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

# PWM Sine Wave Inverter output problem

Started by ●February 28, 2012

Reply by ●February 28, 20122012-02-28

On Feb 29, 1:17=A0am, Myauk <aungkokot...@gmail.com> wrote:> 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** 1/ pi * sqrt(LC) i mean, sorry the equation was wrong!

Reply by ●February 28, 20122012-02-28

Myauk wrote:> 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)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 by ●March 12, 20122012-03-12

On Feb 29, 5:39=A0am, Jon Elson <jmel...@wustl.edu> wrote:> Myauk wrote: > > 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) > > 30 uF???? =A0That sounds HUGE! =A0I think you have to move the knee way a=bove> the desired output frequency. =A0I 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. > > JonFinally, 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. (http:// www.irf.com/technical-info/appnotes/an-978.pdf). 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