Congestion Management

Context: In a regime of increasing uncertainty and variability due to the growing integration of renewable energy sources, the patterns of flows along electricity networks change rapidly and unpredictably. This requires network operators to adapt the dispatch of conventional resources so as to respect the physical limits of operation of network equipment, while also pricing access to network capacity in a way that drives investment of appropriate technologies in appropriate locations of the network.

The management and pricing of high-voltage transmission networks differs notably across worldwide markets. Zonal network management, which is implemented in Europe, sets a unique price for electricity at every zone (left panel below), which is an aggregation of locations (often an entire country in the case of the European market). A re-dispatch procedure then follows, which aims at restoring production schedules that result in flows which respect network constraints. Nodal network management, which is predominant in major US markets (right panel below), uses a different price signal per high-voltage network node.

EU zonal market modeling: The representation of the physical laws of power flow in electricity markets with nodal pricing relies on a linear approximation of the power flow equations. In zonal markets, an aggregate model of network physics is used. The early European zonal market relied on a transportation-based model based on available transfer capacities (ATCs). In recent years, an alternative model has been implemented for the European day-ahead electricity market, which attempts to represent network physics more accurately, and is referred to as flow-based market coupling. Our team has developed a detailed model of the European day-ahead and real-time electricity market, which quantifies the interplay between zonal network management and day-ahead unit commitment. The overall model is described in the figure below, where a day-ahead module which commits units and determines zonal net positions is followed by a balancing and congestion module corresponding to real-time operations.

A challenge in the analysis of zonal market model is that assumptions about the network parameters affect the analysis. This is related to the circularity of zonal market clearing models: the definition of aggregated network parameters depends on assumptions about the point of operation, which in turn depends on the definition itself of network parameters. Our team has developed a methodology for overcoming this circularity. The idea, presented in the right panel of the figure below, determines the set of zonal net positions for which we can find nodal injections that are compatible with the physics of the network and the limits of the network elements.

Active network management / transmission switching: In order to deal with overloads in network elements, European transmission network operators often resort to active network management measures, such as transmission line switching, in order to increase their control on the routing of power along network components. Our team has developed preventive and curative models of transmission switching in European day-ahead and real-time operations, as well as algorithmic procedures for resolving the resulting optimization problems. Case studies quantify the important role of transmission switching in moderating the costs of congestion management as increasing levels of renewable resources are being integrated in the European network.

Zonal pricing in EU balancing platforms: Zonal network models are also being adopted in the common European balancing markets that will be used for the activation of secondary (PICASSO) and tertiary reserves (MARI). This raises a challenge of operational security, since – in contrast to day-ahead system operations – violations in balancing platforms leave little time to network operators for corrections. In the context of a collaboration with Norwegian system operator Statnett and N-SIDE, our team has developed a proposal for hierarchical balancing. The procedure works as indicated in the left panel of the figure below, whereby a system operator aggregates balancing offers of domestic resources in a bid-blending process, which produces an aggregate bid for the balancing platforms. Such an aggregate bid is indicated in the right panel of the figure below. The dispatch of the balancing platforms is then disaggregated to indvidual balancing resources, in a disaggregation step which represents the network constraints of the network operator.

Read more

Q. Lété, A. Papavasiliou, Impacts of Transmission Switching in Zonal Electricity Markets – Part I, IEEE Transactions on Power Systems, forthcoming

Q. Lété, A. Papavasiliou, Impacts of Transmission Switching in Zonal Electricity Markets – Part II, IEEE Transactions on Power Systems, forthcoming

A. Papavasiliou, M. Bjorndal, G. Doorman, N. Stevens, Hierarchical Balancing in Zonal Markets, 17th International Conference on the European Energy Market, 2020

I. Aravena, A. Papavasiliou, Renewable Energy Integration in Zonal Markets, IEEE Transactions on Power Systems, vol. 32, no. 2, pp. 1334-1349, March 2017

J. Han, A. Papavasiliou, The Impacts of Transmission Topology Control on the European Electricity Network, IEEE Transactions on Power Systems, vol. 31, no. 1, pp. 496-907, January 2016

J. Han, A. Papavasiliou, Congestion Management through Topological Corrections: A Case Study of Central Western Europe, Energy Policy, vol. 86, pp. 470-482, November 2015