PWM Sine Wave Inverter output problem

Dear All,

I am building a PWM Sine Wave Inverter using H-Bridge IGBT Configuration.

The inverter has the following stages:

  1. A Sine Wave Oscillator
  2. An unity gain inverting amplifier to generate inverted sine wave
  3. A Triangular wave generator
  4. Two Sets of Comparators to generate PWM waveform for positive and negative cycles
  5. Two Half Bridge IGBT Drivers to generate A and A' signals for each of the half bridge with death time considered.
  6. IGBT H Bridge
  7. Output filter.

I have calculated the pass band for output filter using 1/2 * pi * sqrt{LC} to get 20.6mH inductance and 30uF capacitance with a pass band of 100 Hz. Feeding the H Bridge output to LC filter, to my surprise, the output is almost zero, as I use the scope, I have found a very small sine signal with peak to peak voltage of 100mV! (The H Bridge output has a peak to peak of 24V)

Any suggestions?

I am just thinking that it might have something to do with the modulation index when mixing the sine waves to the triangular wave using the comparator.

Regards

Reply to
Myauk
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** 1/ pi * sqrt(LC) i mean, sorry the equation was wrong!
Reply to
Myauk

30 uF???? That sounds HUGE! I think you have to move the knee way above the desired output frequency. I use a filter with a knee around 20 KHz and a 47 uH inductor and a .1 uF cap in some servo drives.

Your 30 uF cap has an impedance of j53 Ohms, your inductor is j12 Ohms, at 100 Hz.

Jon

Reply to
Jon Elson

bove

Finally, I have found the problem, I am using IR2111 as IGBT Driver, I used two of them for each Half Bridge of the H-Bridge. I tested it without the bootstrap capacitor between Vb pin and Vs pin.

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I put 33uF capacitor there and now I am getting the desired output.

I am using 50mH and 50uF for this moment in time with fc of 100 Hz. The carrier frequency is 5kHz and it is working fine now.

Regards

Reply to
Myauk

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