Electric energy security is essential, yet the high cost and limited sources of fossil fuels, in addition to the need to reduce greenhouse gasses emission, have made renewable resources attractive in world energy-based economies. The potential for renewable energy resources is enormous because they can, in principle, exponentially exceed the world׳s energy demand; therefore, these types of resources will have a significant share in the future global energy portfolio, much of which is now concentrating on advancing their pool of renewable energy resources. Accordingly, this paper presents how renewable energy resources are currently being used, scientific developments to improve their use, their future prospects, and their deployment. Additionally, the paper represents the impact of power electronics and smart grid technologies that can enable the proportionate share of renewable energy resources.

Renewable energy resources: Current status, future prospects and their enabling technology

Strategies for extracting the three-phase reference currents for shunt active power filters are compared, evaluating their performance under different source and load conditions with the new IEEE Standard 1459 power definitions. The study was applied to a three-phase four-wire system in order to include imbalance. Under balanced and sinusoidal voltages, harmonic cancellation and reactive power compensation can be attained in all the methods. However, when the voltages are distorted and/or unbalanced, the compensation capabilities are not equivalent, with some strategies unable to yield an adequate solution when the mains voltages are not ideal. Simulation and experimental results are included

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Comparison of Control Strategies for Shunt Active Power Filters in Three-Phase Four-Wire Systems

Optical sensing systems for microfluidic devices: a review.

Microfluidic systems have become more and more important in the field of analytical chemistry. Detection methods on these microsystems are essential for the identification and quantification of chemical species that are being analyzed. This review concentrates on the latest developments of optical detection methods and mass spectrometry in conjunction with microfluidic systems. Electrochemical methods are discussed in another review in the same issue of this journal. Within the optical detection section, topics such as multiplexed detection and the use of waveguides are discussed. Within the discussion of mass spectrometry, the main focus is on electrospray emitters as interfaces between microsystem and spectrometer. Apart from optical detection and mass spectrometry, other techniques such as flame ionization and nuclear magnetic resonance are also mentioned.

Recent developments in detection for microfluidic systems

The main contribution of this paper is the proposal of new modulation techniques for three-phase transformerless neutral point clamped inverters to eliminate leakage currents in photovoltaic systems without requiring any modification on the multilevel inverter or any additional hardware. The modulation techniques are capable of reducing the leakage currents in photovoltaic systems by applying three medium vectors or using only two medium vectors and one specific zero vector to compose the reference vector. In addition, to increase the system utilization, the three-phase neutral point clamped inverter can be designed to also provide functions of active filter using the p-q theory. The proposed system provides maximum power point tracking and compensation of current harmonics and reactive power. To validate the simulation models, an experimental three-phase inverter is used to evaluate leakage currents and the dc link voltage control.

/pdf/eliminating-leakage-currents-in-neutral-point-clamped-6xv4vbe07l.pdf

Eliminating Leakage Currents in Neutral Point Clamped Inverters for Photovoltaic Systems

Due the intensive use of power converters and other non-linear loads in industry and by consumers in general, it can be observed an increasing deterioration of the power systems voltage and current waveforms. The presence of harmonics in the power lines results in greater power losses in distribution, interference problems in communication systems and, sometimes, in operation failures of electronic equipments, which are more and more sensitive since they include microelectronic control systems, which work with very low energy levels. Because of these problems, the issue of the power quality delivered to the end consumers is, more than ever, an object of great concern. International standards concerning electrical power quality (IEEE-519, IEC 61000, EN 50160, among others) impose that electrical equipments and facilities should not produce harmonic contents greater than specified values, and also specify distortion limits to the supply voltage. Meanwhile, it is mandatory to solve the harmonic problems caused by those equipments already installed. Passive filters have been used as a solution to solve harmonic current problems, but they present several disadvantages, namely: they only filter the frequencies they were previously tuned for; their operation cannot be limited to a certain load; resonances can occur because of the interaction between the passive filters and other loads, with unpredictable results. To cope with these disadvantages, recent efforts have been concentrated in the development of active filters.

https://repositorium.sdum.uminho.pt/bitstream/1822/1921/1/IEEE-IES-Newsletter-00.pdf

Active filters with control based on the p-q theory

The "generalized theory of the instantaneous reactive power in three-phase circuits", proposed by Akagi et al., and also known as the p-q theory, is an interesting tool to apply to the control of active power filters, or even to analyze three-phase power system in order to detect problems related to harmonics, reactive power and unbalance. In this paper it will be shown that in three phase electrical systems the instantaneous power waveform presents symmetries if 1/6, 1/3, 1/2 or 1 cycle of the power system fundamental frequency, depending on the system being balanced or not, and having or not even harmonics (interharmonics and subharmonics are not considered in this analysis). These symmetries can be exploited to accelerate the calculations for active filters controllers based on the p-q theory. In the case of the conventional reactive power or zero-sequence compensation, it is shown that the theoretical control system dynamic response delay is zero.

/pdf/p-q-theory-power-components-calculations-4zypc8wg27.pdf

p-q Theory power components calculations

This paper describes the development of a low cost shunt active power filter with digital control, which allows dynamic power factor correction and both harmonics and zero-sequence current compensation. The active filter controller is based on the instantaneous power theory (p-q theory) and was implemented using a standard 16 bits microcontroller. The p-q theory is introduced followed by the presentation of some active power filters topologies. Then a brief description of the implemented solution is made, including references to software tools used for simulation and system development. Experimental results are also presented, showing the good performance of the developed active filter.

/pdf/shunt-active-filter-for-power-quality-improvement-3exvlcn9yl.pdf

Shunt active filter for power quality improvement

This paper deals with problems related with harmonics in power system networks. Several international standards issued to control power quality problems are briefly described and some important methods to analyse electrical circuits with non-sinusoidal waveforms are introduced and evaluated. One of these methods - the p-q theory - was used to implement the control algorithm of a shunt active filter, which is also described in this paper as an application example. The filter can compensate for harmonic currents, power factor and load unbalance. Both simulation and experimental results are presented, showing that good dynamic and steady-state response can be achieved with this approach.

https://repositorium.sdum.uminho.pt/bitstream/1822/1758/1/PowerTech_01.pdf

Active filters for power quality improvement

This paper describes a biological microsystem (bio-system) for measuring uric acid concentration in serum, plasma or urine. Its operation is based on optical absorption in a well-defined part of the visible spectrum. The bio-system is composed by two dies: one is fabricated in polystyrene and contains the microchannels and the other is fabricated in a CMOS standard process and contains the photodetector and readout electronics. The uric acid concentration is measured by using a mixture of 14 l of infinity TM uric acid reagent with 0.25 lo f sample. The achieved sensitivity is 0.33 mg/dl (±0.6% of the value in urine of a healthy person), with a 1 mm lightpath. Using an optical absorption method, a maximum peak at wavelength λ = 494 nm, is detected. This bio-system can be included in the group of low-cost disposable devices for biological fluids analysis. © 2003 Elsevier B.V. All rights reserved.

/pdf/biological-microsystem-for-measuring-uric-acid-in-biological-358d1keqhy.pdf

Júlio S. Martins

Papers

Active filters with control based on the p-q theory

p-q Theory power components calculations

Shunt active filter for power quality improvement

Active filters for power quality improvement

Biological microsystem for measuring uric acid in biological fluids