| 1. |
- Karatsivos, Evripidis, et al.
(författare)
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A general control system structure for multi-terminal VSC-HVDC systems
- 2014
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Ingår i: IEEE PES Innovative Smart Grid Technologies, Europe.
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Konferensbidrag (refereegranskat)abstract
- Renewable technology expands geographically and in capacity. The long transmission distance and bulk power transfer involved make multi-terminal VSC-HVDC systems a key technology for future power systems. This expansion could be hampered by the pace of development of multi-terminal systems especially when standardization is not reached in hardware or the control system. A general control system structure is proposed in this paper, dividing the control system in control levels for primary and secondary control implementation and focusing on the interface among them for modularity and expandability. Uniform interfaces standardize data exchange and decouple the overall system control from the local substation control. A version of the control system is tested on a simplified model for different scenarios and number of terminals to demonstrate its functionality and ability to integrate additional terminals. The control system structure provides a platform where each part of the control system can be programmed independently.
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| 2. |
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| 3. |
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| 4. |
- Leisse, Ingmar, et al.
(författare)
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Coordinated voltage control in medium and low voltage distribution networks with wind power and photovoltaics
- 2013
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Ingår i: PowerTech (POWERTECH), 2013 IEEE Grenoble.
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Konferensbidrag (refereegranskat)abstract
- Distributed Generation (DG) installations have been increasing during the last years. Wind power and photovoltaics are two of the most common renewable energy sources for DG typically connected to the distribution network (DN) originally planned and built to supply loads. DG units connected to the DN impact the voltage where customers are connected. Network voltage is an important quality criterion in DN. Voltage rise caused by DG units may become one of the limiting factors for the hosting capacity of wind power and photovoltaics in DNs. Increasing the hosting capacity by network rebuilding is possible but it is expensive and time consuming. Coordinated voltage control has been proposed to increase network capacity without the need of reinforcement. Simulations based on an existing medium and low voltage DN with wind power and photovoltaics are presented. It is shown that coordinated voltage control can increase the hosting capacity and avoid network reinforcement.
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| 5. |
- Leisse, Ingmar, et al.
(författare)
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Electricity Meters for Coordinated Voltage Control in Medium Voltage Networks with Wind Power
- 2010
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Ingår i: Innovative Smart Grid Technologies Conference Europe (ISGT Europe), 2010 IEEE PES. - 9781424485086 - 9781424485093 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- During the last years the amount of electricity generated by Distributed Energy Resources (DER), especially wind turbines, has been increasing a lot. These Distributed Generation (DG) units are often connected to rural distribution networks, where they have a large impact on the voltage and the network losses. The network voltage at the customers point of connection is an important quality criteria and has to follow different standards as e.g. EN 50160. Therefore the voltage change caused by the integration of production units in the distribution network is an important aspect when integrating more DG in distribution networks and often a limiting factor for the maximum DG capacity which is possible to integrate into an existing network without reinforcement. Using the available voltage band more efficient by applying coordinated voltage control is a possibility to increase the hosted DG capacity in an existing distribution network without reinforcement of the network. To get the actual network status the new generation of electricity meters, which have the feasibility to communicate real time voltage measurements from the customers side to a network controller, give some benefits to a more flexible and coordinated voltage control in the network. The voltage range in the network will be used adapted to the actual load and generation situation instead of using worst case assumptions as it is good practice until now. A main part of the voltage control in medium voltage distribution networks is done by the on-load tap changer (OLTC) which takes the voltage at the consumers point of connection into account. A generic 10 kV distribution network with three typical types of feeders, as pure load, pure generation and mixed load and generation feeder, has been outlined. Coordinated voltage control is implemented by a central voltage controller. Simulations on the voltage and the network losses have been done and will be presented in this paper. The maximum DG capacity in the test system increases most when introducing coordinated control of the OLTC but also the use of reactive power adds some benefit. Further increase of the DG capacity by more extensive use of curtailment is always possible but due to economical aspects not favoured.
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| 6. |
- Leisse, Ingmar, et al.
(författare)
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Increasing DG Capacity of Existing Networks through Reactive Power Control and Curtailment
- 2010
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Konferensbidrag (refereegranskat)abstract
- Renewable energy sources (RES), especially wind turbines, have become more important during the last years. An increasing number of distributed generation (DG) units are connected to weak medium voltage distribution networks in rural areas where they have a large influence on the voltage and the line losses. Voltage rise is in this case often a limiting factor for the maximum amount of DG capacity. Already current wind turbines with a capacity of 2 MW can often not easily be connected to existing 10 kV feeders. To increase the DG capacity of existing networks without reinforcement DG units can be controlled. This paper proposes abandoning unity power factor used today and letting the converters used as network interface of many new wind turbine generators absorb reactive power to reduce the voltage level. Since reactive power has great influence on losses in the network the use of reactive power is limited. Line losses due to the transfer of reactive power are taken into account in this study. Furthermore the use of curtailment is analysed. Simulations of voltage change and line losses when using reactive power control by the connected wind turbines and curtailment in a simple test system are presented. Without reinforcement of the network it was possible to increase the DG capacity from 2;7MW to more than 4MW in the test network without violating voltage limits. Line losses increase but to a reasonable extent and lost energy due to curtailment is insignificant.
