A - Background and objectives
The European Transmission Network (ETN) has been evolving significantly in the ways that network operators work and cooperate with each other, in particularly by setting up common operating procedures and tools such as network simulation tools. In the domain of power system state estimation and transmission network time simulation, very few innovations have emerged over the past decade (2000-2010) in Europe. Breakthroughs are therefore expected in power system simulation along four directions to serve the ETN: state estimation, optimization algorithms, time domain simulation and power system component modelling.
The PEGASE project aimed to remove several algorithmic barriers related to the monitoring, simulation and optimization of very large power systems, therefore paving the way for improved network operation.
B - Description of the result
The new approach proposed by the PEGASE project , called Iterative Security Constrained Optimal Power Flow (ISCOPF), a potentially huge amount of post-contingency constraints is dealt with using two complementary methods:
In order to reduce the number of contingencies that need to be analysed simultaneously in a constrained optimization problem, a small superset of the binding contingencies is identified in a sequential manner, by using concepts of “constraint domination” or “umbrella contingencies” recently developed in the literature.
In order to reduce the number of variables introduced by each contingency and thus to increase the number of contingencies that may be analysed simultaneously in a constrained optimization problem an original “network compression” method (NC) has been implemented, which exploits the property that the impact of a contingency is limited to a localized region of the network and allows the replacement of the rest of the system by an equivalent network.
The proposed algorithms have been implemented in a full scale prototype which takes into account special devices such as Phase-shifting Transformer (PST) and HVDC (Current Source Converter - CSC and Voltage Source Converter (VSC)) and primary active and reactive control of the generating units. Its computational efficiency has been seriously improved through the parallel computation of inherently independent processes (Security Assessment, Network Compression and Post-Contingency OPF (PCOFF)).
For evaluation of performance and quality of results, the prototype has been put in the hands of actual users of that kind of tool. Number of TSOs participated in and reviewed the performed tests: SO-UPS (Russia), TEIAS (Turkey), HEP (Croatia), Transelectrica (Romania), RTE (France).
In order to demonstrate the possible use of the prototype for large, real systems operation, two test models have been used: the Russian power system and the European and Turkish power system. These large-scale demonstrations show the ability of the method to reduce dramatically and with a satisfactory accuracy the size of the SCOPF problems and to provide the solution in an acceptable computation time. They proved that the SCOPF algorithm is able to solve optimization problems of an unprecedented size, involving large systems and numerous contingencies. Indeed, a SCOPF on the pan European Transmission System with more than 6000 contingencies has been solved in less than 45 minutes, which is still too slow for day-ahead operational planning. The present performances are nevertheless well-suited for operational planning of systems of around 3000 buses, which covers virtually the needs of all European TSOs at the national level.
According to the PEGASE Consortium Agreement, the prototype software is owned 100% by TRACTEBEL, which will lead the ISCOPF prototype commercialization.