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ABSTRACT: This paper proposes a new unit commitment (UC) formulation for a power system with significant levels of wind generation. The proposed scheme departs from existing unit commitments in that it explicitly models the day-ahead predicted residual demand probability density function (PDF) including the effect of wind power curtailment. This PDF is then used to define a constraint on the probability of the residual demand exceeding the scheduled reserve, which is imposed in addition to the standard N-1 deterministic security criterion. This hybrid probabilistic/deterministic form maintains the mixed-integer linear structure that makes the proposed UC compatible with highly efficient commercially available solvers. Numerical examples illustrate the economical and technical benefits obtained by systematically including wind curtailment as decisions variables in the UC. In addition, the paper computes the hourly day-ahead UC schedule over the course of one year for a typical power system to illustrate the impact of wind power penetration on measures such as operation costs, incremental costs, emission levels, on/off unit switching operations, and reserve levels.
IEEE Transactions on Power Systems 03/2011; · 2.68 Impact Factor
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ABSTRACT: We consider an electricity market cleared by merit- order in which generating companies (Gencos) own any number of units and submit offers consisting of multiple blocks of finite generating capacity and constant incremental cost (IC). It has been shown that if the IC block offers can vary continuously, the market outcomes supported by pure strategy Nash equilibria (NE) are fewer than or equal to the number of Gencos and can all be computed through a mixed-integer linear programming (MILP) scheme. Knowledge of these NE then serves to study how an oligopolistic market of this type behaves under a variety of demand and market power conditions.
IEEE Transactions on Power Systems 06/2010; · 2.68 Impact Factor
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ABSTRACT: The authors consider a yearly auction where electricity generating companies (Gencos) bid to receive yearly green house gas (GHG) emission allowances. Gencos sell electricity in an oligopolistic electricity market that clears on an hourly basis and operates under a cap-and-trade emissions regulation scheme. Gencos strategically self-allocate their yearly allowance into hourly allowances that they then use to take part in the hourly electricity market. If a Genco emits above or below its self-allocated allowance for that hour then, in the first case, the hourly deficit is made up by buying an allowance from an external market, whereas in the second the hourly allowance surplus is sold to the external market. Recognising that the levels of power and emissions produced by the Gencos as well as the associated prices throughout the year will be influenced by both the yearly and hourly allowances, the auction maximises an objective function that is equal not only to the total amount bid by the Gencos to obtain allowances but also includes the yearly social welfare. This study proposes an approach that considers all of the above-mentioned points in a coordinated fashion and can be viewed as a mathematical program (the allowance auction) subject to a Nash equilibrium problem (the distribution by each Genco of its yearly allowance into hourly allowances), which in turn is subject to the Cournot-Nash equilibrium conditions of the hourly oligopolistic electricity market.
IET Generation Transmission & Distribution 03/2010; · 1.20 Impact Factor
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ABSTRACT: The impact of wind power generation on the reserve levels has been studied in this paper through the simulation of a one-year daily unit commitment schedule for a benchmark power system. The case study shows that under the hybrid “N-1” plus “ 3σ ” security criterion, there exists a complex relationship among reserve levels, wind penetration and the relative size the conventional units. When such units are relatively large, they dominate the reserve settings for small levels of wind power penetration. However, in systems where the relative weight of individual generators is smaller, the “ 3σ ” security constraint plays a more conspicuous role even at low levels of wind penetration.
Sustainable Alternative Energy (SAE), 2009 IEEE PES/IAS Conference on; 10/2009
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ABSTRACT: In their attempt to cut down on greenhouse gas emissions from electricity generation, several countries are committed to install wind power generation up to and beyond the 10%-20% penetration mark. However, the large-scale integration of wind power represents a challenge for power system operations planning because wind power 1) cannot be dispatched in the classical sense; and 2) its output varies as weather conditions change. This warrants the investigation of alternative short-term power system operations planning methods capable of better coping with the nature of wind generation while maintaining or even improving the current reliability and economic performance of power systems. To this end, this paper formulates a short-term forward electricity market-clearing problem with stochastic security capable of accounting for nondispatchable and variable wind power generation sources. The principal benefit of this stochastic operation planning approach is that, when compared to a deterministic worst-case scenario planning philosophy, it allows greater wind power penetration without sacrificing security.
