Antonio Gómez Expósito

Electricity Market Price Forecasting Based on Weighted Nearest Neighbors Techniques

This paper presents a simple technique to forecast next-day electricity market prices based on the weighted nearest neighbors methodology. First, it is explained how the relevant parameters defining the adopted model are obtained. Such parameters have to do with the window length of the time series and with the number of neighbors chosen for the prediction. Then, results corresponding to the Spanish electricity market during 2002 are presented and discussed. Finally, the performance of the proposed method is compared with that of recently published techniques.

Self-tuning of Kalman filters for harmonic computation

This paper addresses the problem of tuning Kalman filters so that they can properly track harmonic fluctuations. A method for self-tuning of the model error covariance is presented and tested, showing fast adaptive capability under sudden changes of the input signal.

Generalized observability analysis and measurement classification

Network observability analysis is formulated in a way to incorporate the conventional as well as unconventional measurements, including line currents. This formulation has two essential advantages over the existing methods of network observability analysis: (1) it detects not only unobservability but also uniqueness of the observed state, and (2) it can directly identify the unobservable or nonuniquely observable branches without having to remove the irrelevant injections in an iterative manner. In addition, unlike the numerical observability analysis methods proposed so far, it can readily identify residual spread components and critical measurements. The proposed formulation is implemented and tested on sample power systems.

Reference current computation methods for active power filters: accuracy assessment in the frequency domain

This paper focuses on the steady-state response of existing methods for computing the reference current of active power filters. For each class of methods, the main source of discrepancy between the load harmonic current and the computed reference current is identified and the frequency spectrum of the resulting error is analytically determined. Although this topic has been partially addressed in previous publications, the proposed frequency-domain approach provides valuable qualitative information about how the errors are produced and distributed, which is masked when the analysis is carried out in the time domain. First, the frequency-domain formulation is separately presented for each method. Then, a comparison of the resulting errors is performed on a case study. Finally, some experimental results are given to validate the proposed frequency-domain analysis.

A comparison of techniques for state-space transient analysis of transmission lines

This paper reviews and compares several methods to analytically obtain the transient response of transmission lines in the time domain, in those cases where frequency independent parameters can be assumed. The distributed-parameter line is modeled by the cascaded connection of a number of lumped-parameter /spl pi/ circuits, each one representing a fraction of the line length, leading to a linear time-invariant (LTI) circuit. The associated state-space equations are formulated, allowing explicit expressions for the state variables to be written in the time domain. The solution is then obtained by means of three different approaches, all of them requiring that the natural frequencies be previously computed, namely: eigenvector-based procedure, Vandermonde matrix method, and Lagrange interpolation formula. Numerical integration by the trapezoidal rule is also considered for comparison. Two kinds of test results are presented. First, accuracy of the results provided by the LTI lumped-parameter model are compared with those obtained using the Electromagnetic Transients Program. Second, a comparison is performed in terms of the computational cost involved in each method. Two cases of practical interest are assessed, namely solving from scratch the state equations and updating the solution for a new set of initial conditions.

Detecting multiple solutions in state estimation in the presence of current magnitude measurements

This paper investigates the observability problem when the network contains current magnitude measurements. Use of these measurements may lead to multiple solutions and therefore to the loss of unique observability for certain measurement configurations. The paper proposes a simple method based on the commonly used measurement residual covariance matrix, in order to detect the possibility of multiple solutions for a given measurement set. The proposed test is simple to implement and uses the already available matrices and data structures of the commonly used weighted least squares state estimation programs. It can be utilized as a planning tool during the initial stages of measurement system design as well as an online observability analysis tool to enhance the capability of the existing observability programs which can not properly process the current magnitude measurements. Numerical examples are provided to demonstrate the performance of the proposed method on sample power systems.

Time-Series Prediction: Application to the Short-Term Electric Energy Demand

This paper describes a time-series prediction method based on the kNN technique. The proposed methodology is applied to the 24-hour load forecasting problem. Also, based on recorded data, an alternative model is developed by means of a conventional dynamic regression technique, where the parameters are estimated by solving a least squares problem. Finally, results obtained from the application of both techniques to the Spanish transmission system are compared in terms of maximum, average and minimum forecasting errors.

Augmented rectangular load flow model

This paper presents some improvements to the load flow solution in rectangular coordinates. First, in an attempt to use as linear a model as possible, both the nodal equations and the bus constraints are retained. The Newton-Raphson method is then applied to the enlarged set of equations, written in terms of bus voltages and currents. This scheme, combined with a simple procedure to handle PV buses, leads to a computationally efficient algorithm, particularly advantageous in the presence of zero-injection buses. Experimental results are provided comparing the performance of the proposed approach with that of the conventional formulation.

Quasi-coupled three-phase radial load flow

Ignoring mutual coupling in three-phase load-flow computations saves a lot of computational effort but provides inaccurate results for many applications. In this paper, the effect of mutual coupling is taken into account through equivalent branch voltage sources or bus current injections. This simple idea allows accurate enough solutions to be obtained, while much of the computational saving associated with decoupled load flows is retained. Experiments on several unbalanced networks are reported showing the performance of the proposed idea when applied to distribution load flows based on the forward/backward tree sweeps.

Short-term hydro-thermal coordination based on interior point nonlinear programming and genetic algorithms

This paper presents a combined primal-dual logarithmic-barrier interior point and genetic algorithm for short-term hydro-thermal coordination. The genetic algorithm is used to compute the optimal on/off status of thermal units, while the interior point module deals with the optimal solution of the hydraulically-coupled short-term economic dispatch of thermal and hydro units. Inter-temporal constraints both due to cascaded reservoirs and maximum up and down ramps of thermal units are included in the latter module. Results from realistic cases based on the Spanish power system are reported.