15,295 research outputs found
Effects of power electronic compensation on distribution network thermal and voltage violations
No full textThis paper is concerned with the use of medium-voltage power electronics in providing active compensation to distribution networks. The primary purpose of using active compensation is to allow for network growth in the form of distributed generation or customer demand increases. With continuing growth, network thermal and voltage constraints would eventually be violated at some point, even with the use of power electronic compensation. Through the study of increasing generation on several hundred distribution network datasets, trends in the type and location of these constraint breaches are identified for both uncompensated and compensated networks. In comparing the initial types of constraint breaches in uncompensated and compensated networks, the use of power electronics is seen to eliminate overvoltage issues as the primary concern in many cases. In addition, while power electronic compensation is seen to make a significant change in the growth accommodated before constraint breach, the location of these initial breaches is not altered appreciably
Benefits of distribution-level power electronics for supporting distributed generation growth
No full textIt is expected that distribution networks will be required to accommodate large amounts of distributed generation (DG). Keeping power flows and voltages within their limits will require either traditional infrastructure upgrades or active compensation. The form of active compensation (e.g., series, shunt, back to back, multiterminal), quantity, and rating of the compensator should be chosen to realize the best cost-benefit ratio. Distributed-generator and compensator placement algorithms are used with a power-flow and constraint satisfaction algorithm to analyze a large number of case studies (using real U.K. network data). From these cases, assessments of compensator performance are made and summarized statistically. When considering incremental deployment across all networks, with the site of greatest benefit chosen at each increment, it is found that static synchronous compensators provide the most favorable cost-benefit ratio. In contrast, multiterminal voltage-source converters tend to provide the greatest flexibility when considering uniform deployment across all networks. It is also observed that traditional reinforcement enhances the benefits provided by active compensation
Battery Storage System as Power Unbalance Redistributor in Distribution Grids Based on Three Legs Four Wire Voltage Source Converter
No full textThis article discusses the application of battery energy storage systems (BESSs) as power redistributors in three-phase distribution grids as an add-on functionality to typical BESS applications, such as congestion management and energy arbitrage. Combining those ancillary services into a single power unit is not yet performed in practice but may constitute an emerging business opportunity to increase the BESS revenues. The unbalanced operation of the BESS voltage source converter (VSC) leads to the circulation of low-frequency current harmonics in the dc-link through the capacitors and the battery cells. Therefore, it is particularly interesting whether relatively large 50- and 100-Hz currents can safely circulate within these components. Analytical modeling and design guidelines for the dc-link of a three-leg four-wire two-level VSC operating under unbalanced loads are detailed. Furthermore, a low-power VSC prototype is used to demonstrate the working principle of the BESS, providing power unbalance redistribution and symmetric power exchange. Additionally, the ICR18650-26F Lithium-ion cells are cycled to reach end-of-life with different current profiles and C-ratings. The analysis shows that charging with a 100 Hz ripple superimposed to the dc current leads to a 10% increment in degradation
Reducing passive filter sizes with tuned traps for distribution level power electronics
No full textThis paper proposes a filter topology intended for use with medium voltage grid-interfaced power electronics as an alternative to the widely-utilized LCL filter topology. The proposed topology utilizes multiple shunt RLC trap filters with parameters optimized to minimize the overall size of the filter while meeting performance requirements for connection to the distribution grid. Results indicate a potential for reduction of twenty-five to thirty percent in total filter volume for the scenario studied. In addition, total power losses taking place within the filter are slightly reduced
The Song of Deborah (Judges Chapter 5) : studies in the versions and the poetic account of the battle against Sisera
No full textA large part of this thesis consists of an
examination of Judges ch. 5 in the light of the
Versions, Rashi and Kimchi. In addition, the tribal
situation, religious cohesiveness of Israel, as well as
the historical context and date of the battle against
Sisera, are examined. The Song of Deborah presents a
unique situation in the period of the Judges in which
an alliance of many tribes participated in a concerted
action. These tribes are designated by the name
'Israel'. The God of Israel is known as Yahweh, Israel
is the people of Yahweh, and the religious unity of
Israel is based upon a common religious faith in
Yahweh. The Song does not represent Israel as a system
of twelve tribes or as having its cohesiveness in an
amphictyony. This historical battle against Sisera
depicted in the Song probably occurred at a time late
in the period of the Judges, at the end of the 12th
century B.C. or early in the 11th century B.C
The role of prolactin in the regulation of brood care in the cooperatively breeding fish Neolamprologus pulcher
No full textThe hormone prolactin (PRL) is important for the regulation of parental care in
many species of mammals, birds and fish, and for alloparental care (care directed at nondescendant
young) in some mammals and birds. Its significance in alloparental brood care of cooperatively
breeding fish has not yet been assessed. Here, we test the role of PRL in brood care behavior of the
cooperatively breeding cichlid Neolamprologus pulcher. The expression of PRL mRNA was
determined in the pituitary glands of breeders of both sexes, helpers that showed brood care
behavior and nonbreeding fish as controls. In addition, PRL levels were experimentally manipulated
in male breeders and helpers by intraperitoneal injections of ovine PRL, and the behavior of these
test fish was recorded toward standardized clutches. Adult females had higher levels of PRL mRNA
than adult males, which was true both for breeders and nonbreeders. Contrary to expectation, there
was no positive correlation between PRL and brood care behavior in any category of test fish, and the
experimental application of PRL did not change brood care propensity. Interestingly, brood-caring
adult females had significantly lower levels of PRL mRNA than adult female nonbreeders, whereas
there was no difference between helpers and similar-sized nonbreeding group members. PRL mRNA
levels increased with body mass in juveniles, but decreased with body mass in adults. In conclusion,
we found no evidence that elevated levels of PRL are directly involved in the regulation of brood care
behavior in this species.We thank R. Eggler, P. Stettler and E. Zwygart
for their technical assistance, and our colleagues
from the Behavioural Ecology and Evolutionary
Ecology Departments, University of Bern, for the
feedback on experimental design. We thank R.
