Medida de armónicos en el marco de los estándares IEC para la caracterización de variadores de frecuencia

En esta tesis se desarrolla una metodología de caracterización experimental de variadores de frecuencia que excitan motores de inducción, en función de los contenidos armónicos de sus salidas, mediante un plan de ensayos definido y un sistema que unifica todas las medidas, con la finalidad de conocer la calidad de la energía generada y detectar posibles fallos en los motores. Para ello, ha sido preciso primero conocer el contenido armónico que se pretende evaluar en el sistema variador-motor y también la forma de medirlo, para después desarrollar un sistema de medida y procesamiento de dicho contenido, basado en los conocimientos anteriores. Este sistema se ha inspirado en los analizadores de la red eléctrica que ya existen comercialmente y en su misma normativa internacional de medida de calidad de la red, pero adaptándolo a las necesidades específicas de medición a la salida de los variadores de frecuencia ensayados en esta tesis.Departamento de Ingeniería EléctricaDoctorado en Ingeniería Industria

Analysis of the use of the Hanning Window for the measurement of interharmonic distortion caused by close tones in IEC standard framework

Producción CientíficaThe widespread use of devices based on power electronics and other nonlinear loads has led to an increase in harmonic distortion that affects the quality of power systems. Therefore, the correct measurement of harmonic and interharmonic content is necessary. The International Electrotechnical Commission (IEC) standards define the concepts of spectral and time grouping required for such measurements. This paper demonstrates that the procedures defined in the IEC standards are not sufficiently accurate when several close interharmonic tones interact due to the lack of stability of the values that the Discrete Fourier Transform obtains in each sampling window, and to the inaccuracy in the measurement of interharmonic groups and rates when using the Hanning window. This paper proposes novel solutions based on time aggregation and the use of other groupings and alternative windows. The results obtained are compared with the results produced by applying the rectangular window indicated in the standards, using sensitivity analysis varying one of the tones and using experimental results measuring the output signals of frequency inverters driving induction motors. The proposed method achieves greater accuracy and stability in the measurement of spectral groupings and their related distortion rates in signals with abundant and dispersed interharmonic content

A study of the effects of time aggregation and overlapping within the framework of IEC standards for the measurement of harmonics and interharmonics

Producción CientíficaThe increasing incorporation of power electronics and other non-linear loads, in addition to their energy advantages, also implies a poor power quality, especially as regards harmonic pollution. Different solutions have been proposed to measure harmonic content, taking the International Electrotechnical Commission (IEC) standards as a reference. However, there are still some issues related to the measurement of the harmonic, and especially, interharmonic content. Some of those questions are addressed in this work, such as the problem derived from the instability of the values obtained by applying the discrete Fourier transform to each sampling window, or the appearance of local peaks when there are tones separated by multiples of the resolution. Solutions were proposed based on time aggregation and the overlapping of windows. The results demonstrate that aggregation time, window type, and overlapping can improve the accuracy in harmonic measurement using Fourier transform-based methods, as defined in the standards. The paper shows the need to consider spectral and time groupings together, improving results by using an appropriate percentage of overlap and an adaptation of the aggregation time to the harmonic content