| 1. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(författare)
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Chalmers Campus as a Testbed for Intelligent Grids and Local Energy Systems
- 2019
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Ingår i: IEEE International Conference on Smart Energy Systems and Technologies (SEST). - 9781728111568
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Konferensbidrag (refereegranskat)abstract
- This paper presents an overview of a testbed for intelligent distribution grids, local energy systems, and energy flexible buildings, which is being developed at the campus of Chalmers University of Technology in Gothenburg, Sweden. It describes the test sites, the functionalities, and the planned demonstration activities within the scope of on-going research projects. The proposed demonstrations include a local energy market platform, energy management solutions for microgrids and smart buildings, as well as voltage control in distribution grids. The paper aims to show how the physical energy supply systems of the university are being adapted to integrate the communication and control set-ups that provide the technical requirements for smart grid interoperability. As an example, the on-site implementation of remote battery control is presented, where initial results show the feasibility and potential benefits of the external control. Finally, challenges and lessons learned during the development of the testbed are highlighted.
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| 2. |
- Antoniadou-Plytaria, Kyriaki, 1989, et al.
(författare)
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Energy Scheduling Strategies for Grid-connected Microgrids: A Case Study on Chalmers Campus
- 2019
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Ingår i: Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019.
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Konferensbidrag (refereegranskat)abstract
- This paper focuses on the optimal energy management of grid-connected microgrids with battery energy storage systems. The microgrid energy management and the optimal power flow of the distribution network are formulated as mixed-integer linear optimization problems to evaluate microgrid energy scheduling strategies including cost minimization, maximum use of own resources, and minimum energy exchange with the upstream network. The real distribution network of Chalmers University of Technology campus is used as a case study. The study results show that economic optimization yields an annual microgrid cost reduction of 4%. Alternatively, if the microgrid minimizes the energy exchange, virtual islanding operation (zero energy exchange) for 3211 hours can be achieved within a year. The results also present the effects on the operation and cost of the distribution system and highlight a trade-off between microgrid cost minimization and battery lifetime.
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| 3. |
- Balram, Pavan, 1986, et al.
(författare)
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Comparative study of MPC based coordinated voltage control in LV distribution systems with photovoltaics and battery storage
- 2018
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Ingår i: International Journal of Electrical Power and Energy Systems. - : Elsevier BV. - 0142-0615. ; 95, s. 227-238
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Tidskriftsartikel (refereegranskat)abstract
- This paper compares traditional local voltage control strategy with coordinated, optimization-based ones in LV distribution systems with photovoltaics and battery energy storage systems. Optimization-based strategies are formulated within a model predictive control (MPC) framework. Three strategies based on MPC are proposed and implemented, namely, centralized, decentralized and distributed MPC. The formulated strategies for voltage control are compared in a case study using a modified CIGRE European 3-area low-voltage network. Results indicate that decentralized MPC gives a better voltage profile in the network when compared to local voltage control strategy, since the latter inherently fails to maintain voltages of buses in the network not connected to photovoltaics or battery storage system within limits. Centralized MPC strategy is able to provide the optimal voltage profile across the network but utilizes 13% higher reactive power from the control devices to achieve this when compared to decentralized MPC. The latter performs well as long as the reactive power reserves within an area is sufficient but faces drawbacks similar to that of local voltage control strategy when the reactive reserves are completely exhausted. Distributed MPC utilizes 1:3% higher amount of reactive power reserves compared to centralized MPC in order to provide a network voltage profile similar to that of the latter while also yielding architectural advantages of decentralized MPC.
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| 4. |
- Balram, Pavan, 1986, et al.
