Pedro M. Ramos

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.

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.

A Four-Terminal Water-Quality-Monitoring Conductivity Sensor

In this paper, a new four-electrode sensor for water conductivity measurements is presented. In addition to the sensor itself, all signal conditioning is implemented together with signal processing of the sensor outputs to determine the water conductivity. The sensor is designed for conductivity measurements in the range from 50 mS/m up to 5 S/m through the correct placement of the four electrodes inside the tube where the water flows. The implemented prototype is capable of supplying the sensor with the necessary current at the measurement frequency, acquiring the sine signals across the voltage electrodes of the sensor and across a sampling impedance to determine the current. A temperature sensor is also included in the system to measure the water temperature and, thus, compensate the water-conductivity temperature dependence. The main advantages of the proposed conductivity sensor include a wide measurement range, an intrinsic capability to minimize errors caused by fouling and polarization effects, and an automatic compensation of conductivity measurements caused by temperature variations.

Detection and extraction of harmonic and non-harmonic power quality disturbances using sine fitting methods

In this paper, the application of four algorithms based on least square sine fitting methods for power quality measurements is discussed. It is shown how these algorithms can be used to extract power quality disturbances (such as transients or waveform distortions) from the voltage signal. Also, the application of these algorithms for estimation of the total harmonic distortion is discussed and the results are compared with the ones obtained according to the IEC 61000-4-7 standard.

Impedance Measurement using a Least-Squares Waveform Fitting Algorithm

A waveform fitting algorithm is used to measure the frequency response of a linear impedance. This method is capable of determining the harmonic amplitudes of a triangular signal up to the 50th harmonic. Amplitudes 80dB below the fundamental can be measured by using a 16-bit analogue to digital converter (ADC)

Application of genetic algorithms for estimation of impedance parameters of two-terminal networks

A new procedure to estimate the value of the individual components of a two-terminal impedance network is presented. It is based on the application of genetic algorithms to the spectral fitting of the impedances model. The expanded uncertainty of the estimated parameters is obtained through simulations and the algorithm is also applied to the measured frequency response of two impedance networks. Partial knowledge of spectral response is shown to be sufficient for the correct estimation of the individual component parameters.

A New Calibration Method for Current and Voltage Sensors Used in Power Quality Measurements

Sensor calibration plays an important role in instrument development and accuracy. This paper presents a method to calibrate current and voltage sensors specially dedicated to power quality measurements which can significantly reduce the distortions introduced by the sensors. The first approach to sensor calibration is based on the response of sensors to DC values imposed by a calibrator. The second method is an AC calibration, where a 50 Hz power signal is applied to the sensors also through a calibrator. The calibration coefficients are obtained by minimizing the output distortion. The minimized output distortion is assessed by the signal to noise and distortion ratio (SINAD) at the output of the sensor correction module