7,839 research outputs found
Power Quality Enhancement in Electricity Grids with Wind Energy Using Multicell Converters and Energy Storage
In recent years, the wind power industry is experiencing a rapid growth and more wind farms with larger size wind turbines are being connected to the power system. While this contributes to the overall security of electricity supply, large-scale deployment of wind energy into the grid also presents many technical challenges. Most of these challenges are one way or another, related to the variability and intermittent nature of wind and affect the power quality of the distribution grid. Power quality relates to factors that cause variations in the voltage level and frequency as well as distortion in the voltage and current waveforms due to wind variability which produces both harmonics and inter-harmonics. The main motivation behind work is to propose a new topology of the static AC/DC/AC multicell converter to improve the power quality in grid-connected wind energy conversion systems. Serial switching cells have the ability to achieve a high power with lower-size components and improve the voltage waveforms at the input and output of the converter by increasing the number of cells. Furthermore, a battery energy storage system is included and a power management strategy is designed to ensure the continuity of power supply and consequently the autonomy of the proposed system. The simulation results are presented for a 149.2 kW wind turbine induction generator system and the results obtained demonstrate the reduced harmonics, improved transient response, and reference tracking of the voltage output of the wind energy conversion system.Peer reviewedFinal Accepted Versio
Interpolated-DFT-Based Fast and Accurate Amplitude and Phase Estimation for the Control of Power
The quality of energy produced in renewable energy systems has to be at the
high level specified by respective standards and directives. The estimation
accuracy of grid signal parameters is one of the most important factors
affecting this quality. This paper presents a method for a very fast and
accurate amplitude and phase grid signal estimation using the Fast Fourier
Transform procedure and maximum decay sidelobes windows. The most important
features of the method are the elimination of the impact associated with the
conjugate's component on the results and the straightforward implementation.
Moreover, the measurement time is very short - even far less than one period of
the grid signal. The influence of harmonics on the results is reduced by using
a bandpass prefilter. Even using a 40 dB FIR prefilter for the grid signal with
THD = 38%, SNR = 53 dB and a 20-30% slow decay exponential drift the maximum
error of the amplitude estimation is approximately 1% and approximately 0.085
rad of the phase estimation in a real-time DSP system for 512 samples. The
errors are smaller by several orders of magnitude for more accurate prefilters.Comment: in Metrology and Measurement Systems, 201
Impact of hybrid renewable energy systems on short circuit levels in distribution networks
The effects of the distributed generation can be classified as environmental, technical and economical effects. It is playing a very vital role for improving the voltage profiles in electrical power systems. However, it could have some negative impacts such as operating conflicts for fault clearing and interference with relaying. Distribution system is the link between the utility system and the consumer. It is divided into three categories radial, Loop, and network. Distribution networks are the most commonly used to cover huge number of loads. The power system reliability mainly depends on the smooth operation and continuity of supply of the distribution network. However, this may not always be guaranteed especially with the introduction of distributed generation to the distribution network. This paper will examine the impact of hybrid renewable energy systems (using photovoltaic and doubly fed induction generators) on short circuit level of IEEE 13-bus distribution test system using ETAP software
Feed-forward Space Vector Modulation for Single-Phase Multilevel Cascade Converters with any DC voltage ratio
Modulation techniques for multilevel converters
can create distorted output voltages and currents if the DC link
voltages are unbalanced. This situation can be avoided if the
instantaneous DC voltage error is not taken into account in the
modulation process. This paper proposes a feed-forward space
vector modulation method for a single-phase multilevel cascade
converter. Using this modulation technique, the modulated output
voltage of the power converter always generates the reference
determined by the controller even in worst case voltage unbalance
conditions. In addition the possibility of optimizing the DC
voltage ratio between the H-bridges of the power converter is
introduced. Experimental results from a 5kVA prototype are
presented in order to validate the proposed modulation technique
Reliability analysis of single-phase photovoltaic inverters with reactive power support
Reactive power support is expected to be an emerging ancillary requirement for single-phase photovoltaic (PV) inverters. This work assesses related reliability issues and focuses on the second stage or inversion process in PV inverters. Three PV inverter topologies are analyzed and their reliability is determined on a component-by-component level. Limiting operating points are considered for each of these topologies. The capacitor in the dc link, the MOSFETs in the inverting bridge, and the output filter are the components affected. Studies show that varying power-factor operation with a constant real power output increases the energy storage requirement as well as the capacitance required in the dc link in order to produce the double-frequency power ripple. The overall current rating of the MOSFETs and output filter must also be sized to accommodate the current for the apparent power output. Modeling of the inverter verifies the conditions for each of the components under varying reactive power support commands. It is shown that the production of reactive power can significantly increase the capacitance requirement, but the limiting reliability issue comes from the increased output current rating of the MOSFETs
Analysis of the power balance In the cells of a multilevel cascaded H-Bridge converter
Multilevel cascaded H-Bridge converters (CHB)
have been presented as a good solution for high power applications.