(författare)
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Demonstration of Voltage Control in a Real Distribution System using Model Predictive Control
- 2017
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Ingår i: IET Generation, Transmission and Distribution. - : Institution of Engineering and Technology (IET). - 1751-8687 .- 1751-8695. ; 11:16, s. 3922-3929
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results from field tests that were carried out with the aim of verifying the performance of a model predictive control-based voltage controller. A voltage source converter capable of producing or consuming 4 MVAr was used as the reactive power source, which was able to influence the voltage magnitude at a remote bus within a real distribution system in Gothenburg, Sweden. The voltage controller is designed to maintain the remote bus voltage within a pre-defined range while respecting the reactive power output capability of the voltage source converter and an objective of minimum changes to the reference value of its local reactive power controller. Results from the field tests demonstrate that the voltage controller was able to successfully regulate the voltage even with significant errors in the state-space prediction model. An important lesson learned from the field test is that a smoothened voltage measurement feedback is critical to a satisfactory functioning of the controller. Furthermore, it is recommended to design the voltage controller to observe an initial delay, before it is activated for bus voltage control- this would deter it from unnecessarily reacting at the very instant it is brought online.
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| 5. |
- Balram, Pavan, 1986, et al.
(författare)
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Predictive voltage control of batteries and tap changers in distribution system with photovoltaics
- 2016
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Ingår i: Power Systems Computation Conference (PSCC). - 9788894105124
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a model predictive control approach for coordinated secondary voltage control of on-load tap changing transformers and battery energy storage systems in a distribution system to maintain the bus voltage levels in the presence of photovoltaic generation. Optimal control actions are obtained based on a quadratic objective function with linear constraints. The control actions are implemented in a case study using a modified CIGRÉ European low voltage distribution network with corresponding models of the constituent devices and their local controllers. The results indicate that battery energy storage system could aid the system voltages and reduce the number of transformer tap operations if the control is performed in a coordinated manner enabled by the model predictive control framework.
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| 6. |
- Carlson, Ola, 1955, et al.
(författare)
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Grid Code Testing of Wind Turbine by VSC-based Test Equipment
- 2017
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Ingår i: Wind Energy Science Conference 2017, DTU Lyngby, June 2017.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To fulfill the EU target of large amount of wind power in the electric power system, several technical barriers have to be overcome. The main challenge for the wind energy development is to make the wind turbines efficient in respect of costs and safe operation. An important design criterion is the fulfillment of the Grid Codes given by the transmission system operators. The Grid Codes state how wind turbines/farms must behave when connected to the grid in normal and abnormal conditions. In this regard, wind turbine manufactures must show how well their wind turbines can withstand an abnormal condition. This is done by simulations and some simplified tests. Tests of the Grid Code compliance for voltage dips in the grid are today carried out by use of coils and contactors mounted in a container that is connected between the wind turbine and the grid. This equipment has limited testing capability while been able to test only a part of the technical requirements given in the Grid Codes. For example, wind turbine operation with the grid frequency of 49 Hz cannot be tested, but still the requirement exists in today´s Grid Codes. Another solution to realize the grid code tests is to use fully-rated Voltage Source Converter (VSC) in back-to-back configuration. By controlling the turbine-side output of the converter system, a wider spectrum of grid faults can be emulated. Thanks to the full controllability of the applied voltage in terms of magnitude, phase and frequency, the use of VSC-based testing equipment, provides more flexibility as compared with the standard impedance-based test equipment. In addition, the AC grid is decoupled from the tested object when performing the test; meaning that the strength of the grid is not a major limitation. The test results are from the test of the 4 MW wind turbine and the 8 MW test equipment, located in Gothenburg, Sweden. In the tests the wind turbine operates at rated power when the voltage dip is applied. The turbine copes very well with the dip while a minor influence on the current and in the reactive and active power is observed.
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| 7. |
- Carlson, Ola, 1955, et al.
(författare)
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Wind Turbines on Ships
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The start-up company PROPit AB together with Division of Electric Power Engineering has developed a concept for harnessing sea winds for simultaneous electricity generation and thrust, by using conventional, but modified wind turbines onboard merchant vessels. The primary market should be tankers and bulk ships with large and open deck space, operating on routes and in areas with favourable wind conditions. The business idea is to create substantial fuel savings while simultaneously reducing harmful greenhouse gas emissions.
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| 8. |
- Espinoza, Nicolas, 1984, et al.
