AN3137 datasheet(40/42 Pages) STMICROELECTRONICS

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Source code examples

AN3137

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Doc ID 16983 Rev 3

FFT analysis:

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16 point FFT calculation of 50 Hz signal is implemented

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FFT is applied on 6 ADC channels: AIN0 - AIN5

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FFT method shows 3-phase AC signal power measurement:

–

even channels (0, 2, 4) represent voltages

–

odd channels (1, 3, 5) represent currents

–

power is calculated as sum of the power of each harmonic frequencies (16 point

FFT = 7 harmonic)

Pa=U1*I1*cosF1 + ... + Un*In*cosFn

(n=7) ... for phase “a”

Pb=U1*I1*cosF1 + ... + Un*In*cosFn

(n=7) ... for phase “b”

Pc=U1*I1*cosF1 + ... + Un*In*cosFn

(n=7) ... for phase “c”

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connect 6 signals to AIN0 - AIN5 pins; signals should have frequency CCA 50 Hz

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the calculation takes CCA up to 3 seconds

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the second line on LCD shows calculation results: phase number, effective values of U

and I, harmonic power, phase shift, distortion of U and I (all for each of the 3 phases)

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to stop the method press the “Key” button (wait for the end of the result list, “done” will

appear on the screen)

Now the program starts again from the averaging method.

A.2.3

Hardware and software requirements

To run the project example you must have installed STVD (version 4.1.3 or newer) and

Cosmic/Raisonance compiler for STM8L/STM8A microcontrollers. Both tools are free for

download from STMicroelectronics and Cosmic/Raisonance websites.

The hardware requirement is to have the STM8L1526 evaluation board with the

STM8L152C6 chip installed.

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