LC Filter for Power Inverter

Hello everyone
I'm designing an single phase Impedance source power inverter which provides both buck and boost operation. My aim is to keep the output AC voltage constant(20v peak) for two conditions
1.Input less than output (I/p-13.5 D.C,O/p-20vpeak)

2.Input greater than output( I/p-25 to 33.3 DC O/P-20vpeak)

My load resistance is constant at 12ohm. I'm using Sinusoidal PWM technique for switching my MOSFETS. My switching frequency is 10Khz and output frequency is 50 Hz.

I've simulated the circuit using MATLAB and got the output,now i need to design a LC filter at the output stage. I tried different values of L and C,i've got the frequency to be 50 Hz but the load voltage is greatly varying.

For the first case when my I/P is less than O/P without the filter i got 20v peak but with filter my output is reduced to 5 Vpeak. Now when i use the same filter values for my second case i'm getting the output to be around 25V.
SO Basically how do i design a optimum filter values that works for both my cases. What are the steps in doing so? The output volage needs to be 20V peak(atleast around 19v),cant compromise on that and frequency at 50 HZ.

Thanks in advance

You need to post the circuit and the value of the inductor and capacitor you are using. It's difficult to tell exactly what you are doing from your description.

Normally the inductor and capacitor are sized to remove the high frequency switching frequency. They should not be resonant at anywhere near 50Hz.

Thanks for the reply crutschow.
I've simulated the circuit using MATLAB. Its kinda big and untidy right now. I'll post my circuit in a day or two.

hi there

i too designed a inverter both the three phase and single phase using IGBT as a switching device. i searched in Google for an LC low pass filter design and i used the values i got in the design and i got the sinusoidal output.
but for three phase inverter i am getting uneven output up-to certain extent.
i am using powersim(PSIM) as software. i am using the demo version so i was unable to use all 3filters at a time for three phase inverter.
but i am got result for two phases which has some distortion
data: 24v input;65hz frequency for IGBT;
butterworth LC low pass filter
L : 15915uH(inductance)
cutoff frequency: 1Khz;output impedance:50 ohms
c1=c2=3183100pF(capacitance). how should i reduce distortion.pls help me
i am sending the circuits which i have simulated and the outputs of them which may be useful....

regards from
nitish.k
EEE