(författare)
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Field-test of wind turbine by voltage source converter
- 2019
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Ingår i: Wind Energy Science. - : Copernicus GmbH. - 2366-7451 .- 2366-7443. ; 4:3, s. 465-477
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Tidskriftsartikel (refereegranskat)abstract
- One of the main challenges for wind energy development is making wind turbines efficient in terms of costs whilst maintaining safe and reliable operation. An important design criterion is to fulfil the grid codes given by the transmission system operators. Grid codes state how wind farms must perform when connected to the grid under normal and abnormal conditions. In this regard, it is well-known that not all technical requirements can be tested by using actual impedance-based test equipment. Therefore, test equipment comprising a fully rated voltage source converter in back-to-back configuration is proposed. Thanks to the full controllability of the applied voltage in terms of magnitude, phase and frequency, the use of voltage-source-converter-based test equipment provides more flexibility compared to actual test systems. As demonstrated in this paper, the investigated test device not only can recreate any type of fault, including its recovery ramp, but also can carry out steady-state tests, such as frequency variations and frequency scan, on the test object. Finally, test results from a 4.1 MW wind turbine and 8 MW test equipment located in Gothenburg, Sweden, are shown to validate the investigated grid code test methodology.
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| 9. |
- Espinoza, Nicolas, 1984, et al.
(författare)
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Frequency Characterization of Type-IV Wind Turbine Systems
- 2016
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Ingår i: 2016 IEEE Energy Conversion Congress and Exposition (ECCE), Milwaukee, WI, USA, 2016. - 2329-3721. - 9781509007370 ; , s. Article no 7855126-
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Konferensbidrag (refereegranskat)abstract
- The continuous need for renewable energy sources is a driving force for a fast development of wind turbine technologies. It is well known that control interactions can arise if the wind farms and the interconnecting system, for example ac collector system or high voltage direct current (HVDC)-link, are not properly integrated. One tool to assess the stability of the system is to analyse the input impedance of the wind farm together with the connecting grid impedance. In this regard, this paper investigates the impact of different system parameters in the input admittance of the generating unit. The admittance is analysed for a wide range of frequencies. Moreover, the passive and non-passive behavior of the admittance is highlighted and the risk of interaction between the wind turbine and other elements of the grid is discussed.The system under consideration consists of a multi megawatt type-IV wind turbine system and a fully-rated voltage source converter (VSC)-based testing equipment used as verification tool for frequency scanning. First, the mathematical model of the system and the scanning method are presented. The input admittance is calculated for a variety of operating conditions including variations of control settings such as phase-locked loop (PLL) and close-loop current control bandwidth and system parameters, such as the output filter configuration. Finally, the investigated methodology is verified using time-domain simulations and field test results.
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| 10. |
- Espinoza, Nicolas, 1984, et al.
(författare)
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Novel LVRT Testing Method for Wind Turbines Using Flexible VSC Technology
- 2015
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Ingår i: IEEE Transactions on Sustainable Energy. - : Institute of Electrical and Electronics Engineers (IEEE). - 1949-3029 .- 1949-3037. ; 6:3, s. 1140-1149
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Tidskriftsartikel (refereegranskat)abstract
- Wind energy is one of the fastest growing renewable energy sources. For this reason, several countries have included requirements in their grid codes to guarantee proper operation of wind turbines under stable operations of the power systems as well as under grid disturbances. This paper presents a novel methodology for grid code testing of wind turbines based on voltage source converter (VSC) technology. In particular, this paper focuses on a low voltage ride through (LVRT) test of a full size converter-based wind turbine. The investigated testing setup consists of a 4-MW wind turbine and an 8-MW back-to-back VSC system, operated as test equipment. The control algorithm of the testing device is derived in detail and validated through time-domain simulations. The risk of poorly damped resonances and possible interaction between the testing equipment and the tested object is investigated through small signal analysis. The obtained results demonstrate the flexibility of the proposed approach in controlling the voltage at the wind turbine terminals, including the ability in emulating the short-circuit impedance of the grid at the connection point.
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