Multi-Area Power System Security using Polyhedral Transfer Capacities. Dr. Alexander Fuchs (ETH Zürich, Research Center for Energy Networks)

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1 Multi-Area Power System Security using Polyhedral Transfer Capacities Dr. Alexander Fuchs (ETH Zürich, Research Center for Energy Networks)

2 Goals of this presentation How does flexible generation affect multi-area network security? How is network security ensured during continuous operation? Given an information policy for continuous operation, what is the optimal use of the available network capacity? What are alternatives to the current ATC/NTC approach? Polyhedral Transfer Capacities A. Fuchs 2 / 17

3 Flexibility and network security Outline Flexibility and network security General polyhedral transfer capacities Application examples Polyhedral Transfer Capacities A. Fuchs 3 / 17

4 Flexibility and network security Flexibility bounds are important Liberalization separated the network operation from the energy supply chain. Security of supply requires coordination between TSO and producers within an area... TSOs of different areas Increasing share of unscheduled flows (due to RES, load uncertainty, flow-based market coupling...). The lack of coordinated and efficient capacity calculation methods is one of the key missing elements for achieving the efficient use of the network infrastructure and the internal energy market in general. (ACER Market Monitoring Report 215) Polyhedral Transfer Capacities A. Fuchs 4 / 17

5 Flexibility and network security Nominal network capacities Determined through (linear) load flow studies Characterized through Power Transfer Distribution Factors (PTDF) and thermal line limits 3 N- Capacity Example: Network capacity of a 3-node system (yellow), nominal operating point (blue). Power node 2 to 3 [MW] intra-day flexibility * day-ahead dispatch Power node 1 to 3 [MW] Polyhedral Transfer Capacities A. Fuchs 5 / 17

6 Flexibility and network security N-1 congestions and network capacities Leistung Knoten 2 zu 3 [MW] Leistung Knoten 1 zu 3 [MW] Leistung Knoten 1 zu 3 [MW] Leistung Knoten 1 zu 3 [MW] Polyhedral Transfer Capacities A. Fuchs 6 / 17

7 Flexibility and network security N-1 network capacity Secure network operation only when line loss can be tolerated N-1 Kapazität Superposition of N-1 capacities (red) yields the secure operation range of the network (green) Leistung Knoten 2 zu 3 [MW] Leistung Knoten 1 zu 3 [MW] Polyhedral Transfer Capacities A. Fuchs 7 / 17

8 Flexibility and network security Intra-day operation (using nominal network) Multiple time scales (continuous operation, intra-day ) Ideally every change in power flow is verified with a full continuous global load flow simulation, no flexibility bounds needed not really possible for technical, computational, organizational and political reasons approximations required, current state of the art: ATC Power node 2 to 3 [MW] AT C i P i AT C + i N- Capacity ATC 1 - ATC 2 + ATC Power node 1 to 3 [MW] * ATC 1 + ATC flow constraints are potentially very limiting! Polyhedral Transfer Capacities A. Fuchs 8 / 17

9 General polyhedral transfer capacities Outline Flexibility and network security General polyhedral transfer capacities Application examples Polyhedral Transfer Capacities A. Fuchs 9 / 17

10 General polyhedral transfer capacities Aggregation procedure Two inputs required: 1. Detailed network model (n nodal injections x) 2. An assignment of nodes to regions (m n regional injections y = T x) Generator and line constraints: P G = {x R n : A G x b G } P L = {x R n : A L x b L } Weakly feasible regional injection y: x P G, y = T x : x P L Optimistic, some corresponding nodal injection x needs to be secure Strongly feasible regional injection y: x P G, y = T x : x P L Pessimistic, all corresponding nodal injections x must be secure. Polyhedral Transfer Capacities A. Fuchs 1 / 17

11 General polyhedral transfer capacities Computation and implementation Computation following the day-ahead (flow-based) dispatch: The weakly feasible constraint set is a polyhedral projection. The strongly feasible constraint set is a polyhedral set difference computation. Security preserving approximations and intermediate formulations possible. Straightforward implementation during intra-day operation: Aggregated injection changes P are tracked. Market for transfer capacity tranches possible. Fast evaluation of polyhedral constraints without optimization. Same information exchange as for ATC. Contrary to ATC, no artificial path for power exchange needs to be chosen and reserved. Polyhedral Transfer Capacities A. Fuchs 11 / 17

12 Application examples Outline Flexibility and network security General polyhedral transfer capacities Application examples Polyhedral Transfer Capacities A. Fuchs 12 / 17

13 Application examples Six bus network example 15 MW 1 3 MW Net power export to south Center region is aggregated Constraint sets: Net power injection after dispatch (star). Generator limits (red) Weak feasibility constraints (yellow) Strong feasibility constraints (green) Maximized secure ATC constraints (blue) Pnet south [MW] MW 15 MW 4 2 MW 2 MW MW 3 MW ATC Pessimistic Optimistic Pnet center [MW] Polyhedral Transfer Capacities A. Fuchs 13 / 17

14 Application examples European network example NL DE PL BE CZ SK UK CH AT HU FR SI RO HR Original Pegase model with >9 nodes Partitioning into 4 regions (with 3 degrees of freedom) Weak feasibility constraints (yellow), obtained using polyhedral projection algorithm Power Center [MW] PT ES IT BA RS MK AL GR BG Power North [MW] Power South West [MW] Polyhedral Transfer Capacities A. Fuchs 14 / 17

15 Application examples Swiss network example Original model of CH and neighbors with >2 nodes Partitioning of CH into 7 regions Additional power injections from 4 EU regions and 4 nuclear power plants Separate modeling of supply and demand variables Aggregated network model as input for several projects (ISCHESS, NEXUS, SCCER-FURIES, Swiss-Hydro, CH Security studies) Diverse applications (study of ES25, adequacy, security, risk assessment) Polyhedral Transfer Capacities A. Fuchs 15 / 17

16 Application examples Conclusion Flexibility bounds in multi-area networks are important. Current ATC approach is conservative due to restrictive parameterization with cross-boundary power exchanges. Computation of reduced power system models for diverse application studies. With polyhedral transfer capacities, network can be used to its full potential while respecting the security requirements. Polyhedral Transfer Capacities A. Fuchs 16 / 17

17 Application examples Thank you for your attention! FEN - Research Center for Energy Networks Thank you for the collaboration: Marc Scherer (Swissgrid) ETH Zentrum SOI CH-892 Zurich Dr. Alexander Fuchs Sonneggstrasse 28 Tel: Fax: fuchs@fen.ethz.ch Web: Polyhedral Transfer Capacities A. Fuchs 17 / 17