A Practical Primer On Motor Drives (Part 15): Low-Pass And Harmonic Filtering Of Power Measurements

by Ken Johnson, Teledyne LeCroy, Chestnut Ridge, N.Y., How2Power Today, Apr 17 2017

Focus:
Most power analyzers utilize an analog-to-digital conversion system to digitize the voltage and current waveforms, and then perform power calculations on each acquired cycle. By default, the instrument’s analog bandwidth and digital sample rate combine to determine the maximum (full-spectrum) frequency of the acquired voltage and current signals, and thus the number of harmonic orders present in the power calculations. One may employ analog or digital low-pass filters, complex harmonic filters, or any combination of these, to achieve filtering of the acquired full-spectrum signals. This part explains how these different filtering options work and shows how they are configured on Teledyne LeCroy’s Motor Drive Analyzer. Measurement examples of motor drive waveforms that have been processed using a discrete Fourier transform (DFT) digital harmonic filter demonstrate the impact of filter settings on calculated power values. Finally, the last section in this part discusses the impact of line-to-reference voltage probing of PWM signals on drive outputs and how the analyzer’s harmonic filtering can be used to remove the high common- mode voltage present on such measurements.

What you’ll learn:

• How to understand the different filter options for motor drive power measurements
• How to apply analog or digital low-pass filters, complex harmonic filters or a combination of these to motor drive measurements made using Teledyne LeCroy’s Motor Drive Analyzer

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