Iov, Florin

Nainar, Karthikeyan

English

Integration of renewable energy sources (RES) such as wind power plants and solar PV to electric power systems is a global phenomenon to reduce emissions of green house gases and combat climate change. Majority of the RES are connected to medium and low-voltage distribution grids. Power transmission grids, owned and operated by transmission grid operators (TSOs), are generally well interconnected, monitored on a continuous basis and have standardized control policies. On the other hand, distribution grids operated by distribution system operators (DSOs) have limited observability, communication infrastructure with slow bandwidth, less automated functions and lack of coordination with TSOs. Power production from RES, for example, wind power plants is intermittent depending upon the wind speed. In future distribution grids, at higher penetration levels of wind power plants, grid congestion in the form of node over-voltages, over-currents in the lines may be experienced. To alleviate grid congestion, DSOs can curtail the power output of the wind generators. However, curtailment of wind power will cause revenue loss to wind power plant owners, and it can hamper the green energy transition. At present, the control and coordination among TSOs and DSOs are limited and not automated. Assuming an improved interface between TSOs and DSOs, during grid congestion, controllable resources in the transmission grid can be utilized for mitigation. In this paper, a detailed review of the current interface between TSOs and DSOs, in the context of few European countries including Denmark, will be conducted. A practical example of grid congestion in a representative distribution grid due to varying power production from wind power plants will be analyzed by simulation studies. The required functionalities on the TSO-DSO interface to address the grid congestion problem will be studied. The possibilities of utilizing the transmission grid assets such as on-load tap changing transformers, STATCOMs etc., to aid the DSO in managing the grid congestion will be explored. A simple case study will be performed illustrating the effectiveness of improved TSO-DSO interface for congestion management in a representative distribution grid. Recommendations for improving the TSO-DSO interface to tackle the future operational challenges of power system with large share of renewable generation will be provided

