Delay

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espepe
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Joined: Fri. Mar 20, 2009
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Posted by espepe: Fri. May 22, 2009 - 12:16 PM
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Hi
I developed a program into a ATmega32. It determines the actual phase angle of the three-phase utility.
I use the internal ADC to read the voltage values and after the calculation a PWM signal is generated, which is filtered by a low-pass filter (simple R-C). The output signal is a sawtooth signal between 0-5V (0 means 0degree and 5V means 360 degree).
Today I made measurements and I saved the measured values with a Oscilloscope to compare it with the simulation results in matlab. The shape of the output signal is the same as the simulation result, but there is a 1.3ms delay between the two signals, which is relative high comparing it with the 20ms time period of the output signal.
When I tested the program in the AVR Studio I find that the code works properly.
My question is that has anybody any idea why this delay occur? It is comes from the filtering?
I use a filter with 5kHz cut off frequency, and I use 9bit fast PWM with the 15Mhz clock signal.
Thanks any advice

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Tools, Compilers and General Programming, ATmega32
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abugg046
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Posted by abugg046: Fri. May 22, 2009 - 01:11 PM
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For a first order low-pass filter, the output voltage will always lag the input voltage by some phase delay between 0-90 degrees. For the a 20ms period, 1.3ms is ~23 degrees.

You would have to examine the phase response of your filter to verify that the the delay is not coming from other sources.

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