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