| 1. |
- Abid, Fahim, et al.
(författare)
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Intermodulation due to interaction of photovoltaic inverter and electric vehicle at supraharmonic range
- 2016
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Ingår i: 2016 17th International Conference on Harmonics and Quality of Power. - Piscataway. NJ. - 9781509037926 ; , s. 685-690
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Konferensbidrag (refereegranskat)abstract
- Advent of power electronic switching is introducing more and more non-linear loads in the low voltage grid. Besides harmonic current generation in the frequency range below 2 kHz, these non-linear loads are also responsible for current emission in the range of 2 kHz to 150 kHz, commonly known as supraharmonic emission. Supraharmonic currents mainly flow between nearby appliances and heavily influence the overall emission of neighboring devices. This paper presents an analysis of supraharmonic interaction between a photovoltaic inverter and an electric vehicle. It has been noticed that intermodulation distortion arises as a result of interaction between different switching frequencies used by the devices. Later, additional household equipment were added to photovoltaic and electric vehicle to observe their effect on intermodulation distortion. All the measurements were conducted in a controlled laboratory environment imitating a domestic customer.
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| 2. |
- Abrahamsson, Lars, et al.
(författare)
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AC cables strengthening railway low frequency AC power supplysystems
- 2017
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Ingår i: ASME/IEEE 2017 Joint Rail Conference. - : ASME Press. - 9780791850718
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Konferensbidrag (refereegranskat)abstract
- In present-day railway power supply systems using an AC frequency lower than the one in the public power system of 50/60 Hz, high voltage overhead transmission lines are used as one measure of strengthening the railway power supply system grids. This option may be economically beneficial, compared to strengthening the grid purely by increasing the density of converter stations or increasing the cross section areas of the overhead catenary wires. High voltage AC transmission lines in the railway power supply system allow larger distances between converter stations than would otherwise be possible for a given amount of train traffic. Moreover, the introduction of AC transmission lines implies reduced line losses and reduced voltage level fluctuations at the catenary for a given amount of train traffic. However, due to the increased public and government resistance for additional overhead high voltage AC transmission lines in general, different alternatives will be needed for the future improvements and strengthening of railway power systems. For a more sustainable transport sector, the share and amount of railway traffic needs to increase, in which case such a strengthening becomes inevitable. Earlier, usage of VSC-HVDC transmission cables has been proposed as one alternative to overhead AC transmission lines. One of the main benefits with VSC-HVDC transmission is that control of power flows in the railway power systems is easier and that less converter capacity may be needed. Technically, VSC-HVDC transmission for railway power systems is a competitive solution as it offers a large variety of control options. However, there might be other more economical alternatives reducing the overall impedance in the railway power system. In public power systems with the frequency of 50/60 Hz, an excess of reactive power production in lowly utilized cables imposes an obstacle in replacing overhead transmission lines with cables. In low frequency AC railway power system, the capacitive properties are less significant allowing longer cables compared to 50/60 Hz power systems. Moreover, in converter-fed railways, some kind of reactive compensation will automatically be applied during low-load. At each converter station, voltage control is already present following the railway operation tradition. Therefore, in this paper, we propose AC cables as a measure of strengthening low-frequency AC railway power systems. The paper compares the electrical performances of two alternative reinforcement cable solutions with the base case of no reinforcement. The options of disconnecting or toggling the cables at low load as well as the automatic reactive compensation by converter voltage control are considered. Losses and voltage levels are compared for the different solutions. Investment costs and other relevant issues are discussed.
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| 3. |
- Abrahamsson, Lars, 1979-, et al.
