Congestion management by commitment & dispatch in the balancing market

Introduction of the electricity markets has brought into attention the need to prepare the day ahead generation schedules required for the dispatch of the electric power system. The schedules have to ensure secure operation of the power system taking into account the capacity of the transmission lines and the possibility of congestion that may appear when the schedules are implemented. The preparation of the schedules requires information on the network operating conditions including network constraints. Such conditions and constraints are verified using various software packages for power flow simulation. However, the information obtained from such simulation is difficult to implement directly into optimization software for commitment and dispatch of generating units and loads. There is a need for the determination of a simple way of communication between network operators and market participants in order to remove the network congestion in the prepared schedules. One of the most effective ways is to transfer the network conditions into nodal constraints. Several categories of the nodal constraints, if adequately defined, can be applied to remove network congestion by the generating unit schedules. The paper presents a method of congestion management during the process of unit commitment and dispatch using a binary linear approach taking into account the nodal constraints. The following topics are discussed in the paper: nodal constraints as a way of communication of network operating conditions; use of the nodal constraints in commitment & dispatch of generating units as the tool for the congestion management; the binary linear programming commitment & dispatch method for the determination of schedules of generating units. The paper presents a practical experience with managing congestion in the Polish balancing market that has been operating successfully since 2001