Antonio Jordán López

Power System Frequency Measurement Under Nonstationary Situations

A new method for the measurement of the instantaneous power-system frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is developed that diminishes the variance of the estimation. The procedure is applied to the case of single- and three-phase networks, and uncertainty in the frequency estimation is obtained with simulated signal and severe conditions of signal quality. A frequency variation has been assumed as plusmn2 Hz around the nominal value, with a maximum rate of change of 1 Hz/s. The uncertainty of 25 mHz and 3.5 mHz has been obtained for single- and three-phase signals, respectively. A low-cost virtual instrument has been developed to make frequency measurements over the actual voltage signal.

Power Quality Factor for Networks Supplying Unbalanced Nonlinear Loads

A single indicator [i.e., the power quality factor (PQF)] in the range between 0 and 1 is suggested in this paper to integrally reflect the power transfer quality of a general three-phase network feeding unbalanced nonlinear loads. The prominent power quality aspects considered in the paper are the following: 1) the voltage and current harmonic levels; 2) the degree of unbalance; and 3) the phase displacement factor in the different phases at the fundamental frequency. A network that supplies balanced sinusoidal currents at balanced sinusoidal voltages with zero phase displacement between the corresponding currents and voltages yields a PQF of unity. The measurement of the PQF is discussed. Practical examples illustrate the use and relevance of the new quality factor.

Random Generation of Arbitrary Waveforms for Emulating Three-Phase Systems

This paper describes an apparatus for generating a signal representative of steady-state and transient disturbances in three-phase waveforms of an ac electrical system as described in IEEE Std 1159-09. It can be configured as a synthesizer of randomly distorted signals for different applications: for testing the effects of disturbed grid on equipment and to generate patterns of electrical disturbances for the training of artificial neural networks, which are used for measuring power quality tasks. For the first purpose, voltage and current amplifiers are added in the output stage, which allows the generation of disturbed signals at grid level.

Voltage quality analyzer

The Voltage Quality Analyzer is a virtual instrument for diagnosing voltage quality of three-phase signals: instantaneous frequency deviations, harmonic spec- trum, total harmonic distortion and instantaneous symmetri- cal components. Accurate measurement of the instantaneous frequency and the harmonic content are obtained and the three-phase electrical waveforms and their symmetrical components are displayed. A voltage quality factor in the range between 0 to 1 is defined and measured.

Power quality factor and line-disturbances measurements in three-phase systems

A power quality meter (PQM) is presented for measuring, as a first objective, a single indicator, designated power quality factor (PQF), in the range between zero to one, which integrally reflect the power transfer quality of a general three phase network feeding unbalanced nonlinear loads. PQF definition is based on the analysis of functions in the frequency domain, separating the fundamental terms from the harmonic terms of the Fourier series. Then, quality aspects considered in the PQF definition can be calculated: a) the voltage and current harmonic levels b) the degree of unbalance and c) the phase displacement factor in the different phases at the fundamental frequency. As a second objective, the PQM has been designed for detecting, classifying and organizes power line disturbances. For monitoring power line disturbances, the PQM is configured as virtual instrument, which automatically classifies and organizes them in a database while they are being recorded. The type of disturbances includes: impulse, oscillation, sag, swell, interruption, undervoltage, overvoltage, harmonics and frequency variation. For amplitude disturbances (impulse, sag, swell, interruption, undervoltage and overvoltage), the PQM permits the measurement of parameters such as amplitude, start time and final time. Measurement of harmonic distortion allows recording and visual presentation of the spectrum of amplitudes and phases corresponding to the first 40 harmonics. Software tools use the database structure to present summaries of power disturbances and locate an event by severity or time of occurrence. Simulated measurements are included to demonstrate the versatility of the instrument.

The geometric algebra as a power theory analysis tool

In this paper, a multivectorial decomposition of power equation in single-phase circuits for periodic n-sinusoidal /linear and nonlinear conditions is presented. It is based on a frequency-domain Clifford vector space approach. By using a new generalized complex geometric algebra (GCGA), we define the voltage and current complex-vector and apparent power multivector concepts. First, the apparent power multivector is defined as geometric product of vector-phasors (complex-vectors). This new expression result in a novel representation and generalization of the apparent power similar to complex-power in single-frequency sinusoidal conditions. Second, in order to obtain a multivectorial representation of any proposed power equation, the current vector-phasor is decomposed into orthogonal components. The power multivector concept, consisting of complex-scalar and complex-bivector parts with magnitude, direction and sense, obeys the apparent power conservation law and it handles different practical electric problems where direction and sense are necessary. The results of numerical examples are presented to illustrate the proposed approach to power theory analysis.

Instantaneous line-frequency measurement under nonstationary situations

A virtual instrument for the measurement of instantaneous power-system-frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is further developed that diminishes the variance of the estimation. The procedure is applied to the case of single and three-phase networks and relative errors in the frequency estimation are obtained. Low cost hardware, consisting of compatible PC, standard data acquisition card and signal conditioning module, has been used in conjunction with a software application developed with LABVIEW/spl trade/. Finally, measurements using single and three-phase signals, simulating severe conditions of signal quality, were performed. A variation of the frequency throughout the measurement time has been assumed, according to a sinusoidal signal of 5 Hz, within a /spl plusmn/1 Hz margin. The developed tool has been proven, with worst case data and relative errors of 0.1% and 0.025% having been obtained for single and three-phase signals, respectively.

Analysis of instantaneous NSV&C in polyphase systems

(N-1)-phase N-wire systems are analyzed into an orthonormal-coordinate system using the fundamental laws of polyphase systems and the condition of zero neutral-current. N-dimension voltage vectors are referenced to a virtual star-point and the current vectors are decomposed into three mutually orthogonal components, two of them are responsible of the active power. Without the condition of zero neutral-current, results are modified: the current vector is decomposed into a power-current vector and a complementary current vector. Only the first component transports the instantaneous collective power, the other is useless. The analysis is valid for a general situation and shows the condition of line losses minimization after compensation with active power filters.

Voltage quality index

A voltage quality index (VQI) is proposed for evaluation of the voltage quality aspects (QAs) of three-phase voltage signals: instantaneous frequency-deviations, total harmonic distortion and instantaneous symmetrical components. A VQI in the range between 0 to 1 is defined and measured. Accurate measurement of these Qas and VQI are obtained with a virtual instrument: the voltage quality analyzer (VQA)

Classification of Disturbances in Electrical Signals Using Neural Networks

This paper describes a currently project accomplished by the authors in the area of Power Quality (PQ) using artificial neural networks (ANN). The efforts are oriented to obtain a product (Power disturbances monitor for three-phase systems) that permits a real time detection, automatic classification, and record process of impulsive or oscillatory voltage transients, long term disturbances, and waveform distortions in electrical three-phase AC signals. To classify the electrical disturbances, we consider using a fully connected feedforward ANN with a backpropagation learning method based on Generalized Delta Rule. In order to select the best alternative more than 200 network architectures were tested. Long-term disturbances, like swells or long-duration interruptions, have been detected using a method based on the test of the RMS value of the signal. Short-term disturbances, like sags, are detected by sampling a cycle of the electrical signal, and waveform distortions are detected using the main harmonics of the signal. To train the ANN we have developed a three-phase virtual generator of electrical disturbances. In order to compress the ANN input data we use the Wavelet Transform.