If i am measuring PWM signals from the micro-controller and for simulation process DC-link of the rectifier can be calculated by knowing the modulation index . is there anyway to calculate or to visualize the modulation index from the measure PWM signals ? If the supply voltage is given ?
Dear Abdullah, I think this approach should work.
Observe the minimum period and the maximum period of the pulses or calculate from the software. The modulation index will be given by:
Mod. index = (maximum period + minimum period)/ (Maximum period - Minimum period)
You can find ON/OFF ratio using a low pass filter at the PWM signal output. DC coefficient of rectangular pulse train is C = A*tao/T, where A is the amplitude of PWM signal, tao is ON time and T is signal period. The low pass filter transform PWM signal in a constant signal with values between 0 and A, which indicate ON/OFF ratio. Ideally that idea works but the idea low pass filters do not exist
Abdullah,
Welcome,
The modulation index of pulse width modulated waveform representing an output of a dc to ac inverter is purposely defined by the amplitude of fundamental frequency component contained in the output waveform divided by the a reference inverter obtained by the fundamental frequency clocking FFC. The reference waveform which is a bipolar square wave gives an an amplitude of 2/pi Vidc, the input Dc voltage.
The the modulation index= Vof/ (2/pi) Vidc,
where Vof is the fundamental amplitude of the output pulse modulated wave form.
Then all what do need if to fiter the fundamental and measure its amplitude.
In fact you need to measure the amplitude of your output sine wave after the low pass filtering.
For more information please refer to the link:https://www.eal.ei.tum.de/fileadmin/tueieal/www/courses/PE/tutorial/2013-2014-W/07_PWM.pdf
Best wishes
- Badges
- Science topic