred comparative analysis addresses the static and dynamic performances considering the PV systems operating under the action of the FFCL, as well as performing active power-line conditioning. Simulation and experimental results are presented to evaluate and validate the proposed study.
This study presents a procedure for tuning proportional–integral/proportional–integral-derivative controllers using the frequency response method via Bode diagrams, which is relatively simple and ...easy to understand, and can be used when phase margin and 0 dB gain crossover frequency are project specifications. The method is validated in a practical power electronics application, considering the current and the DC-bus voltage loops of a shunt active power filter (SAPF). A detailed analysis related to the obtaining of the DC-bus voltage loop is also provided. In addition, a stability analysis is presented, considering how the SAPF compensation current is influenced according to the load current, taking into account different values of the grid impedance. Simulation and practical results show the effectiveness of the proposed scheme and its simplicity for being considered in practical cases.
This paper presents a comparison analysis involving four multifunctional grid‐tied photovoltaic (MPV) systems, divided in single‐stage and double‐stage architectures. The functionalities can be ...pointed out as generation/injection of active energy into the utility grid, and active power conditioning including reactive power and load unbalance compensation, as well as load harmonic currents suppression. Thus, beyond the photovoltaic systems' conventional functions, the MPV systems also contribute to improve power quality indicators. Single‐phase full‐bridge (1‐FB) inverters are used to build two grid‐tied inverter configurations. In the first, called as MPV‐FB, three 1‐FB inverters share the same DC‐bus, while in the second, named as MPV‐3FB, each of the three 1‐FB inverters operates with an individual DC‐bus. Each inverter configuration integrates the MPV system architectures with single‐stage and double‐stage, where in the single‐stage configuration the photovoltaic array is directly connected to the inverter DC‐bus, whereas in the DS one, a step‐up DC–DC converter is inserted between the photovoltaic array and the inverter DC‐bus. Under several scenarios of operation, the four MPV systems named as MPV‐FB‐SS, MPV‐FB‐DS, MPV‐3FB‐SS and MPV‐3FB‐DS, are experimentally tested to compare constructive aspects, evaluate static/dynamic performances and power quality issues, as well as capability to operate with photovoltaic array failure.
The cattle tick Rhipicephalus microplus is a hematophagous ectoparasite that causes important economic losses in livestock. Different species of ticks harbor a symbiont bacterium of the genus ...Coxiella. It was showed that a Coxiella endosymbiont from R. microplus (CERM) is a vertically transmitted mutualist symbiont, comprising 98% of the 16S rRNA sequences in both eggs and larvae. Sequencing of the bacterial genome revealed genes for biosynthetic pathways for several vitamins and key metabolic cofactors that may provide a nutritional complement to the tick host. The CERM was abundant in ovary and Malpighian tubule of fully engorged female. Tetracycline treatment of either the tick or the vertebrate host reduced levels of bacteria in progeny in 74% for eggs and 90% for larvae without major impact neither on the reproductive fitness of the adult female or on embryo development. However, CERM proved to be essential for the tick to reach the adult life stage, as under antibiotic treatment no tick was able to progress beyond the metanymph stage. Data presented here suggest that interference in the symbiotic CERM-R. microplus relationship may be useful to the development of alternative control methods, highlighting the interdependence between ticks and their endosymbionts.
Summary
This work proposes a 3‐phase 4‐wire unified power quality conditioner (UPQC) structure, which has ability to operate with per‐phase independent grid current control, reduced dc‐bus voltage ...and inverted/dual compensation strategy. Since the grid currents are controlled by the series converter, two distinct strategies, namely, independent current compensation strategy (ICCS) and load unbalance compensation strategy (LUnCS) can be employed. Using the ICCS, the controls of the grid currents are performed independently per‐phase, such that the UPQC can operate even when grid voltage outage occurs in one or two phases of the power source. Furthermore, to guarantee the proper parallel converter operation, the dc‐bus voltage amplitude must be higher than the grid voltage peak amplitude. Thus, since the parallel converter operation is assured, the functioning of the series converter is also guaranteed because it needs lower dc‐bus amplitude to operate. However, depending on the converter topology adopted in the parallel converter, the series converter could be subjected to operate with dc‐bus voltage higher than necessary. Thus, to minimize this aspect, this paper proposes a UPQC scheme composed of 3‐Leg split‐capacitor (3‐Leg‐SC) and 4‐Leg topologies, operating as series and parallel converters, respectively. Thus, besides the use of the ICCS, lower dc‐bus voltage is allowed when compared to the UPQC composed of two 3‐Leg‐SC converters, as well as reduced power switches number is achieved when the propose scheme is compared to UPQC composed of two 4‐Leg converters. Extended experimental results based on digital signal controller are presented to evaluate the effectiveness and performance of the proposed UPQC.