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| 7. |
- Safari Tirtashi, Mohammad Reza, et al.
(författare)
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Control strategies for reactive shunts to improve long-term voltage stability
- 2013
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Ingår i: Power Engineering Conference (UPEC), 2013 48th International Universities.
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Konferensbidrag (refereegranskat)abstract
- Voltage collapse was one of the main causes for many recent blackouts. The direct link between voltage stability and reactive power balance in the system leads to more attention toward reactive power resources in the power systems. Shunt reactors and capacitors are used to balance reactive power in the power systems. The strategy to control them in both normal and emergency conditions is an important issue. This paper deals with two different strategies for automatic switching of shunt reactors and capacitors in the power systems. The first control strategy, called the local scheme, switches the shunt when the voltage at the local bus is outside the tolerance band. In the second control strategy, called neighboring scheme, local voltage as well as voltage at neighboring buses are used. Dynamic simulations of the NORDIC 32 test system show that the neighboring scheme improves voltage compared to the local one. In the simulated scenario a blackout is avoided by using the neighboring scheme. This is explained using PV curves for a new test system reflecting the key behavior of NORDIC 32.
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| 8. |
- Safari Tirtashi, Mohammad Reza, et al.
(författare)
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Long-Term Voltage Collapse Analysis on a Reduced Order Nordic System Model
- 2014
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Ingår i: 2014 49th International Universities Power Engineering Conference (UPEC). - 9781479965564 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- This paper analyzes and explains the mechanism behind long-term voltage collapse in the NORDIC32 test system. For this purpose a simplified test system called N5area, reflecting the key voltage collapse characteristics of NORDIC32 is proposed. Applying control algorithms is much easier in N5area than in NORDIC32. Load recovery and generator excitation current limiter actions which are two important factors contributing to long-term voltage collapse are considered. Dynamic simulation results for a specified long-term voltage instability scenario are explained and discussed. The effect of generator current limiters is analyzed using PV curves. Furthermore, two different control strategies for controlling the shunt capacitors are applied as countermeasures to save the system. The two strategies are explained and compared and it is shown that control using the voltage at neighboring buses gives better performance.
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| 9. |
- Sulla, Francesco, et al.
(författare)
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Fault Behaviour of Wind Farms with Fixed-Speed and Doubly-Fed Induction Generators
- 2011
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Ingår i: PowerTech, 2011 IEEE Trondheim. - 9781424484195 ; , s. 1-7
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedThis paper focuses on the fault current contribution of wind farms with Fixed-Speed (FSIG) and Doubly-Fed Induction Generators (DFIG). The fault current delivered by a single FSIG during both symmetrical and unsymmetrical faults is found analytically and validated through simulations. Simulations of a detailed model of a wind farm with several FSIG or DFIG are then performed to investigate the total fault current contribution at the Point of Common Coupling. The scope is to check the validity of a single-machine approach to predict the fault contribution of the wind farm. It has been found that both in the case of FSIG and DFIG wind farms, the single-machine approach is reasonable. For DFIG wind farms, the initial operating point of each DFIG has an important impact on its fault current and the single-machine should be given an initial slip close to the average slip of all DFIG in the wind farm.
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| 10. |
- Sulla, Francesco, et al.
(författare)
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Short-circuit analysis of a doubly fed induction generator wind turbine with direct current chopper?protection
- 2013
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Ingår i: Wind Energy. - : Wiley. - 1099-1824 .- 1095-4244. ; 16:1, s. 37-49
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Tidskriftsartikel (refereegranskat)abstract
- Modern doubly fed induction generator (DFIG) wind turbines can ride through a symmetrical fault in the network by using a chopper protection on the direct current (DC) link without triggering a crowbar protection. A novel method to model the DC link system of such wind turbines as an equivalent resistance during symmetrical faults is presented in this paper. The method allows looking at the DFIG with chopper protection as to one with an equivalent crowbar protection and, hence, to apply to the former type of DFIG short-circuit calculation methods developed for a DFIG with crowbar protection. This may be a valid help in short-circuit calculations, for example, for protection settings. It also allows simulating for short-circuit studies a DFIG with chopper protection, often not available in a standard power system simulation software, by using an equivalent DFIG with crowbar protection, which is a standard model in power system simulation software. The results for the short-circuit current obtained through the proposed method are compared with simulations of a detailed model of a DFIG with chopper protection under different conditions, which showed good agreement. It is also shown that the DFIG with chopper protection delivers lower short-circuit current than a DFIG with standard crowbar protection, especially for low initial loading. Copyright (C) 2011 John Wiley & Sons, Ltd.
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