Power System Security in Market Clearing and Dispatch Mechanisms

This paper presents and discusses some typical market clearing and dispatch mechanisms based on security-constrained (SC) optimal power flow (OPF) techniques that are currently being utilized in various jurisdictions throughout the world, concentrating on how system security is accounted for in these auction systems and the effect that this has on the system dispatch schedules and energy prices. The Ontario market is used as an example to illustrate the practical application of these security-constrained clearing and dispatch mechanisms. The need for a better representation of system security in the existent auction systems is also discussed, based on the fact that "unexpected" dispatch solutions, resulting from diverse bidding patterns and the mechanisms used to clear and dispatch the market, may render ineffective the predetermined system security limits typically used in most auction models, leading to insecure operating conditions and/or unnecessary high prices associated with an unrealistic modeling of system congestion. The latter is illustrated using a simple 6 bus test system, comparing the dispatch levels and prices, as well as the general system operating conditions, obtained from a SC-OPF auction mechanism with respect to those obtained using a voltage-stability-constrained technique, which better represents system security