Summary
Brazil has one of the largest varieties of aquatic ecosystems and rich freshwater biodiversity, but these components have constantly been damaged by the expansion of unsustainable activities. ...Free-living nematodes are an abundant and ubiquitous component of continental benthic communities, occurring in all freshwater habitats, including extreme environments. Despite this, hardly any studies have examined the generic composition of nematodes in different latitudes and the geographic overlap of assemblages. We provide data on nematode genera from six regions in Brazil, over a north-south gradient spanning about 4000 km, encompassing rivers, coastal lakes, and reservoirs with different levels of human impact. Interpolation/extrapolation curves were generated and the zeta diversity was used to assess the overlap of nematode assemblages. Freshwater nematode assemblages comprised 54 families and 132 genera. Mononchidae, Monhysteridae, Chromadoridae, Tobrilidae and Dorylaimidae were the most diverse families. Differences in diversity and high turnover of genera were found among regions, probably related to stochastic processes. Mononchus was the only widely distributed genus. Our results revealed a high biodiversity of free-living freshwater nematodes among the regions. The limited spatial coverage of the data reveals an enormous knowledge gap in a country with 12% of the world’s freshwater resources. The lack of spatial patterns, e.g., latitudinal variation, suggests that freshwater nematode assemblages are primarily structured by the intrinsic properties of habitats. This reinforces the uniqueness of freshwater ecosystems and suggests that the nematode assemblages may be sensitive to environmental disturbances, since the limited distributions of taxa may lead to lower resilience.
This paper aims to present an alternative methodology to improve the tuning of proportional-integral multiresonant (PI-MR) controller applied to the current control loop of a shunt active power ...filter (SAPF) by using a differential evolution (DE) metaheuristic method. For computing the PI-MR controller gains, the methodology based on Naslin polynomial (NP) can be employed, although its performance is limited. On the other hand, tuning procedures accomplished by trial-and-error methods have been largely used. In order to fill the lack of methodological procedures to determine the PI-MR controller gains, the use of DE metaheuristic optimization algorithm is proposed to perform an optimal adjustment. The DE algorithm operates minimizing an appropriate cost function, taking into account the total harmonic distortion of the source current, the error of the compensation current control loop, and the saturation limit of the control action. The effectiveness of the proposed methodology is compared to the NP-based method, applied to a single-phase SAPF. The proposed methodology is validated by means of both simulation and experimental results. The evaluation of the static and dynamic performances is obtained from experimental tests performed based on a digital signal processor.
The species Inga laurina is native to the Brazilian Cerrado. There are no studies about the chemical composition and biological activities of extracts of this endangered species. The ethanolic ...extract and its successive fractions are rich in phenolic compounds and presented good antifungal activities. HPLC/MS-MS/MS and H1/C13 analysis led to the identification of seventeen compounds, most of which are gallic acid derivatives, myricetin and quercetin glycosides. The ethyl acetate fraction (EAF) contained high levels of total phenolics, expressed in milligrams of gallic acid equivalents per gram of extract (475.3 ± 1.9 mg GAE gextract-1) and flavonoids expressed in milligrams of quercetin equivalents per gram of extract (359.3 ± 10.6 mg QE gextract-1). This fraction was active against fungi of the Candida genus. The EAF showed MIC value 11.7 μg mL−1 against C. glabrata and a selectivity index of 1.6 against Vero cells. The flavonol glycoside myricetin-3-O-rhamnoside was isolated for the first time from the Inga laurina. These results make I. laurina a promising plant as a source of pharmaceutical and biological active antifungal compounds.
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