Juan-Carlos Montaño

Wavelet and neural structure: a new tool for diagnostic of power system disturbances

The Fourier transform can be used for the analysis of nonstationary signals, but the Fourier spectrum does not provide any time-domain information about the signal. When the time localization of the spectral components is needed, a wavelet transform giving the time-frequency representation of the signal must be used. In this paper, using wavelet analysis and neural systems as a new tool for the analysis of power system disturbances, disturbances are automatically detected, compacted and classified. An example showing the potential of these techniques for diagnosis of actual power system disturbances is presented.

Reviewing Concepts of Instantaneous and Average Compensations in Polyphase Systems

According to the target of minimal line losses and a power factor that is equal to one, this paper studies two concepts of instantaneous compensation of nonactive current which are generally applied to polyphase systems. The analysis is defined both on the bases of the instantaneous-value concept, for arbitrary voltage and current waveforms, and the average-value concept, for steady-state and periodic conditions. The results of using these concepts for instantaneous compensation are compared by simulations.

Analysis of power losses for instantaneous compensation of three-phase four-wire systems

This paper deals with the effect that the instantaneous compensation in three-phase four-wire systems, including or not the compensation of the neutral current, has on the supply line power losses. Thus, for three-phase circuits, the instantaneous compensation criterion has been established based on the instantaneous power theory. According to the instantaneous value concept the noninstantaneous power current is reduced, without altering the instantaneous active power. Two approaches are marked in this paper for instantaneous compensation: the first one is for eliminating the total noninstantaneous power current but the neutral current can still flow. The second one for eliminating the modified noninstantaneous power current, thus the neutral current component is compensated. It demonstrates that, in common situations of medium and low relative-values of the zero-sequence voltage, the total losses (line and neutral losses) obtained with the second approach are lower than those obtained with the first approach. The same results are obtained when a criterion based on the average value concept is used. Simulated and experimental results are obtained to confirm the theoretical properties and to show the compensator performance.

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.

Clifford Theory: A Geometrical Interpretation of Multivectorial Apparent Power

In this paper, a generalization of the concept of electrical power for periodic current and voltage waveforms based on a new generalized complex geometric algebra (GCGA) is proposed. This powerful tool permits, in n-sinusoidal/nonlinear situations, representing and calculating the voltage, current, and apparent power in a single-port electrical network in terms of multivectors. The new expressions result in a novel representation of the apparent power, similar to the Steinmetzs phasor model, based on complex numbers, but limited to the purely sinusoidal case. The multivectorial approach presented is based on the frequency-domain decomposition of the apparent power into three components: the real part and the imaginary part of the complex-scalar associated to active and reactive power respectively, and distortion power, associated to the complex-bivector. A geometrical interpretation of the multivectorial components of apparent power is discussed. Numerical examples illustrate the clear advantages of the suggested approach.

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.

Disturbance Ratio for Optimal Multi-Event Classification in Power Distribution Networks

This paper presents an effective approach to identify power quality (PQ) events based on IEEE Std 1159-2009 caused by intermittent power sources like those of renewable energy. An efficient characterization of these disturbances is granted by the use of two useful wavelet-based indices. For this purpose, a wavelet-based global disturbance ratio (GDR) index, defined through its instantaneous precursor [instantaneous transient disturbance ITD(t) index], is used in power distribution networks (PDNs) under steady-state and/or transient conditions. An intelligent disturbance classification is done using a support vector machine (SVM) with a minimum input vector based on the GDR index. The effectiveness of the proposed technique is validated using a real-time experimental system with single event and multi-event signals.

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.