(författare)
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Evaluating a constant-current load model through comparative transient stability case-studies of a synchronous-synchronous rotary frequency converter-fed railway
- 2019
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Ingår i: 2019 Joint Rail Conference. - : ASME Press.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper continues the pursuit of getting a deeper understanding regarding the transient stability of low-frequency AC railway power systems operated at 16 2/3 Hz synchronously to the public grid. The focus is set on the impact of different load models. A simple constant-current load model is proposed and compared to a previously proposed and studied load model in which the train’s active power is regulated.The study and comparison is made on exactly the same cases as and grid as with the already proposed and more advanced load model. The railway grid is equipped with a low-frequency AC high-voltage transmission line which is subjected to a fault. The study is limited to railways being fed by different distributions of RFC (Rotary Frequency Converter) types. Both AT (auto transformer) and BT (booster transformer) catenaries are considered.The RFC dynamic models are essentially Anderson-Fouad models of two synchronous machines coupled mechanically by their rotors being connected to the same shaft.The differences in load behaviour between the proposed constant-current load model and the previously proposed and studied voltage-dependent active power load model are analyzed and described in the paper.
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| 4. |
- Abrahamsson, Lars, 1979-, et al.
(författare)
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Further studies on the transient stability of synchronous-synchronous rotary frequency converter fed railways with low-frequency AC high-voltage transmission
- 2018
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Ingår i: International Journal of Energy Production and Management. - : WIT Press. - 2056-3272 .- 2056-3280. ; 3:4, s. 266-276
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Tidskriftsartikel (refereegranskat)abstract
- This paper continues the pursuit of getting a deeper understanding regarding the transient stability of low-frequency AC railway power systems operated at 16 2/3 Hz that are synchronously connected to the public grid. Here, the focus is set on such grids with a low-frequency AC high-voltage transmission line subject to a fault. The study here is limited to railways being fed by different distributions of Rotary Frequency Converter (RFC) types. Both auto transformer (AT) and booster transformer (BT) catenaries are considered. No mixed model configurations in the converter stations (CSs) are considered in this study. Therefore, only interactions between RFCs in different CSs and between RFCs, the fault, and the load can take place in this study. The RFC dynamic models are essentially two Anderson-Fouad models of synchronous machines coupled mechanically by their rotors being connected to the same mechani- cal shaft. Besides the new cases studied, also a new voltage-dependent active power load model is presented and used in this study.
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| 5. |
- Ahmed, Kazi Main Uddin, 1989-, et al.
(författare)
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Electrical Energy Consumption Model of Internal Components in Data Centers
- 2019
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Ingår i: Proceedings of. - : IEEE.
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Konferensbidrag (refereegranskat)abstract
- In the context of modern information technology (IT) industry, cloud computing is gaining popularity for big data handling. Therefore, IT service providers like Google, Facebook and Amazon are expanding their technical resources by building data centers to improve the data processing and data storage facilities under cloud service pattern. However, data centers consume a large amount of electrical energy. In recent years, a lot of research has been done to reduce the electrical energy consumption of data centers by high performance computing. However, very few researchers have focused on the electrical energy consumption by the electrical components inside the data center. In this paper, a component based electrical energy consumption modelling approach is presented to identify the losses of different components as well as their interactions to the total electrical energy consumption of the data center. The electrical energy consumption models of servers and other components are presented as a function of server utilization.
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| 6. |
- Alhamwi, Mouaz, et al.
(författare)
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Empirical Analysis of Voltage Variations in Low Voltage Distribution Grids from Photovoltaic
- 2019
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Ingår i: Solar Integration Workshop 2019. - : Energynautics GmbH. - 9783982008042
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The rapid expansion of photovoltaic (PV) systems has raised voltage concerns. This paper investigates voltage variations measured at four hundred on-line PV installations in Sweden. Small (<10 kW inverter size) three phase residential PV systems had the least impact whereas single phase systems had the most impact for the same amount of power injected per phase. PV systems were grouped based on post code location into urban and rural areas. Urban areas were found to be more resilient to PV induced voltage fluctuations with a narrower back-ground voltage band in comparison to rural areas, indicating that PV inverter measurements can be an efficient method to empirically determine grid strength.
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| 7. |
- Alvarez, Manuel, 1980-, et al.