    Aalborg UniversitetAn Overview of Coordinated Control via TSO-DSO Interface for CongestionManagement in Distribution NetworksNainar, Karthikeyan; Iov, FlorinCreative Commons LicenseUnspecifiedPublication date:2021Document VersionPublisher's PDF, also known as Version of recordLink to publication from Aalborg UniversityCitation for published version (APA):Nainar, K., & Iov, F. (2021). An Overview of Coordinated Control via TSO-DSO Interface for CongestionManagement in Distribution Networks. Abstract from Wind Energy Science Conference, Hannover, Germany.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: August 24, 2021An Overview of Coordinated Control via TSO-DSOInterface for Congestion Management in DistributionNetworksKarthikeyan Nainar and Florin IovDepartment of Energy TechnologyMay 25, 2021OutlineIntroductionOverview of Wind EnergyModern Power System OperationNeed for TSO-DSO CoordinationAdvanced TSO-DSO InterfaceMethods for CoordinationCongestion ManagementProposed TSO-DSO InterfaceSimulation Case StudyRecommendationsConclusionsDeptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 1/17Wind Energy in EuropeAs per the report [1]Wind energy shares a significantportion of the electricity demand.In Denmark, wind energy share is 48%.Challenges in power balancing withhigh share of wind energy [2].Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 2/17Operation of a Modern Power SystemNetwork Level 1Transmission Networks400 kV, 150 kV, 132 kV Biomass Coal powerOff-shore windElectricity import and exportNetwork Level 2Trans-regional Distribution Networks60 kVNetwork Level 3Network Level 4Regional Distribution Networks20 kV, 10 kVLocal Distribution Networks0.4 kVCombined Heat andPower plantLarge-scale industryWind farmSolar farm Wind farm Energy storage IndustryMicro-wind turbineRoof-top solarElectric vehicleHeat pumpResidentialloadsHV/MV transformerPrimary distribution transformerSecondary distribution transformerTSODSOFigure 1: Layout of modern power system [3].Power grids may be“stressed” due to varyingrenewable energy generation.How DSOs can manage gridcongestion?Can the TSO-DSO interfacebe used for congestionmanagement?Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 3/17Power System OperatorsTransmission System Operator - The TSOoperates the transmission assets and is re-sponsible for the power balance on the trans-mission system. For the example case of Den-mark, it is Energinet.Distribution system Operator - The DSOoperates the distribution grid, and often addi-tionally acts as a retailer. Examples in Den-mark include, e.g., DONG Energy, Syd En-ergi, SEAS-NV, etc.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 4/17Need for TSO-DSO CoordinationIn modern power systems, the tranmission system operator (TSO) requiresancillary services1 by DERs such as WPPs at distribution networks.Ancillary services by WPPs can be used for frequency/voltage regulation [5].However, ancillary services provision may cause bottlenecks at distributionnetworks.The existing grid codes alone cannot address the potential problems.Coordination and exchange of information among the TSO, distributionsystem operators (DSOs) may be a solution [6, 7].This work deals with congestion management by an advanced TSO-DSO Interface1Any type of service provided by network resources (e.g., DERs) procured by the systemoperators to the support power system operations [4].Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 5/17Advanced TSO-DSO InterfaceTSODSODER/AggregatorAncillary services marketTSODSODER/AggregatorAncillary services market(a) (b)information control price manualFigure 2: Interaction in (a) present scenario with manual interaction (b) improved interface involving DSO.At present, the communication between the operators of the TSO and DSO is onmanual basis and it happens only when there is a need.An improved interface is proposed in [8, 6, 9] in which information exchange is doneon a continuous basis between TSO and DSO.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 6/17Coordination between TSO and DSOAt present, TSO utilizes DERs for ancillary services such as freqeuncy restora-tion reserve (FRR) by communicating active power setpoints to DERs.DSOs are not aware of the above process and a new power setpoint to DERsmay cause network congestion.In improved TSO-DSO interface, DSOs can be involved to pre-check if therequested power setpoints by TSO donot cause overvoltages/overcurrents.A congestion management algorithm can be executed to alter OLTC settingsand utilize reactive power capability of DERs to alleviate congestion.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 7/17Proposed TSO-DSO InterfaceTSOAncillary Services MarketDispatching program Request verification(Load flow)Tech. constraints satisfiedDERsCongestion ManagementDSOyesnoBids, , ,g d g dP P Q Q, , ,n b b bV I P Q, , ,g d g dP P Q Q,tap trafon VApproval of bids,g gP QD D,g gP QFigure 3: Flowchart illustrating the proposed TSO-DSO interface.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 8/17Details of the AlgorithmThe key idea here is the execution of a congestion management (CM) algorithmby the TSO to manage the distribution grid voltages and currents within limits.The DSO receives power dispatch from the TSO and checks if it will result inviolations of voltages and currents limits. The CM algorithm is activated toadjust the power dispatch to DERs.An OPF method based on quadratic programming [10, 11] is used to calculateOLTC tap settings and reactive power setpoints of DERs.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 9/17Quadratic Programming Based OPF [10, 11]The objective of the proposed OPF is toMinimize the square of the change in reactive power dispatch of DERs andtransformer secondary voltagesubject to the following constraints.1 Linearized active power balance equations at all nodes of the network.2 Linearized reactive power balance equations at all nodes of the network.3 Voltage limits at each node of the network.4 Current limits at each branch of the network.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 10/17Simulation Studies - TSO-DSO interfaceFigure 4: A representative MV network considered for simulation study [12].Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 11/17Case 1 : Without Proposed TSO-DSO Interface0 4 8 12 16 20 24(a) Time [hr]051015ActivePower [MW] PchpPwt0 4 8 12 16 20 24(b) Time [hr]0.90.9511.051.1Volt[pu]5b1012141517Figure 5: Case 1: Without proposed TSO-DSO interface (a) active powers of WPP and CHP in response to anhypothetical TSO request for up-regulation within the time period marked in vertical red color lines. Solid anddashed lines show the power profile with and without ancillary services, (b) voltages at MV nodes.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 12/17Case 2 : With Proposed TSO-DSO Interface0 4 8 12 16 20 24(a) Time [hr]0.90.9511.051.1Volt[pu]T2M1M2M3M4M50 4 8 12 16 20 24(b) Time [hr]-1-0.500.51Reactivepower [MVAR]QchpQwtFigure 6: Case 2: With proposed TSO-DSO interface (a) voltages at MV nodes (b) additional reactive powersof DERs requested by the DSO (c) updated reactive powers of DERs.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 13/17ObservationsIn case 1, the node voltages are above the limit of 1.1 pu, as the expectedvoltages due to calculated power dispatch are not computed and no preventivemeasures were taken.In case 2, before the power setpoints are communicated to DERs, overvoltagesare estimated by the DSO and the CM algorithm is activated.The CM algorithm computes the OLTC tap setting and Q setpoints for DERsto prevent overvoltages.As a result in case 2, the node voltages are maintained within the limit of 1.1pu.The proposed method is advantageous compared to local volt/var control be-cause the network congestion are pre-checked and the voltage violations areprevented.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 14/17ConclusionsHigh share of wind energy in a power system may cause network congestionduring peak power production.An advanced TSO-DSO interface is proposed wherein, a congestion manage-ment algorithm is utilized to prevent overvoltages during the utilization ofDERs for ancillary services.The proposed method can be implemented practically provided the technicalregulations and communication infrastructure are updated suitably.The proposed ideology can be extended to large active loads such as electricheating systems for provision of ancillary services.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 15/17AcknowledgmentsThe authors would like to acknowledge Net2DG project (www.net2dg.eu) for sup-porting this research work.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 16/17References I[1] I. Komusanac, G. Brindley, and D. Fraile, “Wind energy in Europe in 2019,” Tech. Rep., 2020. [Online]. Available:https://windeurope.org/wp-content/uploads/files/about-wind/statistics/WindEurope-Annual-Statistics-2019.pdf[2] P.-F. Bach, “Towards 50% wind electricity in Denmark: Dilemmas and challenges,” Eur. Phys. J. Plus, vol. 131, no. 5, p. 161, 2016.[3] K. Nainar, “Hierarchical distributed control of active electric power distribution grids,” Ph.D. dissertation, Aalborg University, 2019.[4] EURELECTRIC, “Ancillary services - Unbundling electricity products – an emerging market,” Tech. Rep., 2003.[5] P. Palensky and D. Dietrich, “Demand side management: Demand response, intelligent energy systems, and smart loads,” IEEE Trans. Ind.Informatics, vol. 7, no. 3, pp. 381–388, 2011.[6] P. Michael, R. Carsten, N. Christer, D. Ellen, and P. Seamus, “System operation emphasizing DSO -TSO interaction and coordination,” in Cigre Jt.Work. Gr., no. August, 2018.[7] F. Pilo, F. Silvestro, G. 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Simpson-Porco, “Predictive control of flexible resources for demand response in active distributionnetworks,” IEEE Trans. Power Syst., vol. 34, no. 4, pp. 2957–2969, 2019.[12] M. Altin, X. Han, A. D. Hansen, R. Løvenstein Olsen, N. A. Cutululis, and F. Iov, “Technical Feasibility of Ancillary Services provided by ReGenPlants,” DTU Wind Energy, Tech. Rep., 2018.Deptartment of Energy Technology, AAU WESC 25-28 May 2021, Hannover, Germany May 25, 2021 17/17

An Overview of Coordinated Control via TSO-DSO Interface for Congestion Management in Distribution Networks

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An Overview of Coordinated Control via TSO-DSO Interface for Congestion Management in Distribution Networks

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