IEEE Transactions on Power Systems 06/2008; · 2.68 Impact Factor
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ABSTRACT: In an electricity market cleared by a merit-order economic dispatch we first identify the necessary conditions for the market outcomes supported by pure strategy Nash equilibria (NE) to exist when generating companies (Gencos) game through their incremental cost offers or supply functions. A Genco may own any number of units, each offering to generate power through an incremental cost curve or supply function consisting of multiple blocks. Then, we develop a mixed-integer linear programming (MILP) scheme to find the NE without approximations or iterations. In Part II of this paper, we show how to use these NE to derive a dominant offer strategy in terms of gaming or not gaming that best meet the risk/benefit expectations of the participating Gencos. The MILP scheme is tested on several systems of up to 30 generating units, each with four incremental cost blocks. Finally, based on these results, we carry out a number of numerical analyses of how market power is influenced by the number and size of the competing Gencos.
IEEE Transactions on Power Systems 06/2008; · 2.68 Impact Factor
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ABSTRACT: In an electricity market cleared by a merit-order economic dispatch we make use of the mixed-integer linear programming (MILP) scheme derived in Part I to find the market outcomes supported by a pure strategy Nash equilibria (NE). From these NE, we identify offer strategies in terms of gaming or not gaming that best meet the risk/benefit expectations of the participating Gencos. To do this, a number of measures of potential profit gain and loss are developed that quantify the notion of risk/benefit under the possible multiple NE. The NE identification scheme is tested on several systems of up to 30 generating units, each with four incremental cost blocks, also showing how market power is influenced by the number and size of the competing Gencos as well as by the imposed price cap.
IEEE Transactions on Power Systems 06/2008; · 2.68 Impact Factor
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ABSTRACT: A scheme is developed and tested to negotiate bilateral contracts in mixed pool/bilateral electricity markets. Each negotiating party can choose any of the following three general measures to assess its profit risk: (i) regret; (ii) dispersion-from-the-mean; (iii) value-at-risk. Similarly, a mix of three measures can be used to describe the benefit: (i) expected profit; (ii) expected rate of return; (iii) expected ratio of the actual to ideal profits. The main results include: an analysis and comparison of different measures of risk and benefit on the outcome of a bilateral negotiation; an analysis of the impact on the outcome of the negotiation of various sources of uncertainty.
Power Tech, 2007 IEEE Lausanne; 08/2007
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ABSTRACT: We develop and test an efficient simulator to estimate the sequence of automatic events that follow a contingency leading to islanding and cascading outages. The simulator is based on a quasi-steady-state model o that includes island identification, island power balance, primary frequency regula tion, under-frequency load shedding, over-frequency generator tripping, and island load flow. The simulator first identifies the islands into which the network splits through the null space of the network susceptance matrix. Each island is then analyzed for a surplus or deficit of primary frequency regulation, followed by any necessary corrective load shedding or generation tripping. Next, each island's load flow is solved and tested for possible new line overloads and corresponding line tripping. The overall contingency analysis reruns until either all loads are shed or the islands can operate at some reduced load level within their operational bounds. Simulation results are presented for a 10- bus, 13-line system and for the IEEE 73-bus, 119 line reliability test network.
Power Tech, 2007 IEEE Lausanne; 08/2007
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ABSTRACT: The joint operation of wind energy and traditional power plants has brought new challenges to the operation of power systems. In particular, reserve scheduling may need to be modified in order to accommodate increasing levels of intermittent and random wind power. In this panel we discuss some of the issues and possible solutions regarding reserve considering the wind power characteristics. Specifically, we will outline a methodology to include secondary reserve requirements in the day-ahead operations planning as a set of probabilistic constraints.