(författare)
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A Capacity Mechanism Design for Distribution Network Expansion Planning
- 2018
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Ingår i: 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe). - 9781538651865 - 9781538651872
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Konferensbidrag (refereegranskat)abstract
- Capacity remuneration mechanisms have been originally oriented to ensure availability and continuity of supply on the power generation pool. Equivalent generation-based capacity mechanisms could be implemented to enhance and prolong the usability of the distribution grid. In particular, such capacity mechanisms would provide an alternative to traditional expansion options leading to investment deferral. In this work, a distribution capacity mechanism to fit within a distribution network planning methodology will be proposed and discussed. The capacity mechanism will be outlined following similar guidelines as for the design of capacity mechanisms used in the energy only market. The result of the design is a volume based capacity auction for a capacity-constrained system, oriented to both the active and the reactive power provision.
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| 8. |
- Alvarez, Manuel, et al.
(författare)
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A Smart Distribution Toolbox for Distribution System Planning
- 2015
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Konferensbidrag (refereegranskat)abstract
- The distribution system planner should be able to coordinate smart grid solutions in order to find cost effective expansions plans. These plans should be able to deal with new added system uncertainties from renewable production and consumers while guaranteeing power quality and availability of supply. This paper proposes a structure for distribution systems planning oriented to help the planner in deciding how to make use of smart solutions for achieving the described task. Here, the concept of a system planning toolbox is introduced and supported with a review of relevant works implementing smart solutions. These are colligated in a way that the system planner can foresee what to expect with their combined implementation. Future developments in this subject should attempt to theorize a practical algorithm in an optimization and decision making context.
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| 9. |
- Alvarez Perez, Manuel Alejandro, 1980-, et al.
(författare)
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A Generic Storage Model Based on a Future Cost Piecewise-Linear Approximation
- 2019
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Ingår i: IEEE Transactions on Smart Grid. - : Institute of Electrical and Electronics Engineers (IEEE). - 1949-3053 .- 1949-3061. ; 10:1, s. 878-888
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a generic storage model (GSM) inspired by the scheduling of hydraulic reservoirs. The model for steady state short-term (ST) operational studies interlaces with the long-term (LT) energy scheduling through a piecewise-linear Future Cost Function (FCF). Under the assumption that a Stochastic Dual Dynamic Programming (SDDP) approach has been used to solve the energy schedule for the LT, the FCF output from that study will be processed to obtain an equivalent marginal opportunity cost for the storage unit. The linear characteristic of a segment of the future cost function (FCF) will allow a linear modeling of the storage unit production cost. This formulation will help to coordinate the renewable resource along with storage facilities in order to find the optimal operation cost while meeting end-point conditions for the long-term plan of the energy storage. The generic model will be implemented to represent a battery storage and a pumped-hydro storage. A stochastic unit commitment (SUC) with the GSM will be formulated and tested to assess the day-ahead scheduling strategy of a Virtual Power Plant (VPP) facing uncertainties from production, consumption, and market prices.
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| 10. |
- Alvarez Perez, Manuel Alejandro, 1980-, et al.
(författare)
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A Hydro-Reservoir Generic Storage Model for Short-Term Hydrothermal Coordination
- 2017
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Ingår i: IEEE PES PowerTech Manchester 2017: towards and beyond sustainable energy systems, 2017. - Piscataway, NJ : Institute of Electrical and Electronics Engineers (IEEE). - 9781509042371
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Konferensbidrag (refereegranskat)abstract
- This work presents a linear solution for the short-term hydro-thermal scheduling problem linked to long-term conditions through a piecewise-linear Future Cost Function (FCF). Given end-point conditions to conform long-term water releases, and given actual reservoir conditions, a segment of a pre-built piecewise future cost function will be chosen. The linear characteristic of the FCF segment will allow a linear modeling of the hydro-power plant, in a similar fashion as a thermal unit with an equivalent marginal opportunity cost. A short-term hydro thermal coordination problem will be formulated considering parallel and cascaded hydro-reservoirs. Three study cases involving different reservoir configurations and scenarios will be computed to test the model. The results of this model mimics coherently the future-cost hydro-thermal coordination problem for the different configurations tested. Given similarities with other forms of energy storage, a new theoretical model for generic storage will be proposed and discussed.
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