| 1. |
- Gil-de-Castro, A., et al.
(författare)
-
LED street lighting: A power quality comparison among street light technologies
- 2013
-
Ingår i: Lighting Research and Technology. - : SAGE Publications. - 1477-1535 .- 1477-0938. ; 45:6, s. 710-728
-
Tidskriftsartikel (refereegranskat)abstract
- High-pressure sodium lamps are currently the main lamps used in public lighting. However, the possibility of using high-power light emitting diode (LEDs) for street lighting is growing continuously due to their greater energy efficiency, robustness, long life and light control. The aim of this paper is to study the power quality of high-power lighting networks based on LED and high-pressure sodium lamps. Both electromagnetic and dimmable electronic ballasts, which can dim the lamp output smoothly and uniformly, have been used connected to high-pressure sodium lamps. High-pressure sodium lamps connected to electronic equipment have been tested with different arc power levels using dimming on a 230 V power supply. The study presented in this paper is completely based on measurements, including harmonic currents in the frequency range up to 150 kHz for all the technologies. The main results show a broadband spectrum in LED lamps which confirms other research in fluorescent lamps powered by high-frequency ballasts. Results also indicate a decrease in the harmonic value with increasing harmonic order, and a decrease in the harmonic value at half load (60%) compared with full load (100%). Although total harmonic distortion of the current is lower with high-pressure sodium lamps connected to electronic rather than electromagnetic ballasts, LED lamps achieved the lowest total harmonic distortion of current.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Carvalho, J. M., et al.
(författare)
-
Voltage sag index calculation: Comparison between time-domain simulation and short-circuit calculation
- 2008
-
Ingår i: Electric Power Systems Research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 78:4, s. 676-682
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a case study where voltage sags indices are estimated using Monte Carlo approach combined with ATP (Alternative Transient Program) and short-circuit calculation program. Voltage sag magnitude and frequency are used to evaluate the correlation between both programs. The results indicate that time-domain simulation and short-circuit calculation gives similar voltage sag indices. Considering the high correlation between the results, short-circuit calculation programs are preferable over the time-domain simulation tools as the modelling for time-domain simulation is more complex, time consuming, and rarely covers the whole network. (C) 2007 Elsevier B.V. All rights reserved.
|
|
| 5. |
- Ehnberg, Jimmy, 1976, et al.
(författare)
-
Reliability of a small power system using solar power and hydro
- 2005
-
Ingår i: Electric Power Systems Research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 74:1, s. 119-127
-
Tidskriftsartikel (refereegranskat)abstract
- This paper studies the availability of the electricity supply when the sources consist of a combination of solar energy and a small hydro installation. Instead of flow-of-river, a small reservoir is used. By not using the hydro energy during sunny periods, the natural flow-of-river fills up the reservoir for later use. A model for global solar radiation is proposed with an astronomical part (deterministic) and a meteorological part (stochastic). The meteorological part is based on a Markov model of the cloud coverage. The solar model does not require solar radiation measurements, just cloud observations. A case study has been performed for Timbuktu (16.75degreesN, 0.07degreesW) in which generation availability is simulated for four different cases: solar power only; solar power with storage; solar and hydro power and solar and hydro, power with storage. To be able to use exclusively renewable energy sources, a combination of sources is needed to secure the reliability of the supply. Using solar cells in combination with a small reservoir is favorable. Even with a weak flow the affect of the flow on the day time reliability is minor, but great benefits can be found for reliability during low load hours (night time).
|
|
| 6. |
- Ehnberg, Jimmy, 1976, et al.
(författare)
-
Simulation of global solar radiation based on cloud observations
- 2005
-
Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 78:1, s. 157-162
-
Tidskriftsartikel (refereegranskat)abstract
- A stochastic model for simulating global solar radiation on a horizontal surface has been developed for use in power systems reliability calculations. The importance of an appropriate model for global solar radiation has increased with the increased use of photovoltaic power generation. The global solar radiation shows not only regular yearly and daily variations but also a random behaviour. The yearly and daily variations can be described in a deterministic way while the random behaviour has a high correlation with the state of the atmosphere. The astronomic effects can easily be described mathematical with only some minor simplifications but the atmospheric effects are more complicated to describe. The transmittivity of solar radiation in the atmosphere depends on various factors, e.g. humidity, air pressure and cloud type. By using cloud observations as input for the simulations, the local meteorological conditions can be accounted for. The model is usable for any geographical location if cloud observations are available at the location or at locations with similar climatological conditions. This is especially useful for development countries where long-term solar radiation measurement can be hard to obtain. Cloud observations can be performed without any expensive equipment and have been a standard parameter for many years throughout the world. Standard observations are done according to the Oktas-scale. It is the interval between observations that sets the resolution of the simulation: the observations are normally only every hour or every third hour. The model can easily be combined with cloud coverage simulations, has been proposed, for a more general model. For some calculations higher resolution may be needed. This can be obtained by including a stochastic model for the short-term variations and simple model has been proposed. Errors and limitations of the model are estimated and discussed.
