low pass lc filter design

[--BawA--]

I dont have variable dc supply more than 32 volts.
But I have variable ac supply upto 260v . Can I simply rectify the supply using bridge rectifier and capacitor and use it as a dc bus in my hbridge.? Coz it will not be a pure dc.
One more thing I want to ask to fvm ."as u said that I should use a big value resistance than 1k at gate to source. Now I have decided to use 4.7k resistance .also I have calculated that using 4.7k resistance , will drop the voltage to 9.1v after 10ms. .
In all the circuits before, I was using 1k resitance , was the reason for damaging of mosfet was same that I was using 1k resistance between gate to source which was responsible for the voltage drop to 6.3v of my bootstrap capacitor (22ufd).

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I dont have variable dc supply more than 32 volts.
But I have variable ac supply upto 260v . Can I simply rectify the supply using bridge rectifier and capacitor and use it as a dc bus in my hbridge.? Coz it will not be a pure dc.
One more thing I want to ask to fvm ."as u said that I should use a big value resistance than 1k at gate to source. Now I have decided to use 4.7k resistance .also I have calculated that using 4.7k resistance , will drop the voltage to 9.1v after 10ms. .
In all the circuits before, I was using 1k resitance , was the reason for damaging of mosfet was same that I was using 1k resistance between gate to source which was responsible for the voltage drop to 6.3v of my bootstrap capacitor (22ufd).

 

[FvM]

As I already said, tripping of the bootstrap undervoltage-lockout should not cause transistor damage, at least I don't know why. But it' surely an unwanted effect.

 

[--BawA--]

FvM, is it necessary to use a damper resistor in the LC filter designed for the output of hbridge ?

As a rule of thumb, the filter inductor should be selected with a fundamental wave reactance of 1 .. 4 % of the characteristic inverter impedance Vrated/Irated

which means that whether my carrier frequency is 16KHz or 40KHz, the size of the indctor is same .
in my latest design i have used UNIPOLAR SPWM of carrier 20KHz , so the output LC filter will see a frequency of 40KHz. so probably smaller inductor can be used as compared to my earlier design which was 5mH , but according to you ,if i use equation XL=2*pi*F*L, where XL in my design is 1.3 ohms , F= 50HZ,
now the L is not depending on carrier frequency ,however C has decreased drastically.
so my filter L is same while capacitor is very small , so how can we reduce the size of inductor?

 

[--BawA--]

please reply FvM

 

[shegzzyy]

Can we use electolytic capacitor to design a low pass lc filter for filtering spwm from h bridge ?

i think most people use inductor and non polarized capacitor for their lc filter.the inductor design is the major headache for me.

 

[FvM]

You are right,the inductance can be reduced with higher carrier frequency. The 1 - 4 % rule is an estimation of maximum inductance related to the 50 Hz impedance and voltage drop. It applies if you want maximum filter effect with a second order filter. Other parameters that determine the design are acceptable reactive inverter load and intended carrier frequency suppression.