This paper addresses the main challenges to the security constrained optimal power flow (SCOPF) computations. We first discuss the issues related to the SCOPF problem formulation such as the use of a limited number of corrective actions in the post-contingency states and the modeling of voltage and transient stability constraints. Then we deal with the challenges to the techniques for solving the SCOPF, focusing mainly on: approaches to reduce the size of the problem by either efficiently identifying the binding contingencies and including only these contingencies in the SCOPF or by using approximate models for the post-contingency states, and the handling of discrete variables. We finally address the current trend of extending the SCOPF formulation to take into account the increasing levels of uncertainty in the operation planning. For each such topic we provide a review of the state of the art, we identify the advances that are needed, and we indicate ways to bridge the gap between the current state of the art and these needs. * Corresponding author Email addresses: capitane@montefiore.ulg.ac.be (F. Capitanescu), camel@us.es (J.L. Martinez Ramos), patrick.panciatici@rte-france.com (P. Panciatici), kirschen@uw.edu (D. Kirschen), alejandromm@us.es (A. Marano Marcolini), ludovic.platbrood@gdfsuez.com (L. Platbrood), l.wehenkel@ulg.ac.be (L. Wehenkel) Preprint submitted to Electric Power Systems ResearchMay 2, 2011Keywords: mixed integer linear programming, mixed integer nonlinear programming, nonlinear programming, optimal power flow, security constrained optimal power flow MotivationThe SCOPF [1,2] is an extension of the OPF problem [3,4] which takes into account constraints arising from the operation of the system under a set of postulated contingencies. The SCOPF problem is a nonlinear, nonconvex, large-scale optimization problem, with both continuous and discrete variables [1,2]. The SCOPF belongs therefore to the class of optimization problems called Mixed Integer Non-Linear Programming (MINLP).The SCOPF has become an essential tool for many Transmission System Operators (TSOs) for the planning, operational planning, and real time operation of their system [5,6, 7,8]. Furthermore, in several electricity markets (e.g. PJM, New-England, California, etc.) the locational marginal prices calculated using a DC SCOPF are used to price electricity. This approach is also under consideration in other systems [9,10,11].Several papers discussing the challenges to the OPF problem were published during the 90's [5,6, 7,8]. Since then several important changes have taken place not only in power systems operation and control but also in mathematical programming:• Power systems operate today in conditions that are more "stressed" and were not foreseen at the planning stage. In particular the increase in load has not been supported by an adequate upgrade of the generation and transmission systems. Furthermore the creation of electricity markets has led to the trading of significant amounts of electrical energy over lo...
The high proliferation of converter-dominated Distributed Renewable Energy Sources (DRESs) at the distribution grid level has gradually replaced the conventional synchronous generators (SGs) of the transmission system, resulting in emerging stability and security challenges. The inherent characteristics of the SGs are currently used for providing ancillary services (ASs), following the instructions of the Transmission System Operator, while the DRESs are obliged to offer specific system support functions, without being remunerated for these functions, but only for the energy they inject. This changing environment has prompted the integration of energy storage systems as a solution for transfusing new characteristics and elaborating their business in the electricity markets, while the smart grid infrastructure and the upcoming microgrid architectures contribute to the transformation of the distribution grid. This review investigates the existing ASs in transmission system with the respective markets (emphasizing the DRESs’ participation in these markets) and proposes new ASs at distribution grid level, with emphasis to inertial response, active power ramp rate control, frequency response, voltage regulation, fault contribution and harmonic mitigation. The market tools and mechanisms for the procurement of these ASs are presented evolving the existing role of the Operators. Finally, potential barriers in the technical, regulatory, and financial framework have been identified and analyzed.
Abstract-In this paper, we propose to analyse the pratical task of dealing with uncertainty for security management by Transmission System Operators in the context of day-ahead planning and intraday operation. We propose a general but very abstract formalization of this task in the form of a threestage decision making problem under uncertainties in the minmax framework, where the three stages of decision making correspond respectively to operation planning, preventive control in operation, and post-contingency emergency control. We then consider algorithmic solutions for addressing this problem in the practical context of large scale power systems by proposing a bilevel linear programming formulation adapted to the case where security is constrained by power flow limits. This formulation is illustrated on two case studies corresponding respectively to a synthetic 7-bus system and the IEEE 30-bus system.Index Terms-operation planning, intraday operation, security management under uncertainties, transmission system operator, worst case analysis, mathematical programming I. OUTLINE D AY-AHEAD operational planning as well as intraday operation of power systems is affected by an increasing amount of uncertainty due to the coupling of wind power intermittency, cross-border interchanges, market clearing, and load evolution. In this context, a deterministic approach that consists of forecasting a single best-guess of the system injections for the next day or hours, and of ensuring system security along this trajectory only, becomes inappropriate. The Transmission System Operator (TSO) will rather determine his strategic decisions by considering a set of scenarios reflecting his uncertainty and by making sure that under the worst of these scenarios the system security is still controllable.In this paper, we analyze the practical problem of security management in operation planning and intraday operation of large scale systems, and then formalize it in an abstract and generic way as a multi-stage decision making problem under uncertainties. We also propose and illustrate some practically feasible algorithms to address this problem for large scale systems. These algorithms are targeted towards solving a set of manageable subproblems of practical interest. In the practical context of operation planning and operation of power systems, decision making is carried out in an iterative fashion at different timeframes from day-ahead to minutesahead. The objective is to ensure system security at the lowest possible cost; the strategy to reach this objective is based on the evaluation of possible future scenarios so as to identify the most difficult ones and to determine strategic "ahead of time" decisions enabling operators to cope with these difficult scenarios during the next periods of time. In this context, a reasonable and in practice commonly adopted strategy consists in (i) searching in advance for the potentially most difficult operating scenarios, and (ii) postponing the commitment of the most costly actions at the latest ...
This paper focuses on improving the solution techniques for the AC SCOPF problem of active power dispatch by using the DC SCOPF approximation within the SCOPF algorithm. Our approach brings two benefits compared to benchmark SCOPF algorithms: it speeds-up the solution of an iterative AC SCOPF algorithm thanks to a more efficient identification of binding contingencies, and allows improving the objective by an appropriate choice of a limited number of corrective actions for each contingency. The proposed approach is illustrated on 5 test systems of 60, 118, 300, 1203, and 2746 buses.
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