Unit commitment with ramp multipliers

This paper presents a new decomposition method, based on the Lagrangian relaxation technique, for solving the unit commitment problem with ramp rate constraints. By introducing an additional vector of multipliers to represent the cost of “system ramping demand”, this method can handle the coupling constraints between time periods while still keeping the simplicity of the original decomposition method. A new algorithm for updating multipliers is also proposed. Similar to the bundle algorithm, this algorithm maintains the previous iteration history to approximate the dual envelope. Unlike the bundle algorithm, this new algorithm generates an update step along the subgradient direction without any quadratic programming (QP) code. The new algorithm combines the bundle algorithm's smooth approach to the dual optimum with the sub-gradient method's fast update     

Efficient integer optimization algorithms for optimal coordinationof capacitors and regulators

The optimal coordination of switched capacitors and tap-changing transformers in a radial distribution system is considered. The formulation incorporates voltage constraints. The coordination problem is approximated by a constrained discrete quadratic optimization using the results from the corresponding unconstrained continuous problem. The discrepancy between the actual and approximating problem is discussed. Two algorithms are proposed to seek solutions to the approximating optimization problem. The first is a randomized algorithm that runs fast but for which there is no guarantee of optimality. The second is a deterministic algorithm, the run time of which is polynomially bounded in the problem size. For large systems the run times of these algorithms may be significantly less than the run times of explicit search or branch and bound algorithms. Test results on a 70 node system confirm the theoretical predictions     

State estimator condition number analysis

This paper develops formulas for the condition number of the state estimation problem as a function of the different types and number of measurements. We present empirical results using the IEEE RTS-96 and IEEE 118 bus systems that validate the formulas     

A comparison of distributed optimal power flow algorithms

We present an approach to parallelizing optimal power flow (OPF) that is suitable for coarse-grained distributed implementation and is applicable to very large interconnected power systems. The proposed distributed scheme can be used to coordinate a heterogeneous collection of utilities. Three mathematical decomposition coordination methods are introduced to implement the proposed distributed scheme: the auxiliary problem principle (APP), the predictor-corrector proximal multiplier method (PCPM), and the alternating direction method (ADM). We demonstrate the approach on several medium size systems, including IEEE Test Systems and parts of the ERCOT (Electric Reliability Council of Texas) system     

Border Flow Rights and Contracts for Differences of Differences: Models for Electric Transmission Property Rights

In this paper, a property rights model for electric transmission is proposed and its properties analyzed. The proposed rights, called "border flow rights," support financial hedging of transmission risk and merchant transmission expansion through associated financial rights, called "contracts for differences of differences." These financial rights allow for forward trading of both energy and transmission by a unified exchange, avoiding the bifurcation in current markets between decentralized long-term energy trading and centralized long-term transmission trading. Such long-term trading can help to support the financing of both generation and transmission assets. We consider incentive properties of such a right in the absence of lumpiness, economies of scale, and market power.     

Variation of distribution factors with loading

Power transfer distribution factors depend on the operating point and topology of an electric power system. However, it is known empirically that, for a fixed topology, the power transfer distribution factors are relatively insensitive to the operating point. We demonstrate this result theoretically for systems of arbitrary topology with losses, but only for the special case of having reactive compensation sufficient to keep voltages constant at all busses. We also analyze a power to current distribution factor that more closely relates to thermal constraints. We provide empirical corroboration for the theoretical result.     

Proteins associated with purified human cytomegalovirus particles

Virion-associated proteins isolated from purified human cytomegalovirus particles (strain AD169) were used as substrates for chemical sequence analysis. Extracellular virions, noninfectious enveloped particles, and dense bodies were purified by negative viscosity-positive density gradient centrifugation, and their component proteins were separated by denaturing polyacrylamide gel electrophoresis. The deduced amino acid sequence of individual protein bands was used to identify six corresponding viral genes whose products have not previously been identified as virion constituents: UL47, UL25, UL88, UL85, UL26, and UL48.5. In addition, a 45-kDa cellular protein was identified, and the protein fragments sequenced have a high degree of amino acid identity with actin. However, antiactin monoclonal and polyclonal antibodies did not react with a specific protein in the virus preparations, suggesting that this 45-kDa protein is an immunologically distinct isoform of actin. The newly identified viral and cellular proteins were resistant to protease treatment of purified virions, suggesting that they are unlikely to be contaminants of the viral preparations.     

State estimation distributed processing [for power systems]

This paper presents an application of a parallel algorithm to power systems state estimation. The authors apply the auxiliary problem principle to develop a distributed state estimator, demonstrating its performance on the Electric Reliability Council of Texas (ERCOT) and the Southwest Power Pool (SPP) systems     

Supply function equilibrium bidding strategies with fixed forward contracts

During the last 15 years, the regulatory framework for the wholesale sector of the electricity industry has been replaced in many countries by market competition. In such an environment, electric firms compete through both spot market bidding and bilateral contract trading. Firms have to consider their forward contract positions when they make spot market decisions. In this paper, we propose a linear asymmetric supply function equilibrium (SFE) model with transmission constraints to develop firms' optimal bidding strategies considering forward contracts. The characteristics of firms' behaviors are analyzed under the induced equilibrium conditions. The model is applied to the real-time energy market of the Electric Reliability Council of Texas (ERCOT). The effects of forward contracts on the ERCOT market are evaluated. It is shown that the model is able to capture features of bidding behaviors in the ERCOT market.     

Transmission planning issues in a competitive economic environment

In the increasingly competitive electric utility industry, there is an emerging need for the diverse parties using the transmission system to understand transmission planning. In this paper, the authors discuss features of transmission planning that are problematic in such an environment. Reference is made to a number of transmission system expansion and access disputes. Transmission software models are also discussed