In this way, several control and modulation techniques
have been proposed for this power converter topology. In this
paper the steady state power balance in the cells of the single
phase two cell CHB is studied. The capability to be supplied with
active power from the grid or to deliver active power to the grid
in each cell is analyzed according to the dc-link voltages and
the desired ac output voltage value. Limits of the maximum and
minimum input active power for stable operation of the CHB are
addressed. Simulation results are shown to validate the presented
analysis
DC-Voltage-Ratio Control Strategy for Multilevel Cascaded Converters Fed With a Single DC Source
Recently, a multilevel cascaded converter fed with a single DC source has been presented. An analysis of the steady-state working limits of this type of converter is presented in this paper. Limits of the maximum output voltage and the minimum and maximum loading conditions for stable operation of the converter are addressed. In this paper, a way to achieve any DC voltage ratio (inside the stable operation area of the converter) between the H-bridges of the single-DC-source cascaded H-bridge converter is presented. The proposed DC-voltage-ratio control is based on a time-domain modulation strategy that avoids the use of inappropriate states to achieve the DC-voltage-ratio control. The proposed technique is a feedforward-modulation technique which takes into account the actual DC voltage of each H-bridge of the converter, leading to output waveforms with low distortion. In this way, the dc voltage of the floating H-bridge can be controlled while the output voltage has low distortion independently of the desired DC voltage ratio. Experimental results from a two-cell cascaded converter are presented in order to validate the proposed DC-voltage-ratio control strategy and the introduced concepts.Ministerio de Ciencia y TecnologĂa TEC2006-03863Junta de AndalucĂa EXC/2005/TIC-117
AnĂĄlisis de armĂłnicos variando en el tiempo en sistemas elĂ©ctricos de potencia con parques eĂłlicos, a travĂ©s de la teorĂa de la posibilidad
This paper focuses on the analysis of the connection of wind farms to the electric power system and their impact on the harmonic load-flow. A possibilistic harmonic load-flow methodology, previously developed by the authors, allows for modeling uncertainties related to linear and nonlinear load variations. On the other hand, it is well known that some types of wind turbines also produce harmonics, in fact, time-varying harmonics. The purpose of this paper is to present an improvement of the former method, in order to include the uncertainties due to the wind speed variations as an input related with power generated by the turbines. Simulations to test the proposal are performed in the IEEE 14-bus standard test system for harmonic analysis, but replacing the generator, at bus two, by a wind farm composed by ten FPC type wind turbines.En este trabajo se analiza el impacto de la conexiĂłn de parques eĂłlicos, en el flujo de cargas armĂłnicas en un sistema de potencia. Algunos generadores eĂłlicos producen armĂłnicos debido a la electrĂłnica de potencia que utilizan para su vinculaciĂłn con la red. Estos armĂłnicos son variables en el tiempo ya que se relacionan con las variaciones en la velocidad del viento. El propĂłsito de este trabajo es presentar una mejora a la metodologĂa para el cĂĄlculo de incertidumbre en el flujo de cargas armĂłnicas, a travĂ©s de la teorĂa de la posibilidad, la cual fue previamente desarrollada por los autores. La mejora consiste en incluir la incertidumbre debida a las variaciones de la velocidad del viento. Para probar la metodologĂa, se realizan simulaciones en el sistema de prueba de 14 barras de la IEEE, conectando en una de las barras un parque eĂłlico compuesto por diez turbinas del tipo FPC. Los resultados obtenidos muestran que la incertidumbre en la velocidad del viento tiene un efecto considerable en las incertidumbres asociadas a las magnitudes de las tensiones armĂłnicas calculadas.Fil: Romero Quete, AndrĂ©s Arturo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Juan. Instituto de EnergĂa ElĂ©ctrica. Universidad Nacional de San Juan. Facultad de IngenierĂa. Instituto de EnergĂa ElĂ©ctrica; ArgentinaFil: Suvire, Gaston Orlando. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Juan. Instituto de EnergĂa ElĂ©ctrica. Universidad Nacional de San Juan. Facultad de IngenierĂa. Instituto de EnergĂa ElĂ©ctrica; ArgentinaFil: Zini, Humberto Cassiano. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Juan. Instituto de EnergĂa ElĂ©ctrica. Universidad Nacional de San Juan. Facultad de IngenierĂa. Instituto de EnergĂa ElĂ©ctrica; ArgentinaFil: Ratta, Giuseppe. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Juan. Instituto de EnergĂa ElĂ©ctrica. Universidad Nacional de San Juan. Facultad de IngenierĂa. Instituto de EnergĂa ElĂ©ctrica; Argentin
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