THD of the output voltage

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ASIF ALI
ASIF ALI 2023-5-25
编辑： Abhishek 2025-6-23
I am trying find THD of signal but it doesnot give any result, as shown in image attached

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Abhishek
Abhishek 2025-6-23
编辑：Abhishek 2025-6-23
Hi @ASIF ALI,
The message "Selected signal. FFT window not shown (invalid settings)" typically appears when the configuration of the FFT analysis in Simulink is not valid for the signal being analyzed.
In most cases, this is due to a mismatch between the simulation settings and the requirements of the FFT tool. For example, the simulation time must contain an integer number of cycles of the fundamental frequency. If the number of cycles or the fundamental frequency is incorrect, the FFT window cannot be defined properly, which prevents the tool from performing the calculation.
To solve this issue, you can try out the following steps:
  • Ensure the signal is properly logged: Right-click the signal you want to analyze and select "Log Selected Signals". This ensures the signal appears in the FFT analysis window.
  • Verify fundamental frequency and number of cycles: In the “Powergui FFT” analysis dialog, make sure the fundamental frequency matches your signal, and that the number of cycles selected covers full periods of the signal.
  • Check simulation time: The simulation stop time should be set so that it includes an integer number of cycles of the fundamental frequency. For example, for a 60 Hz signal and 6 cycles, use a stop time of 0.1 seconds.
  • Use appropriate solver settings: Ensure that the simulation uses a discrete solver, especially when working with power systems. Sample time and solver type should be compatible with the FFT tool.
  • Avoid conflicting blocks or configurations: Check for other blocks that might interfere with signal access or modify the data unexpectedly before it reaches the FFT tool.
You can refer to the official MATLAB documentation for more details:
Hope it helps.

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