Teodosio and O. Mu¨hlemann for their technical
assistance during the hormonal analyses and
S. Geiser, T. Ott and E. Jutzeler for their
assistance during fish observations. I. M. Hamilton
helped with data analyses and provided useful
comments on the manuscript. The project was
supported by the Swiss National Science Foundation
(SNSF grants 3100-064396 and 3100A0-
105626 to M. T. and SNSF grants 3234-
069260.02/1 and PIOIA-103213 to N. B.), by the
Hochschulstiftung der Burgergemeinde Bern to N.B. and by the pluriannual funding program of the
Centro de Cieˆncias de Mar from the Portuguese
Foundation of Science and Technology to D. M. P
Increasing Distributed Generation Penetration using Soft Normally-Open Points
No full textThis paper considers the effects of various voltage control solutions on facilitating an increase in allowable levels of distributed generation installation before voltage violations occur. In particular, the voltage control solution that is focused on is the implementation of `soft' normally-open points (SNOPs), a term which refers to power electronic devices installed in place of a normally-open point in a medium-voltage distribution network which allows for control of real and reactive power flows between each end point of its installation sites. While other benefits of SNOP installation are discussed, the intent of this paper is to determine whether SNOPs are a viable alternative to other voltage control strategies for this particular application. As such, the SNOPs ability to affect the voltage profile along feeders within a distribution system is focused on with other voltage control options used for comparative purposes. Results from studies on multiple network models with varying topologies are presented and a case study which considers economic benefits of increasing feasible DG penetration is also given
Increasing photovoltaic penetration with local energy storage and soft normally-open points
No full textThis paper considers the use of energy storage to mitigate the effects of power output transients associated with photovoltaic systems due to fast-moving cloud cover. In particular, the combination of energy storage with `soft' normally-open points (SNOPs), referring to an AC/AC power electronic conversion device in place of switchgear, is considered. This paper will demonstrate the use of SNOPs with energy storage for providing this damping functionality simultaneous to its other functions. A formula to estimate the level of energy storage required to handle worst-case transient conditions, as well as two high-level control schemes for the SNOP are proposed then tested experimentally through simulation on typical distribution systems with measured historical insolation data
Maximum Power Point Tracking Injection Method for Islanding Detection of Grid-Connected Photovoltaic Systems in Microgrid
No full textThis paper proposes a novel islanding detection method (IDM) for grid-connected photovoltaic systems (GCPVSs) through a disturbance injection in the maximum power point tracking (MPPT) algorithm. When an absolute deviation of the output voltage exceeds a threshold, the applied disturbance shifts system operating point from its maximum power point (MPP) condition. This leads to a sharp active power output reduction and consequently, a significant voltage drop in islanded mode beyond the standard voltage limit. The proposed algorithm is defined in a way that the distributed generator (DG) can be restored to MPP after islanding classification. It is thereby effective in microgrid in where the power injection at maximum level to cater the critical loads and maintain the stability of the isolated area are pursued. An intentional time delay has also been considered to avoid nuisance tripping in short-circuit faults which do not require tripping. The assessment of the proposed technique has been conducted for a sample network containing two GCPVSs in a real-time platform including actual relays in hardware-in-the-loop (HiL). The provided results under extensive islanding scenarios defined in islanding standards endorse timely and accurately detection with negligible non-detection zone (NDZ) as well as no false tripping in non-islanding disturbances. The comparative analysis of the presented scheme with a few recent IDMs for GCPVS highlights its overall superiorities, including very small NDZ, fast detection, thresholds self-standing determination, no adverse effect on power quality, and simple and inexpensive integration.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid
Reconfigurability, Modularity and Redundancy Trade-offs for Grid Connected Power Electronic Systems
No full textPower electronic converters (PECs) are workhorses of emerging distribution networks. PEC interfaced grids can function as flexible power corridors facilitating compact and efficient energy exchange between distribution generation, load and storage elements. Introducing adequate Reconfigurability, Modularity, and Redundancy (RMR) in such PEC-driven hybrid ac-dc distribution networks can enhance power delivery, thus enabling infrastructure savings. In this paper, an approach for implementing adequate RMR is introduced that can be applied at both converter- and system-level; therefore, the system's reliability can be improved. Furthermore, in this discussion, the impact of integrating renewable energy sources, charging stations and storage systems with the grids is considered with regard to the methodologies of applying RMR to improve the reliability. Potential applications include various power electronics converters, parallel ac-dc links, embedded PEC energy routers, dc hubs, and multi-parallel converter systems capable of regulating power flows between different nodes in the grid with fault-tolerant topologies.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
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