Power Engineering Society General Meeting, 2007. IEEE; 07/2007
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ABSTRACT: In mixed pool/bilateral electricity markets, participants can sign forward bilateral contracts several months in advance of its delivery. In addition, generators may sell to and loads may buy from the pool at the spot price through the day-ahead or balancing markets. Forward bilateral contracts have the advantage of price predictability in comparison with the uncertain spot price. However, the risk is that such a contract commits the partners to a price that may be disadvantageous compared to the spot price. Here, we propose a systematic negotiation scheme through which a generator and load can reach a mutually beneficial and risk tolerable forward bilateral contract, either physical or financial. Under this approach, the generator and load respond rationally to a stream of bilateral bids/counter-bids and offers/counter-offers considering their respective benefits while accounting for the risks incurred by the prediction uncertainty in the pool spot price and other market parameters over the length of the contract. Each negotiating party can choose its own definition of risk which can be influenced by regret, value-at-risk or dispersion from the mean. Numerical tests show that this flexible negotiating approach can be readily put into practice
IEEE Transactions on Power Systems 06/2007; · 2.68 Impact Factor
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ABSTRACT: This paper looks at the important couplings that tie short-term electricity market equilibrium to the enforcement of power system security requirements. We first address the equilibrium implications of embedding security constraints in these markets-in the form of explicit constraints specifying the minimal levels of operating reserves. Second, we assess the equilibrium properties for more general contingency-driven security-constrained market-clearing formulations, which specify implicitly the levels of operating reserves. We finally concentrate our attention on proposed security-constrained market-clearing formulations for which the power system operator accounts for the uncertainty in the demand as well as in the generator and line random availabilities
Power Systems Conference and Exposition, 2006. PSCE '06. 2006 IEEE PES; 12/2006
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ABSTRACT: This paper presents an approach for the allocation of transmission network costs by controlling the nodal electricity prices. The proposed approach introduces generation and nodal injection penalties into the traditional economic dispatch so as to create nodal price differences that recover the required transmission revenue from the resulting congestion rent. As a consequence, the new electricity prices reflect not only the marginal costs of production subject to transmission constraints but also the capital costs of the network. This is the approach commonly adopted with most commodities whose price includes the unit cost of the good itself as well as the transportation cost from the production centers to the final consumer.
IEEE Transactions on Power Systems 03/2006; · 2.68 Impact Factor
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ABSTRACT: Current practice in some electricity markets is to schedule energy and various reserve types sequentially, first clearing the energy market, followed by the reserves needed. Since distinct reserve services can in fact be strongly coupled, and the heuristics required to bridge the various sequential markets can ultimately lead to loss of social welfare, simultaneous energy/reserves market-clearing procedures have been proposed and are in use. However, they generally schedule reserve services subject to exogenous rules and parameters that do not relate to actual operating conditions. The weaknesses of the current approaches warrant the investigation of alternatives. In that regard, we present a different methodology to the simultaneous market clearing of energy and reserve services. This approach avoids the pitfalls of the sequential procedures, while at the same time its basis for scheduling reserve services does no longer rely on some rules of thumb. The salient feature of the proposed approach is that, under marginal pricing, it yields a single price for all reserve types scheduled at a bus, unlike the current approaches. We show that this common price is given by the nodal marginal cost of security. We present two specific implementations of a simultaneous security-constrained market-clearing procedure, one deterministic and one probabilistic. An example of joint market clearing of energy with reserves required for primary and tertiary regulation illustrates how their strong coupling affects their schedule and prices.
Proceedings of the IEEE 12/2005; · 6.81 Impact Factor
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ABSTRACT: This paper analyzes the market-clearing formulation with stochastic security developed in its companion paper through two case studies solved using mixed-integer linear programming techniques. The generation and reserve schedules as well as the nodal prices of energy and security are assessed under various conditions such as a) line flow limits, b) when nonspinning reserve is excluded from the formulation, c) demand-side valuation of energy not served, d) generator ramping limits, and e) the set of pre-selected contingencies.