|
|
| 7. |
- Etherden, Nicholas, et al.
(författare)
-
Quantification of ancillary services from a virtual power plant in an existing subtransmision network
- 2013
-
Ingår i: Innovative Smart Grid Technologies Europe (ISGT EUROPE). - Piscataway, NJ : IEEE Communications Society. - 9781479929849 ; , s. 1-5
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the results of a feasibility study of a virtual power plant (VPP) in central Sweden designed to provide ancillary services to a 50-kV distribution network. The VPP consists of a wind park, hydro plant and reservoir as well as solar PVs and battery energy storage. The 50-kV subtransmission network was modeled in order to evaluate the ancillary services that could be provided by coordinating existing distributed energy resources in the network. Simulations were performed using measured hourly variations in production and consumption at all network nodes. The studied ancillary services include both reactive and active power control. Contribution from the VPP is evaluated for balancing, to enable a producer to meet spot markets bids and avoid purchases of balancing power minimize peak load in order to reduce subscribed power and tariff to the regional 130-kV network decrease network losses the contribution from reactive power control using the power converters to reduce the reactive power flow to the overlying network. Quantification of the economic gains from each operation case is provided.
|
|
| 8. |
|
|
| 9. |
- Nagata, Erick A., et al.
(författare)
-
Real-Time Voltage Sag Detection and Classification for Power Quality Diagnostics
- 2020
-
Ingår i: Measurement. - : Elsevier. - 0263-2241 .- 1873-412X. ; 164
-
Tidskriftsartikel (refereegranskat)abstract
- This work proposes an innovative approach to detect, segment and classify voltage sags according to their causes. To detect and segment, Independent Component Analysis is used, with the advantage of being fast and with low computational effort in the operational stage, once it uses only 1/8 cycle of the fundamental component. For classification purposes, Higher-Order Statistics are used for feature extraction and the classifiers are based on Neural Networks and Support Vector Machines. It was tested signal windows of 1, 1/2, 1/4 and 1/8 cycle. For both detection/segmentation design and feature selection, it was used the metaheuristics Teaching-Learning-Based Optimization. Encouraging results were achieved for the simulated signals. In addition, real signals were used to evaluate the detection and segmentation method and good results were achieved in which a detection error rate of 0.86% was achieved.
|
|
| 10. |
- Ahmed, Kazi Main Uddin, 1989-, et al.
(författare)
-
A Novel Reliability Index to Assess the Computational Resource Adequacy in Data Centers
- 2021
-
Ingår i: IEEE Access. - NY : IEEE. - 2169-3536. ; 9, s. 54530-54541
-
Tidskriftsartikel (refereegranskat)abstract
- The energy demand of data centers is increasing globally with the increasing demand for computational resources to ensure the quality of services. It is important to quantify the required resources to comply with the computational workloads at the rack-level. In this paper, a novel reliability index called loss of workload probability is presented to quantify the rack-level computational resource adequacy. The index defines the right-sizing of the rack-level computational resources that comply with the computational workloads, and the desired reliability level of the data center investor. The outage probability of the power supply units and the workload duration curve of servers are analyzed to define the loss of workload probability. The workload duration curve of the rack, hence, the power consumption of the servers is modeled as a function of server workloads. The server workloads are taken from a publicly available data set published by Google. The power consumption models of the major components of the internal power supply system are also presented which shows the power loss of the power distribution unit is the highest compared to the other components in the internal power supply system. The proposed reliability index and the power loss analysis could be used for rack-level computational resources expansion planning and ensures energy-efficient operation of the data center.
|
|
