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PI-based controller for low-power distributed inverters to maximise reactive current injection while avoiding over voltage during voltage sags
This paper is a postprint of a paper submitted to and accepted for publication in
IET Power Electronics and is subject to Institution of Engineering and Technology Copyright. The copy of record is
available at the IET Digital Library.In the recently deregulated power system scenario, the growing number of distributed generation sources should be considered as an opportunity to improve stability and power quality along the grid. To make progress in this direction, this work proposes a reactive current injection control scheme for distributed inverters under voltage sags. During the sag, the inverter injects, at least, the minimum amount of reactive current required by the grid code. The flexible reactive power injection ensures that one phase current is maintained at its maximum rated value, providing maximum support to the most faulted phase voltage. In addition, active power curtailment occurs only to satisfy the grid code reactive current requirements. As well as, a voltage control loop is implemented to avoid overvoltage in non-faulty phases, which otherwise would probably occur due to the injection of reactive current into an inductive grid. The controller is proposed for low-power rating distributed inverters where conventional voltage support provided by large power plants is not available. The implementation of the controller provides a low computational burden because conventional PI-based control loops may apply. Selected experimental results are reported in order to validate the effectiveness of the proposed control scheme.Peer ReviewedPostprint (updated version
Can winds driven by active galactic nuclei account for the extragalactic gamma-ray and neutrino backgrounds?
Various observations are revealing the widespread occurrence of fast and
powerful winds in active galactic nuclei (AGNs) that are distinct from
relativistic jets, likely launched from accretion disks and interacting
strongly with the gas of their host galaxies. During the interaction, strong
shocks are expected to form that can accelerate non-thermal particles to high
energies. Such winds have been suggested to be responsible for a large fraction
of the observed extragalactic gamma-ray background (EGB) in the GeV-TeV range
and the diffuse neutrino background in the PeV range, via the decay of neutral
and charged pions generated in inelastic collisions between protons
accelerated by the forward shock and the ambient gas. However, previous studies
did not properly account for processes such as adiabatic losses that may reduce
the gamma-ray and neutrino fluxes significantly. We evaluate the production of
gamma-rays and neutrinos by AGN-driven winds in some detail by modeling their
hydrodynamic and thermal evolution, including the effects of their
two-temperature structure. We find that they can only account for less than
% of the EGB flux, as otherwise the model would violate the
independent upper limit derived from the diffuse isotropic gamma-ray
background. If the neutrino spectral index is steep with , a
severe tension with the isotropic gamma-ray background would arise as long as
the winds contribute more than % of the IceCube neutrino flux in the
TeV range. Nevertheless, at energies ~TeV, we find that the
IceCube neutrino flux may still be accountable by AGN-driven winds if the
spectral index is as small as . The detectability of
gamma-ray point sources also provides important constraints on such scenarios.Comment: 17 pages, 10 figures, to appear in Ap
Modulation Mechanism of TeV, GeV, and X-ray Emission in LS5039
The emission mechanism of the gamma-ray binary LS5039 in energy bands of TeV,
GeV, and X-ray is investigated. Observed light curves in LS5039 show that TeV
and GeV fluxes anticorrelate and TeV and X-ray fluxes correlate. However, such
correlated variations have not been explained yet reasonably at this stage.
Assuming that relativistic electrons are injected constantly at the location of
the compact object as a point source, and that they lose energy only by the
inverse Compton (IC) process, we calculate gamma-ray spectra and light curves
by the Monte Carlo method, including the full electromagnetic cascade process.
Moreover, we calculated X-ray spectra and light curves by using the resultant
electron distribution. As a result, we are able to reproduce qualitatively
spectra and light curves observed by HESS, Fermi, and Suzaku for the
inclination angle i = 30 dig and the index of injected electron distribution p
= 2.5. We conclude that TeV-GeV anticorrelation is due to anisotropic IC
scattering and anisotropic gamma-gamma absorption, and that TeV-X correlation
is due to the dependence of IC cooling time on orbital phases. In addition, the
constraint on the inclination angle implies that the compact object in LS5039
is a black hole.Comment: 27 pages, 7 figures, published in The Astrophysical Journa
Stepwise investment plan optimization for large scale and multi-zonal transmission system expansion
This paper develops a long term transmission expansion optimization methodology taking the probabilistic nature of generation and demand, spatial aspects of transmission investments and different technologies into account. The developed methodology delivers a stepwise investment plan to achieve the optimal grid expansion for additional transmission capacity between different zones. In this paper, the optimization methodology is applied to the Spanish and French transmission systems for long term optimization of investments in interconnection capacity
Point estimate method for voltage unbalance evaluation in residential distribution networks with high penetration of small wind turbines
Voltage unbalance (VU) in residential distribution networks (RDNs) is mainly caused by load unbalance in three phases, resulting from network configuration and load-variations. The increasing penetration of distributed generation devices, such as small wind turbines (SWTs), and their uneven distribution over the three phases have introduced difficulties in evaluating possible VU. This paper aims to provide a three-phase probabilistic power flow method, point estimate method to evaluate the VU. This method, considering the randomness of load switching in customers’ homes and time-variation in wind speed, is shown to be capable of providing a global picture of a network’s VU degree so that it can be used for fast evaluation. Applying the 2m + 1 scheme of the proposed method to a generic UK distribution network shows that a balanced SWT penetration over three phases reduces the VU of a RDN. Greater unbalance in SWT penetration results in higher voltage unbalance factor (VUF), and cause VUF in excess of the UK statutory limit of 1.3%
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