A.C. Serra

PQ Monitoring System for Real-Time Detection and Classification of Disturbances in a Single-Phase Power System

This paper presents a system for detection and classification of power quality (PQ) voltage disturbances. The proposed system applies the following methods to detect and classify PQ disturbances: digital filtering and mathematical morphology are used to detect and classify transients and waveform distortions, whereas for short- and long-duration disturbances (such as sags, swells, and interruptions), the analysis of the root-mean-square (RMS) value of the voltage is employed. The proposed combined approach identifies the type of disturbance and its parameters such as time localization, duration, and magnitude. The proposed system is suitable for real-time monitoring of the power system and implementation on a digital signal processor (DSP).

Simulation and experimental results of multiharmonic least-squares fitting algorithms applied to periodic signals

A new generation of multipurpose measurement equipment is transforming the role of computers in instrumentation. The new features involve mixed devices, such as analog-to-digital and digital-to-analog converters and digital signal processing techniques, that are able to substitute typical discrete instruments like multimeters and analyzers. Signal-processing applications frequently use least-squares (LS) sine-fitting algorithms. Periodic signals may be interpreted as a sum of sine waves with multiple frequencies: the Fourier series. This paper describes an algorithm that is able to fit a multiharmonic acquired signal, determining the amplitude and phase of all harmonics. Simulation and experimental results are presented.

New Spectrum Leakage Correction Algorithm for Frequency Estimation of Power System Signals

A new algorithm for the estimation of the frequency of single-tone signals is presented in this paper. The algorithm works in the frequency domain and is based on best fitting a theoretical spectrum of a single-tone signal that is windowed using a rectangular window on the spectrum of the sampled signal. Using this iterative process, the algorithm compensates the spectrum leakage caused by incoherent sampling and a finite number of samples. Due to leakage compensation, the algorithm provides accurate estimates of the signals frequency, amplitude, and phase. The influence of noise and harmonic and interharmonic distortions on the proposed algorithm was investigated and is reported here. The algorithms performance was compared with several other frequency-estimation algorithms (mostly those working in the frequency domain). Since the algorithm is intended for power quality measurements (although it is not limited to this application), it was also tested on signals measured in a single-phase power system.

Combined spectral and histogram analysis for fast ADC testing

The integral nonlinearity (INL) of analog-to-digital converters (ADCs) can be described by a behavioral error model expressed as one-dimensional image in the code domain. This image consists of low and high code frequency components which allow describing the ADC performance with a small number of parameters. This paper presents new methods for low code frequency and high code frequency testing. The identification of the low code frequency components is performed by multiharmonic sine fitting in the time domain. The high code frequency components are estimated in the statistical domain by a narrow band histogram test using a triangular stimulus signal. The performance of the proposed method is assessed for various ADC devices.

An ADC histogram test based on small-amplitude waves

Abstract This paper deals with a new method improving the static test for analogue-to-digital converters. The method is based on a histogram procedure using as test signals small-amplitude triangular waves superimposed on suitable constant offset values. The histogram is built over the converter fullscale by varying the offset step by step systematically. A small amplitude and a reduced time slope in comparison to the converter range and slew rate, respectively, lead to static test conditions. This procedure allows inexpensive function generators to be used and the test duration to be dramatically reduced. Experimental results of tests aimed at validating, characterizing, and comparing the proposed method on two different converter architectures are presented.

Least Squares Multiharmonic Fitting: Convergence Improvements

The robustness of least squares (LS) algorithms combined with the increased processing capabilities of DSPs will enable the development of a new brand of low-cost flexible instrumentation based on LS methods. Sine-fitting algorithms estimate the sine wave parameters of a digitized signal by minimizing the LS error. They can be used in a large number of important applications such as characterization of analog-to-digital converters, measurement of impedances, and test of the frequency response of linear systems. For signals with harmonics, multiharmonic fitting algorithms estimate the harmonic amplitudes and phases. In this paper, the convergence of the LS multiharmonic fitting algorithm is analyzed. Improvements are presented to increase convergence and minimize the number of iterations.

Recent Developments on Impedance Measurements With DSP-Based Ellipse-Fitting Algorithms

In this paper, recent advances of a new digital-signal-processor (DSP)-based impedance measurement instrument under development are presented. The digital signal processing algorithms are based on ellipse fitting for the extraction of the acquired sine signal parameters. so that the impedance magnitude and phase can be determined. Special attention is devoted to the improvement of the algorithms efficiency, i.e., by enabling the acquisition of a large number of samples by processing nonconsecutive data segments with no extra memory requirements. This capability is shown to reduce the experimental uncertainties of the estimated parameters. The systematic errors caused by the two different acquisition channels are measured and taken into account. The combined experimental measurement uncertainty is evaluated for the frequency sweep measurement of a particular impedance.

Gaussian Jitter-Induced Bias of Sine Wave Amplitude Estimation Using Three-Parameter Sine Fitting

In this paper, the bias on the estimated amplitude, which is caused by Gaussian jitter, is studied in case of the IEEE 1057 standard three-parameter sine-fitting method. Because no analytical study exists, this source of uncertainty is usually not considered. Nowadays, it is becoming more and more important due to the ever increasing sampling rates available in analog-to-digital converters (ADCs), which are used in innumerable application like high-speed digital oscilloscopes. The effect of additive noise is also taken into account.

Fast ADC Testing by Repetitive Histogram Analysis

Modeling the integral nonlinearity by the unified behavioral error model which is expressed as one dimensional image in the code k domain requires a minimal number of error parameters. The unified error model consists of low and high code frequency components. The paper presents new methods for low code frequency and high code frequency testing. The identification of low code and high code frequency components is based on a stochastic analysis of both components by using harmonic signals with reduced amplitude. The high code frequency component for code bins with extraordinary high nonlinearities is estimated in the statistical domain by a narrow band histogram using sinusoidal stimulus. The uncertainty of the proposed method is being assessed in the paper for various ADC representatives

A comprehensive phase-spectrum approach to metrological characterization of hysteretic ADCs

A phase-spectrum-based approach to the dynamic characterization of hysteretic analog-to-digital converters is proposed. Analytical relations between hysteresis of the dynamic transfer characteristic and out-of-phase components of the output Fourier spectrum are given. On this basis, an error model, a figure of merit, and a procedure for dynamic hysteresis testing are presented. Results of numerical characterization and experimental validation tests highlight the practical effectiveness of the proposed approach and its suitability for standardization.