Motor drive analyzers get harmonics calculation option

Nov. 4, 2015

Chestnut Ridge, NY. Teledyne LeCroy has introduced a new harmonics calculation option for the MDA800 motor drive analyzer series. This optional software package enhances the standard capabilities of the motor drive analyzer software by adding advanced harmonic filtering for AC input and drive output numeric table measurements; total harmonic distortion (THD) measurement parameters for voltage, current, and power; and a new harmonic order table with spectral waveform displays.

The standard motor drive analyzer software provides either full-spectrum (no harmonic filter applied) or fundamental-only harmonic filters. The new option adds a fundamental + N and a range filter. The fundamental + N filter allows the user to specify how many (N) harmonics from the fundamental to include in the numerics table calculations. The range filter is similar, but differs in that it allows the user to specify a starting point for the range other than the fundamental. These filters provide the flexibility and capability drive engineers need to isolate measurements and behaviors to specific frequency bands in order to understand the harmonic heating effects in a motor winding, or to isolate specific harmonics and correlate them to specific drive behaviors. This approach is superior to a simple low pass filter with limited filtering selectability, especially for a variable frequency drive output where the output frequency changes dramatically under different operating conditions, making simple low-pass filters nearly useless.

The harmonics calculation option adds THD measurement parameters to the Numerics table display. As with other numerics table parameters, users may observe the per-cycle behavior of these parameters by simply touching the Numeric table parameter value to plot a per-cycle THD waveform(s) over time. This waveform is time-correlated with other waveforms acquired by the MDA and can be used to correlate complex drive behaviors to other control or power system waveforms, and to debug drive system problems. Statistical detail of the measurement set can also be displayed. This additional information greatly aids debugging under dynamic operating conditions and goes well beyond what is provided by a typical power analyzer.

A new table displays a detailed list of harmonic contributions for voltage, current, and power by harmonic order. The table presents harmonic measurement values and spectral displays for up to nine waveforms (voltage, current, and power for each phase of a three-phase system). Users may perform calculations in both steady-state (fixed-frequency) and dynamic (varying frequency) operating conditions. The fixed-frequency method provides capabilities similar to that found in a typical power analyzer (up to 100 harmonic orders). The dynamic capability provides maximum flexibility for variable-frequency drive outputs (up to 50 harmonic orders). The dynamic, varying frequency mode utilizes a per-cycle discrete Fourier transform (DFT) and a software algorithm that overcomes the PLL bandwidth limits of a typical power analyzer and permits harmonic analysis under highly dynamic drive output operating conditions in which drive frequency is rapidly changing.

Each of the per-order harmonic measurements results in a spectral waveform display. The spectral waveforms are a bar graph display that contains a bar representing the harmonic order value for each harmonic order specified. The spectral waveforms bin the surrounding frequency components to the harmonic orders, which results in a clean, easy-to-read display.

The MDA Harmonics Calculation option’s U.S. list price is $1,500.

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