IEEE Transactions on Power Systems 12/2005; · 2.68 Impact Factor
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ABSTRACT: The unit commitment problem with tertiary reserve requirements has been broadly studied. Such reserves, when needed, are centrally deployed with relatively slow time constants of the order of minutes. In contrast, the scheduling of units offering primary frequency regulation reserve deployable in a decentralized manner within seconds of a contingency has received relatively little attention. In this paper, we formulate and solve a multiperiod unit commitment that simultaneously accounts for both primary and tertiary reserve constraints. What makes this scheduling problem particularly challenging is the characteristic that primary frequency regulation reserves have a common single degree of freedom, namely, the system frequency deviation.
IEEE Transactions on Power Systems 12/2005; · 2.68 Impact Factor
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ABSTRACT: The first of this two-paper series formulates a stochastic security-constrained multi-period electricity market-clearing problem with unit commitment. The stochastic security criterion accounts for a pre-selected set of random generator and line outages with known historical failure rates and involuntary load shedding as optimization variables. Unlike the classical deterministic reserve-constrained unit commitment, here the reserve services are determined by economically penalizing the operation of the market by the expected load not served. The proposed formulation is a stochastic programming problem that optimizes, concurrently with the pre-contingency social welfare, the expected operating costs associated with the deployment of the reserves following the contingencies. This stochastic programming formulation is solved in the second companion paper using mixed-integer linear programming methods. Two cases are presented: a small transmission-constrained three-bus network scheduled over a horizon of four hours and the IEEE Reliability Test System scheduled over 24 h. The impact on the resulting generation and reserve schedules of transmission constraints and generation ramp limits, of demand-side reserve, of the value of load not served, and of the constitution of the pre-selected set of contingencies are assessed.
IEEE Transactions on Power Systems 12/2005; · 2.68 Impact Factor
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ABSTRACT: We show that the system loss function in a power network is bounded below by any number of supporting hyper-planes in the space of generalized injections. A supporting hyper-plane is defined by the linear Taylor series expansion of the system loss function around a given operating point. The supporting hyper-plane property is valid provided that the expansion point is sufficiently near the flat-voltage profile. We have assessed experimentally the range of validity of this assumption, called the range of hyper-plane support (RHS), showing that for typical networks, the RHS is broad, particularly when the bus voltages are controlled near 1 per unit. The supporting hyper-plane model was also tested as part of an economic dispatch with transmission losses to demonstrate that this linear model provides the same results as when the losses are treated as a nonlinear function.
IEEE Transactions on Power Systems 12/2005; · 2.68 Impact Factor
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ABSTRACT: The concept of electrothermal coordination (ETC) in power system operation introduced in Part I proposes to exploit thermal inertia to coordinate line temperature dynamics with existing power system controls, thus increasing power transfer capability and enhancing system security and economic performance. In this Part II, the characteristics of ETC and its benefits in operational functions such as augmenting power transfer capability, emergency control, congestion management, and system loadability are numerically analyzed through a number of case studies. This paper also examines some practical issues concerning the deployment of ETC.
IEEE Transactions on Power Systems 12/2005; · 2.68 Impact Factor
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ABSTRACT: This paper deals with the problem of transmission cost allocation (TCA) in very large networks with multiple interconnected regions or countries. The basis of one scheme recently put forward is a single-area TCA algorithm from which inter-regional compensations are computed. One concern about this approach is that an international operator (IO) must have access to detailed information that autonomous regions or countries may not be willing or able to share. This led to the development of a new multiarea TCA scheme, called multiarea decoupled (MAD), in which each region carries out its own TCA, while the IO carries out a region-wise TCA on the network of tie lines. In MAD, the IO does not require detailed and possibly proprietary information about regional networks, relying only on the characteristics of the tie-line network and the extent to which each region uses such a network. This is a key issue, especially in North America, considering FERC's intention to provide Regional Transmission Organizations (RTOs) with exclusive autonomy to provide transmission service and to set and administer their own transmission-use tariffs. Numerical studies on the proposed scheme are described, including a four-area system based on the IEEE reliability test system (RTS) network.
IEEE Transactions on Power Systems 09/2005; · 2.68 Impact Factor
